Left Ventricular Pacing Vector Research Articles

Acute hemodynamic impact of atrioventricular delay and left ventricular pacing vector programming in MultiPoint Pacing.

The benefits of cardiac resynchronization therapy (CRT) in heart failure patients have been shown to depend on device programming, particularly atrioventricular delay (AVD) and left ventricular (LV) pacing site selection. This study compared the hemodynamic AVD optimization for commonly used biventricular (BiV) and MultiPoint Pacing(MPP, Abbott) LV vector selection strategies. After de novo CRT-D (Abbott Quadra Assura MP) and quadripolar LV lead (Abbott Quartet) implant, acute LV pressure was measured across a range of AVDs (60-225 ms) in four pacing modes: BiV with most proximal cathode, BiV with most distal cathode, MPP using two cathodes with earliest and latest right ventricle (RV)-LV activation times, and MPP using two cathodes with maximal anatomical separation. Hemodynamic improvement was evaluated by changes in maximum LV pressure first-derivative versus RV pacing (ΔdP/dt). Twenty patients (64 years old, 68% male) completed the acute pacing protocol at six centers in China. Hemodynamic improvement versus RV pacing for BiV (proximal), BiV (Distal), MPP (electrical), and MPP (anatomical) was 22.1% ± 13.6%, 23.7% ± 13.4%, 24.5% ± 13.4%, and 25.1% ± 13.9%, respectively. The best MPP setting was marginally superior to the best BiV across all patients (25.8% ± 13.4% vs. 24.5% ± 13.1%, p = .040) and in the majority of patients (75.0% vs. 25.0%, p = .004). AVD programmed as little as 20 ms from optimum significantly reduced the ΔdP/dt benefit for all modes. The maximal hemodynamic improvement across AV delays in this population was greater with MPP than BiV. Furthermore, patient-specific AVD programming was critical in achieving the full hemodynamic response for all BiV and MPP modes.

MultiPole pacing in non-responders to cardiac resynchronization therapy: Results from the QP ExCELs/MPP sub-study.

Multisite LV stimulation therapy allows for stimulation of two different left ventricular pacing vectors within a single LV lead and may improve responsiveness to cardiac resynchronization therapy (CRT). This study prospectively evaluated the safety and efficacy of the MultiPole Pacing (MPP) feature in CRT non-responder patients. CRT non-responders with a standard CRT-D indication were eligible for enrollment into the MPP Sub-Study. Patient status, NYHA classification, Patient Global Assessment (PGA), and adverse events were collected at follow-up. A clinical composite score (CCS) was determined at the 6 month follow-up visit. The primary objective was defined as the proportion of patients with an improved CCS. Safety was evaluated as freedom from MPP system related adverse events requiring additional invasive intervention to resolve. A total of 53 patients were enrolled across 26 U.S. centers. The cumulative follow-up duration was 24.1 years. CCS was improved in 35.6% of patients (p<.0001 when compared to a performance goal of 3%) after 6 months of MPP therapy. When incorporating patient feedback into a modified CCS, 60.0% of patients showed an improvement. Three patients (5.7%) experienced hospitalization for heart failure, and three patient deaths occurred over the follow-up period. No MPP system-related events were reported for an AE-free rate of 100% (95% CI 93.28% to 100.0%). The results of this small, non-randomized study suggest that the MPP feature is safe, and may be effective at converting a percentage of CRT non-responders to responders. Larger, randomized studies are needed to confirm this result.

