Biological effects of shock waves: Induction of arrhythmia in piglet hearts

Abstract

During lithotripsy by electrohydraulic or electromagnetic lithotripters, the application of extracorporeal shock waves has to be synchronized with the electrocardiogram to reduce the induction of arrhythmias. The relation between the refractory period of the cardiac cycle and arrhythmia induction by shock waves, and the underlying mechanism have so far not been examined. In this experiment, the cardiac response to shock waves administered at 20 kV by an electrohydraulic lithotripter was assessed in nine piglets. The focus was positioned 5, 10 and 15 cm caudal to the apex of the left ventricle, and in some piglets also at the apex. The interval following the R-wave was determined during which the heart was refractory to shock wave stimulation by either single discharges or shock-wave bursts, i.e., groups of discharges separated by 10 ms intervals. This mechanical refractory period was compared to its electrical counterpart, which was determined by transvenous intracardiac atrial stimulation. As a result, mechanical refractory periods following the R-wave were at 5 cm distance 60 ms for single discharges and 70 ms for bursts (medians; range 10–180 ms); both stimulation modes were highly correlated ( r = 0.88). While a similar result was obtained with the focus positioned directly at the cardiac apex, at 10 cm distance from it, bursts elicited a cardiac response significantly more often (in nine vs. two piglets). At 15 cm distance, no response was obtained at all. Both mechanical and electrical atrial refractory periods were in a similar range. The more effective cardiac stimulation by shock-wave bursts at 10 cm distance is compatible with the induction of arrhythmia by a cavitation-based instead of a direct shock wave effect.