Studies on the regulation of the coronary circulation in man. I. Atropine-induced changes in cardiac rate

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.

Halothane anaesthesia and suxamethonium I: the significance of preoperative atropine administration. A double-blind study

Preoperative administration of atropine was evaluated during induction of halothane anaesthesia with two administrations of suxamethonium 1 mg/kg body weight, 5 min apart. Sixty-eight healthy, adult patients were studied. They were divided into five groups according to dose and route of administration of atropine. ECG was continuously monitored. Serum potassium, pH, PaCO2, PaO2 and standard bicarbonate were measured at appropriate intervals. It was found that neither atropine 0.01 mg/kg body weight given intramuscularly 1 h beofre the anaesthesia nor atropine 0.01 mg/kg body weight given intravenously 5 min prior to induction protected against serious bradycardias (defined as heart rate below 20 beats per minute) following the second dose of suxamethonium. No serious brady-arrhythmias were seen in patients given either a combination of intramuscular and intravenous atropine in the above-mentioned doses or in patients given atropine 0.015 mg/kg body weight intravenously 5 minutes prior to induction. However, a decrease in heart rate to around 40-50 beats per minute occurred in some of these patients. Furthermore, these large doses of atropine caused an increase in heart rate during induction to more than 120 beats per minute in about 50% of the patients and to more than 140 beats per minute in about 25% of the patients. Our results suggest that preoperative administration of atropine does not protect against serious brady-arrhythmias following a second dose of suxamethonium, unless doses of atropine are used which cause tachycarida of considerable degree.

Effects of Norepinephrine on the Coronary Circulation in Man

The effect of norepinephrine infusion on the coronary circulation has been studied in 21 subjects. In doses ranging from 2 to 17 µg. base per minute norepinephrine caused a pari passu rise in perfusing pressure and coronary flow of 16 per cent above the control state. Despite an increase in cardiac oxygen consumption, coronary vascular resistance was unchanged, suggesting no vasodilatation in the coronary bed. On the contrary, oxygen extraction across the heart increased, implying that oxygen needs were inadequately met by rise in flow. An increase in vascular tone induced by norepinephrine is inferred from the unchanged coronary resistance at a higher perfusion pressure.

Responses of the normal and failing left ventricle groups were qualitatively the same as for the group as a whole. The failure group showed greater tendency to meet oxygen needs by increased extraction than did the normal hearts.

Although these observations are not strictly applicable to the role and effects of norepinephrine in states of clinical shock, nonetheless it seems likely that norepinephrine induces a suboptimal rise in coronary flow that may set the stage for ultimate myocardial ischemia, particularly when coronary perfusion pressure is inadequate.

Effect of Exercise on Cardiac Performance in Human Subjects with Coronary Artery Disease

Cardiac performance and oxygenation have been studied in resting and exercising subjects with coronary artery disease. Disturbances exist in myocardial function and energetics, characterized by preservation of pressure development, but with impaired systolic ejection and failure to increase mechanical efficiency during exercise. Resultant elevation of myocardial oxygen need by impaired performance undoubtedly aggravates coronary reserve inadequacy during exercise.

Action of nitroglycerin on the coronary circulation in normal and in mild cardiac subjects

Nitroglycerin has been used extensively as a coronary vasodilator. Its remarkable clinical effect has been presumed to be related to a direct action on the smooth muscle of the coronary arteriole. No observations have been made of nitroglycerin action on the coronary circulation in man. This report presents studies of changes induced by the drug in 10 normal or nearly normal subjects. The authors present evidence that although coronary vasodilatation does indeed occur, it appears to be secondary to changes in myocardial oxygen requirements. Hemodynamic observations revealed a general decrease in pressures in both peripheral and pulmonary circuits; caution is urged concerning the occasional severe hypotensive effects of nitroglycerin.