Temporal relationship of implantable cardioverter defibrillator discharges and environmental physical activity

Studies by our group have shown an inverse relationship between sudden death and cardiac rhythm disturbances and environmental levels of geomagnetic activity (GMA). The aim of this study was to use the precise data provided by automatic implantable cardioverter defibrillators (ICDs) regarding the onset of ventricular fibrillation and ventricular tachycardia to link these events to GMA level.

The study group included 25 patients (22 men; 22 with ischemic cardiomyopathy) aged 28-81 years in whom an ICD had been implanted between 1995 and 2004. Patients were referred to the cardiac intensive care unit after each event that induced one or more discharges. The number of events and the day on which they occurred were recorded. Data on GMA and other cosmophysical parameters were obtained from the U.S. National Geophysical and Space Service Centers and the Russian Academy of Sciences. GMA levels, graded from I (quiet) to IV (stormy) in the middle latitutes, were recorded for 1974-2003 (10,954 days) and for each day on which an ICD discharge occurred.

A total of 402 discharges were recorded on 137 days during the study period. Forty-six percent of the discharges took place on days of GMA I, compared with 38% - II, 13% - III, and 3% - IV. The daily distribution of GMA was as follows: level I - 35.2%, II - 37.3%, III - 21.86%, IV - 5.61%. Comparison of ICD discharge days and actual multiyear levels of GMA (in percent) yielded a ratio of 1.326 for GMA I, 1.076 - II, 0.459 - III, 0.390 - IV. There was a significant inverse correlation between GMA level and number of discharges (r =-0.97, P = 0.03) and days of treatment (r =-0.96, P = 0.039), and a significant difference between ICD discharges on days of GMA I and GMA II-IV (chi(2)= 5.05, P = 0.02).

The higher number of ICD discharges on days of lowest GMA may be explained by a possible antiarrhythmic effect of GMA. Environmental arrhythmogenic factors that act inversely to GMA may be activated at times of low GMA.