Long-term reverse remodeling and clinical improvement by MultiPoint Pacing in a randomized, international, Middle Eastern heart failure study

PurposeCardiac resynchronization therapy (CRT) with multipoint left ventricular (LV) pacing (MultiPoint™ Pacing, MPP) has been shown to improve CRT response, although MPP response using automated pacing vector programming has not been demonstrated in the Middle East. The purpose of this study was to compare the impact of MPP to conventional biventricular pacing (BiV) using echocardiographic and clinical changes at 6-month post-implant.MethodsThis prospective, randomized study was conducted at 13 Middle Eastern centers. After de novo CRT-D implant (Abbott Unify Quadra MP™ or Quadra Assura MP™) with quadripolar LV lead (Abbott Quartet™), patients were randomized to either BiV or MPP therapy. In BiV patients, the LV pacing vector was selected per standard practice; in MPP patients, the two LV pacing vectors were selected automatically using VectSelect. CRT response was defined at 6-month post-implant by a reduction in LV end-systolic volume (ESV) ≥ 15%.ResultsOne hundred and forty-two patients (61 years old, 68% male, NYHA class II/III/IV 19%/75%/6%, 33% ischemic, 57% hypertension, 52% diabetes, 158 ms QRS, 25.8% ejection fraction [EF]) were randomized to either BiV (N = 69) or MPP (N = 73). After 6 months, MPP vs. BiV patients experienced greater ESV reduction (25.0% vs. 15.3%, P = 0.08), greater EF improvement (11.9% vs. 8.6%, P = 0.36), significantly greater ESV response rate (68.5% vs. 50.7%, P = 0.04), and significantly greater NYHA class improvement rate (80.8% vs. 60.3%, P = 0.01).ConclusionsWith MPP and automatic LV vector selection, more CRT patients in the Middle East experienced reverse remodeling and clinical improvement relative to conventional BiV pacing.

Safety of magnetic resonance imaging scanning in patients with cardiac resynchronization therapy–defibrillators incorporating quadripolar left ventricular leads

Magnetic resonance imaging (MRI) scanning of magnetic resonance (MR)-conditional cardiac implantable cardioverter-defibrillators (ICDs) can be performed safely following specific protocols. MRI safety with cardiac resynchronization therapy-defibrillators (CRT-Ds) incorporating quadripolar left ventricular (LV) leads is less clear. The purpose of this study was to evaluate the safety and effectiveness of ICDs and CRT-D systems with quadripolar LV leads after an MRI scan. The ENABLE MRI Study included 230 subjects implanted with a Boston Scientific ImageReady ICD (n = 39) or CRT-D (n=191) incorporating quadripolar LV leads undergoing nondiagnostic 1.5-T MRI scans (lumbar and thoracic spine imaging) a minimum of 6 weeks postimplant. Pacing capture thresholds (PCTs), sensing amplitudes (SAs), and impedances were measured before and 1 month post-MRI using the same programmed LV pacing vectors. The ability to sense/treat ventricular fibrillation (VF) was assessed in a subset of patients. A total of 159 patients completed a protocol-required MRI scan (MRI Protection Mode turned on) with no scan-related complications. All right ventricular (RV) and left LV PCT and SA effectiveness endpoints were met: RV PCT 99% (145/146 patients), LV PCT 100% (120/120), RV SA 99% (145/146), and LV SA 98% (116/118). In no instances did MRI result in a change in pacing vector or lead revision. All episodes of VF were appropriately sensed and treated. This first evaluation of predominantly CRT-D systems with quadripolar LV leads undergoing 1.5-T MRI confirmed that scanning was safe with no significant changes in RV/LV PCT, SA, programmed vectors, and VF treatment, thus suggesting that MRI in patients having a device with quadripolar leads can be performed without negative impact on CRT delivery.

Performance of a novel active fixation quadripolar left ventricular lead for cardiac resynchronization therapy: Attain Stability Quad Clinical Study results.

