Publications (13)28.15 Total impact

Article: High Mechanical Efficiency of Left Ventricular Arrhythmic Contractions during Atrial Fibrillation
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ABSTRACT: We analyzed the frequency distribution of the left ventricular (LV) mechanical efficiency of individual arrhythmic beats during electrically induced atrial fibrillation (AF) in normal canine hearts. This efficiency is the fraction of the external mechanical work (EW) in the total mechanical energy measured by the systolic pressurevolume area (PVA). The mean, median, and mode of this efficiency (EW/PVA) were as high as 78%, 80%, and 81%, respectively, on average in six hearts. These high efficiencies were comparable to that of the regular beats in these hearts. The frequency distribution of the EW/PVA during AF tended to skew to the higher side in all the hearts. Since the EW/PVA is directly related to both the ventriculoarterial (or afterload) coupling ratio (E(a)/E(max); E(a) = effective arterial elastance, E(max) = endsystolic ventricular elastance) and the ejection fraction on a perbeat basis, we also analyzed their frequency distributions. We found them to skew enough to account for the rightward skewed frequency distribution of the EW/PVA during AF with the unexpectedly high mean EW/PVA. These results indicate that the LV arrhythmia during AF per se does not directly suppress the mean level of LV mechanical efficiency in normal canine hearts.  [Show abstract] [Hide abstract]
ABSTRACT: We have reported that the contractility index (E(max)) and the total mechanical energy (PVA) of arrhythmic beats of the left ventricle (LV) distribute normally in canine hearts under electrically induced atrial fibrillation (AF). Here, E(max) is the ventricular elastance as the slope of the endsystolic (ES) pressurevolume (PV) relation (ESPVR), and PVA is the systolic PV area as the sum of the external mechanical work within the PV loop and the elastic potential energy under the ESPVR. To obtain E(max) and PVA, we had to assume the systolic unstressed volume (V(o)) as the Vaxis intercept of the ESPVR to be constant despite the varying E(max), since there was no method to obtain V(o) directly in each arrhythmic beat. However, we know that in regular stable beats V(o) decreases by approximately 7 ml/100 g LV with approximately 100 times the increases in E(max) from ~0.2 mmHg/(ml/100 g LV) of almost arresting weak beats to approximately 20 mmHg/(ml/100 g LV) of strong beats with a highly enhanced contractility. In the present study, we investigated whether E(max) and PVA under AF could still distribute normally, despite such E(max)dependent V(o) changes. The present analyses showed that the E(max) changes were only approximately 3 times at most from the weakest to the strongest arrhythmic beat under AF. These changes were not large enough to affect V(o) enough to distort the frequency distributions of E(max) and PVA from normality. We conclude that one could practically ignore the slight E(max) and PVA changes with the Emaxdependent V(o) changes under AF.  [Show abstract] [Hide abstract]
ABSTRACT: We previously found the frequency distribution of the left ventricular (LV) effective afterload elastance (E(a)) of arrhythmic beats to be nonnormal or nonGaussian in contrast to the normal distribution of the LV endsystolic elastance (E(max)) in canine in situ LVs during electrically induced atrial fibrillation (AF). These two mechanical variables determine the total mechanical energy [systolic pressurevolume area (PVA)] generated by LV contraction when the LV enddiastolic volume is given on a perbeat basis. PVA and E(max) are the two key determinants of the LV O(2) consumption per beat. In the present study, we analyzed the frequency distribution of PVA during AF by its chi(2), significance level, skewness, and kurtosis and compared them with those of other major cardiodynamic variables including E(a) and E(max). We assumed the volume intercept (V(0)) of the endsystolic pressurevolume relation needed for E(max) determination to be stable during arrhythmia. We found that PVA distributed much more normally than E(a) and slightly more so than E(max) during AF. We compared the chi(2), significance level, skewness, and kurtosis of all the complex terms of the PVA formula. We found that the complexity of the PVA formula attenuated the effect of the considerably nonnormal distribution of E(a) on the distribution of PVA along the central limit theorem. We conclude that mean (SD) of PVA can reliably characterize the distribution of PVA of arrhythmic beats during AF, at least in canine hearts.  [Show abstract] [Hide abstract]
