The importance of being synchronous: on the prognostic value of ventricular conduction delay in heart failure

The Past, Present and Future of Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) has revolutionized the care of the patients with heart failure with reduced ejection fraction and electrical dyssynchrony. The current guidelines for patient selection include measurement of left ventricular systolic function, QRS duration and morphology, and functional classification. Despite consistent and increasing evidence supporting CRT use in appropriate patients, CRT has been underutilized. Notwithstanding the heterogeneous definitions of non-response, more than one-third of patients demonstrate a lack of echocardiographic reverse remodeling or poor clinical outcome following CRT. Since the causes of this non-response are multifactorial, it will require multidisciplinary efforts to overcome including optimal patient selection, procedural strategies, as well as optimizing post-implant care in patients undergoing CRT. The innovations of novel pacing approaches combined with advanced imaging technologies may eventually offer a personalized CRT system uniquely tailored to each patient's dyssynchrony signature.

Indications for cardiac resynchronization therapy

Initial studies established patient selection criteria for cardiac resynchronization therapy (CRT) as left ventricular ejection fraction less than or equal to 35%, QRS greater than or equal to 120 ms, and New York Heart Association 3-4. Based on newer data, post hoc analyses, and meta-analyses, these criteria have been refined and guidelines updated, highlighting left bundle branch morphology and QRS greater than 150 ms in selecting patients with a likelihood of favorable outcomes. Guidelines will change as more data become available; the decision to apply CRT should be based on patient clinical profile and the balance of risk tolerance and likelihood of benefit.

Prevalence of mechanical dyssynchrony in patients with heart failure and preserved left ventricular function (a report from the Belgian Multicenter Registry on dyssynchrony)

The present study evaluated the prevalence of mechanical inter- and intraventricular dyssynchrony in patients with heart failure and preserved left ventricular (LV) ejection fraction (LVEF). We studied 138 patients with heart failure (age 67+/-11 years; 76% men); 60 patients had preserved LVEF (>40%). Using conventional Doppler echocardiography, an interventricular mechanical delay>or=40 ms was defined as interventricular dyssynchrony. Using pulse-wave tissue Doppler imaging, the time from the beginning of the QRS complex to onset of systolic motion was measured in 4 basal LV segments. A dispersion of >or=60 ms was defined as intraventricular dyssynchrony. The prevalence of inter- and intraventricular dyssynchrony was lower in patients with preserved LVEF than in those with reduced LVEF (17% vs 41%, p<0.01 for interventricular dyssynchrony, 18% vs 36%, p<0.01 for intraventricular dyssynchrony). However, patients with preserved LVEF and a QRS width>or=120 ms had higher values for the parameters for inter- and intraventricular dyssynchrony than patients with a QRS width<120 ms (interventricular mechanical delay 33+/-20 vs 20+/-16 ms, p<0.05; tissue Doppler imaging dispersion 42+/-26 vs 33+/-22 ms, p<0.05). In patients with a QRS width>or=120 ms, the prevalence of inter- and intraventricular dyssynchrony was comparable for patients with preserved and reduced LVEF (42% vs 55%, p=NS for interventricular dyssynchrony and 45% vs 46%, p=NS for intraventricular dyssynchrony). In conclusion, the prevalence of inter- and intraventricular dyssynchrony was low (17% and 18%, respectively) in patients with heart failure and preserved LVEF. However, in the presence of a QRS width of >or=120 ms, this prevalence increased to almost 50%, comparable to that for patients with heart failure and reduced LVEF and a QRS width of >or=120 ms.

Association of Prolonged QRS Duration With Death in a Clinical Trial of Pacemaker Therapy for Sinus Node Dysfunction

Background— Prolonged QRS duration (QRSd) is an important prognostic indicator for death and heart failure hospitalization in patients with systolic heart failure. The relationship of baseline QRSd to death and heart failure hospitalization in patients with sinus node dysfunction who require pacemaker therapy is unknown.

Methods and Results— Baseline QRSd from 12-lead ECGs before pacemaker implantation were analyzed in the Mode Selection Trial (MOST), a 6-year, 2010-patient randomized trial of dual-chamber versus ventricular pacing in sinus node dysfunction. Baseline QRSd was ≥120 ms in 23.4% of patients and was associated with older age, lower ejection fraction, cardiomyopathy, and prior heart failure. Adjusted Cox models demonstrated baseline QRSd ≥120 ms was a strong independent predictor of death (hazard ratio [95% CI] 1.35 [1.07, 1.70], P =0.010) but not heart failure hospitalization. The risk of death increased with increased QRSd from 60 to 120 ms ( P =0.002 and hazard ratio [95% CI] 1.14 [1.05, 1.23] for 10-ms increase in this range) after adjustment for other death predictors.

Conclusions— Baseline QRSd ≥120 ms was associated with increased risk of death during pacemaker therapy for sinus node dysfunction.