Europace Advance Access originally published online on April 10, 2008
Europace 2008 10(5):574-579; doi:10.1093/europace/eun085
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ALTERNATIVE VENTRICULAR PACING SITES
Long-term outcomes in patients with atrioventricular block undergoing septal ventricular lead implantation compared with standard apical pacing
First Department of Internal Medicine, Cardiovascular Division, Academic Teaching and General Hospital Linz, Krankenhausstrasse 9, A-4020 Linz, Austria
Manuscript submitted 20 July 2007. Accepted after revision 11 February 2008.
* Corresponding author. Tel: +43 732 7806 6210; fax: +43 732 7806 6205.E-mail address: robert.hofmann{at}akh.linz.at
See page 572 for the editorial comment on this article (doi: 10.1093/europace/eun087)
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Abstract |
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Aims: Left ventricular function may be altered by right ventricular apical pacing. The aims of the study were to compare the long-term course of different parameters of left ventricular dysfunction in patients undergoing implantation of a dual-chamber pacemaker with the ventricular lead in a septal position vs. in a standard apical position.
Methods: We randomized 98 patients with atrioventricular block (AV-block) undergoing pacemaker implantation to positioning the ventricular lead in the high or mid septum (n = 53) or in the apex (n = 45) of the right ventricle. N-terminal pro-brain natriuetic peptide (BNP) levels, left ventricular ejection fraction (LVEF), and exercise capacity were analysed 3 days, 3 months, and 18 months after the implantation. The primary endpoints were the changes of these parameters from baseline to 18 months.
Results: Changes of BNP levels, LVEF, and exercise capacity from baseline to 18 months were statistically not different between septal and apical stimulation. The clinical occurrence or deterioration of overt heart failure was similar in both treatment arms.
Conclusion: With regard to different parameters of congestive heart failure, a septal stimulation site is not superior to conventional apical pacing in unselected patients undergoing pacemaker implantation for AV-block.
Key Words: Apical pacing, Septal pacing, Ventricular function, Congestive heart failure
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Introduction |
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Similar to what can be observed in a left bundle branch block, ventricular function may be altered by chronically pacing of the apex of the right ventricle. Previous data have shown that pacing the right ventricle can result in a reduction of left ventricular performance and in adverse clinical outcome.1
–5 There are some studies that suggest a possible role in the specific right ventricular pacing site with preliminary results in favour of a septal stimulation site.6–8 However, long-term clinical data are limited to non-randomized studies or investigations including relatively few patients.9–11 The aims of the study were to compare the long-term course of different parameters depending on left ventricular dysfunction in patients undergoing implantation of a dual-chamber pacemaker with the ventricular lead in a septal position vs. in a standard apical position. |
Methods |
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Patients with atrioventricular block (AV-block) undergoing elective permanent pacemaker implantation were eligible for study participation from May 2003 to December 2005. Inclusion criteria consisted of a symptomatic chronic II° or III° AV-block with a class I indication for implantation of a permanent pacemaker system according to the current guidelines.12
Patients had to have a 24 h pre-operative monitoring period revealing a permanent II° or III° AV-block and an unpaced ventricular rate below 50 bpm, thus guaranteeing a high proportion of ventricular pacing after implantation. Exclusion criteria consisted of overt congestive heart failure, use of intravenous diuretics prior to implantation or 3 days thereafter, recent (3 months) myocardial infarction, scheduled invasive cardiac procedure, a history of atrial fibrillation requiring cardioversion, suspected bi-nodal disease, clinically significant co-morbidity with an estimated life expectancy of <2 years, and the inability to perform a bicycle stress test. Patients were randomized to undergo permanent ventricular stimulation either in the septum or in the apex of the right ventricle. Randomization was performed in a simple envelope drawing. The primary endpoints of the study were the changes of plasma levels of N-terminal pro-brain natriuetic peptide (BNP), left ventricular ejection function (LVEF), and exercise tolerance from baseline to 18 months. Secondary endpoints consisted of the occurrence of overt congestive heart failure, mortality, and long-term safety of the alternative pacing site defined as non-necessity of lead repositioning, and stable values of lead impedance, R-wave, and pacing threshold.
