| Summary: | Background: Nitroglycerin (NTG) reduces cardiac pre-load and after-load through venodilation and arterial dilation respectively but the relative contributions of these effects to reduction in myocardial wall stress is unknown.
Methods: We estimated myocardial wall stress from transthoracic echocardiographic imaging of the left ventricle (LV) and LV pressure estimated from carotid tonometry during systole. Nineteen subjects aged 43.3 ± 2.7 (mean ± SE) years were studied before and 7–12 min after NTG (400 ìg sublingually). Carotid pressure calibrated by mean and diastolic blood pressure (BP) was used to calculate time-varying LV wall stress from endocardial and epicardial volumes obtained from Tomtec wall tracking analysis. The relative contributions of reductions in systolic pressure and in LV volumes and to overall reduction in LV wall stress were calculated assuming that volume or pressures after NTG were identical to baseline values.
Results: NTG decreased peak LV stress (pre: 387±22; post: 329±22kdynes/cm2, P<0.001), mean stress (pre: 335±19; post: 277±20 kdynes/cm2, P<0.001) and peak stress time over ejection time (pre: 0.37±0.03; post: 0.30±0.01, P<0.05) due to reduction of LV end-diastolic volume (pre: 107±7.3; post: 95.6±7.3ml, P<0.01), end-systolic volume (pre: 47.9±4.4; post: 40.1±3.7ml, P<0.01) and central systolic BP (pre: 138±5.9; post: 122±4.8 mmHg, P<0.001). Percentage change in mean stress attributable to reductions in pressure and volume were 11.2% and 9.5% respectively demonstrating that pre-load and after-load contributed approximately equally to the reduction of LV wall stress.
Conclusions: NTG reduces myocardial stress and increases myocardial contraction efficiency as a result of similar contributions from reductions in pre- and after-load.
P5.03 Withdrawn by author
|
|---|
