Constant-pressure coronary artery perfusion during aortic valve operations.

We considered the theoretical differences between the normal relationships of coronary blood flow and perfusion pressure in the working heart and those obtained with continuous, steady-flow perfusion by a roller pump during aortic valve replacement. Steady pump perfusion should deliver less blood flow to the endocardium because: 1. For the same mean artery perfusion pressure, the average coronary blood flow is less with constant-flow pump perfusion. 2. With constant pump perfusion, pressure would be excessively high during systole, and during diastole it would be significantly lower than the mean perfusion pressure. Instantaneous pressure and flow were measured in the left coronary artery in 8 patients undergoing aortic valve replacement, employing either roller pump perfusion or a gravity flow system to provide a steady pressure source. Although we did not attempt to demonstrate improved endocardial flow, the mean left coronary flow was always greater with gravity perfusion (297 versus 153 ml/min), lending support to the theoretically proposed differences between the two perfusion methods.

Four hundred consecutive patients with permanent transvenous pacemakers.

Between April 1, 1965, and May 1, 1973, we inserted permanent transvenous pacemakers in 400 consecutive patients. Patients considered for this type of pacing were those with any episode of heart block and those with other types of bradyarnhythmias who had unexplained vertigo or syncope. There was one operative death and one instance in which the primary unit became infected. Problems with catheter dislocation, electrode fracture, and exit block were few and were easily corrected. We believe transvenous permanent pacing to be the best method of cardiac pacmaking in these patients. It is well tolerated by largely avoidable and easy to correct.

The effects of intra-aortic counterpulsation on cardiac performance and metabolism in shock associated with acute myocardial infarction.

The effect of intra-aortic counterpulsation (IACP, 22-94 hr) on hemodynamics and cardiac energetics was evaluated in 10 patients in shock after acute myocardial infarction. The data clearly indicate that IACP improves myocardial oxygenation, enhances peripheral perfusion, and probably improves myocardial contractility in the severely diseased heart. Before treatment, decreases in cardiac index (mean value, 1.22 liter/min per m(2)), systolic ejection rate (67 ml/sec), and time-tension index per minute (1280 mm Hg.sec/min) were observed. Systemic vascular resistance varied widely. Low coronary blood flow (68 ml/min per 100 g) was associated with increased myocardial oxygen extraction (79%), low coronary sinus oxygen tension (20 mm Hg), and abnormal myocardial lactate-pyruvate metabolism. During 4-6 hr of IACP, systolic pressure and left ventricular outflow resistance decreased by 18% and 24%, respectively, while cardiac index improved by 38%. Diastolic arterial pressure rose 98%. Increase in coronary blood flow from an average of 68 to 91 ml/100 g per min (P < 0.001) was significantly correlated with rise in mean arterial pressure (r = 0.685). This correlation was best expressed in a third-order curve, which intercepts the point of no flow at a mean aortic pressure of 30 mm Hg. The flow-pressure curve is relatively flat above 65-70 mm Hg, but becomes steeper as mean aortic pressure falls below this point. Myocardial oxygen consumption remained essentially unchanged during early IACP and tended to rise during the later stages. However, the relationship of cardiac work performed to oxygen availability was markedly improved. Myocardial lactate production of 6% shifted to 15% extraction (P < 0.001). After termination of IACP, hemodynamics and myocardial perfusion and metabolism remained improved in the four patients who could be reevaluated. Although the acute shock state was reversed in all patients, only one left the hospital. Extensive myocardial damage limits the long-term survival of such patients. Therefore early IACP seems desirable, when subtle evidence of pump failure after acute myocardial infarction occurs. Early use of IACP may prevent the development of severe coronary shock or may stabilize cardiac energetics in severe shock facilitating subsequent surgical intervention.