We used conventional dual-chamber pacemakers without rate response functions (C50DTM, VitatronTM, Arnhem, The Netherlands), or pacemaker with inactivated rate response function (DDD mode) (EnpulseTM, MedtronicTM, Minneapolis, MN, USA). Steroid eluting bipolar leads came from the same manufacturers (Act Fix ICF09B and ICL08B, VitatronTM, and Novus 5076TM and Novus 5054TM, MedtronicTM). Backup atrial pacing was set at 50 bpm in all patients, thus providing effective ventricular-atrial-trigger pacing most of the time. All programmable functions for reduction of ventricular pacing (e.g. AV hysteresis) had to be programmed ‘off’. The AV delay was programmed after implantation according to the echocardiographical optimization protocol described in the CARE-HF study.13 BNP levels, echocardiography and physical stress test results were analysed 3 days, 3 months, and 18 months after implantation. The cumulative percentage of ventricular pacing was determined from stored pacemaker diagnostic data at each follow-up visit. Patients were treated with cardiovascular medication if indicated. Medication relevant to congestive heart failure (CHF) was recorded at the time of hospital discharge and at each follow-up visit. The study complies with the Declaration of Helsinki and was approved by our Institutional Review Board. Each patient gave written informed consent at least 24 h before randomization.
Pacemaker implantation technique
All procedures were performed in the electrophysiology laboratory. Two grams of cefazolin was given intravenously and 0.5–1 mg flunitrazepam orally at least 1 h before the procedure. Implantations were performed under local anaesthesia by two electrophysiologists who were experienced in permanent pacemaker implantation. In all cases, the right subclavian vein was used as access to the heart. Standard screw-in leads with a length of 52 cm were used for atrial implantation and fixed in the right atrial free wall or the right atrial appendage depending on intra-operative measurements. Patients randomized to the septal position underwent implantation of an active fixation lead. The primary target was the right ventricular outflow tract. The stylet was shaped to show a 60°–90° angle. Under postero-anterior fluoroscopy, the lead was advanced to a position near the pulmonary valve and then turned in a septal orientation as verified by an LAO view. If the targeted high septal position could not be reached despite two or three attempts of reshaping the stylet, a mid septal position was chosen (11 patients). The definition of a true high or mid septal position consisted of (i) leftward orientation of the lead confirmed by 45° LAO fluoroscopy plus (ii) a negative deflection of lead I and positive initial R-waves of the paced ventricular complex in leads II and III.14–16 The definition of a conventional apical position of a passive-fixation ventricular lead required fluoroscopic superimposition of the tip of the lead with the diaphragm. All measurements during pacemaker implantation were performed with the Carelink 2090 AnalyserTM (MedtronicTM). A pacing threshold of <1 V, an R-wave >5 mV, and a resistance of 500–1500 
were required for a successful implantation. The P-wave had to be >1 mV. After suture of the leads to the subcutaneous tissue, the final measurements were analysed immediately before connecting the leads to the generator to avoid artifacts resulting from injury current of the screw-in leads. Implantation duration was defined as the time between skin incision until suture.
For measurement of the paced QRS duration, a standard 12-channel surface ECG at 25 mm/s speed was recorded with the digital ECG writer AT 2 Plus (SchillerTM, Baar, Switzerland). The software of this device allows accurate determination of cardiac intervals and those values were taken for statistical analysis. The QRS duration defined as the length of time from the beginning of the pacing artifact to the end of the QRS complex was automatically measured from the mean duration of all 12 leads.
Echocardiography protocol
Transthoracic echocardiography was performed using a standard echocardiographic Doppler system (Sonos 7500TM, SiemensTM). Patients were examined shortly after, 3 months after, and 18 months after their pacemaker implantation. Left ventricular ejection fraction was determined by biplane measurements using the modified Simpson’s formula.
The programming of the AV delay depended on echocardiography guided optimization according to the methods used in the CARE-HF study:13 in summary, the AV delay was set at a value that provides maximum separation of the E- and A-waves, representing passive ventricular filling and atrial contraction, respectively.
Exercise stress test
A bicycle exercise stress test was performed according to a standardized protocol. The work load was elevated every 2 min in 25 W steps starting at 25 W. During the test, heart rate, blood pressure, and heart rhythm were monitored continuously. The test was discontinued as soon as the patients had reached their personal limits or if symptoms of coronary ischaemia or an inadequate blood pressure response during incremental resistance increase were observed.
Functional status
Patients were thoroughly interrogated and examined in order to detect signs or symptoms of CHF. Clinical examination and documentation of cardiovascular medication was determined by physicians unaware of the randomized pacing site.
