Localization of regional myocardial ischemia by recording of monophasic action potentials.

Abstract

Identification of regional myocardial ischemia by TQ-ST segment mapping, while comnmonly used, is relatively imprecise and nonspecific. In 41 open-chest dogs we examined whether monophasic action potentials (MAPs) recorded from the myocardial surface by means of a new contactelectrode technique could be used to more precisely and specifically index regional myocardial ischemia. After ligation of the left anterior descending coronary artery (LAD), epicardial and endocardi-al MAPs from the ischemic region demonstrated shortening of plateau duration followed by a progressive loss in amplitude to 48 ± 8% and in maximum upstroke velocity (dV/dtmax) to 9 2% of control (n = 7). Regional hyperkalemia produced by intracoronary injection of potassium chloride also resulted in regional decreases in duration, amplitude, and dV/dtmax of the MAP. Similar to previously reported effects on transmembrane action potentials, ischemia-or hyperkalemia-induced loss in MAP amplitude was due to decreases in both diastolic (negative) and systolic (positive) potential and paralleled TQ segment depression and "true" ST segment elevation in unipolar direct current-coupled electrograms recorded from an adjacent site. In eight canine hearts we compared the abilities of MAP recordings and TQ-ST segment measurements in defining a region of myocardial ischemia. Transmural ischemia with a sharp flow border was produced by LAD ligation and distal embolization with dental rubber. One hour later simultaneous MAP and TQ-ST mapping was performed in each dog at 45 to 65 epicardial sites inside and outside the ischemic region. TQ-ST voltage was significantly increased 10 to 20 mm outside the visible cyanotic border, reaching a maximum just inside the border and decreasing progressively toward the center of the ischemic region to values not significantly different from those from sites 10 mm outside the ischemic border. In contrast, MAP amplitude and dV/dtmax were normal up to 5 to 10 mm outside the cyanotic border, decreased sharply across a lateral transition zone of only 8 mm to 8.7 + 2.3% and 4.3 + 0.9% of control, respectively, at sites 4 to 6 mm inside the border, and were uniformly abnormal across the entire ischemic region. Recordings made 3 hr after LAD ligation revealed an overall decline in the magnitude of TQ-ST, making definition of the ischemic border by TQ-ST even less precise, whereas the differences between MAPs from normal and ischemic myocardium had become even more pronounced than after 1 hr. Thus, unlike TQ-ST segment measurements, MAP recordings uniquely define ischemic and nonischemic sites and more precisely localize the border of an ischemic region. The similarities between the effects of regional ischemia and potassium chloride administration on MAPs and on transmembrane action potentials, as previously reported, further suggest that MAP recordings provide specific information about local electrophysiologic alterations. Endocardial and epicardial MAP mapping by this technique may allow assessment of the efficacy of int...

Monophasic action potential mapping in human subjects with normal electrocardiograms: direct evidence for the genesis of the T wave.

“…In this study, we recorded MAPs from multiple endocardial and epicardial sites in the human ventricle in situ by means of the contact electrode technique.7 8 The contact electrode has a tip diameter of 1 14 In our study, the longest average APD was measured in the septal and diaphragmatic area and the shortest at anteroapical and posterolateral sites. There are no endocardial data from a large mammalian species with which to compare this gradient.…”

“…All patients appeared to be free from subepicardial ischemia at the recording sites at the time of study, as judged by previously identified indexes of ischemia in the MAP. 8 Data analysis. Because of the sequential spread of excitation, activation at different left ventricular recording sites does not occur simultaneously but with varying delay.…”

Mechanoelectrical feedback: independent role of preload and contractility in modulation of canine ventricular excitability.

“…This system permitted accurate control and measurement of ventricular volume. The contractile state of the ventricle was quantified using concepts that have been developed in this laboratory (5 MAPs were recorded from the epicardial surface ofthe ventricle using a newly designed contact electrode (9). The recording device consists of an L-shaped cantilever with two electrodes (sintered Ag-AgCI) mounted on its distal end.…”

Preliminary Animal and Clinical Experiences Using an Electromechanical Endocardial Mapping Procedure to Distinguish Infarcted From Healthy Myocardium

“…Monophasic action potentials recorded from ischemic endocardial surfaces in dogs have demonstrated a progressive and significant loss of electrical amplitude and upstroke velocity within minutes after LAD occlusion. 13 Thus, electrical signals derived from ischemic and/or infarcted regions could differentiate between normal, necrotic, and ischemic myocardium and might be used as a sensitive quantitative tool for the assessment of myocardial viability.…”