Incidence of Ventricular Arrhythmia in ICD Recipients Varies by Season, Time of Day
Key findings
- In a pooled population of 3,969 patients using implantable cardioverter-defibrillators for primary prevention of sudden cardiac death, the incidence of ventricular arrhythmia (VA) was significantly higher during the spring than during the summer
- During fall and winter, the estimated chances of VA were not significantly different than during the spring
- Patients were more likely to experience VA between 8 a.m. and 10 p.m. than between 10 p.m. and 8 a.m.
- There were no significant differences between individual months of the year or individual days of the week with regard to the incidence of VA
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Over the past 15 years, cardiologists have come to understand that shocks from implantable cardioverter-defibrillators (ICDs) can negatively affect short and long-term patient outcomes. Even so, little is known about when ventricular arrhythmia (VA) is most likely to occur.
In the largest cohort of ICD recipients ever assembled, Cardiac Electrophysiology Fellow Abhishek Maan, MD, ScM, and E. Kevin Heist, MD, PhD, director of the Clinical Cardiac Electrophysiology Fellowship Program at Massachusetts General Hospital, and colleagues detected a significantly greater incidence of VA during the spring than during the summer. In JACC: Clinical Electrophysiology, they report that VA is more likely during normal waking hours than at night.
Study Design
The research team pooled data on 3,969 subjects from six prospective clinical trials of various ICDs. Patients were eligible if they received their ICD for primary prevention of sudden cardiac death and there had been at least one device interrogation.
The clinical trials varied in how settings pertaining to the number of intervals to detection were programmed. To maximize homogeneity, the researchers included only patients whose devices were programmed to 12/16 or 18/24, the most commonly used settings.
The average follow-up per participant was 1.8 years. Each episode of ventricular tachycardia or ventricular fibrillation included in the study (with or without device therapy) was independently reviewed by an electrophysiologist as part of the clinical trials and also by an independent panel of physicians.
Risk of VA by Season
- The estimated chance of at least one episode of VA was 0.86% during spring and 0.70% during summer (P = .009)
- During fall and winter, the estimated chances of VA were not significantly different than during the spring
- The seasonal variations in VA occurrence were not influenced by sex or age group (≤55 years old vs. >55 years old)
Risk of VA Over Other Time Periods
- There were no significant differences between individual months of the year or individual days of the week with regard to the incidence of VA
- Patients were more likely to experience VA between 8 a.m. and 10 p.m. than between 10 p.m. and 8 a.m.
- Over the course of one year, the estimated probability of at least one episode of VA during a given hour of the daytime period was 35% to 63% higher than from midnight to 1 a.m.
What Might Cause Temporal Changes?
In previous studies, a number of seasonal changes have been proposed to influence the risk of arrhythmia:
- Environmental temperature
- Barometric pressure
- Humidity
- Air pollution
- The patient's physical activity
- The patient's fluid and diet intake
The findings of variation in risk according to time of day might reflect changes in autonomic tone, adrenergic stimulation or other factors that may be modulated by normal variations in circadian rhythm.
Improvements in understanding how these factors affect the incidence of VA could enhance how devices are programmed to avoid unnecessary and inappropriate ICD therapies.
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