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First prospective, multi-centre clinical experience with a novel left ventricular quadripolar lead

Johannes Sperzel, Wilfried Dänschel, Klaus-Jürgen Gutleben, Wolfgang Kranig, Peter Mortensen, Derek Connelly, Hans-Joachim Trappe, Karlheinz Seidl, Gabor Duray, Burkert Pieske, Jochem Stockinger, Giuseppe Boriani, Werner Jung, Richard Schilling, Linda Saberi, Benoit Hallier, Marcus Simon, Christopher A. Rinaldi
DOI: http://dx.doi.org/10.1093/europace/eur322 365-372 First published online: 11 October 2011


Aims Cardiac resynchronization therapy (CRT) is sometimes complicated by elevated pacing thresholds and phrenic nerve stimulation (PNS), both of which may require that the coronary sinus lead be repositioned. The purpose of this study was to evaluate the performance of a novel quadripolar electrode lead and cardiac resynchronization therapy-defibrillator (CRT-D) device that enables electrical repositioning, potentially obviating a lead reposition procedure.

Methods and results Patients indicated for CRT were enrolled and received a quadripolar electrode lead and CRT-D device (Quartet®model 1458Q and Promote Q®; St Jude Medical, Sylmar, CA, USA). Electrical data, and the presence of PNS during pacing from each left ventricular (LV) configuration, were documented at pre-hospital discharge and at 1 month. Seventy-five patients were enrolled and 71 were successfully implanted with a Quartet®lead. Electrical measurements were stable over the follow-up period. Ninety-seven per cent (64 of 66) of patients had one or more programmable configurations with a threshold <2.5 V and no PNS vs. 86% (57 of 66) if only conventional bipolar configurations were considered. Physicians were able to use the increased programming options to manage threshold changes and PNS.

Conclusion The new quadripolar electrode LV lead provides more programming options to address common problems faced when managing CRT patients. Electrical measurements from new vectors are comparable with conventional configurations. Furthermore, 11% of patients in the study suffered PNS on all conventional bipolar vectors.

  • Cardiac resynchronization therapy
  • Quadripolar lead
  • Left ventricular pacing
  • Phrenic nerve stimulation
  • LV lead complications


Heart failure is the leading cause of mortality, morbidity, and hospitalization in patients aged 60 years and above.1Cardiac resynchronization therapy (CRT) can produce significant clinical benefits including: reduced mortality, improvements in patients' symptoms, quality of life, and reduced heart failure hospitalization.27The European Society of Cardiology now recommends CRT in a broad population of patients with heart failure.8Cardiac resynchronization therapy is accomplished by pacing from a right ventricular (RV) lead and left ventricular (LV) lead usually placed in a tributary of the coronary sinus (CS) via a trans-venous approach.9Over the past decade, improvements in LV lead technology have been driven by the need to better manoeuvre within the cardiac venous anatomy and to reach a stable position which provides an acceptable pacing threshold and avoids phrenic nerve stimulation (PNS). Leads have become progressively thinner and more manoeuvrable and provide bipolar electrode rather than only unipolar pacing.10

Despite these improvements, the following challenges are sometimes encountered during and after CRT device implant: placement of the lead in the target vein, inability to find a stable position with acceptable pacing thresholds (particularly at points that are proximal within a vein branch), LV lead displacement, increased pacing thresholds after implantation, PNS during and following implantation.1115These potential complications can be mitigated at implant by repositioning the lead and managed post-implant by exploring limited programming options such as changing the pacing vector or reducing the pacing output to avoid PNS, which sometimes means compromising the output safety margin. However, sometimes, these challenges require that an additional invasive procedure be performed to physically reposition the lead, that a surgical procedure be performed to place a lead on the LV epicardium, or that CRT be discontinued (LV pacing disabled). A recent study by Forleo et al.16showed that use of a novel quadripolar electrode lead resulted in low rates of lead dislocation and PNS. Which suggests that the use of this lead may allow clinicians to address PNS and elevated pacing thresholds without the need to physically reposition the lead.

This prospective observational study, sponsored by SJM international Inc., is the first multi-centric evaluation of the acute performance of a new quadripolar pacing technology (Quartet™ model 1458Q and Promote Q®; St Jude Medical, Sylmar, CA, USA) allowing for up to 10 programmable LV pacing vectors and which represents the latest evolutionary step in LV lead technology.


