Shock in acute myocardial infarction: evolution of physiologic therapy

In the past 25 years the treatment of shock in myocardial infarction has evolved into a physiologic approach based on on-line measurements of hemodynamic variables. This has aided in the development of new pressor agents so that a family of pharmacologic agents is now available. Appropriate use of vasodilators and recognition and treatment of intravascular volume depletion have increased survival. Recognition and appropriate treatment of the preshock state have decreased the incidence of shock. The criteria for use of mechanical support and surgical intervention are soundly established; the use of thrombolytic therapy and balloon angioplasty for this syndrome is ready to be evaluated.

Risk factors related to progressive narrowing in aortocoronary vein grafts studied 1 and 5 years after surgery

Factors related to late narrowing of aortocoronary vein grafts are poorly understood. Repeat aortocoronary bypass graft angiography was performed in 34 patients at 13 +/- 5 months and 61 +/- 13 months after surgery. In these patients, 61 of 65 grafts (94%) were patent at 1 year; at 5 years, 39 of these patent grafts (64%) remained unchanged, 21 (34%) had become progressively narrowed and one (2%) was totally occluded. There appeared to be no predilection for progression to occur at specific segments or in particular grafts: Eight of 28 left anterior descending (29%), seven of 17 right coronary artery (41%) and seven of 16 circumflex artery grafts (44%) (NS) showed further narrowing. Progressive graft narrowing occurred in 15 of 34 patients (44%). Risk factors (incidence of smoking, diabetes mellitus, hypertension, and triglyceride and cholesterol levels) in these 15 patients were compared with those in the 19 patients whose grafts were unchanged between 1 and 5 years. The incidence of smoking, diabetes mellitus (fasting blood sugar greater than or equal to 110 mg % or 2-hour postprandial sugar greater than or equal to 140 mg %) and hypertension (systolic blood pressure greater than 140 mm Hg or diastolic pressure greater than or equal to 95 mm Hg) were 46%, 27% and 33%, respectively, in the patients with progressive graft narrowing and 68%, 16%, 26% in the patients whose grafts were unchanged (NS). The average mean triglyceride levels were 617 +/- 785 mg % (+/- SD) and 195 +/- 86 mg %, respectively (p less than 0.05). The average mean cholesterol levels were 279 +/- 53 mg % and 234 +/- 35 mg %, respectively (p less than 0.01). In patients who have had aortocoronary bypass surgery, total graft occlusion is rare between 1 and 5 years after surgery. Progressive narrowing of grafts is common and appears to be associated with elevated blood lipids.

Progression of coronary artery disease in medically and surgically treated patients 5 years after randomization

Repeat angiography was performed at 63 +/- 9 months in 26 medically treated patients and at 66 +/- 10 months in 32 surgically treated patients with chronic angina. The native coronary arteries were divided into three major trunk vessels and 15 angiographic segments. Progression of disease was defined as the appearance of new (greater than 50%) obstruction or significant worsening of existing lesions in a segment or vessel. The incidence of progression was similar in medical and surgical patients, comparing individual segments (69 of 312 [22%] and 91 of [23%], respectively) or vessels (49 of 78 [63%] and 60 of 96 [63%], respectively). In both medical and surgical patients, segments initially free of disease showed a 14% incidence of developing new lesions, compared with the 37% progression in segments initially diseased (p less than 0.001). In the surgical patients, progression occurred in 48 of 219 (22%) nongrafted and 43 of 177 (24%) grafted segments (NS). When analyzed by major trunk vessel, progression occurred in 40 of 57 grafted arteries (70%) and 20 of 39 nongrafted arteries (51%) (NS). The incidence of new total occlusions was similar in medical and surgical patients (6% and 8%, respectively); new total occlusions occurred predominantly in diseases segments (15% and 22%, respectively). In patients with stable angina pectoris who have medical or surgical treatment assigned by randomization, progression of coronary disease at 5 years is not influenced by which mode of therapy was received. Vessels initially free of disease are at relatively low risk for development of disease within 5 years. In surgical patients, grafted and nongrafted vessels show similar rates of progression.

Delayed pulse generator malfunction after D.C. countershock

Immediate pacemaker malfunction following defibrillation or cardioversion has been reported. In this paper we report one patient whose pacemaker appeared to be functioning normally after D. C. countershock but malfunctioned 13 days later manifested by changing from an R-wave inhibited to an R-wave synchronous mode.

