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Heart rate, PR, and QT intervals in normal children: A 24-hour Holter monitoring study
Clinical Cardiology
Abstract
A dynamic electrocardiographic Holter monitoring study was performed in 32 healthy children (20 males and 12 females, age range 6-11 years old), without heart disease, according to clinical and noninvasive instrumental examination. We evaluated atrioventricular conduction time (PR), heart rate (HR), and QT interval patterns defining the range of normality of these electrocardiographic parameters. The PR interval ranged from 154 +/- 10 ms (mean +/- SD) for HR less than or equal to 60 to 102 +/- 12 ms for HR greater than or equal to 120 (range 85-180). The absolute mean HR was 87 +/- 10 beats/min (range 72-104), the minimum observed HR being 61 +/- 10 (range 51-79), the maximum 160 +/- 20 beats/min (range 129-186). Daytime mean HR gave a mean value of 93 +/- 10 (range 71-148), while during night hours it was 74 +/- 11 (range 54-98). The minimum QT interval averaged 261 +/- 10 ms for HR greater than 120 and the maximum 389 +/- 9 ms for HR less than or equal to 60; the corresponding mean value of QTc (i.e., QT corrected for HR) ranged from 388 +/- 8 for HR less than or equal to 60 beats/min to 403 +/- 14 ms for HR greater than 120 beats/min. The results of the present study provide data of normal children which can be readily compared against those of subjects in whom cardiac abnormalities are suspect or patient.(ABSTRACT TRUNCATED AT 250 WORDS)
... 22 Earlier studies on corrected QT intervals in all the ECGs either had very few participants or showed methodological weaknesses. 7,10,11,35 About 25 years ago, three studies on the circadian pattern of the heart rate in healthy children were carried out by Scott et al., 10 Southall et al., 11 and Lindinger and Hoffmann. 7 These showed a nocturnal heart rate that was lower than the diurnal heart rate. ...
... There is only one published study to date focusing on the corrected QT intervals in 24 h ECGs in healthy children. 35 This study included only 20 boys and 12 girls aged 6 to 11 years. Children aged below 6 years (in our study 54%) and all children above 11 years (in our study 64 children, 23%) were not included. ...
The study was designed to detect changes in corrected QT intervals over day and night in both sexes in healthy children.
The corrected QT interval was calculated from 24 h ECGs obtained from 282 healthy children aged 6 months to 18 years. The QTc interval as measured by the 24 h recording differs to the standard ECG measurement which is in average of 40-50 ms shorter. The QTc interval changes little over a 24 h period and is remarkably constant despite significant heart rate changes in healthy children.
The routine ECG-even if the calculated values differ markedly from those obtained over 24 h-seems to be a good screening method for the measurement of corrected QT intervals, because the corrected QT interval is kept constant over the whole day in healthy children.
... The corresponding ambulatory reference ranges are highly context dependent; e.g., they vary depending on the intensity of physical exercise, age, and medical conditions a study subject might have, presenting a bigger challenge for data interpretation compared to the spot check data collection method. The data are available from Holter monitoring studies [30,31], but this technique does not account for physical activity which has an impact on the range of measures. Moreover, skin temperature measured at the chest wall is different from the oral body temperature, being more impacted by environmental factors. ...
Clinical safety findings remain one of the reasons for attrition of drug candidates during clinical development. Cardiovascular liabilities are not consistently detected in early-stage clinical trials and often become apparent when drugs are administered chronically for extended periods of time. Vital sign data collection outside of the clinic offers an opportunity for deeper physiological characterization of drug candidates and earlier safety signal detection. A working group representing expertise from biopharmaceutical and technology sectors, US Food and Drug Administration (FDA) public-private partnerships, academia, and regulators discussed and presented a remote cardiac monitoring case study at the FNIH Biomarkers Consortium Remote Digital Monitoring for Medical Product Development workshop to examine applicability of the biomarker qualification evidentiary framework by the FDA. This use case examined the components of the framework, including the statement of need, the context of use, the state of the evidence, and the benefit/risk profile. Examination of results from 2 clinical trials deploying 510(k)-cleared devices for remote cardiac data collection demonstrated the need for analytical and clinical validity irrespectively of the regulatory status of a device of interest, emphasizing the importance of data collection method assessment in the context of intended use. Additionally, collection of large amounts of ambulatory data also highlighted the need for new statistical methods and contextual information to enable data interpretation. A wider adoption of this approach for drug development purposes will require collaborations across industry, academia, and regulatory agencies to establish methodologies and supportive data sets to enable data interpretation and decision-making.
... The standard ECG records only a brief period of cardiac rhythm, and it often fails to reveal many dynamic and transient phenomena. A long-term ECG Holter monitoring with a portable 24 h tape recorder, coupled with a playback analysis of the data, has been used in the examination of human patients (Brodsky et al. 1977, Kennedy & Caralis 1977, Viitasalo et al. 1982, Romano et al. 1988) and dogs (Tilley 1985, Miller & Tilley 1988. Direct storage of ECG data on a mini tape, giving 15 min of playing time, by recording device carried on the horse, has been reported (Brownlie 1987, Gatti & Holmes 1990), but no reports concerning the examination of the heart rate and rhythm with a long-term tape recording in horses have been found in the available literature. ...
The electrocardiogram of 9 horses was continuously recorded for 24 h with Holter monitoring to examine the variations in heart rate and rhythm during daily routine procedures and at night. Three horses had transient sinus bradycardia, and 3 had periods of sinus tachycardia. Heart blocks were detected in 3 horses, and all horses had periods of sinus arrhythmia. These changes in the heart rate and rhythm were apparently caused by variations in autonomic nervous system tone and they are probably “normal” findings in resting, undisturbed horses. Ventricular premature depolarisations were not observed in any horse, but some single supraventricular premature contractions were detected. There was preliminary evidence that in order to register the real resting heart rate and rhythm of a horse the ECG should be recorded over a long period, and also at night and without the presence of the investigator.
