Author + information
- Received August 10, 2011
- Revision received August 22, 2011
- Accepted August 23, 2011
- Published online November 22, 2011.
- Joep Thijssen, MD⁎,
- C. Jan Willem Borleffs, MD, PhD⁎,
- Victoria Delgado, MD, PhD⁎,
- Johannes B. van Rees, MD⁎,
- Eline A.Q. Mooyaart, MD⁎,
- Rutger J. van Bommel, MD⁎,
- Lieselot van Erven, MD, PhD⁎,
- Eric Boersma, PhD†,
- Jeroen J. Bax, MD, PhD⁎ and
- Martin J. Schalij, MD, PhD⁎,⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Martin J. Schalij, Department of Cardiology, Leiden University Medical Centre, Albinusdreef 2, Leiden 2333 ZA, the Netherlands
Objectives The purpose of this study was to evaluate the impact of upgrading implantable cardioverter-defibrillator (ICD) therapy to cardiac resynchronization therapy (CRT) combined with defibrillator (CRT-D) on the occurrence of ventricular arrhythmia (VA) and appropriate ICD therapies.
Background CRT has been shown to improve left ventricular (LV) systolic function and induce reverse LV remodeling. In addition, it has been hypothesized that CRT may reduce the incidence of VA.
Methods Heart failure patients receiving an upgrade from ICD to CRT-D were evaluated. Patients were considered responders to CRT if LV end-systolic volume reduced ≥15% at 6 months of follow-up. Episodes of VA, triggering device therapy (anti-tachycardia pacing and shocks) were recorded before and after upgrade for the overall population. In addition, these outcomes were compared between CRT responders and nonresponders during the follow-up period after CRT response was assessed.
Results One hundred fifteen patients (93 males [81%], age 65 ± 12 years) were evaluated during a mean follow-up of 54 ± 34 months before CRT-D upgrade and 37 ± 27 months after upgrade. In CRT responders (n = 70), the frequency of VA requiring appropriate device therapy demonstrated a trend toward a decrease from 0.51 ± 0.79 to 0.30 ± 0.59 per patient per year after CRT-D upgrade (p = 0.052). In CRT nonresponders (n = 45), the frequency of VA requiring appropriate device therapy significantly increased from 0.40 ± 0.69 to 1.21 ± 2.53 per patient per year after CRT-D upgrade (p = 0.014).
Conclusions After upgrade from ICD to CRT-D, nonresponders to CRT showed a significant increase in VA burden requiring appropriate device therapy.
- cardiac resynchronization therapy
- device upgrade
- implantable cardioverter-defibrillator
- ventricular arrhythmias
Cardiac resynchronization therapy (CRT) has been demonstrated to be an effective treatment in patients with advanced heart failure: it improves clinical symptoms, reduces heart failure–related hospitalization rates, and improves long-term survival (1–4). These beneficial effects have been related to left ventricular (LV) reverse remodeling after CRT implantation. In addition, heart failure patients with a low ejection fraction (EF) are at risk of sudden arrhythmic death, and prophylactic implantable cardioverter-defibrillator (ICD) implant is indicated for many of these patients (5,6). However, the effects after upgrade from ICD to CRT-defibrillator (CRT-D) on the occurrence of ventricular arrhythmias (VAs) are controversial so far (7–10). Whereas some studies have demonstrated a significant decrease in the burden of VA along with significant LV reverse remodeling (7,9), other studies have shown no reduction or even an increase in the frequency of VA or appropriate ICD therapies (8,10). In addition, the association between LV reverse remodeling after CRT upgrade and changes in VA burden and frequency of appropriate ICD therapies is unclear.
Patients who received an ICD may have heart failure symptoms at follow-up. Upgrading these patients to CRT has shown to improve clinical symptoms and LV function (11). Importantly, this subgroup of patients provides a unique opportunity to evaluate the effects of CRT-D upgrade on the burden of VA. Accordingly, the present evaluation assessed the impact of CRT-D upgrade on the occurrence of VA and appropriate therapies. In addition, the association between LV reverse remodeling and VA burden was evaluated.
Patient population and data collection
Since 1996, data from all patients who received an ICD device at the Leiden University Medical Center were prospectively collected in the departmental cardiology information system (EPD-Vision, Leiden University Medical Center, Leiden, the Netherlands). Characteristics at baseline and data from the implant procedure and follow-up visits were recorded. For the current analysis, ICD patients who underwent an upgrade to CRT-D were selected.
