Europace Advance Access originally published online on April 3, 2008
Europace 2008 10(5):566-571; doi:10.1093/europace/eun081
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CARDIAC RESYNCHRONISATION THERAPY
Significance of QRS morphology in determining the prevalence of mechanical dyssynchrony in heart failure patients eligible for cardiac resynchronization: particular focus on patients with right bundle branch block with and without coexistent left-sided conduction defects
1 Department of Pacemaker and Electrophysiology, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, PO Box 15745-1341, Mellat Park, Vali-E-Asr Avenue, Tehran 1996911151, Iran; 2 Department of Pacemaker and Electrophysiology, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran; 3 Department of Echocardiography, Baghiyatallah Hospital, Baghiyatallah University of Medical Sciences, Tehran, Iran; 4 Department of Echocardiography, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran
Manuscript submitted 13 December 2007. Accepted after revision 16 March 2008.
* Corresponding author. Tel: +98 21 2392 2931; fax: +98 21 2204 8174.E-mail address: majid.haghjoo{at}gmail.com or haghjoo{at}rhc.ac.ir
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Aims: The aim of this study was to assess the significance of QRS morphology in determining the prevalence of mechanical dyssynchrony in heart failure (HF) patients considered eligible for cardiac resynchronization.
Methods and results: A total of 200 consecutive HF patients (158 males, mean age 56 ± 13.5 years) with standard indications for cardiac resynchronization therapy (CRT) were evaluated prospectively. The prevalence of an interventricular mechanical delay 
40 ms was lower in patients with pure right bundle branch block (RBBB) than that in those with RBBB plus left fascicular hemiblock (RBBB-LFH) and those with left bundle branch block (LBBB) (33 vs. 50 vs. 54%, P = 0.05). A maximal difference in peak myocardial systolic velocity among all 12 segments (Ts)>100 ms was found in 63% of the patients with LBBB, whereas it was present in 31% of the patients with pure RBBB and in 42% of those with RBBB-LFH (P < 0.001). A standard deviation of Ts (Ts-SD)>34 ms was present in 58% of the LBBB subjects, but in only 29% and 42% of the patients with pure RBBB and RBBB-LFH, respectively (P < 0.001). Intraventricular dyssynchrony, however, was not different in patients with pure RBBB and in those with RBBB-LFH in terms of maximal difference in Ts (P = 0.25) and Ts-SD (P = 0.17).
Conclusions: Although LBBB was more often associated with intraventricular dyssynchrony, ECG sign of additional left ventricular (LV) conduction delay is not a helpful tool for the identification of intra-LV mechanical dyssynchrony in HF patients with RBBB who would benefit from CRT.
Key Words: Congestive heart failure, Right bundle branch block, Left-sided conduction defect, Left bundle branch block, Electrocardiography, Colour tissue Doppler imaging
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Cardiac resynchronization therapy (CRT) has emerged as an established therapy for congestive heart failure (HF) due to severe left ventricular (LV) systolic dysfunction.1
–3
Current selection criteria for patients eligible for CRT include New York Heart Association (NYHA) functional class III–IV, despite optimal medical therapy; LV ejection fraction (LVEF) 
35%; LV end-diastolic diameter >55 mm; QRS duration 120 ms; and sinus rhythm.4 Recent large-scale clinical trials have confirmed the favourable effects of CRT on symptoms, quality of life, exercise capacity, LV function, and mortality risk.5–9 Although this treatment modality is effective in the majority of patients, up to 30% of the patients fail to respond to CRT, despite a prolonged QRS duration.10–16
Most patients (85–90%) enrolled in CRT trials had a left bundle branch block (LBBB) configuration.3,5–8 From a mechanistic point of view, CRT in patients with LBBB may coordinate the dyssynchronous ventricular contraction and reduce mitral regurgitation (MR). Thus, the benefit of CRT may be obvious when there is a mechanical delay in LV activation. However, no significant benefits are expected to be derived from CRT in patients with right bundle branch block (RBBB) and intact left bundle conduction. This hypothesis is supported by data from Garrigue et al.,17 who demonstrated that only HF patients with complete RBBB (QRS width >140 ms) and associated intra-LV dyssynchrony in colour tissue Doppler imaging (TDI) were likely to respond to CRT. Previous studies17,18 suggested that associated left-sided electrical conduction delay may identify appropriate candidates (those with mechanical LV dyssynchrony) for CRT among RBBB patients; nevertheless, this hypothesis has never been tested in a prospective study. We designed an echocardiographic study to test the hypothesis that there is a significant difference in the prevalence of mechanical dyssynchrony in HF patients eligible for CRT with different QRS morphologies, despite similar QRS durations; we particularly focused on patients with RBBB with and without additional left-sided conduction defects.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Characteristics of congestive heart failure population
