Ventricular arrhythmias following thermal damage of epicardial tissue: Possible causes and clinical implications

Epicardial heating may be used for ventricular tachycardial (VT) ablation a nd transmyocardial revascularization. However, the potential risks of therm al epicardial injury, including arrhythmia, have not been fully explored. T his study relates the pathologic and arrhythmic sequellae of epicardial hea ting when applied with a diode laser at varying doses. Acute pathology and dosimetry were determined in a group of normal dogs using 2-3 W over 30-90 seconds. Another group received a similar dose range before undergoing 24-h our monitoring, and electrophysiological testing was done at 4 weeks. In th is group, four dogs each received 12 lesions (90-180 J) according to a rand omized block design. Another dog received nine lower dose lesions (30-120 J ). Acute lesions measured 2.5-8.0-mm wide by 4-8.5-mm deep. Charring and va porization were common when 3 W were applied over 45 seconds. Within 24 hou rs, VT with features of abnormal automaticity occurred in all dogs receivin g this dose. The dog in whom lower doses induced coagulation only had no VT . Four weeks later, electrophysiological study induced no VT. At this time fibrosis and granulation tissue were organizing the contraction band necros is seen acutely, and some lesion borders were becoming calcified. No major vessels had been damaged. Abnormal automaticity and VT may occur if thermal damage of the epicardium exceeds coagulation. This could be related to tis sue injury caused by sudden water vaporization, and may have clinical relev ance given the growing indications for myocardial heating.