Contribution of mechano-electric coupling to ventricular arrhythmias during reduced perfusion

The monophasic action potential may have a better relationship to reduced myocardial perfusion than the S-T segment of the electrocardiogram. This was addressed because of the need to monitor ischaemic areas in open chest surgery. The precise relationship between the action potential and myocardial motion during reduced perfusion also requires addressing because of the potential importance in arrhythmias. Landrace pigs were anaesthetised and their chests opened to expose the heart. Snares were placed around a branch of descending coronary artery, and the ascending aorta. Arterial and intraventricular pressures were monitored. Monophasic action potentials and local segment mechanical behaviour were recorded from predefined areas. Radiolabeled microspheres were used to measure regional myocardial blood flow. After 60 min ischaemia, regional blood flow showed a good relationship with action potential duration, reducing with blood flow reductions, whereas the S-T segment of the ECG showed no correlation. Both regional ischaemia, and aortic constriction in normal heart, produced paradoxical wall motion, (lengthening instead of shortening during electrical systole and contraction), associated with early afterdepolarisations. The latter were occasionally accompanied by ventricular ectopic beats. Alternans was regularly noted with ischaemia. All the observations could be seen in the period preceding arrhythmia. The results suggest that the monophasic action potential per se may be used in monitoring ischaemia during cardiac surgery, and the 'Mechano-electric feedback' interactions could have implications for arrhythmias.