To the Editor,
Cardiac resynchronization therapy (CRT) has been shown to be an effective, economically viable tool1 in patients with severe acute heart failure and intraventricular conduction disorders.
Recent publications suggest the presence of electrical remodeling in patients with smaller ventricular volumes after CRT.2 We undertook a pilot study to determine the potential relationship between ventricular and electrical remodeling.
The study included 20 patients with idiopathic dilated cardiomyopathy and an indication for CRT, in whom the QRS duration and ventricular volumes were measured before implantation and after 6 months. The study excluded patients with atrial fibrillation or previous pacing by a pacemaker, as well as when the patients’ own rhythm precluded measurement of the native or intrinsic QRS width. The study complied with all principles of the Declaration of Helsinki.
Left ventricular reverse remodeling was defined as a decrease ≥10% in end-systolic volume at 6 months, and electrical remodeling as a decrease in intrinsic (unpaced) QRS width.
Of the 20 patients included (age, 61 [10] years; 40% women), 15 (75%) had echocardiographic evidence of reverse remodeling. These patients showed a significant decrease in intrinsic or unpaced QRS on follow-up (169 [15] vs 154 [12] ms; P=.032) compared to the others (180 [23] vs 180 [16] ms; P=.977), in addition to a significant decrease in left ventricular end-diastolic volume (P<.01) and an improvement in ejection fraction (P=.02). Both groups showed similar clinical and echocardiographic profiles at baseline and similar device programming characteristics, but the patients who presented a decrease in QRS on follow-up were characterized by a shorter paced QRS achieved with CRT implantation (121 [15] vs 146 [24] ms; P=.021) (Table).
Comparative Analysis of Clinical, Electrical, and Echocardiographic Variables According to Presence or Absence of Left Ventricular Reverse Remodeling at the 6-Month Follow-up.
| LV reverse remodeling (n=15) | Absence of reverse remodeling (n=5) | |||
| Baseline | Follow-up | Baseline | Follow-up | |
| Age, years | 61 (11) | — | 62 (8) | — |
| Women, % | 47 | — | 20 | — |
| Ejection fraction, % | 21 (7) | 39 (8) a | 25 (4) | 24 (13) b |
| LVEDD, mL | 190 (83) | 130 (57) a | 264 (62) | 284 (73) b |
| LVESD, mL | 146 (65) | 81 (35) a | 191 (57) | 215 (82) b |
| ERO, cm2 | 0.15 (0.13) | 0.06 (0.02) | 0.27 (0.16) | 0.13 (0.20) |
| Intrinsic QRS, ms | 163 (15) | 153 (31) a | 180 (23) | 182 (15) b |
| Paced QRS | 121 (15) | 122 (17) | 146 (15) c | 140 (14) |
| AV, ms | 145 (22) | — | 125 (7) | — |
| VV, ms | –20 (15) | — | –12 (02) | — |
AV, programmed atrioventricular delay; ERO, effective regurgitant orifice area; LV, left ventricle; LVEDD, left ventricular end-diastolic volume; LVESD, left ventricular end-systolic volume; VV, programmed interventricular delay.
Data are expressed as mean (standard deviation).
a P<.05 compared to intragroup follow-up.
b P<.05 compared to intergroup follow-up.
c P<.05 compared to intergroup baseline.
The main finding of this pilot study is a significant reduction in the intrinsic or unpaced QRS width in patients who present a decrease in ventricular volumes on follow-up, which is consistent with the findings of recent publications that report an improvement in intraventricular conduction among patients who present reverse remodeling.2 This finding differed from the results reported by Stockburger et al.,3 who found no such relationship, but the series was much smaller and included patients with ventricular dysfunction of various etiologies, unlike this study which specifically analyzed patients with idiopathic dilated cardiomyopathy, a characteristic that could explain the different results obtained. The presence of mitral regurgitation has also been associated with the appearance of intraventricular conduction disorders.4 In our study we observed a decrease which was not statistically significant (probably due to sample size) but could partly be due to an improvement in electrical conduction after CRT. Another noteworthy finding is the possible relationship between the presence of ventricular and electrical reverse remodeling with the duration of the QRS complex achieved with implantation. It has been extensively reported in the literature that patients with wider QRS before resynchronization present a higher response rate to therapy although an adequate cut-off point has not yet been achieved; however, the degree of QRS narrowing in the implant5, 6 is probably more important for prognosis than the actual duration of the baseline complex. Our findings support those results and underscore the importance of adequate left ventricular lead placement during implantation, as well as accurate programming to obtain the narrowest paced QRS possible.
The inherent limitations of sample size and the descriptive nature of the study should be pointed out. The new data we present may be useful in routine clinical practice, although clinical trials with more patients are needed. Because the series contains patients with idiopathic dilated cardiomyopathy, the results cannot be extrapolated to other etiologies.
In patients with idiopathic dilated cardiomyopathy, the decrease in left ventricular end-systolic volume after CRT is related to electrical remodeling. This phenomenon appears to be determined by the smaller paced QRS width in the implant.
Corresponding author: juferpas@secardiologia.es