Study devices

The Quartet®Model 1458Q (St Jude Medical) is a new quadripolar lead designed to pace the left ventricle from the CS venous system (Figure 1). The Quartet®lead is a pre-shaped, quadripolar electrode, over-the-wire LV lead that can accommodate the use of either a stylet or a guidewire and is available in lengths of 75, 86, or 92 cm (Figure 2). The LV lead body has a maximum diameter of 4.7F with ring electrode diameters of 5.1F and provides pacing capability from four titanium nitride-coated platinum–iridium alloy electrodes (tip and three rings). The three ring electrodes are located 20, 30, and 47 mm from the distal tip electrode. The lead is insulated with 100% Optim®insulation. Using different cathode/anode combinations of these four electrodes and the RV coil, 10 pacing configurations are programmable, including 6 bipolar configurations (when both cathode and anode are located on the Quartet®lead) and 4 extended bipolar configurations (when RV coil is used as the anode electrode). In this study, the quartet lead was connected to the Promote Q®model CD3221-36 cardiac resynchronization therapy-defibrillator (CRT-D) device (St Jude Medical), which is equipped with a new IS4 header.

Figure 1

Example of a coronary sinus venogram and final position of the quartet lead.

Figure 2

Close-up of the lead with electrode distances.

Patient population

Consecutive patients with a standard indication for CRT-D system implantation and who fulfilled all of the inclusion and none of the exclusion criteria were consented and enrolled prior to device implant at 15 centres in 5 European countries between October and November 2009. Following successful implantation, patients were seen prior to hospital discharge and at 1 month post-implant (±7 days). The study was conducted in accordance with the declaration of Helsinki and approved by the appropriate ethics committees. All patients provided written informed consent. Patients were ineligible to participate if they had previously been implanted with a LV pacing lead, had a life expectancy of <6 months, were participating in a clinical investigation that included an active treatment arm, were pregnant, or were <18 years of age. Patient demographic details were collected at enrolment.

System implant and data collection

Implantation of the Promote Q®CRT-D device and the Quartet™ LV lead was attempted in all participants per standard clinical practice. The protocol allowed for the implantation of any commercially available right atrial (RA) pacing leads or RV pacing/defibrillation leads.

At implant, lead impedance, signal amplitude, and capture threshold (at pulse width of 0.5 ms) were recorded for RA and RV leads and capture threshold and lead impedance of the traditional bipolar vector (Distal 1 to Mid 2) was recorded. Additional procedural data recorded at implant included: the number of times and reasons that the LV lead was repositioned prior to final lead placement; the lead/delivery system handling characteristics; procedure time and fluoroscopy time. The protocol did not define testing of all lead vectors or request that any challenges (e.g. PNS) be addressed using electrical repositioning so that the implant procedure did not differ from that of a standard LV lead. Investigators were not restricted from testing other vectors or using electrical repositioning if they wished but the incidence of these approaches was not documented.

Before hospital discharge and at 1 month post-implant, LV capture thresholds and lead impedances were measured for all 10 pacing configurations. The presence of PNS at 7.5 V and 0.5 ms pulse width was determined for all 10 vectors at both visits, PNS thresholds were determined at the 1-month visit.

At each visit, final programming of the LV pacing configuration was left to the judgement of the physician.

Usable programmable pacing configurations

In order to compare the available vectors a pacing configuration was defined as usable if PNS was not present at a pacing output of 7.5 V and the measured pacing threshold was less than or equal to 2.5 V.

Statistical analysis

Numbers of usable pacing vectors available in conventional vs. quartet vectors were compared using a McNemers test. A mixed model was used to compare the phrenic nerve thresholds. A generalized estimating equation (GEE) model used to compare the presence of PNS between different vectors. A pair-wise comparison was conducted with the three conventional vectors against the five new quartet vectors. In all tests a Pvalue of <0.05 was considered significant. Continuous variables are summarized as mean ± SD and categorical variables are summarized by the count and a portion (%). All tests were carried out in statistics software SAS, version 9.2, and Stata data analysis software (Stata Corp. LP); and were performed by the study sponsor.


Population characteristics

Seventy-five patients whose mean age was 66 ± 10 years were enrolled in this study. The patient population was predominantly male (80%) and had an ischaemic heart disease aetiology (67%). The mean left ventricular ejection fraction was 27 ± 9%. Sixty-eight per cent of patients were scheduled to receive de novodevice implants and 32% were to receive a CRT-D upgrade from a pacemaker or an implantable cardioverter defibrillator (ICD).

