Effects of cardiac resynchronisation therapy in patients with heart failure having a narrow QRS Complex enrolled in PROSPECT

Pathophysiology of narrow complex dilated cardiomyopathy insight derived from the velocity equation: velocity = distance/time

The pathophysiology of narrow complex dilated cardiomyopathy is not defined, so therapeutic options are limited. By utilising the velocity equation, the pathophysiology of narrow complex cardiomyopathy allows above normal conduction propagation velocities. There are two pathophysiological theories that allow above normal conduction velocities and failure to capture the myocardium: (1)insulating fibres of the conduction system extending beyond the apex and (2) reduction of axon branching. A patient with narrow complex cardiomyopathy was subjected to graded increase in amplitude and pulse width pacing to overcome the failure of native conduction to capture the myocardium. Peak systolic strain maps demonstrated a progressive increase in apical contractility with increasing pulse width and amplitude. Ejection fraction improved from 17% to 31%. Understanding the pathophysiology of narrow complex cardiomyopathy leads to proposed therapies. One potential pacing therapy is multi-lead pacing at high amplitude and pulse width to capture myocardial cells not captured by native conduction.

Narrow QRS systolic heart failure: is there a target for cardiac resynchronization?

Cardiac resynchronization therapy has revolutionized the management of systolic heart failure in patients with prolonged QRS during the past 20 years. Initially, the use of this treatment in patients with shorter QRS durations showed promising results, which have since been opposed by larger randomized controlled trials. Despite this, some questions remain, such as, whether correction of mechanical dyssynchrony is the therapeutic target by which biventricular pacing may confer benefit in this group, or are there other mechanisms that need consideration? In addition, novel techniques of cardiac resynchronization therapy delivery such as endocardial and multisite pacing may reduce potential detrimental effects of biventricular pacing, thereby improving the benefit/harm balance of this therapy in some patients.

Effect of study design on the reported effect of cardiac resynchronization therapy (CRT) on quantitative physiological measures: stratified meta-analysis in narrow-QRS heart failure and implications for planning future studies

Background

Biventricular pacing (CRT) shows clear benefits in heart failure with wide QRS, but results in narrow QRS have appeared conflicting. We tested the hypothesis that study design might have influenced findings.

Method and Results

We identified all reports of CRT‐P/D therapy in subjects with narrow QRS reporting effects on continuous physiological variables. Twelve studies (2074 patients) met these criteria. Studies were stratified by presence of bias‐resistance steps: the presence of a randomized control arm over a single arm, and blinded outcome measurement. Change in each endpoint was quantified using a standardized effect size (Cohen's d). We conducted separate meta‐analyses for each variable in turn, stratified by trial quality. In non‐randomized, non‐blinded studies, the majority of variables (10 of 12, 83%) showed significant improvement, ranging from a standardized mean effect size of +1.57 (95%CI +0.43 to +2.7) for ejection fraction to +2.87 (+1.78 to +3.95) for NYHA class. In the randomized, non‐blinded study, only 3 out of 6 variables (50%) showed improvement. For the randomized blinded studies, 0 out of 9 variables (0%) showed benefit, ranging from −0.04 (−0.31 to +0.22) for ejection fraction to −0.1 (−0.73 to +0.53) for 6‐minute walk test.

Conclusions

Differences in degrees of resistance to bias, rather than choice of endpoint, explain the variation between studies of CRT in narrow‐QRS heart failure addressing physiological variables. When bias‐resistance features are implemented, it becomes clear that these patients do not improve in any tested physiological variable. Guidance from studies without careful planning to resist bias may be far less useful than commonly perceived.

Profile of St. Jude Medical's Allure Quadra quadripolar pacemaker system for cardiac resynchronization therapy

Congestive heart failure is a major public health epidemic and economic burden in the USA and worldwide. Cardiac resynchronization therapy is an effective therapy for treating congestive heart failure in conjunction with pharmacologic therapy. The average congestive heart failure admission costs approximately US$ 8 billion annually. Current cardiac resynchronization therapy pacemaker systems from various manufacturers deliver therapy-utilizing bipolar leads including the left ventricle, with electrode spacing ranging from 8 to 22 mm. The Quartet LV™ lead model 1458Q (St. Jude Medical Sylmar, CA) is a quadripolar lead with a 4.0 Fr. tip electrode and three 4.7 Fr. ring electrodes located 20, 30 and 47 mm from the tip. The Quartet lead and Allure Quadra TM allows 14 pacing configurations, providing benefits, including reductions in phrenic nerve stimulation, reduced pacing thresholds, improved battery longevity and potential reductions, in non-responders to cardiac resynchronization therapy. In addition, there is cost benefit data from utilizing quadripolar technology compared with traditional bipolar cardiac resynchronization therapy.