... Consequently, significant dysrhythmia may not be detected during the examination, particularly when the dysrhythmia is intermittent [4]. A LT-ECG Holter monitoring with a portable 24-hour recording device coupled to playback analysis of the data has been used in the examination of HR and rhythm in horses [5], ponies [6], dogs and cats [3,7,8], and in human patients [9][10][11][12]. Sinus arrhythmia, sinus tachycardia, and second-degree atrioventricular blocks were often described in horses at rest, whereas ventricular escape beats were uncommon [13]. ...
... Similar rate-dependence of QT intervals has been reported previously by Romano et al. in a group of children of similar age. 14 In children older than 12 years, higher rate-corrected QT intervals in girls than in boys have been reported. 2,3 This finding could be attributed to the presence of similar heart rates between genders, in the age group of 12 to 18 years, while the differential effects of sex hormones are ensuing. ...
Although the association of repolarization alterations to the development of life-threatening ventricular arrhythmias has received considerable research attention, there is paucity of data regarding what may be considered as normal, especially in children.
To define electrocardiographic (ECG) and vectorcardiographic (VCG) descriptors of ventricular repolarization in healthy school-age children, 12-lead digital ECGs were obtained from 646 children (348 males/298 females, mean age 8.54 ± 1.86 years). All QT intervals were measured manually using the digitally stored ECGs. Orthogonal X, Y, and Z leads were reconstructed from the standard 12-lead ECGs and the maximal amplitudes of the spatial QRS and T vectors were calculated, as well as the spatial QRS-T angle.
The mean heart rate was 95.3 ± 15.8 bpm and the QRS duration was 83.4 ± 9.3 ms. Mean QT interval was 334.1 ± 24.2 ms and the corrected QT interval was 436.5 ± 23.8 ms (Bazzet) and 404.3 ± 19.4 ms (Fridericia). Although the uncorrected maximum and mean QT intervals were significantly higher in boys (P values 0.011 and 0.009, respectively), there was no difference in the rate-corrected QT interval. The spatial QRS and T-vector amplitudes were 1512.0 ± 365.7 μV and 478.8 ± 149.3 μV, respectively. The spatial QRS-T angle was 14.1 ± 8.0 degrees. Although the mean QT interval showed significant increase with age (P = 0.014), all VCG parameters did not show significant variance with age.
A range of ECG and VCG descriptors of ventricular repolarization was determined in a large sample of healthy school-age children to provide a data basis of normal values for future reference.
... The standard ECG records only a brief period of cardiac rhythm, and it often fails to reveal many dynamic and transient phenomena. A long-term ECG Holter monitoring with a portable 24 h tape recorder, coupled with a playback analysis of the data, has been used in the examination of human patients (Brodsky et al. 1977, Kennedy & Caralis 1977, Viitasalo et al. 1982, Romano et al. 1988) and dogs (Tilley 1985, Miller & Tilley 1988. Direct storage of ECG data on a mini tape, giving 15 min of playing time, by recording device carried on the horse, has been reported (Brownlie 1987, Gatti & Holmes 1990), but no reports concerning the examination of the heart rate and rhythm with a long-term tape recording in horses have been found in the available literature. ...
The electrocardiogram of 9 horses was continuously recorded for 24 h with Holter monitoring to examine the variations in heart rate and rhythm during daily routine procedures and at night. Three horses had transient sinus bradycardia, and 3 had periods of sinus tachycardia. Heart blocks were detected in 3 horses, and all horses had periods of sinus arrhythmia. These changes in the heart rate and rhythm were apparently caused by variations in autonomic nervous system tone and they are probably "normal" findings in resting, undisturbed horses. Ventricular premature depolarisations were not observed in any horse, but some single supraventricular premature contractions were detected. There was preliminary evidence that in order to register the real resting heart rate and rhythm of a horse the ECG should be recorded over a long period, and also at night and without the presence of the investigator.
... For example, we often monitor Q-T and Q-Tc intervals in patients treated with amiodarone to detect the prolongation of this index. It would not be reliable, for example, if we compare measurements taken at 7 AM and 5 PM, because even in normal subjects the Q-T values can differ by 30% at different times of the day [35]. Also, it would be not reasonable to compare a short-term heart rate variability result sampled at 10 AM one day with another result sampled at 5 PM on another day. ...
We reviewed recent progress in the study of the chronobiological aspects of the cardiovascular system.
Medline was used as the main search tool, and the full texts of selected papers were obtained.
More than 300 references were found, and 52 of them, representing the major findings in this field, were included in the reference list. Results of these studies confirm that most cardiovascular physiological parameters (such as heart rate, blood pressure, electrocardiogram indices) and pathophysiological events (myocardial ischemia/infarction, sudden cardiac death) show circadian rhythms. Results also suggest that consideration of these rhythms is important for the diagnosis and treatment of cardiovascular disorders and that restoration of normal circadian rhythms may be associated with clinical improvement.
The study of circadian rhythms in the cardiovascular system is emerging as an important area of investigation because of its potential implications for patient management.
Background:
In patients undergoing extracardiac conduit Fontan (ECF) who require postoperative pacing, epicardial leads are usually required because of anatomical constraints. If indicated, these could be conveniently placed at the time of ECF. We have routinely performed ambulatory 24-hour Holter monitoring before ECF to determine the presence or absence of preoperative sinus node dysfunction, in attempt to avoid repeat sternotomy at a later time.
Methods:
We performed a retrospective study of all patients undergoing ECF from January 2000 to December 2015.
