The role of cardiac magnetic resonance in identifying appropriate candidates for cardiac resynchronization therapy — a systematic review of the literature

Heart Failure Reviews - Despite the strict indications for cardiac resynchronization therapy (CRT) implantation, a significant proportion of patients will fail to adequately respond to the...     

Are left ventricular diastolic function and diastolic asynchrony important determinants of response to cardiac resynchronization therapy?

Cardiac resynchronization therapy (CRT) has been shown to reduce symptoms and reverse left ventricular (LV) remodeling. It is not known, however, whether diastolic function will improve after CRT and diastolic asynchrony will predict LV reverse remodeling. Seventy-six patients (mean age 65 +/- 12 years, 74% men) who received CRT were studied at baseline and after 3 months. Diastolic function was assessed by transmitral Doppler and tissue Doppler imaging. LV systolic and diastolic asynchrony were assessed by the time to peak myocardial contraction (Ts) and early diastolic relaxation (Te) using the 6 basal, 6 mid-segmental model. There were 42 responders (55%) with LV reverse remodeling (defined as a reduction of LV end-systolic volume >or=15%). Parameters of systolic function were significantly improved only in the responders. For diastolic function, there were reductions of transmitral E velocity in the 2 groups, without any change in atrial velocity or the E/A ratio. Tissue Doppler imaging revealed that myocardial early diastolic velocity was unchanged in responders but was significantly worsened in nonresponders. The systolic asynchrony index (the SD of Ts of 12 LV segments) correlated significantly with LV reverse remodeling (r = -0.64, p <0.001) but not the diastolic asynchrony index (the SD of Te of 12 LV segments) (r = -0.10, p = NS). The systolic asynchrony index was the only independent predictor of reverse remodeling (beta = -0.99, 95% confidence interval -1.41 to -0.58, p <0.001). In conclusion, CRT improves systolic function and systolic asynchrony but has a neutral effect on diastolic function and diastolic asynchrony. LV reverse remodeling response is determined by the severity of prepacing systolic asynchrony but not diastolic asynchrony or the diastolic filling pattern.     

Electrical remodeling in left ventricular hypertrophy—is there a unifying hypothesis for the variety of electrocardiographic criteria for the diagnosis of left ventricular hypertrophy?

Although electrocardiography has been used to estimate left ventricular hypertrophy and to obtain useful prognostic information in different clinical settings, its correlation with left ventricular mass is poor and, therefore, its sensitivity and specificity for the diagnosis of left ventricylar hypertrophy are low. Experimental work has demonstrated that the increase in voltage and duration of the QRS complex of the electrocardiogram are not only related to left ventricular mass but also to changes in the electrophysiological properties of the myocardium. Therefore, a new strategy is needed to use electrocardiography not to estimate left ventricular mass but aimed to add useful prognostic information.     

Are neurohumoral parameters predictive for the efficacy of cardiac resynchronization therapy? The role of natriuretic peptides

During recent years, heart failure has been recognized as a complex disease involving both hemodynamic abnormalities caused by reduced contractile forces and neurohormonal changes characterized by an increase in sympathetic tone and an activation of the renin-angiotensin-aldosterone system as well as the endothelial pathways. Neurohumoral factors represent the natural response of the individual to heart failure. Among them natriuretic peptides, i. e., brain natriuretic peptide (BNP) and amino-terminal pro BNP (Nt-proBNP) release have recently been shown to be a reliable and rapid marker for diagnosis, optimization of pharmacological treatment and risk stratification in heart failure patients. This article summarizes important aspects of the release of natriuretic peptides as a guide for diagnosis, therapy and prognosis of patients with heart failure and cardiac resynchronization therapy.     

Atrial synchronous left ventricular only pacing with VDD pacemaker system – A cost effective alternative to conventional cardiac resynchronization therapy

Introduction

Atrial synchronous left ventricular (LV) only pacing using two leads and VDD pacemaker could be a cost effective alternative to conventional cardiac resynchronization therapy (CRT).

