The QRS complex during transient myocardial ischemia: studies in patients with variant angina pectoris and in a canine preparation

J E Barnhill, J P Wikswo, A K Dawson, S Gundersen, R M Robertson, D Robertson, R Virmani, R F Smith
1985 Circulation  
We made continuous electrocardiographic recordings on magnetic tape during 15 episodes of ischemia in five patients with variant angina to determine the characteristics of the QRS changes. Orthogonal leads were used and the electrocardiograms were analyzed visually and by digital computer. Changes were quantified by subtracting baseline electrocardiograms from those obtained during ischemia. Large changes in the QRS occurred during ischemia but the waveform quickly returned to baseline when the
more » ... episode subsided. In all patients there was prolongation of the QRS duration and an increase in QRS voltage during the terminal 40 msec of the waveform in the lead(s) showing the most marked ST displacement. The increase in the terminal QRS could be represented by a vector directed toward the ischemic zone. In a given patient the amplitude of ST displacement varied between episodes, presumably because of variation in the intensity of ischemia, but the QRS changes were directionally similar in each episode. In two patients there was also a smaller change involving the initial 40 msec of the QRS that could be represented by a vector directed away from the ischemic zone. To determine the possible mechanism for the electrocardiographic changes, ischemic episodes of 120 to 150 sec were produced in seven dogs and electrocardiographic recording and analysis techniques similar to those used in patients were employed. Myocardial conduction velocity was measured in three directions in the ischemic zone and was correlated with simultaneous electrocardiographic recordings from the body surface. The electrocardiographic changes in the dog preparation were virtually identical to those in the patients and strongly correlated with a fall in myocardial conduction velocity. We conclude that the QRS changes during variant angina result from the altered excitation pattern produced by conduction delay in the ischemic zone. The probable cause for the increase in terminal QRS voltage is delayed (and uncanceled) activation of the ischemic zone. Circulation 71, No. 5, 901-911, 1985. WE HAVE investigated the QRS changes during spontaneous ischemia in patients with variant angina by performing a detailed analysis of electrocardiograms from orthogonal leads. To determine the possible explanation for the changes, we have produced transient myocardial ischemia in a dog preparation and have correlated changes in myocardial conduction velocity with the simultaneous electrocardiographic changes Association. that occurred in surface orthogonal leads similar to those that were obtained in the patients. Methods Studies in patients. All patients admitted to Vanderbilt Hospital and the VA Medical Center, Nashville, to participate in a research study of vasospastic angina were included in this electrocardiographic study if they consented to continuous electrocardiographic monitoring with special leads and had spontaneous episodes of ischemic chest pain at rest and/or transient ST segment displacement of 0.2 mV or greater. Eight patients met these criteria and in five of these recordings were obtained during 15 episodes of ischemia that were satisfactory for analysis. Records from three patients were excluded for strictly technical reasons such as detached electrodes, signals out of the dynamic range of the recorder, or excessive electrical noise. The electrocardiographic recordings were obtained during an observation period before commencing drug trials. Long-acting nitrates, calcium-channel antagonists, 3-adrenoceptor antagonists, and platelet agents were withheld during this phase of the
doi:10.1161/01.cir.71.5.901 pmid:3986980 fatcat:uyjz4hddrrc7xazdcgpqwa5uza