Assessing left ventricular myocardial work and the risk for malignant arrhythmias: does it work?

This editorial refers to ‘Global constructive work is associated with ventricular arrhythmias after cardiac resynchronization therapy’, by H. Saffi et al., https://doi.org/10.1093/ehjci/jead180. Implantation of a cardiac resynchronization therapy (CRT) pacemaker with defibrillator capabilities (CRT-D) in patients with chronic heart failure (HF) with reduced left ventricular (LV) ejection fraction (EF) and conduction delays reduces mortality and morbidity.1 These beneficial effects are mediated by several mechanisms, including LV reverse remodelling, prevention of further LV volume expansion, and termination of ventricular arrhythmias by delivery of a shock or by antitachycardia pacing.1 The guideline-proposed criteria for CRT-D patient selection, based mainly on LVEF and QRS width and morphology, come from landmark randomized clinical trials.1 There have been many attempts to refine or extend these criteria using various imaging-derived parameters, including global longitudinal strain (GLS), extent of myocardial scarring and fibrosis, mechanical dyssynchrony and dispersion, and more recently myocardial work (MW).2 Non-invasive estimation of MW by pressure–strain loops (PSLs) analysis is a tool to characterize LV performance. This method has the advantage of taking into account the effects of afterload on LV deformation.3,4 In practice, LV pressure is estimated from a referral curve scaled using aortic and valvular timings and then merged with strain data to obtain segmental LV PSLs and subsequent MW parameters.5 Previous publications have demonstrated the reliability and reproducibility of the MW parameters in various clinical scenarios, including CRT, HF, and ischaemic heart disease.2,5,6,7,8 A sub-analysis of the NORRE study and a monocentric study have provided reference ranges for MW parameters in healthy subjects.9,10 A ‘how to’ paper published in this journal provides practical details.4 Interestingly, MW has previously been suggested to improve patient selection for CRT rather than to better identify those who require not only CRT but also an implantable cardioverter defibrillator (ICD).2 This issue is important because the indication for an ICD in patients with non-ischaemic dilated cardiomyopathies has been downgraded to some extent in recent guidelines.11 The actual role of LVEF in predicting sudden cardiac death is largely controversial. Newer parameters derived from various cardiac imaging modalities have been reported to have higher prognostic accuracy but only in small, observational studies. Speckle tracking imaging allows quantification of mechanical dispersion, a marker of segmental contraction heterogeneity that predisposes to malignant arrhythmias.12 In addition, cardiac magnetic resonance (CMR) techniques such as T1 mapping and extracellular volume fraction assessment allow quantification of interstitial diffuse fibrosis.13 Although myocardial scar extent and other CMR parameters have shown promising results for predicting ventricular arrhythmias,14 the use of CMR in a patient with a device can be challenging. In addition, nuclear imaging is useful for assessing sympathetic denervation and the risk of sudden cardiac death,14 while newer computed tomography techniques that examine delayed myocardial enhancement allow the identification of focal myocardial scarring. However, nuclear imaging and computed tomography are associated with the risk of ionizing radiation.15 Saffi et al.16 investigated the role of MW in assessing the residual risk of arrhythmias at least 6 months after CRT-D implantation and found that patients whose global constructive work (GCW) was below the median had a five-fold increased risk of ventricular arrhythmias (Figure 1). Of note, the magnitude of mechanical dispersion was similar in patients with and without appropriate defibrillator therapy and sustained ventricular arrhythmia,16 while other parameters for assessing mechanical dyssynchrony were not studied. In addition, it should be noted that patients with GCW below the median value also had wider QRS complexes, larger LV volumes, and lower LVEFs than patients with higher GCW values, suggesting a lower response to CRT in the former group. It can therefore be speculated that, particularly in the absence of pre-implantation data, lower GCW values simply reflect a poorer response to CRT, which was a trigger for ventricular arrhythmias. Without specifically addressing ventricular arrhythmias, it has already been suggested that correction of mechanical dyssynchrony is necessary for CRT to have a prognostic effect.17 The study by Saffi et al.16 highlights the potential role of advanced echocardiography in the follow-up of CRT and CRT-D recipients, although it is not recommended in current guidelines. It would be of particular interest to investigate the potential added value of MW in clinical scenarios with the highest uncertainty, e.g. when deciding for or against ICD implantation in patients with non-ischaemic cardiomyopathies or in CRT non-responders, to aid device optimization. Summary of the potential value of the echocardiographic assessment of mechanical dyssynchrony before and after implantation of the cardiac resynchronization therapy + defibrillator (CRT-D). Value of myocardial work. In addition, it would be of interest to examine the values of MW and other imaging parameters in multiparametric scores that include imaging and clinical data, as previous experience has generally shown that the prognostic value of any parameter is limited when used in isolation. Finally, we need to bear in mind that observational studies cannot provide robust evidence to refine current CRT or ICD patient selection strategies, and this is also true for MW. The additional value of MW and other imaging parameters beyond LVEF in predicting ventricular arrhythmias in HF, and perhaps in cardiomyopathies, needs to be tested in well-designed randomized controlled trials. Without this evidence, it is very likely that MW will share the fate of other promising parameters that are valued in the imaging community but have little or no impact in the clinical setting. Funding: None declared. No new data were generated or analysed in support of this research.