Results:
Two hundred sixteen patients met inclusion criteria. Patients were separated into two groups, those with preoperative Holter monitoring (PHM, n = 150) and those without (No-PHM, n = 66). Ten patients (4.6%) underwent permanent pacemaker implantation at the time of ECF. (8 patients (5.3%) in PHM vs 2 patients (3.0%) in No-PHM, p = 0.46). There were 7 (3.2%) patients who underwent pacemaker implantation after ECF requiring repeat sternotomy (4 patients (2.7%) in PHM vs 3 patients (4.5%) in No-PHM, p = 0.47). Fourteen (6.5%) patients underwent permanent epicardial lead placement without a pulse generator at the time of ECF. None from this group underwent pacemaker implantation to date (median follow up of 5.7 years). The overall incidence of pacemaker implantation was 9.3% (20 patients).
Conclusions:
In our series, arrhythmia disturbances requiring pacing after ECF occurred in just over 9% of patients. While preoperative Holter monitoring in those patients may help predict which patients might require postoperative pacing, this approach did not result in a significant decrease in those patients requiring repeat sternotomy for pacemaker implantation. This article is protected by copyright. All rights reserved.
Long term ECG recording with Holter monitoring has been performed on 23 horses of different breed, age and sex, with rhythm disturbances at rest and, sometimes, clinical evidence of exercise intolerance or during antiarrythmic therapy for conversion to normal sinus rhythm of atrial fibrillation. The effectiveness of Holter monitoring either in the diagnosis and in the electrogenetic study of arrhytmia or in the patient's therapeutic follow-up has been demonstrated. In addition, the usefulness of this technique in sport medicine and in the cardiac research has been proposed.
This study of 50 eleven-year-old boys demonstrates a new procedure for gathering physiological, psychological, and behavioral data on television viewing in the home environment on a normal school day, using a special ambulatory monitoring device capable of storing 23-hour records. The mean time spent watching TV was 123 minutes per day, during which the boys watched mostly entertainment and action shows. Heart rate as compared to the other programs was low for entertainment and high for action shows. Additional heart rate indicating emotional arousal was highest for action shows as well. Compared to school and leisure time, additional heart rate during TV viewing was much higher As opposed to boys who watched little TV, those with high TV consumption displayed lower heart rate and lower emotional arousal during TV viewing. Boys with high TV consumption read fewer books, showed diminished activities outside home, a tendency for reduced school-related homework, and reduced interest in hobbies.
Sinus node dysfunction is known as a major complication after repair of partial anomalous pulmonary venous connection. We retrospectively analyzed the results of the atrial wall flap technique compared with the results of patch repair or direct suturing in the intra-atrial tunnel technique.
Between 1991 and 2007, 23 patients (mean age, 6 years; range, 5 months-17 years) with partial anomalous pulmonary venous connection underwent surgical intervention. The right anomalous pulmonary veins drained to either the right atrium or superior vena cava in 8 and 15 patients, respectively. Patients were divided into 2 groups: group F (n = 14), who had repair with an atrial flap, and group N (n = 9), who had repair without an atrial flap. All patients had normal sinus rhythm preoperatively.
No patients had signs of superior vena cava or pulmonary venous obstruction within a mean follow-up of 4.8 years. One patient in group F required pacemaker implantation. In the early postoperative period, sinus node dysfunction developed in 93% of group F and 44% of group N patients (P < .01) and was prolonged until discharge in 57% of group F and 0% of group N patients (P < .01). At the most recent clinical visit, sinus node dysfunction was identified in 50% of group F patients, whereas all patients in group N had normal sinus rhythm (P < .02).
The atrial flap technique, which requires incision or suture crossing the crista terminalis, could cause sinus node dysfunction, whereas the intra-atrial rerouting method with a patch or direct suture maintains normal sinus node function postoperatively.
Conflicting reports about changes in QT intervals suggest that QT values should be compared at similar heart rates.
Relations between QT and RR intervals were determined after measurement of QT values by Holter recording at heart rates of 50, 60, 70, 80, 90, 100, 110, and 120 beats per minute in 100 healthy young men. Fifteen men underwent a second recording during acute treatment with the beta-blocking agent atenolol. At heart rates between 80 and 120 beats per minute, the QT interval was significantly longer (from 9 to 16 msec), and at a heart rate of 50 beats per minute significantly shorter (26 msec), than values calculated from Bazett's formula. Sleep prolonged QT values by 18 msec at a heart rate of 60 beats per minute and by 21 msec at a heart rate of 50 beats per minute compared with the waking state. Atenolol lengthened QT intervals significantly (by 11-14 msec) at heart rates between 90 and 110 beats per minute and shortened them (by 12 msec) at a heart rate of 60 beats per minute. During sleep, QT intervals were the same before and after atenolol.
The method of plotting QT against RR intervals after measurement of QT values at similar stable spontaneous heart rates before and after intervention allows changes in autonomic state and heart rate to be taken into account. By this method, QT values can be compared without distortion effects caused by correction formulas.
Myocardial infarction (MI), a common occurrence in adults, is generally considered to be rare in children. Electrocardiographic criteria for diagnosis of MI in adults are well known and accepted, but no general criteria exist for children. We report 37 autopsy-proved cases of transmural MI and electrocardiographic evidence of MI in 30 of these cases. A variety of conditions previously reported to produce "pseudo-infarction" are included in these cases of MI, including myocarditis, hypertrophic cardiomyopathy, and the cardiomyopathy of Duchenne's muscular dystrophy. Compilation of the electrocardiographic data in all patients allowed for the development of criteria for this diagnosis of MI in childhood, and include wide Q waves (greater than 35 ms) with or without Q-wave notching, ST-segment elevation (greater than 2 mm), and prolonged QT interval corrected for heart rate (QTc greater than 440 ms) with accompanying Q-wave abnormalities. With use of these electrocardiographic criteria, an additional 3 patients were subsequently diagnosed prospectively with MI and confirmed on autopsy. Pathologic evaluation confirmed the location of infarction predicted by the electrocardiograms in all 3 cases.
