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European Journal of Heart Failure 2007 9(3):300-305; doi:10.1016/j.ejheart.2006.09.003
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© 2007 European Society of Cardiology

Usefulness of bifocal pacing in patients with heart failure and intraventricular conduction delay

Alan Bulava* and Jan Lukl

1st Department of Internal Medicine, University Hospital and Faculty of Medicine Palacky University, Olomouc, Czech Republic

* Corresponding author. I. P. Pavlova 6, 775 20 Olomouc, Czech Republic. Tel.: +420 588443201; fax: +420 588442500. E-mail address: alanbulava{at}seznam.cz


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Limitations
 6. Conclusions
 References
 
Background: Bifocal pacing (BFP) has been proposed as a feasible alternative to cardiac resynchronization therapy.

Aim: To evaluate BFP in patients with severe heart failure and significant intraventricular conduction delay and to compare it with biventricular pacing (BVP).

Methods: Echocardiographic examination including TDI and invasive measurement of haemodynamics was performed under basal conditions, during BFP and during BVP.

Results: Fifty patients were included: 29 with ischaemic heart disease (IHD), 21 with idiopathic dilated cardiomyopathy (IDCM). LV dp/dtmax increased during BFP compared to the basal state (13.4%, 95% CI 9.2–17.6%, p<0.0001) and a further increase was achieved during BVP (29.5%, 95% CI 23.7–35.4%, p<0.0001). A significant correlation was found between the distance of the right ventricular apical and outflow tract leads and percentage of dp/dtmax increase in IDCM patients (r=0.72), but not in IHD patients. Interventricular mechanical delay (IVMD) decreased in BFP (43±22 ms vs. 53±31 ms, p=0.006), but BVP produced even shorter IVMD (22±19ms, p<0.0001). In all patients, regional systolic contraction times were significantly shortened, corresponding with prolongation of the respective regional diastolic filling times during both BFP (p<0.05 for all segments) and BVP (p<0.001 for all segments).

Conclusions: BFP improves LV haemodynamics by decreasing the inter- and intraventricular conduction delays. The leads in the right ventricle should be placed at the longest achievable distance. BVP is superior to BFP.

Key Words: Cardiac resynchronization • Bifocal pacing • Biventricular pacing • Haemodynamics

Received March 3, 2006; Revised June 8, 2006; Accepted September 8, 2006


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 5. Limitations
 6. Conclusions
 References
 
Biventricular pacing (BVP) is an established form of resynchronization therapy in patients with advanced heart failure and intraventricular conduction delay [1]. However, the procedure has been reported to be technically unsuccessful in 5-13% of cases [2-4]. Bifocal pacing (BFP), i.e., simultaneous AV synchronised pacing of the right ventricular apex and the right ventricular outflow tract, has been recently proposed as a possible alternative to resynchronization therapy in such patients [5,6]. The aim of this study was to evaluate bifocal pacing for cardiac resynchronization therapy in patients with severe heart failure and significant intraventricular conduction delay and to assess efficacy compared with biventricular pacing.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 5. Limitations
 6. Conclusions
 References
 
All patients indicated for cardiac resynchronization therapy according to the entry criteria listed in Table 1 were eligible for inclusion in the study. The local ethics committee approved the study and all patients gave written informed consent.


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  		Table 1 Inclusion criteria

 
Eligible patients underwent implantation of temporary bifocal pacing leads. Two quadrupolar electrophysiological catheters were introduced via the right femoral vein under local anaesthesia and were positioned in the right ventricular apex (RVA) and in the right atrial appendage (RAA). Another active-fixation lead (Pacesetter 1488T 58 cm) was introduced via the right internal jugular vein and fixed in the high right ventricular outflow tract (RVOT). The position was defined fluoroscopically: The lead was introduced under fluoroscopic guidance into the anteroposterior projection above the pulmonary valve. Then it was drawn below the pulmonary valve with a slight counter-clockwise rotation. This manoeuvre was controlled in both the anteroposterior (Fig. 1A) and left anterior oblique views (Fig. 1B) to ensure that the lead was oriented and screwed in septally, and not into the anterior or free right ventricular wall. Finally, the distance of the leads in the right ventricle was measured after calibration on the X-ray images. Following echocardiographic evaluation (see below), patients underwent implantation of a biventricular pacemaker. The mid-segments of the lateral or posterolateral branch of the coronary sinus were selected as target sites for implantation of the left ventricular (LV) lead in all cases.