Impact of QRS Morphology and Duration on Outcomes After Cardiac Resynchronization Therapy

Background—

The impact of QRS morphology and duration on the effectiveness of cardiac resynchronization therapy (CRT) has been usually assessed separately. The interaction between these 2 simple ECG parameters and their effect on CRT has not been systematically assessed in a large-scale clinical trial.

Methods and Results—

The Resynchronization–Defibrillation for Ambulatory Heart Failure Trial showed that implantable cardioverter defibrillator-CRT was associated with a significant reduction in the primary end point of all-cause mortality or heart failure hospitalization. For this substudy, we excluded patients in atrial fibrillation and those with a previous pacemaker. All baseline ECGs were reviewed by a panel of 3 experienced electrocardiographers. A total of 1483 patients were included in this study. Of these, 1175 had left bundle-branch block (LBBB) and 308 had non-LBBB. In patients with LBBB receiving implantable cardioverter defibrillator-CRT, there was a reduction in the primary outcome and in each individual component of the primary outcome. Furthermore, there was continuous relationship between QRS duration and extent of benefit. In patients with non-LBBB and QRS ≥160 ms, the hazard ratio for the primary outcome was 0.52 (0.29–0.96; P =0.033); in patients with QRS <160 ms, the hazard ratio was 1.38 (0.88–2.14; P =0.155).

Conclusions—

In patients with LBBB, there was a continuous relationship between broader QRS and greater benefit from implantable cardioverter defibrillator-CRT. However, our data do not support the use of implantable cardioverter defibrillator-CRT in patients with non-LBBB, especially when the QRS duration is <160 ms. There may be some delayed benefit when the QRS is ≥160 ms, but this needs further investigation.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00251251.

Suitability for subcutaneous defibrillator implantation: results based on data from routine clinical practice

OBJECTIVE

To assess the proportion of current implantable cardioverter defibrillator (ICD) recipients who would be suitable for a subcutaneous lead ICD (S-ICD).

DESIGN

A retrospective cohort study.

SETTING

Tertiary care facility in the Netherlands.

PATIENTS

All patients who received a single- or dual-chamber ICD in the Leiden University Medical Center between 2002 and 2011. Patients with a pre-existent indication for cardiac pacing were excluded.

MAIN OUTCOME MEASURE

Suitability for an S-ICD defined as not reaching one of the following endpoints during follow-up: (1) an atrial and/or right ventricular pacing indication, (2) successful antitachycardia pacing without a subsequent shock or (3) an upgrade to a CRT-D device.

RESULTS

During a median follow-up of 3.4 years (IQR 1.7-5.7 years), 463 patients (34% of the total population of 1345 patients) reached an endpoint. The cumulative incidence of ICD recipients suitable for an initial S-ICD implantation was 55.5% (95% CI 52.0% to 59.0%) after 5 years. Significant predictors for the unsuitability of an S-ICD were: secondary prevention, severe heart failure and prolonged QRS duration.

CONCLUSIONS

After 5 years of follow-up, approximately 55% of the patients would have been suitable for an S-ICD implantation. Several baseline clinical characteristics were demonstrated to be useful in the selection of patients suitable for an S-ICD implantation.

Association of left ventricular mechanical dyssynchrony with survival benefit from revascularization: a study of gated positron emission tomography in patients with ischemic LV dysfunction and narrow QRS

PURPOSE

LV mechanical dyssynchrony (LVMD) is a risk marker in narrow QRS cardiomyopathy, but its association with treatment outcome is not well defined. We determined the incremental prognostic value of LVMD in ischemic cardiomyopathy, and assessed its interaction with scar, myocardium in jeopardy and subsequent revascularization.

METHODS

Stress and rest (82)Rb gated PET were performed in 486 consecutive patients (66 ± 11 years of age, 82 % men, LV ejection fraction 26 ± 6 %) with ischemic cardiomyopathy and QRS <120 ms. LVMD was determined as the standard deviation (SD) of the regional time to minimum volume on phase analysis of the gated PET scan. A propensity score was determined to adjust for nonrandomized referral after imaging to coronary artery bypass grafting (CABG). In a Cox proportional hazards model used to determine the association between measures of LVMD and survival time, CABG was included as a time-dependent covariate and the use of an implantable cardiac defibrillator (ICD) after imaging was modeled as a stratification factor.