Comparative effect of intravenous dipyridamole and sublingual nitroglycerin on coronary hemodynamics and myocardial metabolism at rest and during atrial pacing in patients with coronary artery disease

The effects of intravenous dipyridamole (20 mg) and sublingual nitroglycerin (0.6 mg) were compared at rest and during rapid atrial pacing in patients with significant coronary obstruction. Dipyridamole, which had no significant effect on resting systolic blood pressure, caused a significant increase in coronary sinus flow (CSF) and reduction of coronary vascular resistance (CVR) and arterial-coronary sinus oxygen difference (AO2CSO2 delta), whereas nitroglycerin reduced resting systolic pressure but had no significant effect on CSF, CVR, or AO2-CSO2 delta. Although theses effects of dipyridamole and nitroglycerin on resting systolic pressure, CSF, CVR, and AO2-CSO2 delta were qualitatively similar during rapid atrial pacing, the onset of chest pain and ischemic ECG changes occurred at a lower heart rate following dipyridamole (136 +/- 5 beats/min) than following nitroglycerin (149 +/- 6 beats/min, p less than 0.01). However, maximal double product and myocardial oxygen consumption achieved during pacing were similar following both dipyridamole and nitroglycerin and were less than control pacing values. Coronary dilatation following dipyridamole appears to reduce tolerance to pacing-induced ischemia probably by maldistribution of coronary flow away from ischemic myocardium. Nitroglycerin differs from dipyridamole by improving tolerance to pacing; however, this difference appears to be due to systemic vasodilator effects of nitroglycerin rather than to enhancement of flow to ischemic myocardium.

Hemodynamic improvement following a single dose of oral phentolamine. Administration in patients with chronic low output cardiac failure

Hemodynamic studies were made in 15 patients with chronic low output cardiac failure before and following a single dose of oral phentolamine (150 mg). After two hours significant (P less than .05) reduction occurred in mean pulmonary, wedge and right atrial pressures and increases in cardiac index and heart rate. In ten patients studied at four hours, wedge pressure remained significantly reduced (-18 percent) and cardiac index significantly increased (+19 percent) from control values. Oral phentolamine results in significant hemodynamic improvement in patients with severe heart failure. Duration of effect for at least four hours after a single dose suggests that intermittent oral therapy may be useful in the management of such patients.

Use of catecholamines in acute myocardial infarction

We review the hemodynamic effects and clinical usefulness of five natural and synthetic catecholamines. Their actions are best understood by an appreciation of the relative ability of each catecholamine to activate alpha, beta 1 and beta 2 adrenergic receptors in the myocardium and peripheral vasculature. Epinephrine, the first catecholamine isolated, is shown to have little useful role in the therapy of acute myocardial infarction. L-norepinephrine has powerful alpha and moderate beta 1 effects. It is the catecholamine of choice in the initial treatment of cardiogenic shock associated with acute myocardial infarction. Isproterenol markedly increases myocardial contractility and heart rate by beta 1 stimulation, while simultaneously decreasing peripheral vascular resistance and, therefore, arterial pressure through its action on beta 2 receptors. It increases cardiac output, but its metabolic costs are high in the presence of ischemia. Its role in the therapy of acute myocardial infarction has largely been supplanted by more selective agents. Dopamine causes slightly less vasoconstriction than l-norepinephrine and slightly less myocardial stimulation than isoproterenol. In low doses, it increases renal and mesenteric blood flow by activation of a non-adrenergic receptor. Tachycardia and associated metabolic deterioration render it a second-line drug in the treatment of severe cardiogenic shock. Dobutamine, a new synthetic catecholamine, has primarily beta 1 activity. It increases myocardial contractility with little effect on heart rate or peripheral vascular resistance. It is ineffective in cardiogenic shock, but may eventually be shown to have a role in the treatment of left ventricular failure uncomplicated by severe hypotension.

Improved survival after surgical therapy for chronic angina pectoris: one hospital's experience in a randomized trial

Between 1972 and 1974, 121 patients with chronic stable angina pectoris and operative coronary artery disease, excluding significant left main coronary obstruction, were randomized to either medical therapy (60 patients) or surgical therapy (61 patients) as part of a larger Veterans Administration Cooperative Study of Surgery for Coronary Arterial Occlusive Disease. At the time of randomization, medical and surgical groups were similar with regard to clinical and hemodynamic features as well as degree of left ventricular impairment and extent of coronary disease. Follow-up to June 1, 1978, reveals significantly improved survival in surgical patients from 3 through 6 years after randomization. Sixteen cross-over patients (13 medical to surgery, and 3 surgical without surgery) do not appear to influence results. Results of this randomized study from a single hospital differ from the preliminary results of the larger cooperative study, primarily because of a higher mortality in the medical group. The medical mortality in our group is in keeping with other reports of the natural history of patients with angina pectoris, and we propose that the population of patients we randomized closely simulates the usual type of patient with chronic angina being considered for surgical treatment. Our good surgical results thus contrast significantly with the survival of medically treated patients, and this separates our study from the body of the Veterans Administration Cooperative Study.