Patients with congenital QT interval prolongation are at risk of ventricular arrhythmias and sudden death. It has been suggested that the susceptibility to arrhythmias in these syndromes may be related to the abnormal dynamics of ventricular repolarisation. The dynamics of ventricular repolarisation, including assessment of the effect of changing heart rate on the QT interval and the duration of the right ventricular monophasic action potential, were studied in eight patients with congenital long QT syndromes. The effects of altered sympathetic tone on these dynamics were investigated with isoprenaline, propranolol, and left stellate ganglion block. The rate adaptation of the QT interval was abnormal in only a few patients and in some patients this feature may be related to the severity of the condition. These abnormalities may be exaggerated by isoprenaline and lessened by propranolol and left stellate ganglion block. Monophasic action potential dynamics were normal in all patients. The hypothesis that impaired QT rate adaptation may play a role in the genesis of ventricular arrhythmias in these syndromes is not, in general, supported by the present data. However, in patients with impaired adaptation the normalisation of QT dynamics after beta blockade and left stellate ganglion block was consistent with the efficacy of these forms of treatment.
Continuous electrocardiographic (ECG) monitoring was performed over 24 h in 44 children at various stages of chronic renal failure in order to determine the incidence and nature of cardiac dysrhythmias. In addition the ECG was followed during haemodialysis sessions and during dialysate exchanges in continuous ambulatory peritoneal dialysis (CAPD) patients. In contrast to adult patients on haemodialysis life-threatening dysrhythmias were not observed. The proportion of children with premature ventricular complexes (41%) was at the upper limit of that in healthy children. A relatively high heart rate was found in children on CAPD, which varied during the exchange procedure. In 57% of all patients a transient marked prolongation of the QT interval up to 40% greater than normal was observed without obvious changes in the serum electrolyte levels. Continuous ECG monitoring is a useful tool for detecting alterations of cardiac rhythm and conduction in at-risk children with renal failure.
Unlabelled:
Heart rate (HR) was recorded in healthy full-term newborns aged 1-90 days. The aim of this study was to study the existence of circadian and/or ultradian rhythms in HR to determine maturity. HR was recorded during 24 h, at 30-min intervals, at different postnatal ages. Six-groups were investigated: day 1 (group 1); day 7 (group 7); day 15 (group 15); day 30 (group 30); day 60 (group 60), and day 90 (group 90). The chronograms for HR showed peaks and nadirs along the 24-hour periods, and the cosinor analysis proved the existence of 3-hour ultradian rhythm in groups 1, 7 and 30, and a 12-hour ultradian rhythm in group 90 (p < 0.01 in all cases). The same type of analysis confirmed the existence of a circadian rhythm in group 30. Similar results were obtained for groups 60 and 90 (p < 0.05).
In conclusion:
at birth, newborns have an endogenous ultradian period of 3 h. A circadian rhythm appears within 15-30 days of postnatal life.
Sinus node dysfunction has been previously reported to occur in 13% to 16% of patients after the Fontan operation. Although there is concern that an intermediate cavopulmonary connection may increase the risk of sinus node dysfunction, previous studies have not reported on patients routinely staged to a Fontan operation. This study sought to determine the early and late incidences of sinus node dysfunction in patients systematically and uniformly staged to a Fontan operation after a prior hemi-Fontan.
To determine the early incidence of sinus node dysfunction, hospital records and perioperative ECGs were reviewed in all 287 patients having had a staged Fontan operation between January 1990 and December 1995. A cross-sectional analysis was performed on 220 of 239 surviving patients (92%) to determine the late incidence of sinus node dysfunction. Sinus node dysfunction was present in 7% of the patients before and in 15% after the hemi-Fontan. Although most patients (81%) regained normal sinus node function between the 2 stages, 23% had sinus node dysfunction in the early postoperative period after the Fontan. Of the 95 patients followed for > 4 years after the Fontan operation, 44% had sinus node dysfunction. However, at a mean follow-up of 3.5 +/- 1.7 years, only 16 patients (6.7%) had received a pacemaker and only 10 (4.1%) had documented atrial flutter.
Perioperative sinus node dysfunction is common after both the hemi-Fontan and the Fontan procedures. Although many patients regain sinus node function between the 2 stages, late sinus node dysfunction is common and more likely to occur in patients with early sinus node dysfunction and those with longer follow-up.
We studied the diurnal variations of autonomic nervous function in rats. For this purpose, a long-term electrocardiogram (ECG) was recorded from conscious and unrestrained rats using a telemetry system, and the autonomic nervous function was investigated by the power spectral analysis of heart rate variability. No arrhythmias were observed in the ECG of any of the rats. Nocturnal patterns, in which the values of heart rate in the dark phase (2000-0600) were higher than those in the light phase (0600-2000), were observed. All normal rats shared a characteristic pattern in their power spectrum analysis. Both low-frequency and high-frequency power in the light phase were higher than those in the dark phase. However, these differences were not statistically significant (P > .05). The low frequency to high frequency ratio also showed a nocturnal pattern. The value in the dark phase was significantly higher (P < .05) than that in the light phase. These results suggest that the sympathetic nervous activity is predominant in the dark phase in rats. Therefore, we believe that this information may be useful for future biobehavioral studies.
To determine whether operations that theoretically jeopardize the sinus node (hemi-Fontan and/or lateral tunnel Fontan procedures) are associated with a greater risk of sinus node dysfunction than those that theoretically spare the sinus node (bidirectional Glenn and/or extracardiac conduit).
Between January 1, 1996, and December 31, 1999, a prospective cohort study was conducted evaluating the incidence of sinus node dysfunction in patients undergoing a bidirectional Glenn or hemi-Fontan procedure and those in whom the Fontan repair was completed with either an extracardiac conduit or a lateral tunnel. Sinus node dysfunction was defined (1) as a heart rate more than 2 SD below age-adjusted norms or (2) as a predominant junctional rhythm and/or a sinus pause of more than 3 seconds as determined by the resting electrocardiogram and/or ambulatory monitoring at hospital discharge.