Cardiac resynchronization therapy-defibrillator systems were implanted successfully in 71 patients and each patient completed the pre-discharge visit. Sixty-six patients had complete data sets at the 1-month follow-up. One month electrical data were not included from: one patient because they were measured incorrectly; two patients who did not attend that visit, and two patients who died during the interval between discharge and the 1-month follow-up visit.

Procedural data

Procedural data are summarized in Table 1. The overall implant success rate was 95% (71 of 75). Implanting physicians reported the final LV lead position within the first choice target vein in 78% (55 of 71) of cases.

View this table:
Table 1

Procedural data

LV final lead position (%)
 Posterior lateral35
 Anterior lateral9
Vascular access (%)
 Left subclavian77
 Right subclavian6
 Left cephalic4
Procedure times (min ± SD)
 Skin to skin103 ± 54
 CS cannulation to final LV lead placement33 ± 47
 Fluoroscopy19 ± 15
LV lead placement in first choice target vein (%)78
Overall implant success rate (%)95

Five first implant attempts were unsuccessful. In one of the failed cases, a second implant procedure resulted in the successful placement of the LV lead.

Twenty-six patients (37%) required a total of 33 lead repositioning attempts during implant due to the following (some patients required multiple repositions): PNS (5), unsatisfactory pacing thresholds (12), poor lead stability (7), or other causes (9).

Investigators were asked to rate several implant parameters related to the patient's anatomy, lead manoeuvrability, and the novel device header as ‘easy’, ‘normal’, or ‘difficult’. Overall, the patient's native anatomy was rated as difficult in 42% of implant cases. Lead manoeuvrability was rated easy or normal in 91% of implants. Visibility of the LV lead in the device header, set screw tightening, and insertion of the LV lead into the IS4 socket was rated easy or normal in 99% of all implants.

Electrical performance

At implant, the mean LV capture threshold and lead impedance for the traditional bipolar vector (Distal 1 to Mid 2) was 1.4 ± 1.4 V and 995 ± 254 Ω, respectively.

Capture thresholds and lead impedances were measured for all 10 vectors at pre-discharge (up to 7 days post-implant) and 1-month follow-up (Table 2). Electrical measurements were stable between pre-discharge and the 1-month follow-up across all vectors. Left ventricular pacing capture thresholds at 1 month and pre-discharge were not significantly different in any vectors (P> 0.05) except for Mid 2 to RV coil. In this configuration average threshold at 1 month was 1.0 ± 1.1 V, 0.3 V lower than that at pre-discharge 1.3 ± 1.3 V (P= 0.02), although this is not considered to be a clinically significant difference.

View this table:
Table 2

Electrical performance of all vectselect Quartet™ pacing configurations at pre-discharge and 1-month follow-up

Configuration Pre-hospital discharge1 month
Capture threshold at 0.5 ms (V)Impedance (Ω)Capture threshold at 0.5 ms (V)Impedance (Ω)
Conventional configurations
 Distal 1 to Mid 21.4 ± 1.3933 ± 2241.3 ± 1.2977 ± 237
 Distal 1 to RV coila1.3 ± 1.3583 ± 1231.0 ± 1.1576 ± 130
 Mid 2 to RV coila1.5 ± 1.2431 ± 1491.5 ± 1.1499 ± 119
VectSelect Quartet™ configurations
 Distal 1 to Proximal 41.4 ± 1.4909 ± 1811.3 ± 1.3942 ± 203
 Mid 2 to Proximal 42.1 ± 1.8749 ± 1932.3 ± 1.6871 ± 186
 Mid 3 to Mid 22.7 ± 2.2738 ± 2162.7 ± 1.6883 ± 192
 Mid 3 to Proximal 43.1 ± 2.5720 ± 1633.2 ± 2.2869 ± 191
 Proximal 4 to Mid 23.7 ± 2.4761 ± 2023.7 ± 2.2888 ± 197
 Mid 3 to RV coila2.5 ± 2.4419 ± 992.4 ± 2.1495 ± 120
 Proximal 4 to RV coila3.5 ± 2.7400 ± 1093.3 ± 25443 ± 106
  • aDenotes RV coil cathode.

