Electrophysiology studies in patients with dilated cardiomyopathies.

Dilated cardiomyopathy is a diverse group of heart diseases with variable arrhythmia substrates. The response to programmed stimulation is dependent on spontaneous arrhythmia presentation. In patients with dilated cardiomyopathy, the majority of sustained monomorphic VT is caused by a scar-related reentrant mechanism, similar to that of coronary artery disease. The arrhythmia is uniformly inducible and is often refractory to pharmacologic therapy. Sustained VT is associated with more extensive myocardial fibrosis and non-uniform anisotropy, involving both the endocardium and epicardium, compared to those without sustained reentry. The response to programmed stimulation is more variable in patients presenting with nonsustained arrhythmia, cardiac arrest or syncope. Inducibility of monomorphic VT is much lower compared to those with ischemic heart disease. Other non-reentrant mechanism, such as focal automaticity, can also be observed in patients with monomorphic VT, in the absence of myocardial scar or evidence of slow conduction. The utility of electrophysiology studies to determine prognosis and to guide therapy remains limited in this patient population. The clinical outcome does not correlate with arrhythmia inducibility, and suppression of induced arrhythmia does not predict a good prognosis. The diagnosis of sarcoidosis or Chagas' cardiomyopathy should be considered in patients with dilated cardiomyopathy of unknown etiology, particularly in those with marked regional wall motion abnormalities and inducible VT. Epicardial reentrant circuits may be more prevalent in these cardiomyopathies, especially in those with VT related to chronic Chagas' disease. Although bundle branch reentry VT is a common finding in patients with dilated cardiomyopathy, it can occur in cardiomyopathy of any type and may coexist with other myocardial reentrant VT. It often has a typical bundle branch block QRS pattern during VT and is associated with His-Purkinje conduction delay. Evidence of macroreentry involving the bundle branches can usually be demonstrated, and catheter ablation of the bundle branches provides an effective and specific treatment.