Ventricular depolarisation vectors in exercise induced myocardial ischaemia

Abstract

Ischaemia reduces membrane excitability and conduction of myocardial depolarisation. This would alter the synergy of electromotive forces that contribute to a resultant force at any instant. Changes in magnitude and direction of resultant forces are reflected in electrocardiographic signals. Here we show a method for obtaining the coordinates of resultant electrical forces during exercise derived from a bipolar orthogonal lead system for calculation of electrical vectors in three planes. In a trial, analysis of changes in vectors indicated that the extent of reduction in magnitude with exercise was significantly greater in groups of patients categorized by impaired effort tolerance and signs of ischaemia. Measurement of changes in the spectrum of depolarisation vectors during exercise has the potential for non-invasive assessment of myocardial ischaemia. This could be the basis of a portable, low-cost tool for investigation of patients with symptoms suggestive of coronary artery disease.

Changes in ventricular depolarisation vectors during exercise caused by regional myocardial ischaemia

“…Differences in the QRS waveforms were not noticed during the recording but are evident when the data sets are aligned accurately for comparison and calculation of the extent of change. Alignment is a crucial element of the method of analysis of vectors 2 .…”

“…Considering the results of the first study 2 , we intended to confirm the association of reversible reduction in vector magnitude during exercise with reversible defects in regional perfusion shown by MPS, and determine whether enhancement of the magnitude and changes in direction of vectors, together with reduction in magnitude, could provide specific criteria for ischaemia induced by exercise.…”

“…The signals of 3 orthogonal leads, based on the system of McFee and Parungao 4 , were recorded simultaneously, digitised and stored for later computation. Analysis of the data by software developed at AKU involved averaging 30–80 accurately aligned digitised data of ventricular depolarisation 2 . The averaged lead signals represented consistent elements of the QRS waveform at each stage of the Bruce protocol for treadmill exercise and provided the coordinates of vectors at intervals of 1.5 millisecond (ms) in frontal, horizontal and sagittal planes.…”

“…Trial of the method 2 in patients referred for myocardial perfusion scan (MPS) compared with young, healthy volunteers undergoing a standard exercise tolerance test (ETT) showed significant differences in the magnitudes of vectors between patients and volunteers.…”