Statistical analysis
All variables were summarized using frequency distributions for categorical variables and mean ± SD for continuous variables. Comparisons between groups (septal pacing site or apical pacing site) were performed using the non-parametrical Mann–Whitney U-test for continuous variables and 
2 test for categorical variables. Data were analysed on an intention-to-treat basis. P-values of 
0.05 (two-tailed) were considered statistically significant.
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Results |
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Patient population
We randomized 98 patients (mean age 72 years, 68 men) who underwent pacemaker implantation for symptomatic AV-block. Table 1 shows clinical characteristics of the overall patient population.
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Implantation procedure
The implantation success rate in both groups was 100%. There was no crossover from one to the other position. In addition, the desired values for pacing threshold, R-wave amplitude, and resistance could be obtained in all patients. Complications consisted of one case of lead dislodgement in the apical position group requiring re-operation 3 days after the initial procedure and one case of a pocket haematoma in the apical position group, which was treated conservatively. Procedure durations were statistically not significantly different, but with a trend towards shorter procedure times in the septal position group (45 ± 4 vs. 51 ± 5 min). Fluoroscopy times in the septal group were shorter (4.4 ± 2 vs. 5.6 ± 3 min), but again the difference did not reach statistical significance.
Pacing measurements
Capture threshold, lead impedance, and R-wave sensing were measured during implantation and at each follow-up visit. The lead impedance was significantly lower in the septal group during implantation and remained unchanged throughout all follow-up visits. Septal pacing was associated with a significantly shorter QRS than apical pacing (Table 2).
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Parameters of left ventricular dysfunction
Laboratory and echocardiographic data were available in all patients. The attempted exercise test could be performed in 92 patients (94%). Patients allocated to the apical pacing group had higher BNP values at baseline, but LVEF and exercise capacity were not statistically different in either group. In addition, use of cardiovascular medication regarding CHF was similar (Table 1).
Follow-up
All patients came to their scheduled follow-up check-ups after 3 months and 85% after 18 months. Clinically, overt CHF during follow-up occurred in three patients of each group. In all of these patients, LVEF was 40% at the time of pacemaker implantation. Upgrade to biventricular stimulation was performed in one patient in each group, both of them had wide QRS complexes at baseline. The other two patients in each group were treated conservatively for clinical or personal reasons. During follow-up, none of the patients developed persistent or permanent atrial fibrillation.
Nine patients died during follow-up (five septal and four apical). In each group, two patients died from heart failure. Both patients had a LVEF of 40%, and one had a wide QRS ECG at the time of implantation. Sudden cardiac death occurred in three patients (two septal and one apical). All three patients died suddenly at home, and no autopsy was performed. The remaining two patients died of cancer.
Pacing measurements
Lead impedance, R-wave, capture threshold, and QRS duration remained stable throughout the follow-up period (Table 2). Most importantly, no clinical lead failure could be observed.
Pro-brain natriuetic peptide, left ventricular ejection fraction, and exercise capacity
Elevated BNP levels in both treatment arms dropped during the first months after implantation and rose marginally during further follow-up (Figure 1). Left ventricular ejection fraction and exercise capacity remained more or less stable (Figures 2 and 3). Patients randomized to apical stimulation with narrow QRS at baseline revealed a lower statistical distribution of BNP at baseline (mean: 1001, SD: 1599, interquartile range: 934) compared with patients with wide QRS complexes (mean: 2200, SD: 2088, inter-quartile range: 2831). Similar results regarding narrow QRS patients vs. wide QRS patients were found in the septal stimulation group: mean: 736 vs. 1176, SD: 737 vs. 1485, and inter-quartile range: 1058 vs. 1231. However, the decrease of BNP values over time was similar when compared with the entire patient population.