Lack of ouabain effect on pacing-induced myocardial ischemia in patients with coronary artery disease

Sixteen patients with significant two and three vessel coronary artery disease but without clinical congestive heart failure were studied during rapid atrial pacing before and after infusion of 0.015 mg/kg of ouabain. Seven patients with a decreased (less than 50 percent) ejection fraction and nine patients with a normal ejection fraction had a significant (P less than 0.05) increase in resting arterial systolic pressure after the administration of ouabain. However, resting values for coronary sinus flow, coronary vascular resistance, myocardial oxygen consumption and myocardial lactate extraction did not change significantly in either group. During pacing, patients with a decreased ejection fraction demonstrated more ischemia than patients with a normal ejection fraction; however, the administration of ouabain did not significantly alter pacing-related changes in coronary sinus flow, myocardial oxygen consumption, myocardial lactate extraction, ischemic electrocardiographic changes or onset of chest pain in either group. The administration of ouabain has a negligible effect on coronary hemodynamics, myocardial metabolism or clinical signs of ischemia in patients with coronary artery disease with normal or abnormal left ventricular function.

The role of myocardial ischemia in pacing-induced elevation of arterial pressure

One hundred sixteen patients with suspected or proven coronary arterial disease underwent rapid atrial pacing until the occurrence of pain in the chest or a heart rate of at least 160 beats per minute. Significant elevation of arterial systolic pressure of 25 percent or more above control was observed in 17 patients. Each of these patients had significant coronary arterial disease shown by coronary arteriographic studies. During rapid atrial pacing, each of these 17 patients had pain in the chest and ST-segment changes suggesting ischemia, and 15 had abnormal (less than 10 percent) extraction of myocardial lactate. In the 99 patients who did not have increased arterial systolic pressure during rapid atrial pacing, the frequencies of coronary arterial disease, ischemic ST-segment changes, and abnormal extraction of lactate during rapid atrial pacing were significantly (P less than 0.05) less. Increased arterial systolic pressure during rapid atrial pacing appears to be highly indicative of coronary arterial disease and myocardial ischemia. We suggest that myocardial ischemia may, under certain circumstances, be responsible for short-term increases in arterial pressure.

Hemodynamic effects of intravenous phentolamine in low output cardiac failu;e. Dose-response relationships

Nineteen patients with chronic low output cardiac failure were studied before, during and after infusion of phentolamine in doses of 10, 20, 30 and 40 microgram/kg/min. Significant reduction of left- and right-sided pressures and increases in cardiac index and heart rate (HR) were present within 15 minutes of starting phentolamine at the 10 microgram/kg/min dose. Minimal additional effect was observed at 30 minutes. Increased dose from 10 to 20 mu/kg/min resulted in small but significant (P less than 0.05) additional reduction in pressures and increases in HR. No additional significant changes occurred at doses of 30 or 40 microgram/kg/min. Significant hemodynamic changes persisted for at least an hour (53 +/- 3 min) after the phentolamine infusion was discontinued. Near maximal ;emodynamic effects occur within 15 minutes of starting phentolamine infusion and can be achieved at doses of 10 to 20 microgram/kg/min. Increased HR during phentolamine infusion may limit its usefulness in patients with ischemic heart disease.

Sinus node dysfunction. An overview with emphasis on autonomic and pharmacologic consideration

Sinus node dysfunction is a disorder of impulse generation and impulse conduction. Previous works have emphasized that the dysfunction occurs not only within the sinus node but also within the escape pacemaker. Adrenergic and cholinergic mechanisms, as well as pulsations and pressure within the sinus node artery, play an important role in normal sinus node activity. Although perinodal fibers act as a buffer zone for sinoatrial conduction, their role in man is yet to be clarified. During normal sinus node activity, pacemaker shifts from the sinus node to the crista terminalis have been shown to occur. Following sinus node destruction, similar shifts do occur. Clinical methods of determining sinus node function, such as the sinus node recovery time and sinus atrial conduction time, are useful but have limitations. Dynamic electrocardiographic monitoring provides the best clinical method available for detecting sinus node dysfunction. Digitalis appears to improve the parameters of sinus node function by increasing the automaticity of latent atrial pacemakers. The atrial arrhythmia of sinus node dysfunction appears to be related to the characteristics of latent atrial pacemaker and "enhanced" cholinergic tone.

