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Biomedical subjects

A S Most

Publications and source records attributed to A S Most.

At least 55 records · Page 3Linked to original sources
PubMed1983

Role of myocardial ischemia in the genesis of stress-induced S-T segment elevation in previous anterior myocardial infarction.

This study tests the hypothesis that myocardial ischemia is responsible for exercise-induced S-T segment elevation in patients with previous anterior myocardial infarction (MI). Exercise stress testing in conjunction with thallium imaging of the myocardium was performed in 28 patients with previously documented anterior MI. Thallium images were analyzed by computer for the presence of initial uptake defects and evidence of abnormal clearance of the isotope from the myocardium (that is, imaging evidence of ischemia). Total S-T segment elevation (sigma ST) in precordial leads V1 to V6 at rest was subtracted from sigma ST at peak stress in order to quantitate the extent of S-T elevation induced by stress (delta ST). Two groups of patients were identified; 1 with stress-induced S-T elevation (Group I, delta ST greater than or equal to 4.0 mm) and 1 without this abnormality (Group II, delta ST less than 4.0 mm). Evidence of abnormal thallium washout from myocardial scan segments occurred in 12 of 15 Group I patients versus 9 of 13 Group II patients (difference not significant). In addition, abnormal tracer washout from anterolateral or septal scan segments occurred in 5 patients in each group. Likewise, abnormal thallium clearance from inferior or posterior scan segments occurred in 8 of 15 Group I patients versus 7 of 13 Group II patients (difference not significant). The patient with the greatest amount of stress-induced S-T elevation (S-T 11.5 mm) had no evidence of ischemia during the stress test. However, Group I patients did have larger anterolateral plus septal initial thallium uptake defect scores than did those of Group II (10 of 15 with defect score greater than or equal to 350 in Group I versus 1 of 13 in Group II, p less than 0.002). Similarly, resting left ventricular ejection fraction greater than or equal to 30% was present in only 4 of 15 Group I patients versus 13 of 13 in Group II (p less than 0.001). Finally, multiple stepwise linear regression analysis demonstrated that delta ST correlated best with the extent of initial anterolateral plus septal thallium uptake defect score (F = 17.3, p less than 0.001) and to a lesser extent with resting ejection fraction (F = 5.2, p less than 0.05) and change in heart rate from rest to peak stress (F = 8.1, p less than 0.01; corrected multiple correlation coefficient = 0.76, p less than 0.001). Thus, in patients with previous anterior MI (1) exercise-induced myocardial ischemia occurs as often with as without S-T segment elevation, (2) myocardial ischemia is not required for the production of stress-induced S-T segment elevation, and (3) stress-induced S-T elevation primarily reflects the extent of previous anterior wall damage and to a lesser extent an increase in heart rate between rest and peak stress.

Adult↗
PubMed1983

Coronary circulatory dynamics before and after successful coronary angioplasty.

The hypothesis that successful percutaneous transluminal coronary angioplasty restores normal coronary circulatory dynamics was tested. Regional coronary blood flow, myocardial oxygen consumption and lactate extraction were measured at rest and during sustained pacing tachycardia. Before angioplasty, tachycardia stress was associated with an attenuated blood flow and oxygen consumption response and the induction of anaerobic metabolism. After successful angioplasty, blood flow and myocardial oxygen consumption increased during tachycardia stress and aerobic metabolism was sustained. The influence of basal alpha-adrenergic tone in modifying the time course of blood flow response to abrupt pacing was also assessed. Patients with normal coronary arteries demonstrated delayed increase in blood flow after alpha-adrenergic blockade. Alpha-adrenergic blockade did not affect the time course of blood flow response in patients with coronary artery disease, suggesting that alpha-adrenergic tone was chronically withdrawn. In patients undergoing coronary angioplasty, flow response before angioplasty was delayed, consistent with withdrawal of basal alpha-adrenergic tone. After coronary angioplasty, a brisk flow response was observed, indicating that basal alpha-adrenergic tone had been restored. Thus, successful coronary angioplasty restores the normal responsiveness of the coronary circulation.

Adrenergic alpha-Antagonists↗
PubMed1983

Role of adenosine in the maintenance of coronary vasodilation distal to a severe coronary artery stenosis. Observations in conscious domestic swine.

The purpose of this study was to test the hypothesis that adenosine is required to maintain arteriolar vasodilation distal to a severe coronary stenosis. Eight closed-chest conscious pigs were prepared by placing a 7.5-mm long stenosis (82% lumenal diameter reduction) in the proximal left anterior descending coronary artery. Regional myocardial blood flow (microsphere technique) was measured at control 1, after 10 minutes of intracoronary infusion of adenosine deaminase (7-10 U/kg per min) distal to the stenosis, and 20-30 minutes after stopping adenosine deaminase infusion. Studies with 125I-labeled adenosine deaminase were conducted in six additional pigs to document the extent to which infused adenosine deaminase penetrated the interstitial space. 125I-labeled adenosine deaminase was infused for 10 minutes (10-11 U/kg per min) into the left anterior descending coronary artery. Calculated interstitial fluid concentrations of adenosine deaminase ranged between 71 and 272 U/ml and were at least one order of magnitude greater than that required to deaminate all the adenosine which would be released into the interstitium in response to 15-30 seconds of coronary occlusion. In the primary group of animals (n = 8), endocardial flow (ml/min per g) distal to stenosis at control 1 (1.15 +/- 0.33) was reduced vs. endocardial flow in the nonobstructed circumflex zone (1.59 +/- 0.38, P less than 0.05). Flows in epicardial layers were comparable at control 1 (distal zone = 1.40 +/- 0.36 vs. circumflex zone = 1.45 +/- 0.41). Distal zone endocardial and epicardial flows did not change vs. control 1 in response to infusion of adenosine deaminase. However, the distal: circumflex epicardial flow ratio declined vs. control 1 (0.98 +/- 0.14) during adenosine deaminase infusion (0.87 +/- 0.17, P less than 0.05). The distal:circumflex endocardial flow ratio during adenosine deaminase (0.72 +/- 0.20) was unchanged vs. control 1 (0.76 +/- 0.22) but was less than control 2 (0.80 +/- 0.18, P less than 0.05). Thus, destruction of all or most interstitial adenosine caused only slight relative reduction in regional myocardial blood flow distal to a severe coronary artery stenosis. Accordingly, adenosine contributes only modestly to maintenance of arteriolar vasodilation in this setting or else its absence is almost fully compensated for by another mechanism(s).