The Medtronic Attain Stability Quad lead is a quadripolar left ventricular (LV) lead with an active fixation helix assembly designed to fixate the lead within the coronary sinus and pace nonapical regions of the LV. The primary objective of this study was to determine the safety and effectiveness of this novel active fixation quadripolar LV lead. Patients with standard indications for cardiac resynchronization therapy (CRT) were enrolled. All patients were followed at 3 and 6 months post-implant and every 6 months thereafter until study closure. Pacing capture thresholds (PCTs) were measured at implant and each follow-up and adverse events (AEs) were recorded upon occurrence. Of the 440 patients who underwent implant procedures, placement of the Attain Stability Quad lead was successful in 426 (96.8%). LV lead-related complications occurred in 10 patients (2.3%), including LV lead dislodgement in three patients (0.7%). The percentage of patients with at least one LV pacing vector with a PCT ≤2.5 V at a 6-month follow-up was 96.3%. The LV lead was successfully fixated to the prespecified pacing location in 97.4% of cases. This large, multinational study of the Attain Stability Quad lead demonstrated a high rate of implant success with a low complication rate. The active fixation mechanism allowed precise placement of the pacing electrodes at the desired target region with good PCTs and a very low dislodgement rate.

P4526Implant procedure and lead handling characteristics of a novel active fixation quadripolar lead: Results from the Attain Stability Quad clinical trial

Abstract Background Dislodgements of left ventricular (LV) leads are still a challenging problem in cardiac resynchronization therapy (CRT). The Attain Stability Quad (ASQuad) MRI SureScan 4798 steroid-eluting, quadripolar LV lead has a side-helix to enable the lead to be actively fixated to the vessel wall. The uniquely designed active fixation can be advantageous in vessels that are wide or have short take-offs. Further, the helix easily elongates to allow for future extraction. Purpose To report on the handling, performance and safety of ASQuad LV lead in a large clinical study. Methods The ASQuad clinical study is a prospective clinical trial from 50 centers in 10 countries enrolling CRT candidates implanted with the ASQuad LV lead. Aside from evaluating safety and effectiveness of the LV lead, the trial specifically collected data on parameters related to lead stability during and post implant. Results Of 440 enrolled patients (74.8% male, average age 70±11 years) that underwent an implant attempt, 426 (96.8%) were successfully implanted. The helix was mostly affixed in the mid to basal lateral position (62%), followed by mid to basal posterior position (29%). The lead tip placement was most often mid lateral or mid posterior (77%), and in a vein with diameter greater than the pacing electrode diameter (&gt;5.1 French) in the majority (60%) of procedures. Among all subjects (n=421) who underwent pacing capture thresholds (PCT) tests before and immediate after guide catheter slitting, 98% reported ≤1 V difference in PCT, and 86% were within 0.5 V. The interquartile range for the difference in PCT was −0.1 to 0.1 V. The mean PCT at implant for all subjects at the final selected LV pacing vector was 1.15±0.70 V at 0.5 ms pulse width. The average LV lead implant time was 16±21 minutes. Targeted pacing location was achieved in 97% of successful implants, and 98% of implanters reported good or fair stability after guidewire removal. The overall handling of the LV lead was rated as acceptable by implanters in 99% of cases. Three patients (0.7%) experienced LV lead dislodgement post implant, and these complications were resolved by repositioning of the lead (0 and 1-day post implant) in two and by lead replacement when noted at 90 days follow-up in one. Conclusions The ASQuad LV lead was implanted with a high rate of success and ability to achieve the targeted pacing location. Lead handling and stability following guidewire removal were rated as acceptable by nearly all implanters. The side-helix likely improved LV lead stability since 98% of the subjects had ≤1 V difference in PCT before and after catheter slitting during implant procedures, and by demonstrating a low post implant lead dislodgement rate. Acknowledgement/Funding Sponsored by Medtronic