Methods

We implanted right atrial (RA) and LV leads with VDD pulse generator (LV only pacing) in five carefully screened heart failure patients who could not afford conventional CRT. All had NYHA class III/IV symptoms despite maximal guideline directed medical therapy. The sensed atrioventricular delay was programmed to pre-excite the LV and achieve fusion beat. Response to treatment was assessed at 6 months.

Results

Four patients were males. The mean age was 58 ± 12 years. At follow up, there was improvement in electrocardiographic, and echocardiographic parameters: Mean QRS duration decreased from 174 ± 17 msec to 128 ± 10.9 msec (p = 0.009), LV end-diastolic diameter decreased from 73.2 ± 12 mm to 65.8 ± 9.6 mm (p = 0.026), LV end-systolic diameter decreased from 65 ± 12 mm to 54 ± 10 mm (p = 0.020). There was a trend towards reduction of LV end-systolic and end-diastolic volumes. LV ejection fraction improved from 25 ± 6% to 34 ± 6% (p = 0.013) and left atrial dimension reduced from 44 ± 4 mm to 39 ± 5 mm (p = 0.045). All patients improved clinically.

Conclusion

RA-LV pacing using VDD pacemaker is a safe and effective technique of CRT. This may be a cost effective alternative to conventional CRT for patients in developing countries.     

What can post market registries tell us about the use of cardiac resynchronization therapy?

Cardiac resynchronization therapy (CRT) has become an established therapeutic option for patients with dilated cardiomyopathies and New York Heart Association class III congestive heart failure symptoms who also have a widened QRS complex on their electrocardiograms (generally > 120 ms). Results from a number of clinical trials have shown that CRT improves patients' exercise tolerance, quality of life, and survival. There is further evidence that CRT has structural effects on the heart with improved cardiac function. Despite these salutary results, clinical trials in CRT study prespecified populations that fit the inclusion criteria for these trials. Many patients have been excluded from these clinical trials and yet may potentially benefit from CRT. Evaluation of the effects of CRT on these populations might reveal the potential to expand the use of this therapy in larger numbers of patients to CRT who may not have been included in the clinical trial. This review article will assess the limitations of some of the clinical trials in CRT and will discuss the potential for CRT registries that are presently underway to extend the patient population that may benefit from this therapeutic option.     

How to carry out the indications of cardiac resynchronization therapy in practice?

Recent studies have demonstrated that cardiac resynchronization therapy diminish morbidity and mortality of patients with heart failure, who remain symptomatic despite an optimal medical treatment and who have a wide QRS. However, 30% of patients are non-responders. Hence, echocardiography constitutes an interesting tool for the diagnosis of asynchrony. Different echocardiographic indices predict response to cardiac resynchronization therapy. In this article, a practical approach is proposed for these patients.     

Echocardiographic evaluation of cardiac resynchronization therapy: ready for routine clinical use? A critical appraisal

Cardiac resynchronization therapy (CRT) has been proposed as an alternative treatment in patients with severe, drug-refractory heart failure. The clinical results are promising, and improvement in symptoms, exercise capacity, and systolic left ventricular (LV) function have been demonstrated after CRT, accompanied by a reduction in hospitalization and a superior survival as compared with optimized medical therapy alone. However, 20% to 30% of patients do not respond to CRT. Currently, patients are selected mainly on electrocardiogram criteria (wide QRS complex, left bundle branch block configuration). In view of the 20% to 30% of nonresponders, additional selection criteria are needed. Echocardiography (and, in particular, tissue Doppler imaging) may allow further identification of potential responders to CRT, based on assessment of inter- and intraventricular dyssynchrony. In addition, echocardiography may allow optimal LV lead positioning and follow-up after CRT. In the current review, the different echocardiographic approaches to predict response to CRT are discussed. In addition, the use of echocardiography to guide LV lead positioning and follow-up after CRT are addressed.