New data, published in the current issue of European Heart Journal, from the MADIT-CRT study shows that cardiac resynchronisation therapy with a defibrillator (CRT-D) significantly improves both left ventricular dyssynchrony and contractile function compared with an implantable cardiac defibrillator (ICD) in patients with New York Heart Association (NYHA) class I or II heart failure.
Previous studies, including the main MADIT-CRT study (Zareba et al), have shown that CRT may be beneficial in patients with mildly symptomatic heart failure (it is already widely established as a beneficial treatment for advanced heart failure). Other studies have suggested that both left ventricular mechanical dyssnchrony and contractile function are important determinants of CRT benefit. The aim of this new study, by Pouleur et al, was to assess the long-term effects of CRT on left ventricular dyssynchrony and contractile function (by two-dimensional speckle-tracking echocardiography) compared with ICD in patients from the main MADIT-CRT study.
At one year, greater improvements were seen in both left ventricular dyssynchrony and contractile function in patients with a CRT-D than those with only an ICD. Although improvements were seen in all subgroups, the greatest improvements were seen in patients with left ventricular bundle branch block, non-ischaemic cardiomyopathy, and those with wider QRS.
The greater improvements, seen with CRT-D, in left ventricular dyssynchrony and contractile function were associated with lower rates of the study’s primary outcome of death or heart failure (at one year). The authors reported that the results suggested that “improvements in both synchrony and contractile function may account for a considerable portion of the benefit of CRT.” They added: “Moreover, our results demonstrate a weak relationship between the changes in LV [left ventricular] dyssynchrony and contractile function measured by GLS [global longitudinal strain], suggesting that overall benefits may result from a more coordinated contraction of the LV with improved contractile efficiency.” However, they added that they could only speculate that improvement in contractile function was the result of improvement in synchrony “this remains only an association and our data cannot determine which is causal”.
Summarising the data, investigator Scott Solomon said: “These data suggest that with improvement in synchrony with CRT comes improvement in contractile function and that ultimately it is the improvement in contractile function that accounts for the reduced event rate in patients receiving CRT”
Cardiac Rhythm News will review the wider benefits and risks of CRT in patients with mild heart failure in the next issue (issue 14).