Utility of Novel Vectors in a Quadripolar Left Ventricular Lead

Background Two complications which frequently arise with the use of cardiac resynchronization therapy (CRT) are phrenic nerve stimulation (PNS) and/or high pacing thresholds. These complications often result in costly and invasive surgical procedures required to revise an existing left ventricular (LV) lead in order to provide safe and optimal therapy. Quadripolar (QP) left ventricular leads include four electrically active rings which provide redundancy and allow the prescriber to change pacing configurations and optimize CRT delivery. This capability can also be used to resolve PNS or high pacing threshold by programming a new pacing vector, and thus provides a low-risk alternative to traditional invasive procedures. Objective The goal of this study is to evaluate the utility of seven programmable novel LV pacing vectors which utilize one or both distal rings that are unique to quadripolar LV leads. Methods The analysis was part of a multi-center, prospective, non-randomized study. Novel pacing vector data was collected during a clinic follow-up visit at 3 months post implant for subjects implanted with a BIOTRONIK Sentus QP lead in combination with a BIOTRONIK CRT-D implantable device. Novel vectors contained one or both distal LV rings (LV3 and LV4) and were evaluated via a threshold test at a pulse width of 0.4 ms. LV pacing thresholds ≤ 2.5 V at 0.4 ms were considered acceptable. Results A total of 930 subjects were successfully implanted at 76 U.S. and international sites. Of 662 subjects with available novel data at 3 months post implant, there were 509 subjects who underwent threshold testing of at least four of the seven novel pacing vectors. The percentage of subjects in this group with at least one novel vector with an acceptable LV pacing threshold was 89.2% (N=454). Table 1 provides the number and percentage of subjects for the total novel vectors with an acceptable threshold. Conclusion The results demonstrate an ability to provide alternate novel vector pacing configurations for subjects who may otherwise require an invasive procedure to resolve PNS or high pacing threshold.

Shortening of paced QRS duration after electrocardiographic optimization of left ventricular pacing vector in patients treated with Cardiac Resynchronization Therapy

BackgroundChoice of left ventricular pacing vector (LVPV) affects the QRS-duration (QRSd) in patients with Cardiac Resynchronization Therapy (CRT). It is not known whether testing all LVPVs reduces QRSd compared to device-based “standard-programming”. MethodsIn patients implanted with CRT several ECGs were recorded for each usable LVPV (no phrenic nerve stimulation and threshold <3.5 V) and during “standard-programming” after device-based optimization of AV/VV delays. Results22 consecutive patients were included. Average QRSd reduction after CRT + “standard-programming” was 27.3 ± 22 ms. Additional QRSd-reduction was possible in 4 patients by changing the LVPV, and in 5 other patients after optimization of AV- and VV delays without changing LVPV. ConclusionsShortening of QRSd compared to “standard-programming” was possible approximately 40% of these patients treated with CRT by testing all LVPVs and re-optimizing AV/VV delays during follow-up. Studies of clinical effects are needed.

Combination of the best pacing configuration and atrioventricular and interventricular delays optimization in cardiac resynchronization therapy.

Cardiac resynchronization therapy optimization can be pursued by left ventricular pacing vector selection and atrioventricular (AV) and interventricular (VV) delays optimization. The combination of these methods and its comparison with multipoint pacing (MPP) is scarcely studied. Using noninvasive cardiac output (CO) measurement, the best of five left ventricular pacing vectors was determined, then AV and VV delays optimization was applied on top of the best vector. Response to the optimization protocol was defined as a>5% CO increase compared to the standard biventricular configuration. Twenty-two patients (18 men, age 71 ± 9 years) were included. Standard biventricular configuration increased CO compared to baseline (4.65 ± 1.55L/min vs 4.27 ± 1.53 L/min, respectively, P=0.02). The best quadripolar configuration increased CO to 4.85 ± 1.67 L/min (P=0.03 compared to the standard biventricular configuration). AV then VV delay optimization both provided additional benefit (final CO 5.56 ± 2.03 L/min, P=0.001 compared to the best quadripolar configuration). Fifteen (68%) patients responded to the optimization protocol. Anatomical MPP (based on maximal anatomical separation between electrodes) and electrical MPP (based on maximal electrical activation difference between electrodes) were evaluated in 16 patients and yielded a CO similar to that of the optimization procedure. The combination of choosing the best quadripolar pacing configuration and optimizing atrioventricular and interventricular delays resulted in an improvement of cardiac output compared to standard biventricular stimulation in 68% of patients. The final cardiac output was comparable to multipoint pacing.

