Absence of a morning peak in ventricular tachycardia and fibrillation events in nonischemic heart disease: Analysis of therapies by implantable cardioverter defibrillators

A growing number of Japanese patients are being treated with ICDs. Efforts are warranted to minimize the rates of ICD shocks that cause discomfort and anxiety, The circadian distribution of ICD discharges was investigated in 80 patients (57 +/- 10 years of age, 69 men) from ten Japanese medical cent ers. The underlying heart disease was ischemic in 27 versus nonischemic in 53 patients. All patients had refractory VT or VF, and received appropriate shocks confirmed by stored data retrieved from the memory of the IM In the analysis of 354 appropriate shocks delivered in the overall population, a morning peak in VT or VF episodes was observed. However, subgroup analyses of the circadian distribution of ICD shocks revealed that the morning peak in VT or VF episodes was confined to patients with ischemic heart disease a nd was blunted by treatment patients with beta -adrenergic blockers. The ab sence of a morning peak in appropriate ICD shocks among patients with nonis chemic heart disease remains unexplained and was unrelated to the use of be ta -adrenergic blockers. In conclusion, the circadian pattern of appropriat e ICD discharges was related to the underlying heart disease. In patients w ith ischemic heart disease, recurrences of VT or VF peaked in the morning. In contrast, in patients without ischemic heart disease, the episodes of VT or VF were evenly distributed during waking hours. beta -Adrenergic blocke rs appeared to blunt the morning peak in VT or VF among patients with ische mic heart disease.