The observed increase in the
The observed increase in the number of ICD therapies during influenza season is consistent with prior reports describing increased cardiac arrhythmia burden in winter , possibly requiring a larger number of ICD therapies. Influenza vaccination may attenuate this. The low incidence of electrical storms observed in our study is likely a reflection of the small sample size and milder influenza season in 2011. Given the larger trend toward a benefit of influenza vaccination when analyzing appropriate ICD therapies, we speculate that vaccination may reduce the burden of electrical storm in ICD patients.
Our findings support the current Class I recommendations by the American Heart Association and the Canadian Cardiovascular Society for influenza vaccination in patients with calcium channel blocker failure. There is currently little direct evidence supporting the benefit of influenza vaccination in heart failure patients and the recommendation to vaccinate these patients is based on consensus opinion or small studies [3,4]. Our exploratory study adds to existing literature supporting the potential cardiac benefits of influenza vaccination in patients with stable cardiovascular disease. We advocate for larger scale studies to better appreciate the magnitude of cardiac benefit associated with influenza vaccination.
Our findings, particularly if confirmed by other groups, should be communicated to ICD patients to ensure their universal influenza vaccination. Despite the current recommendations for patients with heart failure to be vaccinated against influenza, over 20% of patients in our cohort did not receive the intervention. This less than optimal vaccination rate in cardiac patients has also been demonstrated by others . The potential benefits of a reduction in cardiac arrhythmia suggested by our work, proven non-cardiac benefits of influenza vaccination in adult patients , and current Class I recommendations by various Societies should prompt consideration of the influenza vaccination rate as a performance measure in cardiac electrophysiology.
This study has limitations. First, the sample size was small and the event rate was low, reducing the power to detect statistically significant differences between the two groups. Second, we were unable to assess differences between those who completed the survey and those who did not; unmeasured differences between survey responders and non-responders may have introduced bias and compromised the generalizability of our findings. Third, vaccination status was determined by survey. While this approach may be subject to “recall” bias, it is considered the current gold standard for ascertaining vaccination status . Fourth, clinical details such as hospitalization for a respiratory illness or serologic evidence of acute influenza infection at the time of receipt of ICD therapies were not available, thereby preventing us from further commenting on the association between ICD therapies and acute influenza infection. Finally, although we adjusted for other predictors of ICD therapies, we cannot exclude a “healthy-user” bias – that is this possibility that inherently healthier patients chose to receive the influenza vaccine . This possibility is well known in retrospective studies evaluating use of the influenza vaccine  and is unlikely to be overcome outside of a randomized clinical trial, which is likely unethical given the current Class I recommendations for use of this intervention.
Author contributions Concept/design: Sheldon M. Singh, MD, Russell J. de Souza, ScD, RD, Ramanan Kumareswaran, MD. Data analysis/interpretation: Sheldon M. Singh, MD, Russell J. de Souza, ScD, RD, Ramanan Kumareswaran, MD. Drafting article: Sheldon M. Singh, MD. Critical revision of article: Sheldon M. Singh, MD, Russell J. de Souza, ScD, RD, Ramanan Kumareswaran, MD. Approval of article: Sheldon M. Singh, MD, Russell J. de Souza, ScD, RD, Ramanan Kumareswaran, MD. Statistics: Russell J. de Souza, ScD.