Identifying predictors of electrical storm in patients with implantable cardioverter-defibrillators (ICDs) could help identify those at risk and reduce the incidence of this emergency situation, which has a detrimental effect on mortality and morbidity in patients with ICDs. This retrospective study sought to determine the prevalence and predictors of electrical storm in patients with ICDs. One hundred sixty-two patients (126 men; mean age 58 +/- 13 years) who received ICDs from January 2001 to January 2005 were included in the study. Clinical, electrocardiographic, and ICD stored data and electrograms were collected and analyzed. Twenty-two patients (14%) developed electrical storm during a mean follow-up of 14.3 +/- 10 months. Using Cox multiple regression analysis, it was found that an ejection fraction <25% (p = 0.007), QRS width > or =120 ms (p = 0.002), and a lack of adjunctive angiotensin-converting enzyme inhibitor and beta-blocker therapy (both p < 0.001) were correlated with a greater probability of electrical storm. Adjunctive amiodarone and digoxin therapy, indication of ICD implantation, and age were not correlated with the occurrence of electrical storm during follow-up (all p = NS). In conclusion, electrical storm is not uncommon in patients with ICDs. Optimum medical therapy with beta blockers and angiotensin-converting enzyme inhibitors could reduce the occurrence of electrical storm, and this especially should be considered in those at greater risk for this complication (i.e., those with left ventricular ejection fractions <25% and QRS widths > or =120 ms).