New concepts in the pathophysiology of acute myocardial infarction

Recent findings concerning the pathophysiology of acute myocardial infarction are reviewed and related to the potential for myocardial salvage. The myocardial infarction process can be divided into 2 phases, an early evolving phase (the first 6 hours) and a later convalescent phase. An evolving infarction is associated with an occluded coronary artery; in most cases, a thrombotic occlusion occurs. The human coronary artery normally has an intact endothelium, which has protective vasodilatory and antiplatelet-aggregating effects that are lost when the endothelium is damaged. The endothelium is exquisitely sensitive to trauma and can be damaged by high shear stress produced by narrowing of the coronary arteries that is not associated with reduced coronary blood flow. In addition, during this acute endothelial damage, monocellular infiltration of the coronary arteries has the potential to release factors that may cause platelet aggregation, enhance blood coagulation, attract other white blood cells or exert other effects on the coronary tree. Myocardial damage occurring in the early evolving stage is usually responsive to treatment that either restores myocardial oxygen supply or reduces myocardial oxygen demand. However, coronary events occurring after the first 6 hours usually are not responsive to such treatment. Certain clinical variables may shorten or extend the time period within which damaged myocardium can be saved. The findings suggest important approaches for intervention to modify the acute phase.     

Silent myocardial ischemia in the elderly: current concepts

The traditional approach to managing ischemic heart disease has been to reduce symptoms, eg, angina pectoris. However, recent studies demonstrate that myocardial ischemia often can be found in the absence of common symptoms, including in elderly patients. Since elderly patients may not complain about their symptoms, or may not get enough exercise to test their cardiovascular capabilities and, thus, bring out problems, the geriatrician needs to be highly suspicious of silent myocardial ischemia. A brief overview of diagnostic testing methods suitable for the elderly and medical and surgical management options is presented.     

Silent myocardial ischemia: concepts and controversies

Silent myocardial ischemia is a relatively common, but poorly understood, clinical entity. The most accurate means of detecting silent myocardial ischemia and the precise treatment endpoints remain unclear. However, the amount of ischemic myocardium appears to correlate with the likelihood of future adverse cardiac events. Evidence suggests that patients at highest risk of severe myocardial ischemia, even in the absence of symptoms, derive the greatest benefit from an aggressive diagnostic and therapeutic approach. This paper reviews the diagnosis and treatment of silent myocardial ischemia, and its clinical implication in select patient groups: those without coronary artery disease, those with coronary artery disease, diabetic patients, postrevascularization patients, and women.     

Current concepts of pathophysiology, circadian patterns, and vasoreactive factors associated with myocardial ischemia detected by ambulatory electrocardiography.

Transient ST-segment changes during continuous ECG monitoring occur not only in many clinical ischemic syndromes, but also in a proportion of the normal population. The pathophysiology of episodes of ST-segment change that represent transient periods of myocardial ischemia varies according to the underlying disease process, which may include stable coronary artery disease, unstable angina, variant angina, and syndrome X. Patients with stable coronary artery disease have episodes of ischemia as a result of an imbalance between increases in myocardial oxygen demands and changes in coronary blood flow due to physiologic changes in coronary vasomotor tone. Both these factors are subject to a circadian rhythm that results in a preponderance of ischemia in the morning hours. Vasospasm, often beyond the physiologic range, in localized segments of epicardial coronary arteries causes ischemia and ST-segment changes in variant angina, whereas luminal thrombosis with superimposed vasoconstriction is an important cause of continued ischemia in unstable angina.     

New concepts in the pathophysiology of infective endocarditis

Endocarditis pathogens colonize valves with pre-existing sterile vegetations or valves with minimal endothelial lesions. Inflamed endothelia produce cytokines, integrins, and tissue factor, which in turn attract fibronectin, monocytes, and platelets. Bacteria attaching to such structures further activate the cascade, becoming embedded and protected from host defenses. Staphylococcus aureus also actively invade the endothelium, causing apoptosis and endothelial damage. Knowledge of this interplay identifies host factors as potential therapeutic targets. Blocking infection by modulating host factors might be opportune because host factors are conserved. In contrast, interfering with bacterial virulence factors might be more complicated because they vary among different bacteria.     

Asymptomatic or silent myocardial ischemia in angina pectoris: pathophysiology and clinical implications

Patients with angina pectoris often have asymptomatic myocardial ischemia, which can be detected by exercise testing, ambulatory (Holter) monitoring, and other diagnostic methods. Studies suggest that the presence of frequent and prolonged episodes of ischemia are associated with an adverse prognosis. Standard antiangina strategies have been found to be effective in reducing exercise and spontaneous episodes of ischemia. However, whether the targeted suppression of all ischemic activity should be a therapeutic goal remains unresolved and is the focus of current research efforts.     

Changing concepts in diverticulosis of the colon

Summary The records of 300 patients with diverticula of the colon have been reviewed. Clinical diagnosis of diverticulosis requires roentgenographic confirmation. Diverticulitis is suggested by the presence of localized pain and tenderness, a palpable mass which changes in size, inflammation, bloody stools with otherwise negative findings, and recurrence of episodes. Medical management of uncomplicated diverticulosis is advocated. Definitive indications for surgical intervention in complicated cases have been outlined; these include true complications, possibly malignant lesions, and localized, recurrent, and persistent diverticulitis in carefully selected cases. Prophylactic operation is not generally favored but may be justified in well-selected cases in view of the morbidity associated with complicated surgical procedures.