Between January 2004 and October 2007, a total of 200 consecutive HF patients with standard CRT indications (NYHA class III–IV, LVEF
35%, and QRS 120 ms) were prospectively included. Patients with non-sinus rhythm, previous pacemaker implantation, and primary valvular heart disease were excluded. This study was approved by the local Ethics Committee, and written informed consent was obtained from all patients. About 158 men and 42 women at a mean age of 56 ± 13.5 years were included. The underlying aetiology was ischaemic heart disease in 69% of the patients and primary dilated cardiomyopathy in the remaining 31%. The patients were classified into three groups on the basis of their QRS morphology: 90 patients with LBBB, 48 patients with pure RBBB, and 62 patients with RBBB and concomitant left fascicular hemiblocks (RBBB-LFH) (left anterior fascicular block in 38 and left posterior fascicular block in 24 patients). The patients, who were in NYHA class III (n = 171) or IV (n = 29), underwent a standard 12-lead electrocardiography and a complete echocardiographic examination, including specific evaluations of inter- and intra-ventricular dyssynchrony.
Electrocardiographic analysis
Standard 12-lead electrocardiograms were acquired at a paper speed of 25 mm/s and a scale of 10 mm/mV. The diagnosis of RBBB plus left anterior fascicular block was based on the observation of typical changes of RBBB in precordial lead V1 and initial R waves and prominent S-waves in limb leads II, III, and aVF. The QRS duration should be at least 120 ms, and the frontal-plane axis of the complex should be between –45° and –120°. The diagnosis of RBBB plus left posterior fascicular block was considered when there was no evidence of right ventricular hypertrophy, when there were changes typical of RBBB demonstrated in precordial lead V1, and when there were initial R-waves and prominent S-waves shown in limb leads I and aVL. The duration of the QRS complex should be at least 120 ms, and the frontal-plane axis of the complex should be at least +90°. The measurements of the QRS durations (recorded from the surface leads demonstrating the greatest values) and the assessments of the QRS morphologies were performed by two independent electrophysiologists, who were blinded to the echocardiographic data of the patients.
Echocardiographic protocol
A complete M-mode, two-dimensional, and Doppler evaluation was performed using ultrasonographic equipment (Vivid 7, General Electric, USA). Images were obtained via a 3.5 MHz transducer at an appropriate depth in the parasternal and apical views. Left ventricular end-systolic (LVES) and LVED volumes and LVEF were calculated with the biplane Simpson's technique. Mitral regurgitation was graded according to the jet area method.
Pulse-wave Doppler recordings across the aortic and pulmonary valves were obtained from the apical five-chamber and parasternal short-axis views, respectively. The aortic pre-ejection time was calculated from the beginning of the QRS complex to the onset of the aortic flow velocity recorded in the apical five-chamber view. The pulmonary pre-ejection time was measured from the beginning of the QRS complex to the onset of the pulmonary flow velocity curve recorded in the parasternal short-axis view. The difference between the two values was considered the interventricular mechanical delay (IVMD); according to the previous studies, an IVMD >40 ms was selected as the cut-off point for interventricular dyssynchrony.19,20
Colour TDI was acquired from the apical four-chamber, apical three-chamber, and apical two-chamber views to assess the myocardial regional function. In each view, both the basal and mid-segments were assessed. In this way, the following segments were interrogated: septal, lateral, inferior, posterior, anteroseptal, and anterior at both the basal and middle levels. The regional pre-ejection period was measured for all the segments from the beginning of QRS to the peak of the positive component of the regional systolic velocity (Ts). Maximal delta-Ts, defined as the maximal difference in Ts among all 12 segments, was used as the indicator of intraventricular dyssynchrony; a maximal delta-Ts >100 ms was considered as the cut-off point for intraventricular dyssynchrony based on previous studies.16 The standard deviation of the time to peak myocardial systolic velocity of all 12 segments (Ts-SD) was calculated, and Ts-SD > 34 ms was considered as the cut-off point for intraventricular dyssynchrony based on previous observations.16 All the echocardiographic measurements were performed by two independent echocardiographers who were blinded to the electrocardiographic data of the patients.