ABSTRACT: Left ventricular (LV) O2 consumption (V(O2)) per minute is measurable for both regular and arrhythmic beats. LV V(O2) per beat can then be obtained as V(O2) per minute minute divided by heart rate per minute minute for regular beats, but not for arrhythmic beats. We have established that V(O2) of a regular stable beat is predictable by V(O2) = a PVA + b E(max) + c, where PVA is the systolic pressurevolume area as a measure of the total mechanical energy of an individual contraction and E(max) is the endsystolic maximum elastance as an index of ventricular contractility of the contraction. Furthermore, a is the O2 cost of PVA, b is the O2 cost of E(max), and c is the basal metabolic V(O2) per beat. We considered it theoretically reasonable to expect that the same formula could also predict LV V(O2) of individual arrhythmic beats from their respective PVA and E(max) with the same a, b, and c. We therefore applied this formula to the PVA  Emax data of individual arrhythmic beats under electrically induced atrial fibrillation (AF) in six canine in situ hearts. We found that the predicted V(O2) of individual arrhythmic beats highly correlated linearly with either their V(O2) (r = 0.96 +/ 0.01) or E(max) (0.97 +/ 0.03) while both also highly correlated linearly with each other (0.88 +/ 0.04). This suggests that the above formula may be used to predict LV Vo2 of absolute arrhythmic beats from their Emax and PVA under AF.  [Show abstract] [Hide abstract]
ABSTRACT: Warm ischemia is a major cause of cardiac allograft dysfunction in nonheartbeating donors (NHBDs). We evaluated the cardioprotective effects of nicorandil, an adenosine triphosphatesensitive potassium channel opener, on the early posttransplant left ventricular (LV) function of hearts harvested from asphyxiated canine NHBDs. Hypoxic cardiac arrest was induced in 12 donor dogs. In 6, nicorandil was administered intravenously at 100 micrograms/kg + 25 micrograms/kg/min after respiratory arrest and hearts were preserved with nicorandilsupplemented cardioplegic solution (nicorandil group). The remaining 6 did not receive nicorandil at any time during the experiment (control group). Hearts were orthotopically transplanted after a mean myocardial ischemic time of 4 hours. All 12 recipients were weaned from cardiopulmonary bypass without inotropic support. In the control group, posttransplant cardiac indices and left ventricular endsystolic pressure (LVESP) decreased significantly, while LV maxdP/dt and Tau increased over pretransplant values. No differences were seen in parameters between pretransplant and posttransplant values in the nicorandil group. Posttransplant cardiac indices, LVESP, and LV max + dP/dt were higher in the nicorandil group than in controls, while posttransplant LV maxdP/dt in the nicorandil group was lower. Our results indicate that pretreatment with nicorandil during hypoxic perfusion before cardiac arrest and subsequent preservation with nicorandilsupplemented cardioplegia ameliorates early posttransplant LV dysfunction of hearts harvested from asphyxiated NHBDs. 
Article: Posttransplant function of a nonbeating heart is predictable by an ex vivo perfusion method
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ABSTRACT: We attempted to predict the posttransplant cardiac function of nonbeating donor hearts. A total of 13 dogs were studied. Hearts were left in situ for 45 minutes after cardiac arrest caused by exsanguination. Hearts were then excised and reperfused in an ex vivo perfusion apparatus after 60 minutes of warm ischemia to test whether they could eject against an 80 mm Hg afterload from a preload of 10 mm Hg. Thereafter, all hearts were transplanted orthotopically. Four of 13 hearts were able to eject in the apparatus (group A). However, the other nine hearts could not eject under the defined conditions (group B). All four hearts in group A showed good posttransplant hemodynamics (systolic arterial pressure > 80 mm Hg with mean left atrial pressure < 10 mm Hg) without dopamine. However, none of nine hearts in group B could support the circulation without dopamine. Nonbeating donor heart function evaluated in the perfusion apparatus predicts posttransplant heart function. This method may be applicable for selection of transplantable hearts from nonbeating heart donors. 
Article: Effective Arterial Elastance of Irregular Beats during Atrial Fibrillation in Canine Left Ventricle.
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ABSTRACT: Effective arterial elastance (E(a)) was originally defined as the endsystolic pressure (ESP)/stroke volume (SV) ratio of the left ventricle (LV). E(a) combined with LV contractility (E(max)), E(a)/E(max), proved to be powerful in analyzing the ventriculoarterial coupling of normal and failing hearts in regular beats. However, E(a) sensitively changes with LV E(max), preload, and afterload widely changing among irregular beats. This has discouraged the use of E(a) during arrhythmia. However, we hypothesized that E(a) could serve as the effective afterload (not always arterial) elastance against ventricular ejection under arrhythmia. We tested this hypothesis by analyzing beattobeat changes in E(a) of irregular beats during electrically induced atrial fibrillation (AF) in normal canine in situ hearts. We newly found that during AF in each heart: 1) E(a) changed widely among irregular beats and became markedly high in weak beats with small SVs; 2) E(a) and E(a)/E(max) distributed nonnormally with large skewness but 1/E(a) distributed more normally; 3) 1/E(a) correlated closely with enddiastolic volume, E(max) and preceding beat intervals; and 4) the reciprocal of mean 1/E(a) closely correlated with mean ESP/mean SV. These results support our hypothesis that E(a) can serve as the effective afterload elastance against ventricular ejection on a perbeat basis during AF. E(a)/E(max) can also quantify the ventriculoafterload (not arterial) coupling on a perbeat basis. This study, however, warns that mean E(a) and mean E(a)/E(max) of irregular beats cannot necessarily represent their averages during AF. 