139-02: Comparison of the long-term efficacy of two different programming strategies for multipoint left ventricular pacing

Purpose: Cardiac resynchronization therapy (CRT) with multipoint left ventricular (LV) pacing (MultiPoint™ Pacing [MPP], St. Jude Medical) improves long-term LV reverse remodeling, though questions persist about how to program LV pacing vectors and delays. We evaluated if an empirical method of programming MPP improves CRT response similar to pressure-volume loop (PVL) optimization. Methods: Patients undergoing CRT implant (Quadra Assura MP™ CRT-D and Quartet™ LV lead, St. Jude Medical) received MPP with programmed settings optimized either by PVL measurements at implant (PVL-OPT group) or empirically determined by maximizing the spatial separation between the two cathodes and minimizing delays between the two pacing pulses (MAX-SEP group). CRT response was prospectively defined as a reduction in end-systolic volume (ESV) of ≥15% relative to baseline at 6 months as determined by a blinded observer. Conclusion: Both evaluated methods of MPP programming resulted in similar, high levels of CRT response. Empirical MPP programming by maximum spatial separation of LV cathodes may be an effective, simple, and non-invasive alternative to PVL optimization.

Abstract 14753: A Novel Quadripolar Lead with a Narrow-Spaced Bipole Allows for Effective LV Pacing While Avoiding Phrenic Nerve Stimulation - Attain Performa LV Lead Study Primary Results

Introduction: The Medtronic Attain Performa™ Model 4298 Quadripolar left ventricular (LV) Lead has 4 electrodes, provides 16 different polarities &amp; includes a short bipole (1.3 mm between 2nd &amp; 3rd electrodes). A prospective clinical study was conducted to investigate the safety and effectiveness of this new lead in 20 countries worldwide. Methods: Cardiac resynchronization therapy defibrillator (CRT-D) patients were enrolled &amp; implanted with the Model 4298 LV lead &amp; a Quad CRT-D device. All implanted subjects(SUB) were followed at 1, 3, 6 and every 6 months (M) post-implant. Pacing capture thresholds (PCTs) were measured manually or with automated testing methods. Adverse events (AEs) were reported upon occurrence &amp; reviewed by an independent committee. Events requiring invasive intervention or resulting loss of CRT were considered to be complications. Results: Of 499 SUB (68 + 11 yr, 71% male) who underwent an LV lead implant attempt, 487 (97.6%) had an LV lead implanted, Most (73%) had NYHA Class III or IV symptoms, average LV ejection fraction was 25 ± 7%, QRS duration was 155 ± 24ms &amp; most (71%) had LBBB. There were 20 LV lead related complications in 19 SUB over 6M (LV lead related complication free survival rate = 96%). Phrenic nerve stimulation (PNS) occurred in 31 SUB (6.3%) &amp; resolved with no treatment (N=1) or noninvasive reprogramming (N=29). The average PCT at 6M was 1.1 + 0.7 V at the programmed vector and 93.9% of SUB had a PCT≤ 2.5V. The vast majority (97.7%) of SUB had &gt; 1 additional selectable pacing vector with a PCT ≤ 4V and no PNS. Non-standard pacing polarities (i.e., vectors other than LV1 [LV tip] to right ventricular coil [RVC], LV2 to RVC &amp; LV1 to LV2) were utilized in 56% of SUB. LV1 was not used in the final vector in 46% of SUB. The LV1 to RVC was utilized in 19%, LV1 to LV2 in 18% &amp; the short bipole (LV2 to LV3) in 12%. Conclusions: This large multicenter study demonstrated that implantation of the Model 4298 LV quadripolar lead is associated with a low complication rate and no unanticipated complications. PNS can be readily resolved with reprogramming &amp; that PCT values are low &amp; stable over time. Moreover, At least 1 back-up LV pacing vector was available in the vast majority of SUB. Non-standard vectors, including the short bipole (LV2-LV3) were used in 56% of subjects.

