Indications for cardiac resynchronisation therapy, Arrhythmia 

Patients with severe heart failure and narrow QRS ( < 120 ms)

Dr Yu from Hong Kong pointed out the poor correlation between mechanical dyssynchrony and QRS width. For example in one study 43% of patients with narrow QRS did have mechanical dyssynhrony compared to 64% with wide QRS. Moreover and importantly reverse left ventricular remodelling by CRT seems to be better correlated to the degree of mechanical dyssynchrony than to QRS width. The problem remains that there are a number of mechanical dyssynchrony criteria and that the predicitive power of these criteria to foresee clinical improvement has not been demonstrated in large randomised trials.

Dr Yu compared the results of CRT in NYHA III/IV heart failure patients with wide QRS to patients with narrow QRS with or without mechanical dyssynchrony. The study protocol included 3 months of open CRT treatment followed by 1 month of CRT OFF.

For patients with narrow QRS and mechanical dyssynchrony improvements concerning exercise tolerance, NYHA class and measures of left ventricular reverse remodelling were just as great as for patients with wide QRS. In contrast, for patients with narrow QRS but with no signs of mechanical dyssynchrony no improvements were found. The study indicates that randomised trials to identify the measures of mechanical dyssynchrony criteria that best predict clinical improvements in CRT are urgently needed. The PROSPECT trial is a large non-randomised multicentre trial on this subject which will report in 2007.
Moreover, for patients with narrow QRS and no evidence of mechanical dyssynchrony there is no evidence that CRT is beneficial.

Patients in NYHA II or in NYHA I with prior heart failure symptoms

Dr Abraham reported that since reverse left ventricular remodelling is a consistent finding in CRT trials in patients in severe heart failure it seems natural to assume that reverse remodelling could also occur in less sick patients. In fact the only randomised pilot study published so far that only included NYHAII patients, the MIRACLE ICD II, did demonstrate a benefit in reverse remodelling after 6 months of CRT compared to controls in spite of no clear benefit as regards symptoms. Therefore the role for CRT may be to reverse or delay disease in patients with NYHA II heart failure or in NYHA I with prior symptoms. This is the subject of two large randomised studies, REVERSE and MADIT CRT. REVERSE is a double blind randomised 12 months comparison of optimal medical therapy with or without CRT with clinical improvement as primary and LV remodelling as secondary end points. The study enrolment is complete and it will report early in 2008. MADIT-CRT is a mortality/morbidity trial which will include 1800 patients and compares CRT-ICD to ICD alone in these patients. Since many physicians to date already implant CRT in NYHA II patients we urgently need the scientific proof that this is justified.