RESULTS

Over 1.9 ± 1.4 years, 96 patients (20 %) underwent CABG and 108 (22 %) died. LVMD was a predictor of mortality (HR 1.16. 95 % CI 1.03;1.30, per 10° increase in phase SD, p = 0.02) after adjusting for baseline covariates, prior ICD use, the use of postimaging CABG, and other imaging data. There was a significant interaction between phase SD and CABG. Nested Cox models showed that LVMD carried prognostic information incremental to clinical variables, ejection fraction and CABG.

CONCLUSION

LVMD is an independent predictor of all-cause mortality in ischemic cardiomyopathy, and may identify patients with a differential survival benefit from CABG versus medical therapy.

[Current clinical practise of cardiac resynchronisation therapy in Austria--national results from the European CRT Survey]

Cardiac resynchronization therapy (CRT) has become an established treatment modality in patients with chronic heart failure, reducing both mortality and morbidity. However, patient selection, implantation and follow-up require great clinical experience. Between 2008 and 2010, the European Society of Cardiology initiated the European CRT survey to describe the current practice and routines associated with CRT implantations in 13 countries. Data from 156 patients collected in 10 Austrian centres were analysed compared to the total 2438 patients enrolled. The survey data showed that general practice did not adhere to the present guidelines. More than one third (36%) of the patients had atrial fibrillation and more than one-fourth (29%) had had a device implanted previously. Altogether, 22% of the patients were in NYHA functional class I or II, and 18% had a LVEF > 35%. Approximately one-fourth of the patients were treated with CRT-P devices (Austria 23%, total 27%). In Austria a higher percentage of patients with non-ischemic cardiomyopathy was selected for CRT than in the other European countries (56% versus 40%, p < 0.0001). Less than a quarter of all patients were females. Different from the rest of Europe, only a minority of CRT implantations were performed by cardiologists in Austria (29% as compared to 89% throughout Europe; p < 0.0001).

Presence of mechanical dyssynchrony in Duchenne muscular dystrophy

BACKGROUND

Cardiac dysfunction in boys with Duchenne muscular dystrophy (DMD) is a leading cause of death. Cardiac resynchronization therapy (CRT) has been shown to dramatically decrease mortality in eligible adult population with congestive heart failure. We hypothesized that mechanical dyssynchrony is present in DMD patients and that cardiovascular magnetic resonance (CMR) may predict CRT efficacy.

METHODS

DMD patients (n = 236) were stratified into 4 groups based on age, diagnosis of DMD, left ventricular (LV) ejection fraction (EF), and presence of myocardial fibrosis defined as positive late gadolinum enhancement (LGE) compared to normal controls (n = 77). Dyssynchrony indices were calculated based on timing of CMR derived circumferential strain (ecc). The calculated indices included cross-correlation delay (XCD), uniformity of strain (US), regional vector of variance (RVV), time to maximum strain (TTMS) and standard deviation (SD) of TTMS. Abnormal XCD value was defined as > normal + 2SD. US, RVV, TTMS and SD were calculated for patients with abnormal XCD.

RESULTS

There was overall low prevalence of circumferential dyssynchrony in the entire DMD population; it increased to 17.1% for patients with abnormal EF and to 31.2% in the most advanced stage (abnormal EF with fibrosis). All but one DMD patient with mechanical dyssynchrony exhibited normal QRS duration suggesting absence of electrical dyssynchrony. The calculated US and RVV values (0.91 ± 0.09, 1.34 ± 0.48) indicate disperse rather than clustered dyssynchrony.

CONCLUSION

Mechanical dyssynchrony is frequent in boys with end stage DMD-associated cardiac dysfunction. It is associated with normal QRS complex as well as extensive lateral fibrosis. Based on these findings, it is unlikely that this patient population will benefit from CRT.

Criteria for patient selection in cardiac resynchronization therapy

Since the implementation of cardiac resynchronization therapy (CRT) the prognosis of patients with severe heart failure has been improved owing to a reduction in morbidity and mortality rates, as several multicenter trials have shown. However, several patients treated by CRT still lack improvement or even deteriorate during therapy. In some of them, this might be due to the severity and progression of chronic heart failure. In others, the criteria for the indication of CRT and/or optimized device programming might have not been met. Thus, one important option to improve CRT outcome is to improve CRT patient selection. A lot of publications describing various methods identifying a positive or negative prediction of CRT have been released. In summary, decision making based on all these partly contradictory publications indicate a strong need for guidelines for the use of such expensive therapy. The purpose of this article is to give an overview of CRT and summarize the different methods and the limitations of CRT patient selection parameters. With the focus of the different guidelines, this article tries to give an appropriate overview and aid decision making in CRT patients, including a short view of possible new indications.