[Effects of nitroglycerin on left ventricular geometry and compliance in man]

The effects of nitroglycerin (NTG) on relaxation characteristics of the infarcted and non-infarcted myocardium were investigated by calculating a segment length on the epicardium of the left ventricle for 16 patients with old myocardial infarction. The spatial segment length was measured between two points which were identified as a junction of ramifying branches of the left coronary arteries using biplane coronary cineangiography. Regional myocardial stiffness was expressed as delta P/delta L, where delta P was an increment of left ventricular (LV) diastolic pressure from the lowest LV diastolic pressure to the pressure at the maximal segment length, and delta L was the difference of two segment lengths corresponding to those pressures. Myocardial stiffness decreased from 0.0402 +/- 0.0293 mmHg/mm to 0.0212 +/- 0.0157 with intracoronary NTG (p less than 0.01) and from 0.0220 +/- 0.0090 to 0.0136 +/- 0.0124 with sublingual NTG (p less than 0.001) in the non-infarcted portions. However, it was unchanged with both intracoronary and sublingual NTG in the infarcted portions. NTG may cause venous pooling and may decrease diastolic wall tension of the left ventricle as its indirect effect on the non-infarcted myocardium. Also, the non-infarcted myocardium may be influenced by dilatation of the epicardial coronary artery. Muscle stiffness of the infarcted myocardium was unchanged, probably due to the rigidity of myocardial fibrosis. It was concluded that in myocardial infarction diastolic distensibility of the non-infarcted portion can be improved by NTG both through indirect and direct effects.