Acute echocardiographic optimization of multiple stimulation configurations of cardiac resynchronization therapy through quadripolar left ventricular pacing: A tailored approach

Cardiac resynchronization therapy (CRT) is ineffective in approximately 30% of recipients, in part due to sub-optimal left ventricular (LV) pacing location. The Quartet LV lead, with 2 additional electrodes proximal to conventional bipolar lead electrodes, enables 10 different pacing configurations at four independent LV locations. In a CRT patient cohort, we sought to evaluate the spectrum of echocardiographic and electrocardiographic response over these 10 configurations, to select the optimal one in each patient. Moreover, we sought to evaluate the 6-months clinical and echocardiographic response to a "tailored approach" in which the optimal LV pacing configuration for CRT was determined by echocardiographic measures, QRSd and pacing capture thresholds. Twenty-two consecutive CRT indicated patients were implanted with a quadripolar CRT system (St. Jude Medical). Optimal LV pacing configuration was determined by echocardiographic measures, including velocity time integral (VTI), myocardial performance index (MPI) and mitral regurgitation (MR), and an electrocardiographic measure (QRS duration) during pacing from each of the configurations at pre-discharge. The optimal LV pacing vector was chosen for every patient. Clinical and echocardiographic assessment was repeated after 6 months. Various configurations provided different VTI, MPI, MR and QRSd values. Conventional bipolar vectors (ie, D1-M2, D1-RVc, M2-RVc) were rarely associated with the best echocardiographic improvements and provided significantly worse VTI, MR, MPI, and QRSd values than the best configuration for every patient (P = .005, P = .05 and P = .03 for VTI; P = .01, P = .005 and P = .001 for MPI; P = .003, P = .01 and P = .005 for MR, P > .5, P = .01 and P = .05 for QRSd) Conversely, "unconventional" proximal configurations (ie, making use of P4 and M3 electrodes) were generally characterized by higher acute VTI, MR and MPI improvements. CRT devices were reprogrammed with an "unconventional" LV pacing configuration in 50% of patients. A significant improvement in New York Heart Association class (81%), LV ejection fraction (76%), end-diastolic and end-systolic volumes was observed after 6 months (P = .02, P < .001, P = .02 and P = .003, respectively). In this study, conventional bipolar vectors of quadripolar-CRT were rarely associated with the best echocardiographic improvements. Quadripolar CRT utilizing optimal LV pacing configuration was associated with a significant improvement in New York Heart Association class and LV ejection fraction after 6 months.

Are Unipolar Pacing Thresholds Lower Than Bipolar Pacing Thresholds in Multipolar Left Ventricular Leads?

The novel Quartet™ quadripolar lead/Promote™ Q CRT-D system (St. Jude Medical, Sylmar, CA, USA) offers 4 unipolar and 6 bipolar left ventricular pacing vectors. We compared unipolar to bipolar pacing thresholds at each electrode.

Clinical efficacy of left ventricular pacing vector programmability in cardiac resynchronization therapy defibrillator patients for management of phrenic nerve stimulation and/or elevated left ventricular pacing thresholds: insights from the Efface Phrenic Stim study

