Role of ATP sensitive potassium channel in extracellular potassium accumulation and cardiac arrhythmias during myocardial ischaemia.

Extracellular potassium rises rapidly during myocardial ischaemia, correlating with the onset of ventricular arrhythmias. The extracellular accumulation of potassium can induce abnormalities in both impulse conduction and impulse generation. Inhomogeneities of potassium conductance will elicit regional differences in action potential duration and repolarisation. The resulting spatial dispersion of refractory period will allow for fragmentation of impulse conduction on ensuing beats, the formation of irregular reentrant pathways and ventricular fibrillation. In a similar manner, the spread of injury current from the ischaemic tissue to surrounding normal tissue can trigger extrasystoles (depolarisation induced automaticity). It has been hypothesised that the activation of the ATP sensitive potassium channel contributes significantly to reductions in action potential duration and increases in extracellular potassium accumulation during myocardial ischaemia. ATP sensitive potassium channel antagonists prevent ischaemically induced reductions in action potential duration and the dispersion of refractory period but may induce oscillatory afterpotentials under some conditions (for example, calcium overload). In contrast, potassium channel agonists enhance the dispersion of refractory period ischaemia, which promotes the formation of re-entrant arrhythmias. The pharmacological modulation of the ATP sensitive potassium channels could therefore offer a novel approach for the management of cardiac arrhythmias in patients with ischaemic heart disease. In general, channel antagonists prevent ventricular fibrillation, while high (hypotensive) doses of channel agonists can induce malignant arrhythmias during ischaemia in animal models. However, recent evidence also suggests that potassium channel agonists may promote a better preservation of myocardial mechanical performance during reperfusion while ATP sensitive potassium channel antagonists exacerbate mechanical depression during ischaemia in experimental models.(ABSTRACT TRUNCATED AT 250 WORDS)