Figure 01
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  		Fig. 1 Temporary bifocal stimulation in the anteroposterior projection (Panel 1A) and in the left anterior oblique view 45° (Panel 1B). Note the orientation of the RVOT lead to the interventricular septum (white arrow).

 
Haemodynamic measurements during bifocal and biventricular pacing were conducted using a pigtail catheter introduced via the left femoral artery into the left ventricle and aorta and connected to a pressure transducer. The catheter was flushed with saline infusion and heparin to ensure patency. The maximum rate of LV pressure rise (dp/dtmax) and aortic pulse pressure (Ao-PP) were measured in the basal state (intrinsic rhythm), and during right ventricular apical pacing (RVAP), right ventricular bifocal pacing (BFP), and biventricular pacing (BVP), i.e., RVAP+ LV pacing. All ventricular pacing was performed in VAT mode, i.e., atrial sensed AV synchronous stimulation at the intrinsic heart rate with AV delay set to 120 ms to ensure full pre-excitation of the ventricles. The order of haemodynamic measurements was randomly selected by a simple software routine. A steady state of 5 min was required before data were acquired in each modality. The values were measured three times and then averaged. Variability of measurements was calculated in each pacing modality and during basal state. Care was taken to exclude all premature cardiac beats from the measurement. As tip-manometer catheters were not used in this study, the percentage of dp/dtmax increase was calculated during bifocal and biventricular pacing modalities with respect to the basal measurements and the percentage, not absolute values, were used for statistical analysis.

QRS complex duration was evaluated on the surface 12-lead electrocardiogram (ECG) during bifocal and biventricular pacing (AV delay 120 ms) as well as in the basal state. The longest QRS complex in the precordial leads was used for QRS duration measurement.

2.1. Echocardiographic measurements
Standard two-dimensional (2-D), Doppler and tissue Doppler imaging (TDI) echocardiography were performed according to the guidelines of the American Society of Echocardiography [7,8] using a commercially available ultrasonographic system (Vingmed 7, GE Medical). All three modalities of left ventricular activation (i.e., basal state, bifocal pacing and biventricular pacing) were compared. Left ventricular ejection fraction (LVEF) was measured using the Simpson rule from apical 4- and 2-chamber views. Detailed echocardiographic recordings were obtained for off-line measurement of the following parameters on traditional pulsed wave (PW) flow Doppler recordings: the global CO interval (i.e., the interval lasting from the mitral valve closure to its reopening, which was measured from the end of the A-wave of the preceding cycle to the beginning of the E-wave of the subsequent cycle); the EA interval (i.e., the interval from the beginning of the E-wave to the end of the A-wave); the Q-A2 interval (i.e., the interval from the Q-wave on the surface electrocardiogram to the end of the aortic flow); the LVET (i.e., the left ventricular ejection time, measured as the duration of the aortic flow); the LPEP (i.e., the left ventricular pre-ejection time measured from the Q-wave to the beginning of the aortic flow). The Q-P2, RVET (right ventricular ejection time) and RPEP (right ventricular pre-ejection time) intervals were measured in a similar manner on pulmonary PW Doppler recordings. Aortic (VTIAO) and pulmonary (VTIPU) velocity time integrals were also calculated in each pacing modality and in the basal state. Myocardial performance index was calculated according to Tei [9].

