P6.6 NITROGLYCERIN IMPROVES SYSTOLIC MYOCARDIAL EFFICIENCY

Abstract

Introduction: Nitroglycerin (NTG) has a particularly marked action to reduce augmentation pressure (cAP), attributed to a reduction in timing or amplitude of pressure wave reflection. However, a recent study suggests that cAP is determined in large part by ventricular contraction/relaxation dynamics. We examined whether the reduction in cAP induced by NTG is associated with a change in left ventricular (LV) systolic function. Methods: We estimated myocardial wall stress from transthoracic echocardiographic imaging of the LV and LV pressure estimated from carotid tonometry during systole. Eighteen subjects aged 43.0±11.9 (mean ± SD) years were studied before and 7-12 min after NTG (400 μg sublingually). Carotid pressure calibrated by mean and diastolic blood pressure was used to calculate time-varying LV wall stress from endocardial and epicardial volumes obtained from wall tracking analysis. Tissue Doppler Imaging (TDI) S wave (a measure of LV systolic function) was measured at the basal mitral annulus from an echocardiographic 4-chamber view. Results: NTG decreased cAP from 16.3±3.6 to 4.5±2.9mmHg (means±SEM, P<0.0001) and central systolic blood pressure decreased by a similar amount. Time to peak MWS decreased from 115.9±10.9 to 86.8±4.6ms (P=0.024). This difference persisted after adjustment for change in heart rate and blood pressure (P=0.017). TDI S wave increased from 3.1±0.3 to 4.0±0.4cm/s (P=0.017). By contrast, NTG had no significant effect on ejection fraction or stroke volume. Conclusion: NTG reduces cAP and improves the efficiency of myocardial contraction with a reduction in time to peak MWS.