The patient population consisted of consecutive patients who underwent upgrade from single- or dual-chamber ICD to CRT-D owing to progressive symptoms of heart failure. Before upgrading to CRT-D, all patients underwent complete clinical history, physical examination, 12-lead electrocardiography, and transthoracic echocardiography. Clinical parameters included cardiovascular risk factors, renal function, New York Heart Association (NYHA) functional class, quality-of-life score as assessed with the Minnesota Living with Heart Failure Questionnaire and the 6-min walk distance (12,13). Echocardiographic parameters included LV dimensions and LVEF. At 6-month follow-up after CRT-D upgrade, according to the current clinical protocol, clinical status was reassessed, and a repeat transthoracic echocardiogram was performed to evaluate LV dimensions and systolic function. Patients were considered responders if a reduction in left ventricular end-systolic volume (LVESV) ≥15% was documented (14).
All patients were followed up from the ICD implantation date until September 2010 for the occurrence of all-cause mortality and appropriate therapies due to ventricular tachycardia or ventricular fibrillation. Arrhythmia burden was calculated from the total number of episodes divided by the total number of years of ICD or CRT-D and presented in patient per year basis. These endpoints were prospectively recorded during 2 correlative follow-up periods. The first follow-up period was from the ICD implantation date to the CRT-D upgrade date and from the CRT-D upgrade date until the latest device interrogation follow-up. Changes in number of appropriate therapies and shocks after CRT-D upgrade were evaluated for the overall population. Therefore, each patient served as his or her own control for comparison of frequency of appropriate therapies and shocks before and after CRT-D upgrade. The second follow-up period was from the evaluation of response to CRT-D (at 6-month follow-up) until the last device interrogation follow-up. The incidence of appropriate therapies and shocks and arrhythmia burden after CRT-D upgrade were then compared between responders and nonresponders to CRT-D.
Device implantation and settings
Eligibility for ICD implantation in this population was based on international guidelines for primary and secondary prevention (5,6). Upgrade to CRT-D was performed according to current guidelines: advanced symptoms of heart failure despite optimized medical therapy, LVEF ≤35%, and a wide QRS complex (>120 ms) (15).
Implantation of defibrillator systems was performed transvenously, with conventional right atrial and ventricular leads positioning. During CRT-D implantation, the LV lead was inserted through the subclavian vein followed by cannulation of the coronary sinus. Subsequently, the LV pacing lead was inserted through the coronary sinus with the help of an 8-F guiding catheter and positioned as far as possible in the venous system, preferably in a (postero) lateral vein. Implanted systems were manufactured by Biotronik (Berlin, Germany), Boston Scientific (Natick, Massachusetts, formerly CPI, Guidant, St. Paul, Minnesota), Medtronic (Minneapolis, Minnesota), and St. Jude Medical/Ventritex (St. Paul, Minnesota).
Defibrillators were programmed as follows: a VA monitor zone was programmed in all patients (150 to 188 beats/min). No therapy was programmed in this zone until arrhythmias were detected during follow-up. Any VA faster than 188 beats/min was initially attempted to be terminated with 2 bursts of antitachycardia pacing and, after continuation of the arrhythmia, device shocks were the indicated therapy. A VA >210 beats/min was directly attempted to be terminated by device shocks. Furthermore, atrial arrhythmia detection was set to >170 beats/min with supraventricular arrhythmia discriminators enabled. Settings were adapted, only if clinically indicated (e.g., hemodynamic well-tolerated ventricular tachycardia at high rate; ventricular tachycardia in the monitor zone).
Transthoracic echocardiography was performed with the patients in left lateral decubitus position before CRT-D upgrade and at 6-month follow-up with commercially available ultrasound transducer and equipment (M4S Probe, Vivid 7, GE-Vingmed, Horten, Norway). All images were digitally stored on hard disks for offline analysis (EchoPAC version 108.1.5, GE-Vingmed). The LVESV, left ventricular end-diastolic volume (LVEDV), and LVEF were measured from the apical 2- and 4-chamber views using the modified biplane Simpson's method (16). As previously described, response to CRT was defined by ≥15% reduction in LVESV at 6-month follow-up as compared with baseline echocardiogram (before CRT-D upgrade) (14).