Fifty-one patients had a bidirectional Glenn shunt (mean age 7.8 +/- 5.1 months) and 79 a hemi-Fontan procedure (mean age 6.9 +/- 2.8 months). The incidence of sinus node dysfunction on postoperative day 1 was significantly higher after the hemi-Fontan (36%) than after the bidirectional Glenn shunt (9.8%); however, by hospital discharge this difference was no longer apparent (hemi-Fontan [8%]; bidirectional Glenn [6%]; P = not significant). No difference in early sinus node dysfunction was discernible after the extracardiac conduit (4/30 [13%]) compared with the lateral tunnel Fontan procedure (6/46 [13%]) (P = not significant). No diagnostic or perioperative variables were predictive of sinus node dysfunction.
Avoidance of surgery near the sinus node has no discernible effect on the development of early sinus node dysfunction. Thus, concerns about early sinus node dysfunction should not override patient anatomy or surgeon preference as determinants of which cavopulmonary anastomosis to perform.
Little information is available regarding cardiac morbidity and mortality in children with end-stage renal disease. We sought to determine the incidence of cardiac morbidity and mortality in pediatric chronic dialysis patients.
Medicare incident pediatric (0 to 19 years) dialysis patients from 1991 to 1996 were identified from the United States Renal Data System. Study endpoints included development of arrhythmia, valvular heart disease, cardiomyopathy, or cardiac arrest, all causes of death, and cardiac-related death. Statistical analyses were performed using the Poisson regression model and chi-square test.
A total of 1454 children were eligible for inclusion, 452 (31.1%) of whom developed a cardiac-related event. Arrhythmia was the most common event (19.6%) compared with valvular disease (11.7%), cardiomyopathy (9.6%), and cardiac arrest (3%). Arrhythmia and valvular heart disease incidence were increased in 15- to 19-year-olds (P < 0.0001 for both), females (P = 0.004, P = 0.03) and blacks (P < 0.0001, P = 0.002). Cardiomyopathy incidence was increased in blacks (P = 0.001) and tended to be increased in females (P = 0.053). The adjusted annual cardiomyopathy rate during the first 3 years increased between 1991 and 1996 (P = 0.003). Death occurred in 107 patients, and 41 (38%) were cardiac deaths.
Cardiovascular disease is a significant cause of morbidity and mortality in pediatric chronic dialysis patients. Cardiomyopathy incidence is increasing. Black, female, and adolescent children have increased risk for cardiovascular disease.
Most cardiovascular activities show a circadian rhythm, as do electrophysiological phenomenon. Under the influence of both external stimuli and endogenous homoeostatic mechanisms, cardiac electrophysiological properties change diurnally and enable the cardiovascular system adapt to rest-exercise cycles. According to recent reports, almost all non-invasive electrophysiological phenomena, such as electrocardiographic indices, cardiac refractoriness and conduction, pacing and defibrillation threshold, heart rate variability indices, and even Q-T dispersion and T-wave alternans, show diurnal variability. Furthermore, many of these changes are clinically significant and may affect results of some diagnostic studies. These characteristics of the cardiovascular system require us keep in mind the "time" factor any time we analyze electrophysiological results and make clinical decisions.
This study compares the effects of two techniques for the Fontan procedure-intraatrial lateral tunnel (IALT) and extracardiac conduit (ECC) -on sinus node dysfunction. Between January 1992 and December 1998, 54 patients underwent a total cavopulmonary connection Fontan procedure. Of these, 36 had follow-up 24-hour Holter recordings, and they constitute the population for this study. The 24-hour Holter recordings were performed between January 1998 and March 1999 and were evaluated for sinus node dysfunction and atrial tachycardia. Clinical follow-up (18 +/- 11 months for the IALT group vs 34 +/- 19 months for the ECC group; p = 0.002) and surface electrocardiograms were also reviewed. Among the 36 patients, 19 had an IALT and 17 had an ECC Fontan procedure. The incidence of sinus node dysfunction was 4/19 (21%) in the IALT group and 10/17 (59%) in the ECC group (p = 0.04). No patient from either group had an identified episode of atrial tachycardia. No permanent pacemaker was placed in the IALT group, whereas three were placed in the ECC group, all for sinus node dysfunction. In summary, patients with both IALT and ECC had an important incidence of sinus node dysfunction. The incidence of sinus node dysfunction was higher in the ECC group, which may have been due to longer follow-up in this group. Atrial tachycardia was not observed in either group. Although the IALT group had less sinus node dysfunction than the ECC group and appeared to require less permanent pacing, these data may be too limited to serve as the criteria for choosing between these two techniques for performing the Fontan procedure.
Sinus node dysfunction (SND) is reported to be a troublesome complication following various types of Fontan operations. The correlation of post-Fontan SND with surgical methods was evaluated in this study.
By reviewing the medical records, surface ECGs, and Holter monitoring, the range of heart rate (HR) and the risk of SND at intermediate term after Fontan type operation (follow up: 41.3+/-13.1 months) were analyzed between two age matched groups of patients, consisting of the extracardiac conduit group (EC, n=33) and the lateral tunneling group (LT, n=35).
Junctional rhythm was observed in nine out of 35 patients in LT and five out of 33 patients in EC during the follow-up period. Resting HR was faster in EC than that in LT (108+/-15 vs. 82+/-21, P<0.001). Average and maximal HR in Holter monitoring were also faster in EC than those in LT. SND was found in 13 cases (10 in LT, three in EC) during follow-up and one required pacemaker implantation. In the case of situs solitus heart, SND was less frequent in EC than in LT (0/16 vs. 8/26, P=0.01). In the case of heterotaxy syndrome, SND occurred in similar number of cases (3/17 vs. 2/9). The staged approach to Fontan completion did not influence SND. LT repair was the only factor causing sinus node dysfunction according to multivariate logistic regression (P=0.03, OR 5.96).