The TDI method used in our study for evaluating resynchronization benefits has been described in detail elsewhere [10]. Briefly, TDI analysis was performed in curved M-mode colour and PW modalities. Five basal segments of the left ventricle (septal [IVS], inferior [INF], posterior [POST], lateral [LAT], and anterior [ANT]) were evaluated with respect to the regional events. We measured (1) the regional CO interval (i.e., the interval from the end of the regional A-wave of the preceding cycle to the beginning of the regional E-wave of the subsequent cycle) at the basal level of each of the above-mentioned left ventricular segments (COIVS, COINF, COPOST, COLAT, COANT, respectively), together with its three systolic components (regional isovolumic contraction time [ICT], regional left ventricular ejection time [LVET], and regional isovolumic relaxation time [IRT]); (2) the EA interval (i.e., the interval `from the beginning of the regional E-wave and the end of the regional A-wave in the same cycle); the Q-S1 interval (i.e., the interval from the Q-wave to the beginning of regional sustained left ventricular ejection) for each segment; and (3) the Q-S2 interval (i.e., the interval from the Q-wave to the regional sustained left ventricular ejection peak) for each segment. All standard and TDI echocardiographic measurements were made on three cardiac cycles and values were then averaged.

Each of the left ventricular segments was also evaluated qualitatively, and the contraction pattern was described as (a) I (synchronized), (b) IIA (unsynchronized to a lesser degree), (c) IIB (unsynchronized to a greater degree), (d) IIIA (dyskinetic, reversed early in systole), (e) IIIB (dyskinetic, reversed late in systole), and (f) IV (dyskinetic, entirely reversed in the whole systole).

2.2. Statistical analysis
Statistical analysis was performed using SPSS for MS Windows software. Baseline characteristics were summarized using appropriate descriptive statistics. Analysis of variance (ANOVA) was applied to compare repeated measurements of echocardiographic parameters in the basal state and during bifocal and biventricular pacing, with Bonferroni correction to adjust the p-values. Percentage haemodynamic improvement during different stimulation modes was compared by the one-way t-test and the results were verified by nonparametric Wilcoxon test. Dichotomous variables were compared using the {chi}2 test or Fisher's exact probability test where appropriate. Linear correlations were calculated by Pearson correlation coefficient. A p-value <0.05 was considered statistically significant.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 5. Limitations
 6. Conclusions
 References
 
Clinical and demographic data for the 50 patients included in the study are summarised in Table 2.


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  		Table 2 Clinical and demographic data for the study population

 
3.1. Haemodynamic measures
The LV dp/dtmax did not change significantly between the basal state and RVAP (1.02%, 95% CI –2.2-4.3%, p=0.53). In contrast, the LV dp/dtmax was increased during BFP compared to the basal state, but more prominent increase was achieved during BVP (Table 3). A similar mean increase in LV dp/dtmax during BFP was noted for IDCM and IHD patients. In the IHD subgroup, LV dp/dtmax increased by 12.5% (95% CI 7.1-17.9%, p<0.0001) and by 29.4% (95% CI 22.1-36.6%, p<0.0001) during BFP and BVP, respectively. In the IDCM subgroup, LV dp/dtmax increased by 14.7% (95% CI 7.5-21.8%, p<0.0001) and by 29.0% (95% CI 19.2-40.3%, p<0.0001) during BFP and BVP, respectively.


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  		Table 3 Heart rate, QRS width, haemodynamic and echocardiographic measurements in the basal state (intrinsic rhythm) and during bifocal and biventricular AV synchronous pacing

 
A strong positive correlation was found between the distance of the right ventricular apical and outflow tract leads and percentage of dp/dtmax increase in the IDCM patients (r=0.720, p<0.001, Fig. 2), but not in the IHD patients. The distance between the leads also correlated with the time interval from the sensed local right ventricular apical signal to a signal in the outflow tract (r=0.498, p<0.001).


Figure 02
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  		Fig. 2 Correlation between the distance of RVA and RVOT leads and increase in LV dp/dtmax during bifocal pacing in patients with idiopathic dilated cardiomyopathy.

