Leonard G. Christie

Left main coronary artery stenosis: Clinical spectrum, pathophysiology, and management

Abstract Atherosclerosis is the major cause of LMCAS. Isolated LMCAS occurs only rarely. Marked narrowing of the LMCA is usually indicative of severe, diffuse coronary atherosclerosis. Physiologically significant LMCAS is present in less than 15% of patients with symptomatic ischemic heart disease. Angina pectoris is the most common symptom in patients with LMCAS. The incidence of unstable angina is higher in these patients when compared to patients without LMCAS. Stress testing may help identify patients with LMCAS if the following criteria are met: (1) greater than 2 mm ST segment depression. (2) prolonged duration of ST segment change after exercise, (3) blunted or decreased heart rate response to exercise, and (4) ST segment change suggesting ischemia at a low heart rate. Coronary angiography provides definitive anatomic description of the location, length, and severity of LMCAS. The procedure can be performed at low risk if proper precautions are taken. Experimentally, 85% reduction in diameter of the LMCA is required to reduce resting coronary blood flow. Parameters of LV function begin to deteriorate at this level and progress as the degree of narrowing increases. General principles of good medical therapy for patients with ischemic heart disease also apply to patients with LMCAS. However, it is important to exercise caution when using agents that lower blood pressure. Patients with LMCAS who are in an unstable state should be hospitalized, monitored, and treated vigorously with pharmacologic agents. If pain persists, intraaortic balloon counterpulsation can be tried as a temporizing measure. Prognosis of medically treated patients with LMCAS is influenced adversely by poor ventricular function, coexistent disease of the right coronary artery, and severity of the narrowing in the left main coronary artery. When surgery is being considered, intraaortic balloon counterpulsation can be useful adjunct in patients with continuing chest pain. However, in the usual patient with LMCAS who is responsive to pharmacologic agents, intraaortic balloon counterpulsation is not necessary. Survival of patients with LMCAS treated surgically is better than that of comparable medically treated patients. However, there are subsets of high- and low-risk patients related to ventricular function, degree of narrowing of the LMCA, and associated disease of other coronary vessels. We conclude that current aggressive medical therapy has eliminated the need for emergency or urgent coronary artery surgery in all but a few patients with LMCAS and persistent symptoms. However, despite the initial success of medical management, the long-term prognosis in these patients is poor. At the present time, surgery should be considered in all symptomatic patients with ≥50% LMCAS.

A framework for three-dimensional time-varying reconstruction of the human left ventricle: sources of error and estimation of their magnitude.

Abstract This report summarizes development of a computer/ultrasound system to graphically reconstruct the contracting human left ventricle in three dimensions and calculate indices of cardiac performance. The three-dimensional reconstruction is performed by realignment of five cross-sectional two-dimensional echograms along a single longitudinal section. The spatial position of the cross sections is recorded by a specially developed indexing arm. Cross sections are then realigned perpendicular to the long axis and parallel to each other by the computer. Points at 30° intervals are chosen from the inner and outer muscle boundaries of a cross section and connected by straight lines. Thus areas can be calculated simply by summation of triangular areas with vertices at the origin. Volumes can then be calculated using a modified Simpsons rule. To test these computer programs three hypothetical time-varying computer-generated left ventricular models were developed. Effects of six major anticipated sources of error were determined by systemic introduction of simulated measurement errors into data for these hypothetical models. These results demonstrate that this system is practical for the three-dimensional reconstruction of the left ventricle, that volumes and derived indices of ventricular performance can be calculated, and that anticipated sources of error result in relatively small deviations from true values.