Background: Studies have linked the natural history of many pathologies with environmental physical activity. This study investigated the relationship between the occurrence of ventricular tachycardia/fibrillation (VT/VF) recorded by implantable cardioverter defibrillators (ICD) and geomagnetic and cosmic ray (neutron) activity.

Methods: The study group included 85 patients (73 men) with cardiomyopathy (80% ischemic) who underwent ICD placement in the years 1995-2006; 74% had a left ventricular ejection fraction of < 30%. Data on the days on which VT/VF occurred (total number of days: 284) and the days on which the patients were treated (total number of treatments: 580) were collected from the ICD records. The findings were analyzed against levels of geomagnetic activity (GMA) (I degree -IV degree) and cosmic ray activity (CRA), derived from international observatories, on the same days and throughout the study period.

Results: On days of VT/VF, daily values of GMA level averaged 1.5 +/- 0.7, consistent with level I degree (quiet). The ratios of daily VT/VF episodes and treatment to GMA level for the whole study period were as follows: 1.2 level I; 0.9 level II; 0.69 level III; 0.78 level IV (r = -0.974; p = 0.02). Mean CRA on days of VT/VF was 9246.8 +/- 299.0 imp/min, and for all 4383 days studied, 8805.33 +/- 411.4 imp/min (p < 0.0001).

Conclusions: In patients with predominantly ischemic cardiomyopathy and severe left ventricular dysfunction, VT/VF occurs more often on days of low GMA and high CRA. Further studies are needed to determine the underlying mechanism of the effect of neutron activity on cardiac electrical instability.