Effect of short-term infusion of sodium nitroprusside on mortality rate in acute myocardial infarction complicated by left ventricular failure: results of a Veterans Administration cooperative study

The diagnostic specificity of creatine kinase isoenzymes after transurethral operations

It has been suggested recently that increases in the concentration of the MB isoenzyme of creatine kinase after transurethral operations could result from release of creatine kinase-MB by prostatic or bladder tissues and, therefore, that creatine kinase-MB is not specific for myocardial damage. Our study of 53 patients undergoing transurethral operations and 37 undergoing urethral dilations showed that creatine kinase-MB is not released in significant quantities from the prostate or bladder. Therefore, we believe that an elevated creatine kinase-MB concentration is specific for myocardial infarction in these patients. We also concluded that the increase in total serum creatine kinase activity in these patients probably results from release of the creatine kinase-MM isoenzyme from periurethral muscle damage by electrocautery.

Comparison of intravenous nitroglycerin and sodium nitroprusside in acute myocardial infarction

Initial studies from our institution demonstrated beneficial anti-ischemic effects of short-term infusion of intravenous nitroglycerin in patients with acute myocardial infarction. At lower doses, nitroglycerin was shown to be principally a venodilator; at higher doses, a mixed venous and arterial dilating effect was demonstrated. The acute hemodynamic effects of nitroglycerin varied in the presence or absence of left ventricular failure; patients with the most severe degree of left ventricular dysfunction had the most beneficial hemodynamic effect. Similar differential effects have been demonstrated for nitroprusside in other studies. A comparison of the arterial vasodilating potency of nitroglycerin and nitroprusside in patients in whom acute hypertension develops following coronary artery bypass surgery revealed that equal lowering of arterial pressure and systemic vascular resistance could be demonstrated in 85 percent of the patients with comparable infusion rates. Review of previous clinical and laboratory studies in animals, in which the effects of nitroglycerin and nitroprusside were compared, in most cases revealed opposite effects on intercoronary collateral flow and, thereby, opposite effects on the severity of regional ischemia. Our recently completed randomized placebo-controlled clinical trial employing a 48-hour infusion of nitroglycerin demonstrated a higher incidence of significant improvement in abnormalities noted on scintigraphy when nitroglycerin treatment was initiated within 10 hours of the onset of symptoms. Beneficial effects of early nitroglycerin treatment have also been demonstrated in previous clinical trials. In similar studies, which utilized nitroprusside infusions in patients with acute myocardial infarction, some investigators found an increase in short-term mortality with early nitroprusside treatment whereas others found benefit. The uniformly favorable results of the clinical trials that utilized intravenous nitroglycerin, although not necessarily supporting its routine use in all patients, would support a preference for nitroglycerin over nitroprusside for the treatment of congestive heart failure and/or acute hypertension complicating acute myocardial infarction.

Enzymatic estimation of myocardial infarct size when early creatine kinase values are not available

Estimates of myocardial infarct (MI) size based on plasma creatine kinase (CK) are used widely for prognosis and in the assessment of therapy designed to salvage ischemic myocardium. However, if the initial plasma CK activity is elevated, MI size will be underestimated. To determine the impact of loss of early CK values on estimates of MI size and to develop a procedure to compensate for it, estimates of MI size based on complete and incomplete MB and total CK time-activity curves from 120 patients (experimental group) were compared. Estimates of MI size based on data inclusion intervals beginning at 24, 12, 8, and 4 hours before peak CK were 11, 14, 23, and 47% smaller than values based on complete CK curves, but the correlation was good between complete and incomplete estimates of MI size at any given interval, with r values ranging from 0.91 to 0.98. The derived correction factors were then prospectively applied to a new population (n = 25) with complete CK curves to compensate for purposely omitted early CK values. The corrected estimates of MI size were within 7% of those based on the complete CK curves. Similar results were obtained for transmural and nontransmural and anterior or inferior MI. Thus, if peak plasma CK is known, underestimation of MI size can be compensated for despite the unavailability of early CK values. Since greater than 90% of patients present before plasma CK has reached its peak (24 hours), MI size can be obtained in nearly all patients. Thus, being able to correct for unavailable early CK values makes MI size a more widely applicable endpoint for use in clinical trials and patient management.

Vasodilator therapy for acute myocardial infarction and chronic congestive heart failure

Vasodilator therapy is useful adjunctive therapy in the management of both acute and chronic heart failure. Arteriolar dilators, such as hydralazine, increase cardiac output by decreasing the elevated peripheral vascular resistance that occurs in heart failure. Venodilators, such as nitrates, decrease ventricular filling pressures by redistributing blood so that more is pooled in peripheral veins. Vasodilators that produce both effects (nitro-prusside, prazosin, captopril, for example) are usually helpful in short-term improvement of hemodynamics. Long-term treatment with nonparenteral vasodilators often reduces symptoms and increases exercise tolerance, although there is inconclusive evidence regarding the effects of these agents on mortality. In acute myocardial infarction, intravenous vasodilators frequently improve cardiac performance. Evidence regarding their beneficial effects on infarct size and immediate mortality is encouraging but inconclusive. There is little evidence that they prolong life in patients who survive cardiogenic shock and leave the hospital. Thus, vasodilators can improve hemodynamics and lessen symptoms, but more evidence is needed regarding their long-term effects on survival.

Comparison of the effects of nitroprusside and nitroglycerin on coronary size

Nitroglycerin and nitroprusside are known to differ in their relative degree of systemic arterial and venous dilation. Nitroglycerin has been shown to be a potent large-vessel coronary dilator, but the effects of nitroprusside on coronary artery size are unclear. Accordingly, we studied coronary artery angiographic responses to both nitroprusside and nitroglycerin in 12 patients. Diameters Of left coronary artery segments were measured by quantitative angiography before and during an intravenous infusion of nitroprusside and after sublingual nitroglycerin when both drugs were administered in doses adjusted to achieve reductions in aortic pressure. Dilation of the left coronary artery was observed after nitroprusside and after nitroglycerin. Degrees of dilation were similar in the various left coronary artery segments after either nitroprusside or nitroglycerin. In general, segments located more proximally dilated less than those located more distally after either agent. We conclude that both nitroprusside and nitroglycerin are potent dilators of large epicardial and of smaller intramuscular coronary artery segments. The magnitude of dilation of all measured left coronary artery segments appeared remarkably similar with nitroprusside and nitroglycerin given in doses that produced a similar reduction in aortic pressure.

Vasodilator therapy: implications in acute myocardial infarction and congestive heart failure

The physiologic effects of systemic vasoconstriction on left ventricular performance and the salutary hemodynamic effect of acute administration of vasodilator drugs to patients with heart failure provide a rational basis for vasodilator therapy in acute myocardial infarction and chronic congestive heart failure. Use of vasodilators during the acute phase of myocardial infarction may reduce mortality when left ventricular filling pressure remains markedly elevated for at least 8 hours after the onset of clinical syndrome. Use of chronic vasodilator therapy in patients with congestive heart failure appears to have been effective in some patients in prolonging exercise tolerance; however, the likelihood of a beneficial effect and the impact of this therapy on the natural history of the disease remain unclear. A Veterans Administration Cooperative Study to address these questions is currently in progress. The new effort directed to studying the effects of vasodilator drugs in these syndromes has appropriately focused attention on their pathophysiology and natural history.