Pulmonary pulsus alternans in acute myocardial infarction

Ischemia right ventricular dysfunction

For many years ischemic heart disease involving the right ventricle had received little attention. During the last 15 years, the initial works of Cohn, Isner, and others spawned a number of clinical and experimental studies that extended the understanding of the pathophysiology of ischemia in the right ventricle. Most of the work has been done in the setting of acute myocardial infarction, and information is still lacking in other conditions, such as chronic ischemic heart disease and perioperative right ventricular dysfunction. Acute right ventricular infarction rarely occurs in the absence of left ventricular necrosis and in most cases is the extension of an inferior left ventricular infarct. The majority of patients with right ventricular infarction only exhibit subtle signs of ischemic dysfunction. Elevated right atrial pressure is found only in the typical syndrome of elevated venous pressure; low output syndrome can be found only in 20% of the cases, and cardiogenic shock secondary to right ventricular necrosis is found only in 10%. It is also important to note that there is not a clear correlation between the severity of ischemic right ventricular dysfunction and the necrotic area. The discrepancy may be due to ischemia without necrosis of the right ventricular wall (stunned myocardium), but the intact pericardium and the necrosis of the interventricular septum may also play an important role. In the most severe form of ischemic right ventricular dysfunction, the entire right ventricular wall is akinetic. Right atrial, right ventricular, and pulmonary artery pressures become similar in magnitude and shape, and the pulmonary valve is opened during diastole, demonstrating a passive blood flow from the right atrium to the left ventricle through the low resistance pulmonary capillary bed. Volume loading, administration of dopamine or dobutamine, and careful use of vasodilators under hemodynamic monitoring are the therapeutic measures to control the severe forms of acute ischemic right ventricular dysfunction. The use of thrombolytic agents has decreased the incidence of right ventricular dysfunction after acute myocardial infarction. Mortality is high in the severe forms of acute ischemic right ventricular dysfunction, but after discharge from hospital the prognosis is good and right heart failure is unusual, even in those patients with shock during the first days of evolution of the infarct.

Cardiac alternans: diverse mechanisms and clinical manifestations

OBJECTIVES

The purpose of this review is to assemble the widely dispersed information about cardiac alternans and to categorize the types and mechanisms of alternans, their clinical manifestations and possible therapeutic implications.

BACKGROUND

The phenomena of mechanical and electrical alternans have been of continuing interest to both physiologists and clinicians. Recent studies have enhanced this interest because of the reported association of alternans with experimental myocardial ischemia and cardiac arrhythmias.

METHODS

The review formulates concepts based on extensive review of published studies and personal observations.

RESULTS

Cardiac alternans has been subdivided into the following four categories: 1) mechanical, 2) electrical, 3) in association with myocardial ischemia, and 4) in association with cardiac motion. Mechanical alternans can be explained by hemodynamic or inotropic alterations, or both. Mechanical alternans in the ventricular muscle is accompanied by alternans of action potential shape. In the Purkinje fibers, action potential duration alternates without change in shape and is determined by the duration of the preceding diastolic interval. However, in ventricular muscle fiber, alternans can occur in the presence of constant diastolic intervals. T wave alternans reflects changes in action potential duration and is frequently associated with a long QT interval. Electrocardiographic manifestations of conduction alternans occur at many different sites within the conducting system and myocardium. During myocardial ischemia, additional mechanisms of repolarization alternans have been proposed. Alternans occurring in the presence of a large pericardial effusion is attributed to swinging motion of the heart maintaining two-beat periodicity.

CONCLUSIONS

Since its origin as "pulsus alternans" described by Traube in 1872, the definition of alternans has evolved into a term encompassing multiple physiologic and pathologic phenomena that, although united by the term cardiac alternans, diverge widely with respect to etiology, mechanism and clinical significance.