 
In the IHD subgroup, there was no difference in acute haemodynamic changes in response to BFP between patients with an anterior myocardial infarction and those with an infarction at a different location, when the cut-off value for acute haemodynamic response was defined as ≥5% increase in LV dp/dtmax (58% vs. 70%, p=NS) or ≥10% (58% vs. 47%, p=NS). Of the 7 patients with delta LV dp/dtmax during BVP <10%, only one patient, responded positively to BFP (12.3% increase in LV dp/dtmax). There were also 8 patients (16%) from the whole study group, in whom the LV dp/dtmax during BFP was ≥LV dp/dtmax during BVP. Interestingly, 75% of these patients had IHD.

3.2. Echocardiographic parameters
Left ventricular ejection fraction increased significantly during BFP, but again the increase was more prominent during BVP. Global systolic contraction time (COGLOB) was significantly shortened both during BFP and BVP, thus prolonging the LV diastolic filling time (Table 3). Global myocardial performance index was also significantly decreased during both BFP and BVP.

Interventricular mechanical delay was decreased on BFP compared to the basal state values, but BVP produced an even shorter interventricular delay (Table 3). In all patients, the regional systolic contraction times (COSEP/LAT/INF/POST/ANT) were significantly shortened, corresponding with the prolongation of the respective regional diastolic filling times, during both BFP and BVP. The effect of BVP on regional systole shortening was more pronounced (Table 3). The regional myocardial performance index decreased significantly only during BVP (Table 4).


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  		Table 4 Regional myocardial performance indexes (Tei index) in the basal state (intrinsic rhythm) and during bifocal and biventricular AV synchronous pacing

 
In a multivariate analysis of the echocardiographic parameters, only the lateral regional CO interval (COLAT) in the basal state predicted an acute haemodynamic response to BFP (when defined as ≥10% increase in the LV dp/dtmax). Receiver operator curve identified a cut-off value of the COLAT interval less than 530 ms with 73% sensitivity, 64% specificity and 68% diagnostic accuracy for the response to BFP.

Qualitative patterns of LV segmental contraction significantly improved both during BFP and BVP (Table 5). While only 26% of the LV basal segments showed normal or less dyssynchronized type of contraction (type I or IIA) in the basal state, this number increased to 42% and 79% during BFP and BVP, respectively (p<0.001). Overall, BFP acutely improved qualitative contraction patterns of all basal segments of the LV in 37.6% (p<0.0001), while it remained the same in 48.4% of segments and worsened in 14% of segments. During BVP, however, the qualitative contraction patterns were acutely improved in 70% of segments (p<0.0001), 24.4% of segments remained the same and in 5.6% of segments worsened.


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  		Table 5 Qualitative left ventricular contraction (LV) patterns in the basal state and during bifocal and biventricular AV synchronous pacing. Each column represents a total of 250 LV segments (50 patients, 5 segment LV model) evaluated for the qualitative degree of dyssynchrony

 
3.3. QRS width and heart rate during haemodynamic measures
QRS width decreased significantly during both BFP and BVP (Table 3). The variation in heart rate between BFP and BVP was 0-10 bpm, with an average of 5.5±3.1 bpm.

3.4. Reproducibility of measures
Reproducibility of the LV dp/dtmax measurements was acceptable. Variability of the three measurements fluctuated between 0% and 2.9% (0.36±0.9%), 0% and 3.1% (0.73±1.23%), 0% and 3.7% (1.4±1.54%) and 0% and 3.6% (0.6±1.2%) in the basal state, RVAP, BFP and BVP, respectively. Overall variability of the LV dp/dtmax was 0.8±1.3%. Variability of the echocardiographic interval measurements was below 3% in the whole study population (≤10 ms in absolute values).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
5. Limitations
 6. Conclusions
 References
 
BVP has recently been proposed for the treatment of patients with advanced heart failure and significant electrical conduction delay. However, some studies have reported technically unsuccessful procedures in 5-13% of cases [2-4]. According to the analysis of the CONTAK CHF/CONTAK CD Biventricular Pacing study [4], the most frequent causes of coronary venous lead implantation failure were inability to cannulate the coronary sinus (6%), inability to obtain a stable pacing site (5%), inability to obtain adequate pacing threshold (1%), coronary sinus dissection/perforation (1%) and diaphragmatic stimulation (0.2%).