The mean pacing thresholds for the novel quartet vectors ranged from 1.3 to 3.7 V. The results are reported for the following two groups of pacing configurations: conventional configurations (exclusively using Distal 1, Mid 2, and RV coil) and new VectSelect Quartet™ configurations (any vectors using Mid 3 or Proximal 4 electrodes).

Incidence of phrenic nerve stimulation when pacing at 7.5 V

The overall occurrence of PNS in any vector was between 14 and 23% at pre-discharge and between 11 and 25% at 1 month (Table 3). It is notable that during the 1-month visit, the incidence of PNS was higher in the three conventional pacing configurations (23–25%) than the incidence of PNS in five of the seven quartet only vectors (11–14%), a pair-wise comparison was conducted with the three conventional vectors against the new quartet vectors which showed a trend towards less PNS in the new vectors than in the conventional vector Mid 2 to RV coil (P< 0.05 on all five comparisons). There was no significant difference between the incidence of PNS on any vectors (P= 0.3311) when all were compared using a GEE model. There was no significant difference between the phrenic nerve threshold in any of the 10 vectors (P= 0.1663) when all vectors were compared using a mixed model, indicating that PNS is present in different vectors across the population and there is no trend towards one vector which performs better.

View this table:
Table 3

Incidence of phrenic nerve stimulation at pre-discharge and 1 month

ConfigurationPre-discharge1 month
Presence of PNS at 7.5 V (%)Presence of PNS at 7.5 V (P= 0.1633) (%)PNS threshold at 0.5 ms (V) (P= 0.3311)
Conventional configurations
 Distal 1 to Mid 217234.5 ± 1.5
 Distal 1 to RV coila17233.6 ± 2.1
 Mid 2 to RV coila18273.6 ± 1.9
New VectSelect Quartet™ configurations
 Distal 1 to Proximal 416235.0 ± 2.1
 Mid 2 to Proximal 416143.3 ± 2.2
 Mid 3 to Mid 214124.8 ± 2.2
 Mid 3 to Proximal 418125.2 ± 2.3
 Proximal 4 to Mid 218115.3 ± 1.5
 Mid 3 to RV coila23214.4 ± 1.9
 Proximal 4 to RV coila14124.7 ± 2.0
  • aDenotes RV coil cathode.

Use of programmable pacing configurations

At 1 month, 64 of 66 patients (97%) had one or more usable configuration including configurations only available on the quartet lead (one patient had a pacing threshold of 3 V and one had a pacing threshold of 3.8 V), whereas only 57 of 66 (86%) patients had usable conventional configurations this showed a trend towards better available pacing configurations with quartet than with bipolar configurations (P= 0.0082). The test was performed using McNemar's test. One of these had a threshold of 4.3 V and six had thresholds >7.5 V (Figure 3). Eight of 66 (12%) patients exhibited PNS on all conventional vectors. On an average 5.8 ± 2.7 [1–10] configurations were usable per patient (bipolar: 3.4 ± 1.8, bipolar using RV coil: 2.4 ± 1.2, conventional: 2.1 ± 1.1, new quartet: 3.7 ± 2.1). In 10 of 66 (15%) patients, all 10 configurations were usable.

Figure 3

Number of usable configurations per patient.

Post-implant, the final programmed pacing vector was unique to the Quartet®in 20 of 66 (29%) patients. The rationale for vector selection was reported as absence of PNS in 14 of 66 (21%), best pacing threshold in 37 of 66 (56%), or a combination of best threshold and absence of PNS in 15 of 66 (23%). Although in these cases investigators chose the new vectors for the reasons given above, it is likely that conventional vectors would have been acceptable in some of these patients and the authors do not here suggest that this is a reflection of changes in clinical practice. At 1 month, 16 of 66 (24%) patients left the study programmed to a unique Quartet®lead pacing vector, these included the previously mentioned 6 patients with PNS on all conventional vectors. The rationale stated for choosing the novel configurations for final programming at 1 month were: best pacing threshold or impedance values in 9 of 16 (56%), combination of freedom from PNS with a low pacing threshold in 5 of 16 (31%), and no change from the previous visit's final configuration in 2 of 16 (13%). Eight of the 10 possible configurations were utilized for final programming at pre-discharge and 1-month follow-up.

Adverse events

There were two deaths reported during the course of the study, each prior to the 1-month visit. It is considered unlikely that the two deaths were related to the system, procedure, or study, although their occurrence within 1 month of the procedure means that a relationship to the procedure cannot be completely ruled out. One patient died suddenly following the rupture of a previously unknown aortic aneurysm and the second following cessation of active treatment after development of untreatable slow VT.

