Long-term follow-up of "reversible" dilated cardiomyopathy with improvement of cardiac sympathetic nerve activity after cardiac resynchronization therapy (CRT): Do "CRT superresponders" have "dyssynchrony-induced cardiomyopathy"?

We report a case of idiopathic dilated cardiomyopathy with severe heart failure and complete left bundle branch block (CLBBB) which exhibited an excellent response to cardiac resynchronization therapy (CRT). A 71-year-old male had been treated for 9 years with medication for chronic heart failure. He was referred to hospital with a complaint of dyspnea. An electrocardiogram showed CLBBB, with a QRS-width of 200 ms. Markedly dilated left ventricular (LV) chamber with a low ejection fraction (EF) of 18% and severe mitral regurgitation were registered by echocardiogram. Myocardial neuronal ¹²³I-metaiodobenzylguanidine uptake was reduced, with a heart-to-mediastinum (H/M) ratio of 1.88. Immediately after the introduction of CRT, clinical improvement was observed. At 1-year follow-up, LV chamber size and cardiac function were almost normalized, with an EF of 53%. Cardiac sympathetic nerve activity (CSNA) was simultaneously normalized, with an H/M ratio of 2.32 and a washout rate of 14.7%. However, after the cessation of carvedilol administration, CSNA and LV systolic function were slightly aggravated, with an H/M ratio of 2.20, a washout rate of 15.9%, and an EF of 44%. In the present case, the excellent improvement in cardiac function and CSNA was caused by the combined effects of beta-blocker therapy and CRT.