Statistical analysis
The variables are expressed as mean ± SD for the continuous variables and as absolute or relative frequencies for the categorical variables. The categorical characteristics were compared using the 
2 and Fisher's exact tests for cell count less than 5. Patient's characteristics were compared using Student's t-test in the case of the continuous variables. Otherwise, a non-parametric test of Mann–Whitney U test was used. More than two mean values were simultaneously compared using the one-way analysis of variance (ANOVA) or Kruskal–Wallis H test with the Bonferroni correction. A two-tailed P-value less than 0.05 was considered statistically significant. The software SPSS version 13.0 (SPSS Inc., Chicago, IL, USA) was employed for data storage and analysis.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Baseline characteristics
Two hundred patients completed the electrocardiographic and echocardiographic studies. Of those patients, 90 had LBBB, 62 RBBB-LFH, and 48 pure RBBB. All the included patients had severe HF: 171 were in NYHA class III and 29 in class IV. The underlying aetiology was ischaemic in 69% and idiopathic in 31%. The mean values of the QRS duration and PR interval were 142.5 ± 20.0 ms (120–230) and 191.6 ± 25.4 ms (120–280), respectively. All the patients had sinus rhythm at the time of study. Among the echocardiographic measurements, LVEF, LVES volume, and LVED volume were 19 ± 6.5%, 155.3 ± 54.5 mL, and 197.7 ± 60.8 mL, respectively.
Comparison between left bundle branch block, right bundle branch block-left fascicular hemiblock, and pure right bundle branch block: clinical and electrocardiographic characteristics
Overall comparisons between the three groups defined by conduction abnormality were similar regarding the aetiology of HF, age, gender, NYHA functional class, and MR severity (all P > 0.05). There were also no significant differences in the electrocardiographic parameters of PR interval and QRS duration in the three groups (all P > 0.05). Left ventricular end-diastolic volume and LVES volume were, however, significantly greater in the LBBB group than those in both RBBB-LFH and pure RBBB groups (P = 0.005 and 0.015, respectively). These discrepancies in LV dimensions resulted only in a lower EF in the patients with LBBB when compared with those with pure RBBB (18.80 ± 5.80 vs. 22.40 ± 6.70, P = 0.004). Table 1 shows the clinical, electrocardiographic, and echocardiographic characteristics of the LBBB and two RBBB groups.
|
Pairwise comparisons of the patients with pure RBBB and RBBB-LFH revealed no significant differences in terms of age, gender, aetiology of the cardiomyopathy, MR severity, and NYHA functional class (all P > 0.05). The electrocardiographic parameters of the PR interval and QRS duration were also similar in the two groups. Despite the similar LV dimensions, the EF is low in patients with RBBB-LFH than in those with pure RBBB (18.8 ± 7.0 vs. 22.4 ± 6.7%, P = 0.01). Table 2 depicts the clinical, electrocardiographic, and echocardiographic characteristics of the pure RBBB and RBBB-LFH groups.
|
Comparison between left bundle branch block, right bundle branch block-left fascicular hemiblock, and pure right bundle branch block: prevalence of mechanical dyssynchrony
A greater proportion of patients with interventricular dyssynchrony (IVMD > 40 ms) was observed in the groups with LBBB (49/90 patients, 54.4%) or RBBB-LFH (31/62, 50%) when compared with patients with pure RBBB (16/48, 33.3%) (overall comparison: P = 0.05). When defined as a maximal delta-Ts of >100 ms, significant intraventricular dyssynchrony was found in 57 (63%) patients in the LBBB group as opposed to 15 (31%) patients in the pure RBBB group and 26 (42%) patients in the RBBB-LFH group (overall comparison: P < 0.001). A similar increase was also observed in the absolute values of the maximal delta-Ts across the three groups (76 ms in the pure RBBB group vs. 78.7 ms in the RBBB-LFH group vs. 101 ms in the LBBB group, P < 0.001). When defined as a Ts-SD of >34 ms, significant intraventricular dyssynchrony was present in 53 (58%) LBBB subjects vs. only 14 (29%) patients in the pure RBBB group and 26 (42%) patients in the RBBB-LFH group (overall comparison: P < 0.001). Pairwise comparisons among the patients with pure RBBB and those with RBBB-LFH showed no differences in intraventricular dyssynchrony in terms of maximal delta-TS >100 (P = 0.25) and Ts-SD >34 (P = 0.17). Figure 1 shows the mean values of intraventricular dyssynchrony (maximal difference in TS and Ts-SD) between the three groups.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
The main findings of the present study are as follows: (i) intra-LV mechanical dyssynchrony was frequent in severe HF patients with RBBB (37%), a group of patients are usually underrepresented in clinical trials; (ii) concomitant left-sided electrical conduction defect did not increase the prevalence of intra-LV mechanical dyssynchrony in patients with severe HF and RBBB; and (iii) LBBB was more likely to be associated with significant intra-LV dyssynchrony than with other types of intraventricular conduction defects.