Echocardiographic interpretation of pericardial effusion

Echocardiography has proved to be quite useful in the detection of pericardial effusion. As little as 15 ml of fluid within the pericardial space can be detected. Specific signs of pericardial effusion, such as electrical alternans and paradoxical pulse, have become better understood by echocardiographic study. Yet, with all the benefits of echocardiography, the detection of pericardial effusion still may be quite difficult if careful attention is not given to technique. False-positive diagnosis of anterior pericardial effusion can be seen with epicardial fat pad, pericardial cyst, or foramen of Morgagni hernia. False-positive posterior pericardial effusion can be seen in large left pleural effusion, calcified mitral anulus, or excessively medial transducer angulation. New "switched-gain" circuits have helped detection of pericardial effusion by enhancement of pericardial echoes.

Effects of pharmacologically-induced hypertension on myocardial ischemia and coronary hemodynamics in patients with fixed coronary obstruction

Twenty patients with fixed coronary artery obstruction were studied during rapid atrial pacing and methoxamine infusion. During pacing to heart rates of 142 +/- 4 (mean +/- SEM) beats per minute coronary sinus flow increased from 108 +/- 8 to 187 +/- 15 cc/min and myocardial oxygen consumption increased by + 80 +/- 11%. During methoxamine infusion that raised arterial systolic pressure to 196 +/- 5 mm Hg, similar increases in coronary sinus flow (to 179 +/- 13 cc/min) and myocardial oxygen consumption (+ 77 +/- 12%) occurred. Chest pain and ischemic ST segment changes developed in 17 and 14 patients respectively during atrial pacing, an incidence significantly greater (P less than 0.05) than during infusion of methoxamine (6 and 3 patients). Myocardial lactate extraction which averaged 26 +/- 4% during control was decreased to 10 +/- 8% during pacing and to 24 +/- 7% during methoxamine; the difference between decreases was not significant. The data show that at similar increases in myocardial oxygen consumption stress of increased heart rate results in more myocardial ischemia than stress of increased afterload.

Comparative responses to dobutamine and nitroprusside in patients with chronic low output cardiac failure

The acute hemodynamic effects of dobutamine and nitroprusside were compared in 19 patients with low output cardiac failure. At dosage levels yielding similar increases in cardiac index (12 patients), nitroprusside resulted in significantly lower arterial systolic and wedge pressures and did not increase heart rate suggesting advantages over dobutamine when reduction in myocardial oxygen requirement or pulmonary congestion is a major goal. Systemic arterial mean and diastolic pressures were minimally changed with dobutamine, but fell significantly with nitroprusside suggesting advantages of dobutamine over nitroprusside in patients where hypotension could limit coronary blood flow or perfusion of other vital organs. Reduction in pulmonary arteriolar resistance occurred only with nitroprusside. Arterial hypoxemia developed in three patients during nitroprusside infusion suggesting the possibility of increased right-to-left intrapulmonary shunting resulting from a direct vasodilating effect of nitroprusside on pulmonary arteriole smooth muscle. Although both inotropic and vasodilator drugs can result in hemodynamic improvement when administered to patients with chronic low output cardiac failure, significant differences of potential clinical importance exist between these two modes of therapy.

Treatment of cardiogenic shock in myocardial infarction by intraaortic balloon counterpulsation surgery

Thirty-seven patients in cardiogenic shock due to acute myocardial infarction were treated with intraaortic balloon counterpulsation and/or surgery. Eighteen of these patients were treated with counterpulsation alone; eight survived and five were in functional class I or II at the time of follow-up; two were in functional class III, and one was in functional class IV. Nineteen patients were treated surgically, eight survived and seven were in functional class I or II at the time of follow-up; one was in functional class III. Good functional recovery with counterpulsation alone is most common with inferior infarction. With surgery, functional recovery depends not only on the extent of the infarction and the coronary anatomy, but also on the ability to perform surgery within 12 hours of infarction or to support the patient with mechanical means for 10 to 14 days after the infarction and then perform surgery.