Lateral tunnel type surgical repair was more likely to lead to the development of sinus node dysfunction than extracardiac conduit operation. In the case of heterotaxy syndrome, surgical method had no significant influence.
Sinus node dysfunction (SND) is caused not only by intrinsic sinus node disease, but also by the extrinsic factors. Among the extrinsic factors, autonomic imbalance is most common. Symptomatic SND usually requires permanent pacemaker therapy. However, the clinical characteristics and patient response to medical therapy for hypervagotonic SND have not been properly clarified.
Thirty two patients (14 men, 18 women, 51 +/- 14 years) with hypervagotonic SND were included in this study, but those patients who had taken calcium antagonists, beta-blockers or other antiarrhythmic drugs were excluded. Hypervagotonic SND was diagnosed if the abnormal electrophysiologic properties of the sinus node were normalized after the administration of atropine (0.04 mg/kg).
The presenting arrhythmias were 16 cases of sinus bradycardia (50.0%), 12 of sinus pause (37.5%), 3 of sinoatrial block (9.4%) and 1 of tachy-bradycardia (3.1%). Nine (28.1%) patients had hypertension, 7 (21.9%) smoked, 2 (6.3%) had diabetes mellitus, and 1 (3.1%) had hypercholesterolemia. Among the patients, 3 had no remarkable symptoms, 13 had dizziness, 7 had syncope, 3 had weakness and 6 had shortness of breath. Twenty five (78.1%) patients were treated with theophylline, 1 patient with tachy-bradycardia syndrome was treated with digoxin and propafenone, and 6 (18.8%) were treated with no medication. During the 43 +/- 28 month follow-up, 25 patients remained asymptomatic, but 6 who took no medication developed mild dizziness. One patient needed permanent pacemaker implantation owing to recurrent syncope despite of theophylline treatment.
These results show that hypervagotonic SND has a benign course and most of the patients can be managed safely without implanting a pacemaker. (Ed note: I like the abstract. It is short and direct, as it should be.)
It is now well established that nearly all functions of the body, including those that influence the pharmacokinetics and pharmacodynamics of medications, exhibit significant 24-hour variation. The electrical properties of the heart as well as cardiac arrhythmias also vary as circadian rhythms, even though the suboptimal methods initially used for their investigation slowed their identification and thorough characterization. The application of continuous Holter monitoring of the electrical properties of the heart has revealed 24-hour variation in the occurrence of ventricular premature beats with the peak in events, in diurnally active persons, between 6 a.m. and noon. After the introduction of implantable cardioverter-defibrillators, ventricular tachycardia or fibrillation were also found to peak in the same period of the day. Even defibrillator energy requirements show circadian variation, thus supporting the need for a temporal awareness in the therapeutic approach to arrhythmias. Imbalanced autonomic tone, circulating levels of catecholamines, increased heart rate and blood pressure, all established determinants of cardiac arrhythmias, show circadian variations and underlie the genesis of the circadian pattern of cardiac arrhythmias. Arrhythmogenesis appears to be suppressed during nighttime sleep, and this can influence the evaluation of the efficacy of antiarrhythmic medications in relation to their administration time. Unfortunately, very few studies have been undertaken to assess the proper timing (chronotherapy) of antiarrhythmic medications as means to maximize efficacy and possibly reduce side effects. Further research in this field is warranted and could bring new insight and clinical advantage.
In an unselected population of 2030 newborn infants studied by electrocardiography (ECG) between April 1975 and April 1977, 35 were found to have arrhythmias or other cardiac conduction abnormalities. Further investigation by means of 24-hour ECG monitoring showed that apparently serious tachyarrhythmias, such as ventricular tachycardia and slow heart rates associated with sinoatrial block, may be present without clinical disturbance in some newborn babies. Six infants had both bradycardia and tachycardia in the 24-hour recording, although the screening ECG had shown only one of these abnormalities. The alarming ECG appearance of some of the arrhythmias suggested a possible aetiological link with some unexplained sudden infant deaths: a multicentre study could determine this more readily and is therefore recommended.
This study was supported in large part by research grants from the Commonwealth Fund and from the Rockefeller FoundationPublication was supported by the Publication Division, the Commonwealth Fund
I have proposed that orthodox electrocardiography be implemented, both for research and medical purposes, by the use of long-period,
continuous recording of heart potentials with a portable, self-contained instrument—the electrocardiocorder together with
semiautomatic methods for the rapid analysis of the resulting voluminous data. An electronic system to make this concept practical
has been developed in our laboratory and typical results are described in this article.
Changes in the QT and QTc intervals in 19 patients were studied at a ventricular paced rate difference of 50 beats/min. In all patients the measured QT interval shortened as the pacing rate was increased, from a mean value of 441 ms to 380 ms (p < 0.001), but when correct ed for heart rate the QTc- lengthened from a mean value of 518 ms to 575 ms. In 11 patients the QT in terval was measured at rest and immediately following exercise sufficient to increase the atrial rate by approximately 50 beats/min at identical ventricular paced rates. In all patients exercise-induced QT interval shortening from a mean value of 433 ms to 399 ms (p < 0.001). These results show first that Bazett's formula is unsuitable for correction of QT interval changes induced by ventricular pacing, and second that heart rate and changes in sympathetic tone independently influence the duration of the QT interval. It is suggested that these resuits are relevant to the design of physiological pacemakers in which the duration of the QT interval influences the discharge frequency of the pacemaker and to the consideration of ventricular pacing for the treatment of abnormal repolarization syndromes. (PACE, Vol. 5, May-June, 1982)
Results are reported of portable 24 hour dynamic electrocardiographic monitoring in 50 male medical students without cardiovascular disease, as defined by normal clinical and noninvasive cardiovascular examination. During waking periods, maximal sinus rates ranged from 107 to 180 beats/min (mean +/- 5). Twenty-five subjects (50 percent) had episodes of marked sinus arrhythmia as defined by spontaneous changes in adjacent cycle lengths of 100 percent or more. Fourteen subjects (28 percent) had sinus pauses of more than 1.75 seconds, usually during sinus arrhythmia. Transient nocturnal type I second degree atrioventricular (A-V) block was noted in three subjects (6 percent). Of 28 patients (56 percent) having atrial premature beats, only 1 (2 percent) had more than 100 such beats (141) in 24 hours. Of 25 patients (50 percent) having premature ventricular contractions, only 1 (2 percent) had more than 50 such contractions (86) in 24 hours. In conclusion, frequent atrial and ventricular premature beats are unusual in a young adult male population. In contrast, bradyarrhythmias (including marked sinus arrhythmia with sinus pauses, sinus bradycardia and nocturnal A-V block) are common. These findings are useful in evaluating the clinical significance of arrhythmias detected with portable monitoring.
