Changes in myocardial impedance spectrum during acute ischemia in the in-situ pig heart

In-vivo monitoring of myocardial impedance during ischemia is useful to study the pathophysiological changes occurring after coronary occlusion and to assess tissue damage. Ischemic myocardium impedance spectrum (1 kHz-1 MHz) was measured during 140 min of left anterior descending (LAD) coronary artery occlusion in the open chest chloralose anesthesized pig model. The impedance spectrum shows a double relaxation mechanism. The first relaxation has a central frequency around 300 kHz whereas the second is around 10 kHz and appears after approx. 30 min of ischemia becoming dominant thereafter. The complex plane plot shows a radius increase of both relaxation arcs. This behaviour could explain the reported double step change with time of the myocardium electrical impedance at 1 kHz.