Source of Electrocardiographic ST Changes in Subendocardial Ischemia

Abstract

Abstract-To clarify the source of electrocardiographic ST depression associated with ischemia, a sheep model of subendocardial ischemia was developed in which simultaneous epicardial and endocardial ST potentials were mapped, and a computer model using the bidomain technique was developed to explain the results. To produce ischemia in different territories of the myocardium in the same animal, the left anterior descending coronary artery and left circumflex coronary artery were partially constricted in sequence. Results from 36 sheep and the computer simulation are reported. The distributions of epicardial potentials from either ischemic source were very similar (rϭ0.77Ϯ0.14, PϽ0.0001), with both showing ST depression on the free wall of the left ventricle and no association between the ST depression and the ischemic region. However, endocardial potentials showed that ST elevation was directly associated with the region of reduced blood flow. Insulating the heart from the surrounding tissue with plastic increased the magnitude of epicardial ST potentials, which was consistent with an intramyocardial source. Increasing the percent stenosis of a coronary artery increased epicardial ST depression at the lateral boundary and resulted in ST elevation starting from the ischemic center as ischemia became transmural. Computer simulation using the bidomain model reproduced the epicardial ST patterns and suggested that the ST depression was generated at the lateral boundary between ischemic and normal territories. ST depression on the epicardium reflected the position of this lateral boundary. The boundaries of ischemic territories are shared, and only those appearing on the free wall contribute to external ST potential fields. These effects explain why body surface ST depression does not localize cardiac ischemia in humans.(Circ Res. 1998;82;957-970.)Key Words: ST depression Ⅲ potential mapping Ⅲ bidomain model Ⅲ subendocardial ischemia Ⅲ regional myocardial blood flow E lectrocardiographic ST-segment depression has long been recognized as a sign of ischemia, 1,2 but the explanations of the responsible mechanisms have been controversial. [3][4][5][6] Much of the current opinion regarding the genesis of ST-segment depression is derived from interpretations based on certain theoretical considerations 7,8 and indirect evidence from animal experiments. 1,2 Ischemic muscle generates intracellular currents, which effectively cause TQ depression and ST elevation over the ischemic area 9,10 and which conventional electrocardiography with AC-coupled amplifiers reflects as ST elevation. ST-segment depression recorded at the epicardium has been considered to be secondary to an injury current in the underlying subendocardium. [11][12][13][14] In conventional stress testing, as myocardial demand exceeds the ability of the narrowed coronary arterial bed to increase blood flow, the ischemic threshold is exceeded, and reversible ST-segment depression is produced. However, the location of this ST depression does not enable us to localize...

The Virtual Ventricular Wall: A Tool for Exploring Cardiac Propagation and Arrhythmogenesis

“…Both experimental [1][2][3] and computational [4,5] evidence supports the idea that VF is sustained by re-entrant wave propagation. There can be either a single re-entrant wave with fibrillatory conduction [6] or breakup of an initial re-entrant wave to multiple wavelets, due to cell restitution properties [7], effects of rotational anisotropy in the ventricular wall [8], or dynamic three-dimensional (3D) instabilities [9]: see Figure 1.…”

Epicardial ST Depression in Acute Myocardial Infarction

“…[1][2][3][4][5][6][7][8] As part of a study looking at partial-thickness ischemia in an experimental animal model, 9 we observed that ST depression accompanied some episodes of full-thickness ischemia and not others. The literature reflecting experimental infarction has shown that full-thickness ischemia was associated with a region of epicardial ST elevation over the ischemia with minimal changes elsewhere.…”

“…The details of the surgical procedures have been published previously. 9 The investigation conforms with the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH Publication No. 85-23, revised 1985).…”

“…The RMBF was measured before ischemia and at 20 minutes of ischemia using fluorescent microspheres (Molecular Probes) as previously described. 9,18 Potential Recording, Construction of Isopotential Maps, and Map Display Epicardial potentials were recorded using an epicardial sock containing 64 electrodes (Cardiovascular Research and Training Institute, the University of Utah). Endocardial electrograms were recorded using a homemade 40-electrode basket mapping apparatus.…”

Electrocardiographic Analysis of ST-Segment Duration and Morphology in Sheep and Goats: Effect of Species, Breed, Age and Sex

“…Elevation and depression of this segment in patients represent disorders such as cardiac ischemia and infarction, electrolyte imbalances, electrical conduction abnormalities, and cardiac structure and valves problems (Gertsch, 2009;Häggmark et al, 2005;Li et al, 1998). However, little is known regarding the ST-segment in animals.…”