Follow-up and definition of endpoints
Patients who were lost to follow-up or who died before the 6-month echocardiography after CRT-D upgrade were excluded from the analyses. All remaining patients were followed up in the ICD clinic at 3- to 6-month intervals. Occurrences of appropriate, successful ICD therapies were recorded as events. During device interrogation, episodes were assessed for appropriate ICD therapy (antitachycardia therapies or shocks) and verified by an electrophysiologist. Shocks were classified as appropriate when they occurred in response to ventricular tachyarrhythmia or ventricular fibrillation. Electrical storm was defined as 3 or more therapies for ventricular tachyarrhythmias within 24 h (17).
The burden of VA requiring ICD therapy or shock was determined by calculating the number of episodes per patient per year. The ICD therapies delivered within 24 h after the previous therapy were not included for the analysis of the burden of VA. Separate analyses for appropriate shocks only and for appropriate therapies (including appropriate shock and antitachycardia pacing) were performed.
For reasons of uniformity, summary statistics for all continuous variables are expressed as mean and standard deviation. Dichotomous data are presented as numbers and percentages. The Kolmogorov-Smirnov test was used to evaluate the distribution of continuous data. The Student t test was used to compare continuous data normally distributed whereas the Mann-Whitney U test was used to compare continuous data nonnormally distributed. Categorical variables were compared with the chi-square test (when no cells had an expected frequency <5) and Fisher's exact test (when 1 or more cells had an expected frequency <5). Comparisons of continuous data at baseline and at 6-month follow-up were performed with a paired Student t test (when data distribution was normal) or Wilcoxon signed-rank test (for continuous data non-normally distributed). Specifically, changes in NYHA functional class between baseline and 6-month follow-up were evaluated with Wilcoxon signed-rank test because this parameter followed a non-normal distribution whereas changes in other clinical parameters (quality of life and 6-min walk test) and echocardiographic parameters of LV function and volumes were compared with a paired Student t test. Variables related to VA burden and appropriate ICD therapies and shocks were not normally distributed, and therefore, changes between baseline and 6 months were evaluated with the Wilcoxon signed-rank test.
Cumulative event rates from the date of CRT-D upgrade until the last follow-up were calculated using the Kaplan-Meier method. The log-rank tests for time-to-event data with respect to the endpoints (appropriate shocks and appropriate therapies) were used for statistical comparison between the 2 patient groups dichotomized based on response to CRT at 6-month follow-up. Univariate and multivariate Cox proportional-hazards models were constructed to identify independent determinants of the endpoints (appropriate therapies and appropriate shocks) after CRT-D upgrade. All independent variables with a p value <0.25 were retained in the multivariate model. In addition, ventricular tachycardia (VT) ablation was entered as a time-dependent covariate. A p value of <0.05 was considered significant. All statistical analyses were performed with SPSS software (version 18.0, SPSS, Chicago, Illinois).
A total of 123 patients underwent a successful CRT-D upgrade because of worsening symptoms of heart failure. Eight patients who were lost to follow-up (n = 2, 2%) or who died (n = 6, 5%) before the 6-month echocardiography after CRT-D upgrade were excluded from the analysis. Consequently, 115 patients were included in the analysis with a mean follow-up of 54 ± 34 months after ICD implantation and an additional mean follow-up of 37 ± 27 months after CRT-D upgrade. Demographic, clinical, and echocardiographic characteristics before CRT-D upgrade are summarized in Table 1. Mean age was 65 ± 12 years, and 92 (80%) patients were male. Ischemic heart failure etiology was recorded in the majority of the patients (75%). Most patients had NYHA functional class III heart failure symptoms (93%) and a severely depressed LV function, with a mean LVEF of 26 ± 8%. Mean QRS duration was 167 ± 35 ms. Finally, medical therapy included angiotensin-converting enzyme inhibitors (90%), diuretics (85%), beta-blockers (77%), and amiodarone (40%). During the entire follow-up of the study (from ICD implantation to last follow-up after CRT-D upgrade), 21 (18%) patients underwent successful VT ablation, and 11 (10%) patients underwent successful atrioventricular junctional ablation. Seventeen (81%) and 4 (19%) patients underwent VT ablation before and after CRT-D, respectively.
6-month follow-up after CRT-D upgrade
Clinical and Echocardiographic Parameters
At 6-month follow-up after CRT-D upgrade, a significant improvement in clinical status and LV volumes and LVEF was observed in the overall population. The NYHA functional class improved from 3.1 ± 0.3 to 2.3 ± 0.7 (p < 0.001) and quality-of-life score decreased from 36 ± 18 to 29 ± 17 (p < 0.001). In addition, the 6-min walk distance increased from 320 ± 129 m to 372 ± 138 m (p < 0.001). In the overall population, the LVESV and LVEDV reduced significantly (from 168 ± 66 ml to 143 ± 61 ml, p < 0.001; from 223 ± 76 ml to 204 ± 72 ml, p < 0.001, respectively) with a significant increase in LVEF (from 26 ± 8% to 31 ± 9%, p < 0.001).