The response to CRT was initially considered to result, in part, from the resynchronization of interventricular dyssynchrony. Prior studies demonstrated a good relation between interventricular dyssynchrony and the QRS duration.21–23 These observations tend to support the use of the QRS duration for patient selection. However, results of many CRT studies indicated that 20–30% of the patients failed to respond to CRT, despite a prolonged QRS duration. Except for patients with a very wide spontaneous QRS complex, mechanical intraventricular dyssynchrony is not necessarily related to electrical dyssynchrony judged by the QRS duration. This, among other factors, may at least in part explain why 20–30% of the patients in major trials did not respond to CRT. Our study addresses the well validated, but still intriguing, issue of dissociation between echo-documented mechanical dyssynchrony and electrical dyssynchrony, the latter as evaluated by the QRS duration. Despite a similar QRS duration in the three groups, there was a significant difference in the prevalence of mechanical intraventricular dyssynchrony. These findings have profound clinical implications because patient groups with similar electrical dyssynchrony who would be considered eligible for biventricular device implantation are shown to display significant differences in the prevalence of mechanical dyssynchrony, which has been documented to be predictive of a favourable response to CRT.24
To the best of our knowledge, the present study is the first of its kind to investigate the prevalence of mechanical intra-LV dyssynchrony in HF patients with different types of RBBB. Prior studies have only compared the prevalence of mechanical dyssynchrony in LBBB subjects with that of RBBB patients; no studies have thus far evaluated this parameter in HF patients with pure RBBB and in those with RBBB and concomitant left-sided electrical conduction defect. The question remained unanswered is that is there any difference in intra-LV dyssynchrony between HF patients with pure RBBB and those with RBBB-LFH? Badano et al.25 recently reported the results of their c-TDI study on 103 HF patients (41 with narrow QRS, 22 with RBBB, and 40 with LBBB) and in 59 controls. Intra-LV dyssynchrony was present in 36% of the HF patients with RBBB and 60% of those with LBBB. They finally concluded that the assessment of intra-LV dyssynchrony by colour TDI might be more important than the QRS duration (narrow QRS vs. wide QRS) or morphology (LBBB vs. RBBB) in selecting appropriate candidates for cardiac resynchronization. Similar results were obtained in our study: intra-LV dyssynchrony (defined as Ts-SD >34 ms) was present in 37% of the HF patients with RBBB and 58% of those with LBBB. Schuster et al.26 demonstrated that both patients with a normal QRS width and those with RBBB might exhibit significant intra-LV dyssynchrony when assessed by TDI. Furthermore, Bader et al.24 reported that the intra-LV dyssynchrony as assessed by c-TDI was predictive of HF worsening, independent of the QRS width and LVEF and that the type of bundle branch block did not predict the degree of intra-LV dyssynchrony. Taken together, these data suggest that neither QRS width nor QRS morphology (including surface ECG evidence of additional left-sided conduction delay in patients with RBBB) is a reliable indicator of intra-LV dyssynchrony.
Limitations
The definition of abnormal intra-LV dyssynchrony relies only on maximal delta-Ts and Ts-SD. Therefore, it may turn out that the application of other echocardiographic indicators of abnormal intra-LV dyssynchrony would modify the results of the study.
|
Conclusions |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Although complete LBBB was more often associated with intraventricular dyssynchrony, ECG sign of additional LV conduction delay is not a helpful tool for the identification of intra-LV mechanical dyssynchrony in HF patients with RBBB who would benefit from CRT.
