Ischaemia and reperfusion induced transient QRS vector changes: relationship to size of the ischaemic territory

The aim was to investigate QRS vector changes during the first 30 min of coronary occlusion or the early phase of reperfusion with special reference to location and size of myocardium at risk.

24 h experiments were performed in closed chest anaesthetised pigs. QRS vectors were studied by computerised vectorcardiography via Frank leads. Occlusion of the left anterior descending coronary artery followed by reperfusion was induced in 23 pigs and a sustained occlusion in 20 pigs: left anterior descending coronary artery in seven, right coronary artery in eight, and left circumflex coronary artery in five. Myocardium at risk was measured in postmortem autoradiograms. Eight animals were excluded.

Four minutes after occlusion, QRS(mean) deviated towards the ischaemic region in 34/35 animals and returned thereafter at varying speeds. In half of the reperfused animals, deviation of QRS vectors towards the ischaemic territory was also observed during the first minutes of reperfusion. A paradoxical increase in QRS vector changes, "reperfusion peak", was recorded during the initial minutes of reperfusion in 12/19 animals. Maximum spatial QRS vector magnitude increased in all right coronary or left circumflex coronary occlusion animals compared to 6/25 in left anterior descending coronary occlusion animals. QRS vector difference, change in spatial QRS vector angle, and maximum change in QRS azimuth 4 min after occlusion correlated significantly with extent of myocardium at risk.

Marked directional and quantitative QRS vector changes, with significant relation to size and location of myocardium at risk, were recorded during the initial minutes of ischaemia. The transient increase in QRS vector changes during the first minutes of reperfusion deserves further exploration as a new indicator of reperfusion.