Appropriate device therapy burden before and after CRT-D upgrade in the overall population
During the time elapsed between ICD implantation and CRT-D upgrade (54 ± 34 months), 59 (51%) patients received appropriate therapies. The total number of appropriate therapies was 11 ± 50 per patient and the burden of VA was 0.46 ± 0.75 per patient per year. The appropriate ICD shock burden was 0.36 ± 0.77 per patient per year. A total of 8 (7%) patients experienced an electrical storm before CRT-D upgrade. Of the 59 patients receiving appropriate device therapy before CRT-D upgrade, 9 (15%) patients underwent VT ablation. Cumulative incidence of device therapy was 29% (95% confidence interval [CI]: 21% to 37%) after 1 year, 36% (95% CI: 27% to 45%) after 2 years, and 56% (95% CI: 45% to 66%) after 5 years. After CRT-D upgrade, 49 (43%) patients experienced appropriate therapies during an additional mean follow-up of 37 ± 27 months. The total number of appropriate therapies reduced to 5 ± 17 per patient, although this change was not statistically significant (p = 0.119). In addition, the frequency of VA (0.66 ± 1.70 per patient per year, p = 0.775) and appropriate ICD shocks (0.52 ± 3.01 per patient per year, p = 0.218) remained unchanged. A total of 8 (7%) patients experienced an electrical storm after CRT-D upgrade. Of the 49 patients receiving appropriate device therapy after CRT-D upgrade, 11 (22%) patients underwent VT ablation. Cumulative incidence of device therapy was 25% (95% CI: 17% to 34%) after 1 year, 34% (95% CI: 25% to 44%) after 2 years, and 62% (95% CI: 49% to 75%) after 5 years. Finally, a total of 34 (30%) patients died after CRT-D upgrade.
Changes in appropriate device therapy burden after CRT-D upgrade according to the echocardiographic response
On the basis of a reduction of LVESV ≥15% at 6-month follow-up after CRT-D upgrade, 70 (61%) patients were responders. Table 2 summarizes the changes in clinical status and echocardiographic parameters at 6-month follow-up after CRT-D upgrade for both groups of patients, responders and nonresponders.
In the group of responders, the percentage of patients who received appropriate device therapies decreased from 54% to 33% after CRT-D upgrade. In addition, the total number of appropriate device therapies also decreased from 12 ± 62 to 2 ± 4 per patient after CRT-D upgrade. Furthermore, the frequency of VA requiring appropriate device therapy demonstrated a trend toward a decrease from 0.51 ± 0.79 to 0.30 ± 0.59 per patient per year after CRT-D upgrade (p = 0.052) (Fig. 1). Interestingly, the frequency of appropriate device shocks reduced significantly from 0.21 ± 0.32 to 0.11 ± 0.33 per patient per year (p = 0.009) (Fig. 1). Furthermore, in the group of responder patients to CRT, 3 (4%) patients experienced an electrical storm and 12 (17%) patients underwent VT ablation. In the group of patients who did not show response to CRT, the percentage of patients who received appropriate device therapies was 47% before CRT-D upgrade and 58% after CRT-D upgrade. In these patients, the total number of appropriate device therapies per patient was 8 ± 22 before CRT-D upgrade and 10 ± 25 after CRT-D upgrade. In addition, the frequency of appropriate device shocks remained unchanged after CRT-D upgrade (from 0.24 ± 0.52 to 0.46 ± 1.23 per patient per year, p = 0.333) (Fig. 1). In contrast, the frequency of VA significantly increased from 0.40 ± 0.69 per patient per year before CRT-D upgrade to 1.21 ± 2.53 per patient per year after CRT-D upgrade (p = 0.014) (Fig. 1). In the nonresponder patients group, 5 (11%) patients experienced an electrical storm and 9 (20%) patients underwent VT ablation.