The 24-hour cardiac rhythm was studied in 86 subjects (41 male, 45 female) aged 16-65 years, after exclusion of 15 additional volunteers with suspected abnormalities. The electrocardiogram was recorded continuously for two 24-hour periods. In this apparently normal population, 10 subjects (12%) had disturbances of rhythm which are widely believed to be of serious prognostic significance; they included frequent ventricular ectopic beats, R-on-T and multifocal ventricular ectopic beats, bigeminy, and ventricular tachycardia. Supraventricular tachycardia, infrequent ventricular ectopic beats, junctional rhythm, and second-degree heart block were also observed, and if these are included most of the subjects showed some disturbance of rhythm. Bradyarrhythmias and tachyarrhythmias were equally common in waking hours and during sleep. These disturbances were not confined to the older age-groups. Heart-rate but not the number of arrhythmias was significantly higher in smokers.
In this study, intracardiac electrograms were performed in 20 children--ranging in age from eight months to 18 years and without evidence of conduction disturbances on the scalar electrocardiogram--to determine the normal conduction patterns, response to atrial pacing, and values of refractory periods. Atrial pacing--18 cases--induced a prolongation al AH on increasing heart rates in all; 11 developed Wenckebach block proximal to the bundle of His at the mean pacing rate of 224 per minute +/- 45 (1 S.D.). Refractory periods were shorter than in adults. Study of the pattern of A-V conduction revealed three types of response: (1) the atrium was the limiting structure in 11 cases; (2) the delay occurred in the A-V node only in four cases; and (3) the delay occurred both in the A-V node and His-Purkinje system. This response was observed in one case only.
In the last five years there have been literally hundreds of articles of the world's medical literature regarding sudden infant death syndrome. This work has shed some light on various epidemiologic aspects of the problem, on pathologic anatomy, and on clinical issues such as the relative importance of spontaneous, protracted, idiopathic apnea and prolongation of the Q-T interval. This relatively comprehensive review treats only a limited number of these subjects and publications in an attempt to bring the reader more or less up-to-date on the major aspects of developments over the last five years.
To evaluate whether heart-rate-induced changes of the QT interval are dependent on autonomic tone, we studied 13 healthy subjects, mean age 67.5 years. The maximal uncorrected QT from leads I, II, V1 and V6 was determined during atrial pacing at 90 beats/min and 130 beats/min before and after i.v. administration of propranolol, 0.1 mg/kg, and atropine, 0.02 mg/kg. Significant reductions (p less than 0.01) of QT were induced by the paced increases in heart rate before drugs (10%), after propranolol (10%) and after the combination of atropine and propranolol (9%). Propranolol caused no significant change in the QT interval when heart rate was held constant by pacing. In contrast, atropine produced rate-independent reductions of QT interval (5%) in subjects with beta-adrenergic blockade (p less than 0.05). Bazett's formula for heart-rate correction of the QT interval (QTc) was not applicable for atrial overdrive pacing, as it gave proportionately longer QTc values at higher heart rates. These results show that heart rate is a major determinant of the duration of the QT interval and that paced changes in heart rate induce QT-interval responses that are essentially uninfluenced by autonomic tone. The rate-dependent effect of the QT interval produced by elimination of cholinergic tone suggests a direct influence of cholinergic activity on the repolarization of ventricular myocardium.
We have extended our observations on asymptomatic men with abnormal resting electrocardiograms showing changes indistinguishable from those of myocardial ischaemia but with normal coronary arteriograms. In the present investigation we aimed to separate the effects of heart rate alone from those of the sympathetic nervous system. We therefore studied the effects of atrial pacing alone, pacing and adrenaline infusion combined, pacing after beta-blockade, and pacing after beta-blockade plus atropine. Twenty asymptomatic men, aged 17 to 57, were investigated. All were shown to have unobstructed coronary arteries and normal left ventricular angiograms. Echocardiographic findings were normal. Sixteen had flat or inverted T waves in the lateral leads (designated 'T'), two had ST depression (designated 'ST'), and two had mixed patterns. T wave abnormalities had, to a lesser extent, ST changes returned to normal or regressed after an overnight rest in hospital. Subsequent atrial pacing to 160/minute reproduced or increased the respective abnormalities. When adrenaline was infused in low doses just sufficient to produce discernible effects on the ST-T segment 9between 0.024 and 0.091 μg/kg per min) and atrial pacing was repeated, the effect of the latter was enhanced. Both adrenaline and pacing influenced the ST-T segment in the same direction. Intravenous propranolol (0.2 mg/kg) blocked the effect of adrenaline and its synergistic effect with pacing but exerted little if any influence on the effect of pacing alone. Atropine given intravenously after propranolol (0.04 mg/kg) reduced the effect of atrial pacing on the ST-T configuration. Treadmill exercise tests were positive in nine and borderline in one. After beta-blockade (oral oxprenolol), all tests were negative. As beta-blockade did not prevent pacing-induced ST depression but normalised the false positive exercise test, the latter does not appear to be rate related but more probably the result of the direct influence of catecholamines. Isolated T wave changes and ST depression in the resting electrocardiogram differ in that they are influenced both by heart rate and catecholamines acting synergistically.