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ABSTRACT: We recently found that contractility (Emax) of an individual irregularly arrhythmic beat in electrically induced atrial fibrillation (AF) is reasonably predictable from the ratio of the preceding beat interval (RR1) to the beat interval immediately preceding RR1 (RR2) in the canine left ventricle. Moreover, the monotonically increasing relation between Emax and the RR1toRR2 ratio (RR1/RR2) passed through or by the mean arrhythmic beat Emax as well as the regular beat Emax at RR1/RR2 = 1. We hypothesized that this EmaxRR1/RR2 relation during irregular arrhythmia could be attributed to the basic characteristics of the mechanical restitution and potentiation. To test this, we adopted a known comprehensive equation describing the force restitution and potentiation as a function of two preceding beat intervals and simulated contractilities of irregular arrhythmic beats with randomized beat intervals on a computer. The simulated EmaxRR1/RR2 relation reasonably resembled the one that we recently observed experimentally, supporting our hypothesis. We therefore conclude that the primary mechanism underlying the varying contractilities of irregular beats in AF is mechanical restitution and potentiation. 

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ABSTRACT: We briefly review that ventricular systolic pressurevolume area (PVA) can predict changes in myocardial O2 consumption (VO2) associated with cardiac work production (positive work) and absorption (negative work). PVA represents the total mechanical energy of cardiac contraction as it is an integral of mechanical energy generated during systole in the cardiac chamber. We have shown that PVA linearly correlates with VO2 under varied pre and afterload conditions in the left ventricle of the excised crosscirculated canine heart preparation as well as other heart preparations of different species. PVA is the sum of external mechanical work (EW) and mechanical potential energy (PE) which is almost fully convertible to mechanical work without affecting VO2. To compare the energetic effects of cardiac work production and absorption, we varied the timing of the servo pump motion relative to left ventricular (LV) contraction. When the pump fills the LV during diastole and sucks (allows ejection) during systole, cardiac work is produced by the heart, and hence EW > 0. When the pump fills the LV during systole and sucks during diastole, work is absorbed by the heart, and hence EW < 0. The pressurevolume loop rotates counterclockwise when EW > 0. It rotates clockwise when EW < 0. As the result, PVA (= PE + EW) > PE when EW > 0; PVA < PE when EW < 0. We found that VO2 always linearly correlated with PVA regardless of the polarity of EW. Therefore, PVA is the unique determinant of VO2 in a cardiac chamber in a stable contractility.  [Show abstract] [Hide abstract]
ABSTRACT: How left ventricular (LV) contractility relates to irregular RR intervals during atrial fibrillation (AF) is still unclear. We investigated the relationship between the LV contractility (Emax) of individual beats and their preceding RR intervals during AF in isovolumic contractions is excised crosscirculated canine hearts, and additionally in ejecting contractions in in situ canine hearts. Atrial highfrequency electrical stimulation induced AF. We recorded a LV electrocardiogram, volume and pressure, and calculated the Emax of every arrhythmic beat. Multiple linear regression analysis between Emax and the six preceding RR intervals of all arrhythmic beats during 1 min AF showed the preceding RR interval (RR1) and the prepreceding interval (RR2) to be the predominant predictors of Emax. The EmaxRR1/RR2 scattergram was closely fitted by a linear regression line. We found Emax at RR1/RR2 = 1 on the regression line to be virtually identical with both mean Emax during AF and stable Emax obtained during irregular atrial pacing at the same intervals as the mean RR interval during AF. These results newly indicate that the pressureinterval relationship predominantly characterizes LV irregular beat contractilities and their mean level during AF.
Publication Stats
106  Citations  
28.15  Total Impact Points  
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Institutions

19972005

Okayama University
 Department of Cardiovascular Surgery
Okayama, Okayama, Japan