There were four reported lead implant failures due to the following reasons: inability to cannulate CS (1), CS dissection (1), high impedance (>2000 Ω) on all vectors (1), and unsatisfactory pacing thresholds (>10 V) in all vectors (1). Analysis by the manufacturer of the latter two leads found both leads to be operating within defined tolerances in all tests, suggesting that both of these suspected failures were related to testing cables connecting the leads to the pacing system analyser. However, these disposable items were not recovered for examination. The implanting physician who experienced high lead impedances decided that as the procedure had been complicated and long he would reschedule the LV implant to another day. As there were no IS-4 socket plugs it was not possible to implant a Promote-Q device and try again with another quartet lead so that the patient received a standard bipolar CRT-D. Similarly, for the patient with high thresholds the physician tried five lead positions and measured high thresholds at each. He then decided to implant a standard bipolar CRT-D with the LV port plugged and referred the patient for an epicardial lead placement at a later date.

There were two further events involving the LV lead, one quartet lead was replaced during the procedure as the guidewire could not be advanced through the lead lumen, analysis of this lead showed that a section of the guidewire polytetrafluoroethylene coating had been lost and lodged in the lead lumen. A second lead displaced post-implant leading to a threshold rise and PNS that required lead repositioning.

Although there were 3 of 71 (4.3%) issues related to the LV lead, all affected leads were thoroughly tested and investigated by the manufacturer who detected no issues which would suggest any problems with the safety or performance of the lead. There were no further adverse events involving either the device or the LV lead during the post-implant follow-up period.


Cardiac resynchronization therapy is a recognized and rapidly expanding therapy for heart failure: the recent RAFT study showed that CRT-D reduces death and heart failure hospitalization and all-cause mortality in some New York Heart Association II patients indicated for ICD implantation.17Indications for CRT had already been expanded this year by the European Society for Cardiology8prior to this new clinical publication.

With such increases in indications and resultant implants there comes a greater need for innovative technologies aimed at assisting the implanter and managing patients during follow-up.

Challenges and decisions faced at implantation

Although 60–70% of patients receiving CRT respond to therapy, LV leads cannot be implanted in up to 10% of patients.5,11,15These implant failures are not due to patient selection but rather challenges posed by anatomy leading to lead stability problems, PNS, and poor electrical measurements.12,13Lead repositioning in the same side-branch (in 21%) or lead positioning in other CS side-branches (also in 21%) may be needed in case of unsatisfactory electrical measurements.18

The Quartet®quadripolar electrode lead and Promote Q®CRT-D device provide an opportunity to optimize CRT response and minimize PNS by programming pacing from 1 of 10 bipolar electrode configurations (rather than 3) associated with the best electrical performance. In this study amplitude threshold measurements were better in conventional vectors (using the tip electrode as a cathode) than on the novel vectors. The reason for this is unclear, but it could be due to some of these electrodes being situated more proximally in the vein which may mean that contact with the myocardium is less good. It should be noted that these thresholds are still within acceptable ranges and when the absence of PNS on these vectors is also considered the vectors could still be preferable to a distal vector, which has a low threshold but exhibits PNS.

Acute haemodynamic changes have been observed when measurements are taken during stimulation at different LV sites,19,20indicating that not all LV pacing sites confer the same benefit to CRT patients. Research has suggested that optimizing lead positions could lead to improved CRT response rates. One study showed that patients with leads placed concordantly to the site of latest mechanical activation had better long-term clinical outcomes and more LV reverse remodelling than those with discordantly placed leads.14Further benefits have been shown when comparing apical and basal pacing sites;21variations in inter-electrode spacing;22variations in LV electrical delay;23and stimulating from sites away from ischaemic scaring.24,25

There is high variability between the optimal pacing sites in different patients14,24and the use of a quadripolar electrode lead could assist operators in stimulating otherwise hard to reach proximal positions without compromising lead stability. The quadripolar electrode lead also provides the opportunity for further site optimization post-implantation without the need for an invasive repositioning procedure.

