Duration of diastole and its phases as a function of heart rate during supine bicycle exercise
ABSTRACT The duration of diastole can be defined in terms of mechanical events. Mechanical diastolic duration (MDD) is comprised by the phases of early rapid filling (E wave), diastasis, and late atrial filling (A wave). The effect of heart rate (HR) on diastolic duration is predictable from kinematic modeling and known cellular physiology. To determine the dependence of MDD of each phase and the velocity time integral (VTI) on HR, simultaneous transmitral Doppler flow velocities and ECG were recorded during supine bicycle exercise in healthy volunteers. Durations, peak values, and VTI using triangular approximation for E- and A-wave shape were measured. MDD, defined as the interval from the start of the E wave to end of the A wave, was fit as an algebraic function of HR by MDD=BMDD + MLMDD.HR + MIMDD/HR, derivable from first principles, where BMDD is a constant, and MLMDD and MIMDD are the constant coefficients of the linear and inverse HR dependent terms. Excellent correlation was observed (r2=0.98). E- and A-wave durations were found to be very nearly independent of HR: 100% increase in HR generated only an 18% decrease in E-wave duration and 16% decrease in A-wave duration. VTI was similarly very nearly independent of HR. Diastasis duration closely tracked MDD as a function of HR. We conclude that the elimination of diastasis and merging of E and A waves of nearly fixed durations primarily govern changes in MDD. These observations support the perspective that E- and A-wave durations are primarily governed by the rules of mechanical oscillation that are minimally HR dependent.
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ABSTRACT: Background-Childhood dilated cardiomyopathy (DCM) carries high morbidity and mortality. The echocardiographic systolic to diastolic (S: D) duration ratio, an indicator of global cardiac performance, is elevated in DCM; however, its prognostic implications have not been investigated in this population. Methods and Results-We investigated systolic and diastolic durations and the resultant S: D ratio using pulsed tissue Doppler imaging in children with idiopathic or familial DCM. We studied serial echocardiograms from presentation until the last follow-up echo. Results were compared with heart rate-matched controls and between DCM subgroups based on an acute or insidious presentation. The association between S: D ratio and death or need for transplant was analyzed. All analyses were adjusted for repeated measures per patient. We studied 200 serial echocardiograms of 48 children with DCM (7.0 +/- 6.0 years) and 25 controls. Adjusted for repeated measures through a compound symmetry covariance structure, the S: D ratio was higher in DCM patients (-0.425 [0.072]; P<0.001) because of shortened diastole. A S: D ratio > 1.2 at presentation and on serial evaluation was associated with a hazard ratio of 10.5 (95% confidence interval, 3.9-27.8; P<0.001) for death or transplant. In combined multivariable analysis, a S: D ratio > 1.2 remained significantly associated with hazard of death/transplant (hazard ratio, 9.1; P=0.04) after adjustment for ejection fraction (hazard ratio: 2.2 per -10%; P<0.001). Conclusions-A high S: D ratio is associated with increased risk for death or need for transplant in children with DCM across the spectrum of heart rates and may be a useful prognostic index for serial evaluation of children with DCM.Circulation Cardiovascular Imaging 08/2014; 7(5). DOI:10.1161/CIRCIMAGING.114.002120 · 6.75 Impact Factor
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ABSTRACT: Background:This study assessed the independent significance of color Doppler 3-D vena contracta area (VCA) at rest and during exercise as a predictor of clinical outcome in mild-moderate functional mitral regurgitation (FMR).Methods and Results:The subjects consisted of 62 patients (age, 68±11 years; 76% male) with chronic systolic heart failure and mild-moderate FMR (<2+/4) at rest. All patients underwent VCA assessment at rest and during semi-supine bicycle exercise. During median follow-up of 17 months (IQR, 13-20 months), 15 patients (24%) had composite endpoint of all-cause death (n=3), heart failure admission (n=11), and heart transplantation (n=1). At baseline, patients with vs. without endpoint had significantly larger VCA at rest (17±6 mm(2)vs. 13±7 mm(2), P=0.002) and at peak exercise (35±16 mm(2)vs. 21±12 mm(2), P<0.001). On Cox regression analysis, large (≥15-mm(2)) resting VCA (HR, 7.6; 95% CI: 1.93-13.02; P=0.004) and large (≥20-mm(2)) exercise-induced increase of VCA (HR, 5.1; 95% CI: 1.39-15.21; P=0.014) were independently associated with composite endpoint. Concomitant presence of large VCA at rest and its large increase during exercise occurred in 53% of patients with, vs. in only 8% without, endpoint (negative predictive value, 86%).Conclusions:The presence of relatively large VCA at rest and its significant increase during exercise is independently associated with adverse clinical outcome in patients with mild-moderate FMR at rest.Circulation Journal 10/2014; 78(11). DOI:10.1253/circj.CJ-14-0183 · 3.69 Impact Factor
Journal of the American College of Cardiology 06/2014; 63(22):2438-2488. DOI:10.1016/j.jacc.2014.02.537 · 15.34 Impact Factor