The concept of BFP, simultaneous AV synchronised pacing of the RVA and RVOT appears to overcome these pitfalls. The procedure is technically simple, quick and safe and similar to standard pacemaker implantation. The position of the RVOT lead can be easily controlled fluoroscopically and when using active-fixation leads has been shown to be stable, with excellent pacing and sensing parameters during long-term follow-up [11].

4.1. Haemodynamic benefit
The results of our study suggest that BFP may represent a valuable form of resynchronization therapy, though its acute haemodynamic benefit is clearly inferior to BVP. Thus, BFP should not represent the first line resynchronization strategy.

The significant acute haemodynamic response to BFP was only observed in approximately half of our study group, and was comparable in both IDCM and IHD patients. The positive effect of both BFP and BVP could not have been caused by AV delay optimization, since RVA pacing alone did not improve LV dp/dtmax when compared to the basal state. Since BFP can significantly preexcite anterior and inferior LV segments, optimal haemodynamic benefit was mainly observed in patients with a relatively shorter regional systolic interval of the LV lateral wall.

There are not much data in the literature on the acute haemodynamic effects of BFP. In a study of 14 patients with a mean LVEF 32±4%, Buckingham et al. [12] explored the effect of pacing at the RVOT, RVA and at both sites on systolic and diastolic function. The authors failed to show any significant change in LVEF, cardiac output and peak LV dp/dt during bifocal pacing. However, mean QRS width was only 107±32 ms (6/14 patients had left bundle branch block), suggesting that patients were unlikely to have significant inter- or intraventricular conduction delays which could be corrected by resynchronization therapy.

In our patients with IDCM, the distance between the right ventricular leads in the RVA and RVOT correlated strongly with the improvement in LV contractility, suggesting that the two wave fronts of activation of the left ventricle arising from both right ventricular leads should start as far away from each other as possible, in order to achieve the shortest total LV activation time and to improve haemodynamics. Lack of a similar correlation in IHD patients might be explained by less predictable impulse spreading in the left ventricle due to myocardial scarring post-infarction.

4.2. Long-term effect of bifocal pacing
In our study, we examined only acute haemodynamic changes during BFP which cannot automatically be translated into long-term benefits in terms of clinical improvement and/or left ventricular reverse remodelling. In patients with ischaemic or idiopathic dilated cardiomyopathy, the long-term effect of BFP has not been thoroughly investigated. In a study of patients with conventional indications for CRT, O'Donnell et al. [13] concluded that both patients with BVP and BFP experienced a similar improvement of clinical status. Although tissue Doppler indices of LV synchrony improved earlier in the biventricular group, the improvement was similar in both groups at 6 months. The major drawback of this study was that there were only 6 patients in the bifocal pacing group.

A substudy of the ROVA trial found no improvement in quality of life, functional class, exercise capacity, and ventricular function after 3 months, in 50 patients with bifocal pacing [14]. However, bifocal stimulation was not applied simultaneously, but with RVA-to-RVOT delay of 31 ms, and the study population consisted of patients with atrial fibrillation. Thus, it can be concluded that to date, we lack a prospective double-blind cross-over study evaluating the long-term effects of bifocal pacing on clinical status and/or left ventricular reverse remodelling.


   5. Limitations
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Limitations
6. Conclusions
 References
 
The major limitation of our study was that we did not use tip-manometer catheters during our haemodynamic measurements. However, we were meticulously careful about the patency of the 6 Fr pigtail catheters that were used for these measurements, which were flushed with heparin to prevent any blood clotting and dumping of the signal. We also expressed the LV dp/dtmax as a percentage of increase, avoiding direct comparison with absolute values.