Drugs that affect the autonomic nervous system can influence the Q-T interval directly or by changing the heart rate. Bazett's formula to correct for rate may be misleading after certain drug interventions. This hypothesis was tested in 20 patients receiving both propranolol (0.15 mg/kg intravenously) and atropine (0.03 mg/kg intravenously). Six patients received propranolol first, 7 patients received atropine first, and 7 patients received atropine plus propranolol simultaneously. During control and after drug intervention, the Q-T interval was measured directly in sinus rhythm and during a fixed atrial paced rate, and was calculated using Bazett's formula. The ventricular effective refractory period was also determined in 6 patients after administration of atropine plus propranolol. The sinus cycle length (836 ± 156 to 648 ± 84 ms, mean ± standard deviation), measured Q-T interval (367 ± 26 to 329 ± 26 ms), and atrially paced Q-T interval (330 ± 28 to 315 ±27 ms) shortened after atropine plus propranolol (p <0.001), but the corrected Q-T interval with use of Bazett's formula did not change (402 ± 33 to 412 ± 24 ms). The ventricular effective refractory period also shortened from 241 to 20 to 218 ± 21 ms after atropine plus propranolol (p <0.02). The sinus cycle length increased after propranolol (750 ± 97 to 907 ± 108 ms, p <0.001), but no change occurred in the measured Q-T interval or atrial paced Q-T interval although the corrected Q-T interval using Bazett's formula was greatly shortened (428 ± 15 to 391 ±22 ms, p <0.001). The sinus cycle length, measured Q-T interval, and atrially paced Q-T interval decreased after atropine (p <0.01), but the corrected Q-T interval lengthened (375 ± 29 to 418 ± 28 ms, p <0.01).
The sequential changes and the rate dependence of the Q-T interval were studied in 21 patients 6 hours to 5 days after an anterior (11 cases) or an inferior (10 cases) acute transmural myocardial infarction. The Q-T interval was analyzed at fixed atrial-paced heart rates in leads aVF and V3 recorded at 100 mm/s and at twice the standard amplitude. Values were compared with those of a group of normal subjects matched by age and sex. Severe ventricular arrhythmias, electrolyte or conduction disturbances and pericarditis were excluded in all patients.Sequential changes in the Q-T interval were apparent only in the leads showing the ischemic changes (lead V3 in anterior and lead aVF in inferior myocardial infarction) in 19 of 21 patients. After an initial shortening (first 12 hours), there was a remarkable lengthening of the Q-T interval coinciding with T wave inversion (12 to 24 hours after the myocardial infarction). By the 4th to the 6th day, there was a return to normal values. The lengthening of the Q-T interval was greater in anterior than in inferior myocardial infarction. The rate-dependent shortening of the Q-T interval at increasing rates was more prominent at the beginning of T wave inversion.It is concluded that lengthening of the Q-T interval is common 12 to 24 hours after the onset of an acute myocardial infarction and that prolongation of up to 20 percent over the initial values may occur in cases not complicated by severe ventricular arrhythmias.
Ambulatory monitoring of the electrocardiogram was performed in 131 healthy boys aged between 10 and 13 years for two consecutive periods of 24 hours. When awake the maximal heart rates ranged from 100 to 200 and the minimal from 45 to 80 beats per minute. During sleep maximal rates were 60 to 110 beats and minimal rates 30 to 70 beats per minute. Sinus arrhythmia was seen in every boy and in 36 (27.5%) no other changes were found. Sinuatrial block, Mobitz type I, was not seen. Sinuatrial block, Mobitz type II, occurred twice only. Complete sinuatrial block occurred in 8.4 per cent, never lasted more than one cycle, and was always followed by a junctional beat. First degree atrioventricular block occurred in 8.4 per cent and Mobitz type I atrioventricular block in 10.7 per cent. Premature beats were always single, atrial in 13 per cent, ventricular in 26 per cent, and except in two boys were never more than four in 24 hours. There were no episodes of ventricular or supraventricular tachycardia. Changes in P wave morphology were common and slow junctional rhythm occurred in 13 per cent during sleep.
Twenty-four hour electrocardiographic recordings were made on 104 randomly selected, healthy 7 to 11-year-old children. Ninety-two were technically adequate and suitable for analysis. The mean highest heart rate measured by direct electrocardiographic analysis over nine beats was 164 +/- 17. The mean lowest heart rates were 49 +/- 6 over three beats', and 56 +/- 6 over nine beats' duration. The maximum duration of heart rates less than 55/minute was 40 minutes. At their lowest heart rates 41 children (45 per cent) had junctional escape rhythms, the maximum duration of which was 25 minutes. Nine children showed PR intervals greater than or equal to 0.20 s and included three with Mobitz type I second degree atrioventricular block. Nineteen (21%) had isolated supraventricular or ventricular premature beats (less than 1/hour). Sixty subjects (65%) had sinus pauses that could not be distinguished on the surface electrocardiogram from those previously described as sinuatrial exit block or sinus arrest. The maximum duration of sinus pause measured over 24 hours on each child was 1.36 +/- 0.23 seconds. Thus apparently healthy children show variations in heart rate and rhythm over 24 hours hitherto considered to be abnormal.
I have proposed that orthodox electrocardiography be implemented, both for research and medical purposes, by the use of long-period, continuous recording of heart potentials with a portable, self-contained instrument-the electrocardiocorder together with semiautomatic methods for the rapid analysis of the resulting voluminous data. An electronic system to make this concept practical has been developed in our laboratory and typical results are described in this article.
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