Effects of Afterload Increase on Systolic and Diastolic Functions of the Myocardium After Myocardial Infarction

Abstract

The evaluation of noninfarcted zone function after myocardial infarction by the use of noninvasive methods is very important. The authors speculated that phenylephrine, which increases systemic vascular resistance and blood pressure and has no effect on central ischemic and border-zone myocardium but does have an effect on remote myocardium, could be used as a stress agent as information is gathered about the functional capacity of the left ventricle and the status of coronary arteries in patients with recent myocardial infarction. Forty-six patients with recent myocardial infarction (5 women, 41 men; mean age: 53.6 +/-9.3 years) and 15 individuals with normal findings from coronary angiography and ventriculography (9 women and 6 men; mean age: 39.0 +/-11.2 years) were included in the study. The study was performed on the 4th or 5th day of the myocardial infarction. Preejection period/left ventricular ejection time (PEP/LVET), diastolic mitral flow velocity, isovolumic relaxation time (IVRT), and deceleration time (DT), were measured before and after the phenylephrine infusion, with M-mode, pulse wave, and continuous-wave echocardiography. After pressor stress with phenylephrine infusion, all the parameters were measured again. Coronary angiography and ventriculography were performed on all the patients on the 7th to 10th day of the myocardial infarction. All the patients were grouped according to their ejection fraction and the number of involved coronary arteries. The increase in the PEP/LVET ratio in Group 1 (left ventricle ejection fraction [EF] below 40%) and multivessel coronary artery lesion group was significant (p<0.01). PEP/LVET ratio decreased significantly in both Group C (patients with normal-appearing coronary arteries and ventriculographies) and the single-vessel coronary disease group. Although the early diastole flow/atrial systole flow (E/A) ratio increased significantly in the 3 groups, the 0.5 and more increase in E/A ratio had high sensitivity (86%) and specificity (80%) in differentiating the low EF group. The 0.5 and more increase in E/A ratio had 65% sensitivity and 69% specificity in differentiating the multivessel coronary stenosis group. A deceleration time of 130 msec and below in basal conditions had a high sensitivity (86%) and specificity (92%) for detecting the group in which EF was below 40%. After phenylephrine infusion, the shortening of IVRT was significant in Group 1 (p<0.01). Phenylephrine, which has been shown to be an alpha-1 receptor agonist in low doses and effective only on remote myocardial function, may be given with low complication rates in the early postinfarction period. The increase in PEP/LVET ratio, 0.5 and more increase in E/A ratio, and shortening of DT and IVRT after phenylephrine infusion may be indicators of low LV functional capacity and widespread coronary artery disease. This test may suggest performance of early invasive detection of coronary artery disease and early revascularization. This study may also be interesting from a pathophysiological point o...