Department of Clinical and Experimental Medicine, Federico II University Hospital, Via S. Pansini 5, 80131 Naples, Italy Tel.: +39-81-7462145; fax: +39-81-5466152
Department of Cardiology, University of Siena, Italy
E-mail address: mgalderi{at}unina.it
Dear Editor,
With interest, we read the article of Ghio et al.1 and the Editorial of Breithardt et al.2 in which the usefulness of Tissue Doppler (TD) to detect left ventricular (LV) dyssynergy was reported. Ghio et al.1 defined the intraventricular asynchrony as a difference greater than 50 ms among colour TD-derived regional pre-ejection periods (=time to onset of systolic velocity) between at least two of the four basal and middle segments of LV walls (4- and 2-chamber views). Such asynchrony was observed in a great proportion of patients with low ejection fraction and was independent of the QRS duration (ranging 120 to
150 ms). These data confirm that the mechanical unco-ordination is much more important than the electrical delay3 but, as previously reported, leaves a main question unsolved: which patients can benefit from cardiac resynchronisation therapy (CRT)? This issue is crucial since even 30% of patients do not present an advantage from CRT3 due to technical problems of implantation or, mainly, to erroneous choice of candidates. Due to limitations of standard echocardiography, able to explore the intra-ventricular unco-ordination only partially,3 the TD modalities (pulsed TD, colour TD of mean velocities or Tissue-Tracking combined with Strain Rate Imaging) are earning a predominant position for pre- and post-CRT assessment.3 Since the major advantage of TD corresponds to the possibility of measuring the unco-ordination in each LV segments, efforts should be addressed to quantify the amount of mechanical asynchrony. In this view, Yu et al.,4 by using colour TD but measuring the criticised time to peak systolic velocity (Ts), calculated a asynchrony index (DI), i.e., the standard deviation of Ts in 12 segments (basal and middle LV walls in 4-, 2- and 3-chamber views). All the patients responding to CRT had DI
32.6 whereas DI was always
32.6 in non-responders. By a sophisticated combination of Tissue-Tracking and Strain Rate, Sogaard et al.5 also quantified the amount of LV asynchrony as the percentage of delayed longitudinal contraction (=number of segments with myocardial contraction after aortic valve closure at LV base/total circumference of LV basex100). The attempts of Yu and Sogaard highlight an important aspect: the greater the amount of dyssynergic myocardium the greater the clinical benefit of CRT. On these grounds Ghio et al.1 could also address their findings calculating the variability of the time to onset of contraction in multiple LV segments, adding clinical impact to their valuable data. With this perspective, the evidence of the maximal asynchrony at the lateral wall, where the lead is usually applied, should also be taken into account6. Of note, Ghio et al.1 demonstrated the most delayed movement at the lateral wall only showed in about 1/3 of patients with QRS duration above 120 ms. It is our opinion that efforts to reduce the number of non-responders to CRT could be improved by preferentially using the various TD modalities.
References