The Benefit of Cardiac Resynchronization Therapy and QRS Duration: A Meta-Analysis

Notched QRS complex in lateral leads as a novel predictor of response to cardiac resynchronization therapy

BACKGROUNDS

Notched QRS (nQRS) may be an indicator of ventricular delay. There are very few studies investigating the value of nQRS. The aim of the study was to identify the predictive value of nQRS for response to cardiac resynchronization therapy (CRT).

METHODS

Eighty-two patients with heart failure (HF) and widened QRS (≥120 ms) were implanted with a CRT device. nQRS was defined as presence of ≥2 R waves, or ≥1 notch in the R wave or S wave in ≥2 contiguous leads. Response to CRT was defined as percentage of left ventricular end-systolic volume (LVESV) reduction after 6 months CRT (ΔLVESV%) ≥15%.

RESULTS

nQRS was presented in 62 (76%) patients, 16 of whom had nQRS in anterior leads, 47 in inferior leads, and 42 in lateral leads. The rate of CRT response (65% vs 50%, P = 0.29) and ΔLVESV% (21.7 ± 31.7% vs 7.9 ± 25.4%, P = 0.09) were not different between patients with and without nQRS. But the rate of CRT response was higher in patients with nQRS in lateral leads (nQRS-L) than in those without nQRS-L (76% vs 45%, P = 0.006). ΔLVESV% was greater in patients with nQRS-L than in those without nQRS-L (25.2 ± 34.3% vs 10.1 ± 24.5%, P = 0.004). After adjusting for potential confounders including QRS duration, presence of nQRS-L still predicted positive CRT response (OR = 4.04, P = 0.009).

CONCLUSIONS

nQRS-L may be a novel predictor of response to CRT in patients with HF and widened QRS. Large-scale studies are needed to confirm this prognostic value of nQRS-L.

QRS narrowing is associated with reverse remodeling in patients with chronic right ventricular pacing upgraded to cardiac resynchronization therapy

BACKGROUND

Patients with chronic right ventricular pacing (RVP) upgraded to cardiac resynchronization therapy (CRT) have been excluded from the majority of clinical trials of CRT. Little is known about the predictors of response in this population. We hypothesized that reversal of RVP-induced electrical dyssynchrony (indexed by QRS duration) by CRT would predict a favorable response.

OBJECTIVE

The purpose of this study was to identify baseline characteristics associated with response in patients upgraded to CRT from chronic RVP.

METHODS

Consecutive patients presenting for CRT at the Cleveland Clinic between September 30, 2003, and July 8, 2008, with chronic RVP and serial echocardiograms were included in this analysis. RVP was defined as>85% pacing on a pre-CRT device check, previous AV nodal ablation, or complete pacer dependency per chart notes. Response was defined as a reduction in left ventricular end-systolic volume ≥ 15% from baseline. Clinical, ECG, and echocardiographic data were extracted to determine covariates associated with response.

RESULTS

One hundred twelve patients met inclusion criteria, of whom 72 (64.3%) met criteria for response over median follow-up of 9.9 months (interquartile range [6.5-14.7]). No significant differences were noted in terms of male gender (68.1% vs 75.0%; P = .52), ischemic cardiomyopathy (55.6% vs 55.0%; P = 1), pre-CRT QRS duration (189.1 ± 20.7 ms vs 185.5 ± 26.8 ms; P = .47), duration of RVP before CRT upgrade (5.8 ± 3.9 years vs 6.2 ± 4.0 years; P = .57), or baseline left ventricular end-systolic volume (160.0 ± 60.7 mL vs 172.8 ± 67.2 mL; P = .32) between responders and nonresponders, respectively. Percent reduction in QRS duration between the right ventricular-paced and first biventricular-paced waveforms was significantly greater in responders compared with nonresponders (14.4% ± 13.2% vs 7.2%± 14.0%; P = .01). In multivariate analysis, percent reduction in QRS narrowing was the lone factor associated with response (odds ratio 0.02 [0.001-0.42]; P = .01).

