Implantable cardioverter defibrillators and their role in heart failure progression

Patients with an implantable cardioverter defibrillator (ICD) implanted for primary prevention have an increased mortality rate if they receive appropriate and/or inappropriate ICD shocks. The most common cause of increased mortality is worsening heart failure. ICD shocks cause direct myocardial injury, contraction band necrosis, and fibrosis, and could induce persistent inflammation. These changes likely contribute to the ventricular dysfunction in patients who have a significantly depressed ejection fraction initially. One-third of the patients with ICDs have psychiatric disorders. Studies have demonstrated that the patients have decreased quality of life, including emotional dysfunction, during the month following an ICD shock. Patients with anxiety and depression have an activated hypothalamus-hypophysis-adrenal axis, increased sympathetic activity, and decreased vagal tone. Chronic sympathetic stimulation could directly affect the myocardium and worsen cardiac dysfunction. Consequently, although ICD implantation is life-saving, it may contribute to heart failure progression. Completed trials need reanalysis to determine whether there are unique characteristics of patients receiving shocks that might lead to additional therapy. Furthermore, the interaction between psychiatric disorders and ICD therapy needs more study.