Conflict of interest: none declared.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
[1] Bax JJ, Abraham T, Barold SS, Breithardt OA, Fung JW, Garrigue S, et al. Cardiac resynchronization therapy: part 1—issues before device implantation. J Am Coll Cardiol (2005) 46:2153–67.
[2] Strickberger SA, Conti J, Daoud EG, Havranek E, Mehra MR, Pina IL, et al, Council on Clinical Cardiology Subcommittee on Electrocardiography and Arrhythmias and the Quality of Care and Outcomes Research Interdisciplinary Working Group; Heart Rhythm Society. Patient selection for cardiac resynchronization therapy: from the Council on Clinical Cardiology Subcommittee on Electrocardiography and Arrhythmias and the Quality of Care and Outcomes Research Interdisciplinary Working Group, in collaboration with the Heart Rhythm Society. Circulation (2005) 111:2146–50.
[3] Reynolds MR, Joventino LP, Josephson ME, Miracle ICD Investigators. Relationship of baseline electrocardiographic characteristics with the response to cardiac resynchronization therapy for heart failure. Pacing Clin Electrophysiol (2004) 27:1513–8.[CrossRef][Medline]
[4] Vardas PE, Auricchio A, Blanc JJ, Daubert JC, Drexler H, Ector H, et al, ESC Committee for Practice Guidelines (CPG). Authors/Task Force Members. Guidelines for cardiac pacing and cardiac resynchronization therapy: The Task Force for Cardiac Pacing and Cardiac Resynchronization Therapy of the European Society of Cardiology. Developed in Collaboration with the European Heart Rhythm Association. Europace (2007) 9:959–98.
[5] Arya A, Haghjoo M, Dehghani MR, Alasti M, Alizadeh H, Kazemi B, et al. Effect of cardiac resynchronization therapy on the incidence of ventricular arrhythmias in patients with an implantable cardioverter-defibrillator. Heart Rhythm (2005) 2:1094–8.[CrossRef][Web of Science][Medline]
[6] Cleland JG, Daubert JC, Erdmann E, Freemantle N, Gras D, Kappenberger L, et al, Cardiac Resynchronization-Heart Failure (CARE-HF) Study Investigators. The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med (2005) 352:1539–49.
[7] Bristow MR, Saxon LA, Boehmer J, Krueger S, Kass DA, De Marco T, et al, Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) Investigators. Cardiac Resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure. N Engl J Med (2004) 350:2140–50.
[8] Linde C, Leclercq C, Rex S, Garrigue S, Lavergne T, Cazeau S, et al. Long-term benefits of biventricular pacing in congestive heart failure: results from the multisite stimulation in cardiomyopathy (MUSTIC) study. J Am Coll Cardiol (2002) 40:111–8.
[9] Abraham WT, Fisher WG, Smith AL, Delurgio DB, Leon AR, Loh E, et al, MIRACLE Study Group. Multicenter InSync Randomized Clinical Evaluation. Cardiac resynchronization in chronic heart failure. N Engl J Med (2002) 346:1845–53.
[10] Molhoek SG, Bax JJ, Boersma E, Van Erven L, Bootsma M, Steendijk P, et al. QRS duration and shortening to predict clinical response to cardiac resynchronization therapy in patients with end-stage heart failure. Pacing Clin Electrophysiol (2004) 27:308–13.[CrossRef][Medline]
[11] Lecoq G, Leclercq C, Leray E, Crocq C, Alonso C, de Place C, et al. Clinical and electrocardiographic predictors of a positive response to cardiac resynchronization therapy in advanced heart failure. Eur Heart J (2005) 26:1094–100.
[12] Bleeker GB, Schalij MJ, Molhoek SG, Verwey HF, Holman ER, Boersma E, et al. Relationship between QRS duration and left ventricular dyssynchrony in patients with end-stage heart failure. J Cardiovasc Electrophysiol (2004) 15:544–9.[Web of Science][Medline]
[13] Nelson GS, Curry CW, Wyman BT, Kramer A, Declerck J, Talbot M, et al. Predictors of systolic augmentation from LV preexcitation in patients with dilated cardiomyopathy and intraventricular conduction delay. Circulation (2000) 101:2703–9.