Predictors of combined endpoint after CRT-D upgrade
Figure 2 shows the Kaplan-Meier estimates of the combined endpoint (appropriate ICD therapies) for responder and nonresponder patients after CRT-D upgrade. The cumulative incidence for appropriate ICD therapy in the group of responder patients was 19% (95% CI: 9% to 29%) after 1 year, 29% (95% CI: 17% to 41%) after 2 years, and 51% (95% CI: 33% to 69%) after 5 years. In contrast, in the group of nonresponders, a significantly higher cumulative incidence of 34% (95% CI: 20% to 48%) after 1 year, 42% (95% CI: 27% to 57%) after 2 years, and 76% (95% CI: 59% to 93%) after 5 years was observed (log-rank p = 0.017).
Regarding appropriate ICD shocks, cumulative incidences in responder patients at 1, 2, and 5 years of follow-up were 9% (95% CI: 1% to 16%), 13% (95% CI: 4% to 23%), and 26% (95% CI: 12% to 40%), respectively. In contrast, the group of nonresponders showed significantly higher cumulative incidences of ICD shocks: 23% (95% CI: 11% to 36%) after 1 year, 32% (95% CI: 17% to 47%) after 2 years, and 66% (95% CI: 45% to 88%) after 5 years (log-rank p = 0.001) (Fig. 3).
On multivariate Cox regression analysis, response to CRT defined as reduction in LVESV ≥15% was independently associated with lower risk of appropriate ICD therapies (hazard ratio: 0.439, 95% CI: 0.245 to 0.786, p < 0.001) (Table 3) and ICD shocks (hazard ratio: 0.354, 95% CI: 0.167 to 0.750, p = 0.007) (Table 4).
The findings of the present study can be summarized as follows: 1) “upgrade” of ICD to CRT-D did not result in a significant change in the frequency of appropriate ICD therapies and shocks in the overall population; 2) responder patients to CRT-D (with a significant reduction in LVESV at 6-month follow-up) demonstrated a trend toward a reduction in the frequency of appropriate device therapies and a significant reduction in the frequency of appropriate device shocks; and 3) in contrast, patients who did not show response to CRT had a significant increase in the frequency of VA requiring device therapy.
Effect of CRT-D upgrading on the occurrence of VA
In the present study, the overall population showed significant clinical and echocardiographic improvements at 6-month follow-up after CRT. These findings are in line with previous studies in which CRT was associated with an improved clinical and echocardiographic outcome in heart failure patients (12). Interestingly, these improvements in clinical status and LV systolic performance was not accompanied by a significant change in the number of appropriate ICD therapies or the burden of ICD shocks.
The effects of CRT upgrade on VA have remained controversial, so far. In a study by Ermis et al. (7), in which 18 consecutive ICD patients underwent an “upgrade” to CRT-D, the frequency of arrhythmias and number of appropriate device therapies were reduced after CRT-D implantation. The appropriate shock burden in these 18 patients was 0.58 ± 1.02 per patient per year before CRT and declined significantly (p = 0.05) to 0.04 ± 0.19 per patient per year after CRT. Similar results were found in the study by Kiès et al. (9), in which 17 consecutive ICD patients underwent an “upgrade” to CRT-D. In that study, VA number was significantly (p < 0.01) reduced from 0.92 ± 2.2 episodes per patient per month to 0.12 ± 0.2 episodes per patient per month after CRT-D upgrading. Permanent biventricular pacing has been proposed as 1 of the mechanisms to reduce the frequency of VA requiring ICD therapy. During permanent biventricular pacing, the ventricular conduction delay is reduced, leading to a decrease in the occurrence of reentry, avoidance of pause-dependent tachyarrhythmias, and reduction in the circulating levels of norepinephrine, all known mechanisms that may trigger VA (18,19). Conversely, however, both basic science and clinical studies have shown a proarrhythmic effect of biventricular pacing due to a reversed direction of activation of the left ventricular wall. This reversal of the normal activation sequence may prolong the QT interval and increase the existing transmural dispersion of repolarization, creating the substrate and trigger for reentrant arrhythmias (20).