Elevated left ventricular (LV) pacing thresholds or phrenic nerve stimulation (PNS) might be possible reasons for absence of continuous and effective biventricular stimulation. This study investigated the benefit and clinical efficacy of the ability to choose one out of three different LV pacing vectors for the management of suboptimal LV pacing thresholds and PNS. This prospective, observational multicentre study enrolled 132 patients (Pts) implanted with a cardiac resynchronization therapy defibrillator, that offers three LV pacing vectors: (i) Bipolar; (ii) LVtip ↔ RVcoil; (iii) LVring ↔ RVcoil (RV = right ventricular). Left ventricular pacing thresholds and PNS thresholds were obtained in sitting and left lateral body position for all programmable LV pacing vectors at hospital discharge and follow up (FU). In 97%, a bipolar transvenous LV lead was successfully implanted. In 87% of Pts at least one acceptable pacing vector could be identified that provides good pacing threshold (≤ 2.5 V at 5 ms) and acceptable margin to PNS (≥ 2:1). This is an increase of 18% compared with conventional bipolar systems (74%) with two LV vectors and of 25% compared with unipolar systems (70%). The LVtip ↔ RVcoil vector provided the best LV pacing thresholds, but the highest rate of PNS. The programmability of LV pacing vectors is a powerful feature to avoid PNS and obtain acceptable LV pacing thresholds. In order to retain reprogramming options for LV vectors during FU, LV pacing leads with at least two electrodes should be chosen whenever possible.

Initial Single-Center Experience of a Quadripolar Pacing Lead for Cardiac Resynchronization Therapy

The Quartet model 1458Q (St. Jude Medical, Sylmar, CA, USA) lead is a quadripolar left ventricular (LV) lead with pace/sense capability from four electrodes (tip and three rings). The lead is capable of pacing in 10 different configurations rather than the three that are available in conventional bipolar pacing leads. We describe a single-center initial experience of the use of this lead in patients undergoing cardiac resynchronization therapy (CRT). Twenty-eight patients for a CRT with cardiac defibrillator were implanted between October 2009 and May 2010 with a Quartet lead . Lead position, pacing parameters, stability, complications, and presence of phrenic nerve stimulation (PNS) data were collected at implant and predischarge. Follow-up data were collected at 15 ± 8 weeks for all patients. A Quartet lead was successfully implanted in 96% (27/28) of patients (age 61 ± 15 years; 82% male; ischemic etiology 50%; mean left ventricular [LV] ejection fraction 25 ± 7%; left bundle branch block 68%). PNS was seen at implant in 11 patients (41%) with at least one vector. In eight of these cases (72%), the need for lead repositioning was averted by programming LV pacing utilizing the additional vectors available with the Quartet lead. These initial data suggest that pacing with the Quartet lead is associated with a high implant success rate and stable pacing parameters acutely and at short-term follow-up. The 10 LV pacing vectors available with this lead may allow PNS and capture threshold problems to be easily overcome.

Phrenic Stimulation

Background— Phrenic stimulation (PS) may hinder left ventricular (LV) pacing. We prospectively observed its prevalence in consecutive patients with cardiac resynchronization therapy (CRT) devices. Methods and Results— In the years 2003 to 2006, 197 patients received a CRT device. PS and LV threshold measurements were carried out at implantation and at 6-month follow-up. LV reverse remodeling was assessed by echocardiography before implantation and at follow-up. LV lead placement was lateral/posterolateral in 86% of patients. Both PS and LV reverse remodeling occurred most frequently at the lateral/posterolateral LV pacing sites ( P &lt;0.001). PS was detected in 73 (37%) of patients and was clinically relevant in 41 (22%). The detection of PS at implantation had a poor sensitivity, as it occurred only in left lateral or sitting position in 27 patients. Ten patients (5%) underwent repeated surgery and 4 (2%) had their CRT turned off because of PS. At follow-up, we could manage PS noninvasively in 32 patients with a small PS-LV threshold difference: in 20 by cathode programmability (3 also thanks to automatic management of LV output) and in 12 (without cathode programmability) by programming the LV output as threshold +1 V. Conclusions— PS may seriously hinder CRT. A bipolar LV lead and cathode programmability are mandatory to avoid PS by changing the LV pacing vector at target sites for CRT. LV stability at target sites despite PS should also be pursued by these means. The automatic adjustment of LV pacing output is complementary in patients with a small PS-LV threshold difference.