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Discussion |
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This single centre study compared the long-term effects of conventional apical vs. high or mid septal pacing for chronically AV-Block. After 18 months, no statistically significant difference in clinical outcomes was observed. To detect subclinical signs of congestive heart failure, various clinically easily accessible parameters depending on CHF were measured. In order to approach the topic from as many different views as possible, very dissimilar parameters were chosen for evaluation. A bicycle stress test is a commonly accepted method to examine cardiac capacity and accurately reflects the work load a cardiac patient can endure. Despite some restrictions regarding inter-observer variability, LVEF estimation using Simpson’s formula can be counted as a routine method to determine systolic left ventricular function, especially when always performed by the same investigators. BNP was chosen as a 100% investigator independent laboratory method recognized as a valid method to follow heart failure patients.17
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Several experimental studies have been conducted to evaluate the impact of the position of the right ventricular lead in the pacemaker population.19–21 Most of the clinical studies were accomplished in patients undergoing biventricular pacemaker implantation. However, data are still conflicting. Riedlbauchová et al.22 found a significant beneficial effect in positioning the right ventricular lead in the mid ventricular septum, especially in the subpopulation of patients with non-ischaemic cardiomyopathy. These results could not be confirmed by other investigators who did not observe similar results in a comparable study cohort.23
Regarding dual-chamber right atrial and right ventricular pacing, data are more limited. The intraventricular conduction delay was recognized to serve as a prognostic marker in chronic heart failure. Consequently, early data showed that a shorter QRS duration can be accomplished by a septal positioning of the permanent ventricular pacing lead.24 Some attempts have been made to corroborate the theory that the left ventricular function can be preserved by inserting the right ventricular lead in a certain position, but some questions remain unanswered. Tse et al.7 conducted a study including 24 patients who were divided in two groups, similar to our 98 patients. Differences regarding dipyridamole thallium myocardial scintigraphy and radionuclide ventriculography could be demonstrated after 18 months. However, the important issue of left ventricular function remained untouched. Similarly, Yu et al.8 revealed echocardiographically detectable differences between different pacing modes within 72 h after pacemaker implantation. Victor et al.25 showed also promising but short-term results. Reports on long-term results are limited. Vlay et al. reported on a 9 year experience of right ventricular outflow tract pacing revealing an excellent success rate and stable lead measurements over time. Their findings were similar to ours.10 However, they did not have a comparable group of patients undergoing apical stimulation, either.
Another important issue to consider is the specific pacing site within the right ventricular septum. As Lieberman et al.26 pointed out, the different position of the septal pacing lead could explain the different results reported in literature. Occhetta et al. used a stimulation site which we consider the most proximal to the HIS bundle of all cited studies. He reported excellent results showing a similar QRS complex during intrinsic ventricular activation and parahisian pacing.9 In our study, stimulation sites in the high ventricular septum and the mid septal area were both attributed to the septal stimulation group, thus guaranteeing a 100% implantation success rate. A post hoc splitting in two separate groups does not seem reasonable, since the number of patients in each group is too small to provide reliable conclusions.
Our study cohort consisted of patients with preserved left ventricular function as well as patients with depressed ejection fraction, thus representing a real world scenario of patients requiring pacemaker implantation due to acquired AV-block. The results of our study demonstrate that heart failure presumable caused by asynchronous right ventricular pacing cannot be prevented by a septal pacing site. However, the majority of our patients had apparently normal hearts with a LVEF of >40%. Thus, the results of the study cannot be generalized to all patients with left ventricular dysfunction requiring ventricular pacing. Among the key aspects of CHF following pacemaker implantation is the pre-existing left ventricular function, numerous clinical trials revealed unfavourable effects of asynchronous apical ventricular pacing in the subset of patients with previously depressed left ventricular function.
Consistent to the results of other investigators, a septal fixation of the ventricular pacing lead was not associated with increased short- or long-term complications when compared with conventional apical pacing. In addition, implantation times and fluoroscopy times were shorter in the septal group. Therefore, this stimulation site becomes more and more the default position in our institution although our study did not reveal a significant benefit. Keeping in mind that there might be at least a subgroup of patients who could do better with septal pacing, the non-inferiority of septal pacing could become an argument for a widespread use of this stimulation spot.
Limitations
Despite the higher number of patients in our study compared with former trials, we were not able to judge upon the clinical impact of septal vs. apical pacing due to a low event rate. The study was not powered enough to reveal potential different clinical outcomes. The baseline values for BNP were higher in the apical pacing group most likely by chance. However, an early beneficial effect occurring within the first hours after implantation cannot be excluded. Exercise capacity as well as estimation of LVEF contains methodical limitations.27
Conclusions
This study confirmed the feasibility and safety of permanent septal pacing as a routine procedure in patients with AV-block. Septal pacing is associated with a shorter paced QRS complex, compared with apical pacing. However, our investigation does not support the assumption that septal pacing would be superior to apical pacing in unselected patients undergoing pacemaker implantation for AV-block with regard to protecting patients from developing CHF, even over a long follow-up period. It might be that a larger study including solely patients with severe depressed left ventricular function and comparing only high septal stimulation sites to conventional apical pacing would come to another conclusion. However, before such data eventually become available, we suggest that patients with pre-existing LV dysfunction should preferentially be treated with resynchronization therapy.28,29
Conflict of interest: none declared.
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Europace 2008 10: 572-573.[FREE Full Text]
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