Interestingly, in the MIRACLE-ICD (Multicenter InSync ICD Randomized Clinical Evaluation) trial, the occurrence of appropriate ICD therapies or shocks in the group of patients who received CRT-D did not show a significant reduction (21). In this trial, a total of 369 patients with moderate to severe heart failure symptoms and wide QRS complex were randomly allocated to a biventricular ICD group (CRT on) or to an ICD only group (CRT off). There were no significant differences between groups with respect to the occurrence of appropriate therapies and/or appropriate shocks, despite improved quality of life, functional status, and exercise capacity in the CRT group (21). In addition, in the REVERSE (Resynchronization Reverses Remodeling in Systolic Left Ventricular Dysfunction) study, in which 508 patients with mild heart failure were randomly assigned to activated CRT (CRT on) and activated ICD (CRT off), the estimated event rate for a first treated VA episode was not significantly different between the 2 groups after the 2-year follow-up period (18.7% in the CRT-on group vs. 21.9% in the CRT-off group, p = 0.84) (22). The event rates observed in the REVERSE study are significantly lower as compared to the results of the present study. However, it must be noted that in the REVERSE study, only subjects with mild heart failure were included and therefore the reported outcomes may not necessarily apply to patients with more severe symptoms of heart failure as were those included in the current analysis. The presence of more advanced heart failure status with dilated left ventricles may be associated with an increased likelihood of VA requiring device therapy (10). On the basis of this assumption, it can be hypothesized that patients with LV reverse remodeling after CRT may show a significant reduction in the incidence of VA when compared with the patients who do not show LV reverse remodeling after CRT.
Device therapy in responders and nonresponders
Gold et al. (22), showed that the antiarrhythmic effect of CRT could be explained by induction of a favorable LV reverse remodeling and decreased myocardial wall tension and electrical stabilization of the myocyte membranes. In the present study, the group of responders to CRT showed a trend toward a reduction in the number of appropriate device shocks after CRT upgrading. In the REVERSE study, in which the patients from the CRT-on group who showed LV reverse remodeling had a decrease in the incidence of VA compared with patients who did not have such a favorable reverse remodeling (5.6% vs. 16.3%; hazard ratio: 0.31, p = 0.001) (22). These findings may confirm the hypothesis of Gold et al. (22) in that the improvement in LV dimensions and function, accompanied by a reduction in wall tension, results in a decreased arrhythmogenicity of the myocardium and reducing ICD therapy in responders to CRT-D (after upgrade). Additional studies are warranted to elucidate how much LV reverse remodeling is needed to minimize the number of appropriate ICD therapies in patients who were upgraded to CRT.
This was a retrospective observational analysis of prospectively assessed data evaluating the occurrence of VA requiring appropriate device therapy in a cohort of patients before and after CRT-D upgrade. Because patients received ICDs in a single center over a long period of time, evolving guidelines may result in a heterogeneous population. Furthermore, few patients had multiple device therapies within 24 h after the previous therapy. These episodes were not counted for analysis of the burden of VA. In addition, since all CRT-D devices had antitachycardia treatment function and the oldest implanted ICD devices did not have this function, the number of appropriate shocks in the ICD group might be overestimated when compared with the CRT-D group. To date, definition of response to CRT is still a debated issue. In the present evaluation, a cut-off value of 15% reduction in LVESV was used to divide the patient population into responders and nonresponders to CRT. Using the median value of LVESV reduction at 6-month follow-up would be a valuable option to dichotomize the population. In the present evaluation, however, this value was 17%, and the analysis based on the median reduction in LVESV yielded similar results. In addition, further studies are needed to evaluate whether LV reverse remodeling occurs beyond 6-month follow-up after CRT-D upgrade, and whether that may result in further reduction in VA burden.
In this large single-center study, the frequency of VA requiring appropriate device therapy did not significantly change in the overall population after upgrade of ICD to CRT-D. Most important, however, in the subgroup of patients who showed echocardiographic response to CRT at 6-month follow-up (reduction in LVESV ≥15%), a trend toward a reduction in the frequency of appropriate device therapies and a significant reduction in the frequency of appropriate device shocks was observed. Moreover, echocardiographic nonresponders after CRT-D had a significant increase in the frequency of VA requiring device therapy when compared to the period before CRT.
Dr. Delgado received consulting fees from St. Jude Medical. Dr. van Erven received research grants from Boston Scientific. Dr. Bax received research grants from Biotronik, Boston Scientific, GE Healthcare, Medtronic, and St. Jude. Dr. Schalij received research grants from Biotronik, Boston Scientific, and Medtronic. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. Steven E. Nissen, MD, MACC, served as Guest Editor for this paper.
- Abbreviations and Acronyms
- confidence interval
- cardiac resynchronization therapy
- cardiac resynchronization therapy-defibrillator
- ejection fraction
- implantable cardioverter-defibrillator
- left ventricular
- left ventricular end-diastolic volume
- left ventricular ejection fraction
- left ventricular end-diastolic volume
- New York Heart Association
- ventricular arrhythmia
- ventricular tachycardia
- Received August 10, 2011.
- Revision received August 22, 2011.
- Accepted August 23, 2011.
- American College of Cardiology Foundation
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