Ventricular Tachycardia Burden and Mortality: Association or Causality?

Ventricular tachycardia (VT) is a potentially fatal cardiac rhythm disorder. Implantable cardioverter defibrillators (ICDs) are the primary management strategy for VT and have been shown to reduce the incidence of death but, ICDs do not reduce VT recurrences. Further, mounting evidence indicates that high VT burden, defined as the cumulative number of recurrent VTs or ICD shocks, is associated with an elevated risk of death; however, it is unclear if high VT burden is a cause of death or a marker of severe heart disease. Proposed mechanisms for a causal pathway suggest that multiple VT episodes or potential deleterious effects from ICDs might alter the myocardium of the ventricles to induce worsening heart disease, which might translate to an increased risk of mortality. In this review, we present the evidence to support association and causation hypotheses for the relationship between VT burden and risk of mortality and indicate potential gaps in evidence. Overall, there is insufficient evidence to prove causal hypotheses for the relationship between VT burden and mortality. Consistent definitions for VT burden, randomized controlled trials that assess the relationship between VT burden and mortality, and observational studies that capture VT burden are warranted to investigate if a potential causal relationship exists.