   6. Conclusions
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Limitations
 6. Conclusions
References
 
Biventricular stimulation is superior to bifocal with respect to cardiac resynchronization parameters and acute improvement in LV contractility. Bifocal pacing should be considered for patients, in whom the implantation of an LV lead is not technically feasible, those who refuse to undergo surgical epicardial placement of the LV lead and/or are at a high risk for such procedures performed under general anaesthesia. In potential candidates, the duration of the regional systolic interval of the LV lateral wall should not exceed 530 ms. Electrodes in the right ventricle should be placed at the longest achievable distance. Further studies are needed to evaluate the long-term benefits of this simplified form of cardiac resynchronization therapy with regards to improved clinical status and cardiac function.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 5. Limitations
 6. Conclusions
 References
 

  1. Abraham W.T. Cardiac resynchronization therapy: a review of clinical trials and criteria for identifying the appropriate patient. Rev Cardiovasc Med (2003) 4:S30–S37.
  2. Bulava A., Lukl J. Resynchronization therapy in the treatment of congestive heart disease—a review of literature. Int Med Prax (2005) 7:229–236.
  3. Gras D., Leclercq C., Tang A.S., Bucknall C., Luttikhuis H.O., Kirstein-Pedersen A. Cardiac resynchronization therapy in advanced heart failure the multicenter InSync clinical study. Eur J Heart Fail (2002) 4:311–320.[Abstract/Free Full Text]
  4. Knight B.P., Desai A., Coman J., Faddis M., Yong P. Long-term retention of cardiac resynchronization therapy. J Am Coll Cardiol (2004) 44:72–77.[Abstract/Free Full Text]
  5. Giudici M.C. Right ventricular outflow tract pacing improves hemodynamics in patients with class III-IV heart failure and existing apical leads. Pacing Clin Electrophysiol (1998) 21:751. (Abs).
  6. Pachon J.C., Pachon E.I., Albornoz R.N., et al. Ventricular endocardial right bifocal stimulation in the treatment of severe dilated cardiomyopathy heart failure with wide QRS. Pacing Clin Electrophysiol (2001) 24:1369–1376.[CrossRef][Medline]
  7. Henry W.L., DeMaria A., Gramiak R., et al. Report of the American Society of Echocardiography Committee on nomenclature and standards in two-dimensional echocardiography. Circulation (1980) 62:212–217.[Free Full Text]
  8. Quinones M.A., Otto C.M., Stoddard M., Waggoner A., Zoghbi W.A. Doppler Quantification Task Force of the Nomenclature and Standards Committee of the American Society of Echocardiography. Recommendations for quantification of Doppler echocardiography: a report from the Doppler Quantification Task Force of the Nomenclature and Standards Committee of the American Society of Echocardiography. J Am Soc Echocardiogr (2002) 15:167–184.[CrossRef][Web of Science][Medline]
  9. Kim W.H., Otsuji Y., Seward J.B., Tei C. Estimation of left ventricular function in right ventricular volume and pressure overload. Detection of early left ventricular dysfunction by Tei index. Jpn Heart J (1999) 40:145–154.[CrossRef][Medline]
  10. Ansalone G., Giannantoni P., Ricci R., et al. Doppler myocardial imaging in patients with heart failure receiving biventricular pacing treatment. Am Heart J (2001) 142:881–896.[CrossRef][Web of Science][Medline]
  11. Res J.C., Bokern M.J., Vos D.H. Characteristics of bifocal pacing: right ventricular apex versus outflow tract. An interim analysis. Pacing Clin Electrophysiol (2005) 28:S36–S38.[CrossRef][Medline]
  12. Buckingham T.A., Candinas R., Attenhofer C., et al. Systolic and diastolic function with alternate and combined site pacing in the right ventricle. Pacing Clin Electrophysiol (1998) 21:1077–1084.[CrossRef][Medline]
  13. O'Donnell D., Nadurata V., Hamer A., Kertes P., Mohammed W. Bifocal right ventricular cardiac resynchronization therapies in patients with unsuccessful percutaneous lateral left ventricular venous access. Pacing Clin Electrophysiol (2005) 28:S27–S30.[CrossRef][Medline]
  14. Stambler B.S., Ellenbogen K., Zhang X., et al. Right ventricular outflow versus apical pacing in pacemaker patients with congestive heart failure and atrial fibrillation. J Cardiovasc Electrophysiol (2003) 14:1180–1186.[CrossRef][Web of Science][Medline]

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