Challenges in managing common cardiac resynchronization therapy problems after implantation

Challenges to the management of LV leads do not end following a successful implant. In many patients PNS is not identified until after the implant procedure when movement and postural changes bring the pacing lead into closer contact with the phrenic nerve. Currently, some of these patients can be managed by pacing the LV without a satisfactory safety margin (i.e. pacing close to the amplitude threshold) but many can only be managed via a further invasive procedure (associated with a not insignificant infection risk) to reposition the lead and if this approach is not successful then a minor surgical procedure may be indicated to place a lead on the epicardial surface of the heart. In some cases, where further invasive procedures may be contra-indicated, switching off LV pacing and so withdrawing resynchronization therapy is necessary.13In a study by León et al.26published in 2005 showing complications from three large studies enrolling 2078 patients, 1.2% suffered PNS requiring lead repositioning or replacement. In a more recent study by Crossley et al.27published in 2010, 2.8% of 385 patients experienced PNS requiring an intervention following the implant of a Starfix active fixation lead (Medtronic, Minneapolis, MN, USA), 15% of patients in this study experienced PNS but only a small number of these required lead revision or repositioning.

In this study, we show that 11% of patients had PNS and high pacing thresholds at 1 month in all conventional vectors. No patients had PNS on all of the seven new vectors where 8 of 66 (12%) patients exhibited PNS on all conventional vectors, these patients may not have required invasive repositioning but all the incidences of PNS in this study were able to be managed using the VectSelect Quartet®electrical repositioning option unique to the Quartet®lead. This feature may have simplified the management of these patients some of whom, without this option, could have required lead repositioning in the future. However, based on the studies by Leon and Crossley with combined patient inclusions of >2000 patients it should not be assumed that the number requiring reintervention would have been >2.5%.

Also of interest is that five of the seven new vectors tested exhibited lower rates of PNS (11–14%) compared with the three conventional configurations which showed rates between 19 and 23%.

Other problems arising following implantation and leading to reintervention include threshold rises and lead displacement.12The increased programming possibilities provided by using a quadripolar electrode lead may provide non-invasive alternatives in the management of these challenges reducing time spent addressing the problems and the number of costly reintervention procedures.

Considerations for future research

The availability of the quadripolar electrode Quartet®lead provides the opportunity to explore the use of quadripolar electrode leads in clinical practice. Future studies should address the ability of this technology to reduce costly reintervention procedures and provide programming flexibility to maintain CRT delivery over a longer time period. The possibility to improve outcomes in CRT patients by selecting pacing sites that are associated with optimal haemodynamic, electrical, or mechanical responses also needs to be addressed. Further technological advances will provide the ability to stimulate more than one site on the lead during each pacing cycle which will require further research to address the implications for greater improvement in clinical outcomes.


This prospective multi-centre investigation suggests that the increased programming flexibility offered by the Quartet®lead provides more solutions to common problems faced by physicians when implanting systems and also when managing patients in clinic, 11% of patients enrolled in this study showed PNS and poor thresholds if restricted to traditional vectors and some of these may have avoided invasive reintervention as a result of receiving a Quartet®lead. There is now a need for longer-term follow-up to further evaluate these benefits and investigate the leads potential to improve delivery of resynchronization therapy and a larger study is being planned to address this.

Study limitations

This is an observational study which presents performance of the quartet lead in multiple centres. The small scale of the study does not allow for subgroup analysis of groups such as women (who made up 20% of the population) or ischaemics (37%). A small-scale single-centre study by Forleo et al.16presented controlled data in 55 patients where the quadripolar lead was compared with bipolar leads. Five patients were excluded from analysis for reasons described above and it is recognized that data from these patients could have had a noticeable effect on the results, although it is reasonable to assume that these patients may have shown a similar pattern to those presented here and in other trials. The follow-up period was short (1 month) and so the study cannot exclude the possibility of issues relating to the new lead design arising over a longer follow-up period. A longer-term study is planned in the future to address these issues.

Conflict of interest:K.S. receives a speakers honoraria, consulting fees, research grants, and funds from St Jude Medical; G.D. receives consulting fees from St Jude Medical and lecture fees from Sanofi-Aventis, St Jude Medical, and Biotronik; W.J. receives honorariums from Biotronik, Boston Scientific, Medtronic, St Jude medical, Hansen Medical, Böhringer Ingelheim, MSD, Novartis, Sanofi-Aventis. C.A.R. receives consulting fees from St Jude Medical. L.S., B.H., and M.S. are employees of St Jude Medical.


This study was sponsored by St Jude Medical International Inc.


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