[14] Morris-Thurgood JA, Turner MS, Nightingale AK, Masani N, Mumford C, Frenneaux MP. Pacing in heart failure: improved ventricular interaction in diastole rather than systolic resynchronization. Europace (2000) 2:271–5.
[15] Ghio S, Constantin C, Klersy C, Serio A, Fontana A, Campana C, et al. Interventricular and intraventricular dyssynchrony are common in heart failure patients regardless of QRS duration. Eur Heart J (2004) 25:571–8.
[16] Yu CM, Lin H, Zhang Q, Sanderson JE. High prevalence of left ventricular systolic and diastolic asynchrony in patients with congestive heart failure and normal QRS duration. Heart (2003) 89:54–60.
[17] Garrigue S, Reuter S, Labeque JN, Jaïs P, Hocini M, Shah DC, et al. Usefulness of biventricular pacing in patients with congestive heart failure and right bundle branch block. Am J Cardiol (2001) 88:1436–41.[CrossRef][Web of Science][Medline]
[18] Aranda JM Jr, Conti JB, Johnson JW, Petersen-Stejskal S, Curtis AB. Cardiac resynchronization therapy in patients with heart failure and conduction abnormalities other than left bundle-branch block: analysis of the Multicenter InSync Randomized Clinical Evaluation (MIRACLE). Clin Cardiol (2004) 27:678–82.[CrossRef][Web of Science][Medline]
[19] Leclercq C, Faris O, Tunin R, Johnson J, Kato R, Evans F, et al. Systolic improvement and mechanical resynchronization does not require electrical synchrony in the dilated failing heart with left bundle-branch block. Circulation (2002) 106:1760–3.
[20] Bax JJ, Ansalone G, Breithardt OA, Derumeaux G, Leclercq C, Schalij MJ, et al. Echocardiographic evaluation of cardiac resynchronization therapy: ready for routine clinical use. A critical appraisal. Cardiac resynchronization therapy. J Am Coll Cardiol (2004) 44:1–9.
[21] Haghjoo M, Bagherzadeh AA, Fazelifar AF, Ojaghi Haghighi Z, Esmaielzadeh M, Alizadeh A, et al. Prevalence of mechanical dyssynchrony in heart failure patients with different QRS durations. Pacing Clin Electrophysiol (2007) 30:616–22.[CrossRef][Medline]
[22] Cleland JG, Daubert JC, Erdmann E, Freemantle N, Gras D, Kappenberger L, et al, CARE-HF study Steering Committee and Investigators. The CARE-HF study (Cardiac resynchronization in heart failure study): rationale, design and end points. Eur J Heart Fail (2001) 3:481–9.[CrossRef][Web of Science][Medline]
[23] Rouleau F, Merheb M, Geffroy S, Berthelot J, Chaleil D, Dupuis JM, et al. Echocardiographic assessment of the interventricular delay of activation and correlation to the QRS width in dilated cardiomyopathy. Pacing Clin Electrophysiol (2001) 24:1500–6.[CrossRef][Medline]
[24] Bader H, Garrigue S, Lafitte S, Reuter S, Jaïs P, Haïssaguerre M, et al. Intra-left ventricular electromechanical asynchrony. A new independent predictor of severe cardiac events in heart failure patients. J Am Coll Cardiol (2004) 43:248–56.
[25] Badano LP, Gaddi O, Peraldo C, Lupi G, Sitges M, Parthenakis F, et al. Left ventricular electromechanical delay in patients with heart failure and normal QRS duration and in patients with right and left bundle branch block. Europace (2007) 9:41–7.
[26] Schuster P, Faerestrand S, Ohm OJ. Color Doppler tissue velocity imaging can disclose systolic left ventricular asynchrony independent of the QRS morphology in patients with severe heart failure. Pacing Clin Electrophysiol (2004) 27:460–7.[CrossRef][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  M. Haghjoo, H. R. Bonakdar, M. V. Jorat, A. F. Fazelifar, A. Alizadeh, Z. Ojaghi-Haghjghi, M. Esmaielzadeh, and M. A. Sadr-Ameli Effect of right ventricular lead location on response to cardiac resynchronization therapy in patients with end-stage heart failure Europace, March 1, 2009; 11(3): 356 - 363. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||