Evidence for a link between mechanical and electrical alternans in acutely ischaemic myocardium of anaesthetized dogs

In order to examine the relation between mechanical alternans and associated electrical alternans during acute myocardial ischaemia, we determined the effect of a ventricular premature beat and calcium antagonists on mechanical and electrical alternans during acute coronary occlusion in anaesthetized dogs. Isometric contractions and unipolar electrocardiograms were recorded from ischaemic myocardium. During coronary occlusion, mechanical alternans was accompanied by electrical alternans, which was an alternate change in the ST segment elevation, i.e. the higher ST and the lower ST. Electrical alternans was frequently discordant and in some cases accompanied by discordant mechanical alternans. Both discordant electrical and mechanical alternans became concordant and were potentiated after the ventricular premature beat. In all cases, concordant mechanical alternans was accompanied by concordant electrical alternans and vice versa. In this situation, the higher and the lower ST corresponded to the larger and the smaller contractions respectively. Thus, a fixed correspondence was observed between mechanical and electrical alternans. A fixed correspondence was also observed between mechanical alternans and the variation in the time taken for repolarization of the monophasic action potential. Verapamil and diltiazem inhibited both electrical and mechanical alternans. The present results support the idea that a common mechanism, such as a beat-to-beat cycle of the transmembrane and intracellular movement of calcium ions, may play a role in the mechanisms of electrical and mechanical alternans.

Acute massive (pericardial effusive) pulmonary thromboembolism--pulmonary embolectomy revisited

The most recent patient in a 13-year experience with 14 patients suffering massive pulmonary thromboembolism requiring pulmonary thromboembolectomy is the focus of this report. This 40-year-old woman not only survived life-threatening acute hypoxemia and right heart failure, but was also found to have developed a unique transudative 700 cc pericardial effusion. Pulmonary artery pressure was 90/30 (mean 50 mmHg), accompanied by 17 mm right ventricular alternans. Systemic alternans and tamponade physiology were absent. This unusual natural model for acute right heart failure illustrates a novel mechanism for pericardial effusion physiology.

Effects of calcium antagonists on the electrical alternans of the ST segment and on associated mechanical alternans during acute coronary occlusion in dogs

Effects of calcium antagonists on the ST alternans and associated mechanical alternans during acute coronary occlusion were examined in anesthetized dogs. The heart rate was fixed by atrial pacing. The intravenous administration of 0.2 mg/kg verapamil attenuated the ST alternans as did 0.5 mg/kg diltiazem. Although these drugs significantly attenuated TQ depression during occlusion, the attenuation was observed after a longer period of occlusion and when the degree of TQ depression was comparable to that during the control occlusion. Nifedipine, 0.03 mg/kg, slightly attenuated the ST alternans, but 0.5 mg/kg dipyridamole had no effect. These results support the idea that slow inward currents are involved in the ST alternans. On the other hand, the mechanical alternans was attenuated in six of 11 dogs. It is probable that factors other than the electrical alternans may also contribute to the mechanical alternans.

Pulsus alternans determined by biventricular simultaneous systolic time intervals

This investigation was performed to determine the presence of unilateral or bilateral pulsus alternans in the systemic and pulmonary circulations in heart failure and to estimate the prevalence of pulsus alternans in congestive cardiomyopathy. The subjects were 36 adult patients in heart failure due to a variety of cardiopulmonary diseases. We measured left- and right-sided systolic time intervals from simultaneous dual echocardiograms of both semilunar valves. The alternans was left-sided in seven patients, right-sided in one patient and bilateral in six patients. Pulsus alternans was induced by ventricular premature complexes (VPCs), except in one patient with bilateral and persistent alternans. For a VPC to precipitate alternans, the early beat itself must be associated with an abbreviated ejection time. Echophonocardiographic records of 100 patients with congestive cardiomyopathy were reviewed for evidence of pulsus alternans. We found persistent alternans in 10 patients and VPC-induced alternans in seven patients. We could not measure any difference in severity of disease in patients with pulsus alternans compared with those without.

Isolated right ventricular mechanical alternans in right ventricular infarction

The phenomenon of isolated mechanical alternans of the right ventricle is described in the setting of right ventricular infarction. We also discuss the resemblance of right ventricular infarction to cardiac tamponade or pericardial constriction.