CONCLUSION

Reversal of electrical dyssynchrony predicts response to CRT in chronically RV-paced patients upgraded to CRT. Traditional factors associated with a favorable response to CRT in de novo implants (female gender, nonischemic cardiomyopathy, and wider baseline QRS duration) are not significantly associated with response in upgraded patients. Duration of RVP before CRT upgrade is not an important determinant of response.

QRS prolongation induced by cardiac resynchronization therapy correlates with deterioration in left ventricular function

BACKGROUND

The benefits of cardiac resynchronization in inducing reverse ventricular remodeling in patients with left ventricular (LV) systolic dysfunction have been well established. Still, up to 30% of the patients fail to derive significant improvement from this therapy. A subset of "nonresponders" experience deterioration in LV function following cardiac resynchronization therapy (CRT). Characteristics of this patient population, however, have not been studied.

OBJECTIVE

To determine characteristics of patients who experience deterioration in LV function following CRT.

METHODS

Clinical, electrocardiographic, and echocardiographic data were collected in 856 consecutive patients presenting for a new CRT device. For inclusion, all patients had an LV ejection fraction '40%, a QRS duration '120 ms, and available baseline and follow-up echocardiograms and electrocardiograms. Deterioration in LV function was defined as an absolute decrease of 5% or greater in ejection fraction from baseline. Multivariate models were constructed to identify variables significantly associated with deterioration.

RESULTS

A total of 507 patients met inclusion criteria, of which 60 (11.8%) met criteria for deterioration. Patients with deterioration were more likely to be men (86.7% vs 66.9%; P = .002), have a non-left bundle branch block morphology (41.7% vs 23.7%; P = .001), and a history of atrial fibrillation (66.7% vs 51.7%; P = .03). On comparing the pre-CRT QRS duration with the first biventricular-paced QRS duration post-CRT implant, it was found that patients with LV deterioration had significant QRS widening than did those without deterioration (ms) (+3.9 ± 34.1 vs -9.0 ± 27.4, P = .007, respectively). In multivariate analysis, QRS widening indexed to the baseline QRS duration was significantly associated with LV deterioration (odds ratio 1.14 [1.06-1.23]; P = .001).

CONCLUSION

QRS widening is associated with deterioration in LV function following CRT.

Electrical devices for left ventricular dysfunction and heart failure: do we need revised guidelines?

Three recent trials have demonstrated the benefit of cardiac resynchronization therapy (CRT) in the New York Heart Association (NYHA) class II patients with heart failure (HF) with ischemic or nonischemic cardiomyopathy as well as in NYHA class I (asymptomatic) patients mostly with ischemic cardiomyopathy. Earlier intervention with CRT in asymptomatic or minimally symptomatic patients improves survival and reduces HF hospitalizations. The reduction or the prevention of HF hospitalizations is of paramount importance because the HF episodes seem to alter the natural history of disease and are associated with deterioration of left ventricular (LV) function and a marked increase in mortality. The CRT benefit is greatest in patients with a QRS ≥ 150 ms. At this time, it would seem prudent to consider CRT-D (D = ICD) therapy for class I NYHA patients with a QRS ≥ 150 ms and an LV ejection fraction ≤ 30% regardless of etiology. Although the data for NYHA class I patients with nonischemic cardiomyopathy are scanty, the recommendation for class I patients is justified because CRT achieves a much greater degree of LV reverse remodeling in nonischemic compared to ischemic patients. With regard to lone ICDs, there is no evidence that they prevent sudden cardiac death more efficiently in symptomatic than in asymptomatic patients. Cardiomyopathy should be the primary target for device therapy regardless of symptoms for both CRT and lone ICD therapy. New guidelines are needed to address the role of CRT in hospitalized NYHA class IV HF patients or those who depend on inotropic therapy or an LV assist device because randomized CRT trials have not included these patients. CRT in these patients remains controversial. The mortality of such patients even with CRT is very high despite the occasional positive response. The role of CRT in patients waiting for cardiac transplantation also needs guidelines. With the expansion of CRT indications to minimally symptomatic or asymptomatic patients, the benefit of device therapy must be carefully weighed against the potential risk of lifelong device complications.