Adenosine↗
PubMed1982

The effect of intraaortic balloon counterpulsation on regional myocardial blood flow and oxygen consumption in the presence of coronary artery stenosis in patients with unstable angina.

To determine whether a reduction in myocardial oxygen demand or an increase in coronary blood flow or both are responsible for the salutory effect of intraaortic balloon counterpulsation (IABP) in relieving medically refractory angina, we assessed these variables in six patients in whom IABP was required for relief of myocardial ischemia. IABP decreased the rate-pressure product and aortic end-diastolic pressure, and the peak systolic aortic pressure and regional myocardial oxygen consumption declined in all but one patient. Peak and mean aortic diastolic pressures increased. Changes in regional coronary blood flow paralleled changes in peak systolic aortic pressure (r = 0.92, p less than 0.007). Thus, relief of angina during IABP could not be ascribed to an increase in regional coronary blood flow. Reduction of myocardial oxygen consumption is the most likely mechanism by which IABP relieves myocardial ischemia in patients with unstable angina pectoris.

Aged↗
PubMed1981

Evaluation of the role of coronary angioplasty in patients with unstable angina pectoris.

Seventeen patients presenting with unstable angina pectoris underwent percutaneous transluminal coronary angioplasty (PTCA). Despite vigorous medical therapy, all patients were disabled with 10 experiencing refractory in-hospital angina. PTCA was judged successful in 13 patients and resulted in decreased coronary diameter narrowing from 80 +/- 16% to 34 +/- 13% and reduced transstenotic pressure gradient from 69 +/- 13 to 23 +/- 12 mm Hg. Regional coronary blood flow (CBF) and myocardial metabolism were assessed at rest and during pacing tachycardia in six patients with left anterior descending coronary stenosis. Prior to PTCA, neither regional CBF increased nor coronary vascular resistance declined during rapid pacing; myocardial lactate extraction fell, indicating a shift from aerobic to anerobic metabolism. Following PTCA, however, rapid pacing resulted in increased regional CBF, decreased coronary vascular resistance, and preservation of aerobic metabolism. Following PTCA, successfully dilated patients demonstrated marked relief of angina symptoms, increase in functional capacity, and objective exercise ECG and thallium scintigraphic evidence of relief of previously ischemic myocardium. This investigation demonstrates that PTCA, when combined with medical therapy, can be performed safely and successfully in selected patients who present with otherwise refractory unstable angina, and indicates the procedure deserves further study as a therapeutic alternative in this condition.

Adult↗
PubMed1981

Responsiveness of the coronary circulation to brief vs sustained alpha-adrenergic stimulation.

The effects of brief and sustained pharmacologic alpha-adrenergic stimulation on the coronary arterial circulation were compared in awake pigs. Phenylephrine was administered into the left anterior descending coronary artery (LAD) either as a bolus (eight pigs) or as a 15-minute infusion (eight pigs), with myocardial blood flow measured by the radioactive microsphere technique. Flow in the distribution in the LAD was compared with flow in myocardium perfused by the left circumflex coronary artery (LCF) as the ratio LAD/LCF. This technique corrects for systemic factors capable of modifying oxygen demand, and hence myocardial blood flow, in both zones. After a phenylephrine bolus (50-100 microgram), LAD/LCF fell significantly, whereas no change was observed after the sustained infusion (5-10 and 50-100 microgram/min). Four additional pigs were pretreated with i.v. adenosine to raise myocardial blood flow in excess of demand before sustained stimulation. In this setting LAD/LCF fell significantly during the sustained phenylephrine infusion. Brief alpha-adrenergic stimulation could overcome normal flow regulatory mechanisms and resulted in constriction of coronary resistance vessels. Such changes did not occur after sustained stimulation and suggest an ability of the coronary circulation to offset chronic vasoconstrictive effects. When the myocardium is overperfused, sustained alpha-adrenergic stimulation does not jeopardize myocardial oxygenation and its vasoconstriction potential is unmasked.

Adenosine↗
PubMed1980

Clinical, angiographic and hemodynamic characteristics of patients with a strongly positive exercise test.

To determine the clinical, angiographic and hemodynamic characteristics of patients with a strongly positive exercise test, 37 subjects demonstrating greater than or equal to 3 mm S-T segment depression were identified among 892 consecutive diagnostic treadmill evaluations. Typical angina by history was present in 78%. 30 patients (81%) had a normal resting electrocardiogram. The strongly positive exercise response was elicited at < 90% of the predicted maximal heart rate in 31 patients (84%). 20% of patients did not experience angina during testing. 20 patients underwent cardiac catheterization. All 20 demonstrated multivessel disease and each had significant stenosis of either the left main (25%) or left anterior descending (95%) coronary artery. Left ventricular function was well preserved.

Adult↗