Influence of pacing configurations, body mass index, and position of coronary sinus lead on frequency of phrenic nerve stimulation and pacing thresholds under cardiac resynchronization therapy

WiSE CRT Is Beneficial for Heart Failure Patients as a Rescue Therapy: Evidence From a Meta-Analysis

Background

Leadless endocardial left ventricular (LV) pacing resynchronization therapy is a novel solution for patients with heart failure (HF) in whom conventional cardiac resynchronization therapy (CRT) failed.

Methods

PubMed and the Cochrane Library were searched for relevant cohort studies. Clinical outcomes of interest such as ejection fraction (EF), QRS duration (QRSd), and left ventricular end-systolic volume (LVESV) were extracted and analyzed.

Results

Five studies involving 175 HF patients for WiSE CRT were included, and patients were followed-up for 6 months. The implanted success rate ranged from 76.5 to 100%. WiSE CRT resulted in significantly narrower QRSd [mean difference (MD): −38.21 ms, 95% confidence interval (CI): −44.36 to −32.07, p < 0.001], improved left ventricular ejection fraction (MD: 6.07%, 95% CI: 4.43 to 7.71, I2 = 0%, p < 0.001), reduced left ventricular end-systolic volume (MD: −23.47 ml, 95% CI: −37.18 to −9.13, p < 0.001), and reduced left ventricular end-diastolic volume (MD: −24.02 ml, 95% CI: −37.01 to −11.03, p = 0.02).

Conclusion

Evidence from current studies suggests that leadless endocardial LV pacing resynchronization is effective for HF patients who failed conventional CRT or needed a device upgrade, and it may be an interesting rescue therapy.

Left ventricle pacing challenges in cardiac resynchronization therapy systems

Left ventricle (LV) pacing can be considered peculiar due to its different lead/tissue interface (epicardial pacing) and the small vein wedging lead locations with less reliable lead stability. The current technologies available for LV capture automatic confirmation adopt the evoked response (ER), as well as "LV pace to right ventricular (RV) sense" algorithms. The occurrence of anodal RV capture is today completely solved by the use of bipolar LV leads, while intriguing data are recently published regarding the unintentional LV anodal capture beside the cathodal one, which may enlarge the front wave of cardiac resynchronization therapy (CRT) delivery. The LV threshold behavior over time leading to ineffective CRT issues (subthreshold stimulation or concealed loss of capture), the extracardiac capture with phrenic nerve stimulation (PNS), the flexible electronic cathode reprogramming and the inadequate CRT delivery related to inadequate AV and VV pace timing (and its management by LV "dromotropic pace-conditioning") are discussed. Moreover, recently, His bundle pacing (HBP) and left bundle branch pacing (LBBP) have shown growing interest to prevent pacing-induced cardiomyopathy as well as for direct intentional CRT. The purpose of the present review is to explore these new challenges regarding LV pacing starting from old concepts.

Phrenic nerve stimulation, a rare complication of pacemaker: A case report

RATIONALE

The phrenic nerve stimulation (PNS) is a rare complication after pacemaker setting. We report a case report that describes this complication and how it can be resolved.

PATIENT CONCERNS

An 88-year-old man presented himself to the emergency geriatric unit with intermittent painless abdominal contraction due to phrenic nerve stimulation. He has a history of transcatheter aortic valve implantation with cardiac resynchronization therapy pacemaker due to persistent left bundle branch block.

DIAGNOSES

All the usual causes for abdominal spasms were eliminated and the possibility of a link with the pacemaker was considered. The phrenic nerve stimulation is a rare complication of a pacemaker implantation. It can be clinically nonrelevant but challenging to diagnose for those not familiar with cardiac devices technology.

INTERVENTIONS

Initial setting was an axis of stimulation between distal left ventricular (LV) and right ventricular. It was changed to LV and D1-M2.

OUTCOMES

This noninvasive procedure managed to eradicate the involuntary abdominal spasms.

LESSONS

PNS could be challenging to diagnose for those not familiar with cardiac devices technology but easy to manage with noninvasive methods.

Super-response to cardiac resynchronization therapy may predict late phrenic nerve stimulation

Aims

Changes in the anatomical relationship between left phrenic nerve and coronary veins may occur due to the reverse remodelling observed in super-responders to cardiac resynchronization therapy (CRT) and might be the underlying mechanism in patients developing late-onset phrenic nerve stimulation (PNS) without evidence of lead dislodgement (LD). In this study, we sought to evaluate the role of super-response (SR) to CRT as a potential predictor of late-onset PNS.

Methods and results

Consecutive patients implanted with a left ventricular (LV) lead in a single centre were retrospectively analysed. Phrenic nerve stimulation was classified as 'early' when it occurred within 3 months of implantation and 'late' for occurrences thereafter. 'Late' PNS was considered related to LD (LD-PNS) when LV threshold differed by > 1 V or impedance >250 Ω from baseline values or in case of radiological displacement. Cases not meeting the former criteria were classified as 'non-LD-PNS'. Super-response was defined as a decrease ≥30% of the left ventricluar end-systolic volume at 1-year echocardiography. At 32 ± 7 months follow-up, PNS occurred in 20 of 139 patients. Late non-LD-PNS incidence was significantly higher in the SR group (8/61; 13.1%) when compared with the non-SR (1/78; 1.3%) (P = 0.010). Super-response remained the only predictor of non-LD-PNS at multivariate analysis (odds ratio: 11.62, 95% confidence interval 1.41-95.68, P = 0.023).

Conclusion

Incidence of late non-LD-PNS is higher among SR to CRT, suggesting a potential role of the changes in the anatomical relationship between left phrenic nerve and coronary veins.

[Leadless endocardial ultrasound based left ventricular stimulation : WISE CRT System: alternative to conventional methods]

There are still several limitations in delivering cardiac resynchronisation therapy (CRT). After 6 months, 20-40% of patients fail to have clinical benefit due to various reasons. Endocardial stimulation rather than conventional epicardial pacing has been shown to be more physiological, improves electrical stimulation of the left ventricle (LV), has less dispersion of electrical activity and results in better resynchronisation. The WiSE™ CRT System ("Wireless stimulation endocardial system"; EBR Systems, Sunnyvale, CA, USA) provides an option for wireless, LV endocardial pacing triggered by a conventional right ventricular pacing spike from a co-implant. The feasibility of the WiSE™ CRT System has been successfully demonstrated in a population of failed cardiac resynchronisation patients with either failed implantation of a conventional system, nonresponse to conventional therapy or upgrade from pacemaker or defibrillator, where a conventional system was not an option. The WiSE™ CRT System is an innovative technology with promising safety, performance and preliminary efficacy.

Impact of intraoperative mechanical ventilation on left ventricular lead function in cardiac resynchronization therapy

BACKGROUND

Intraoperative controlled mechanical ventilation (CMV) changes the intrathoracic geometry and may impact postoperative left ventricular (LV) lead function after CRT implantation. This multicenter study investigates the effect of intraoperative ventilation setting (spontaneous breathing [SB] vs CMV) on postoperative LV lead function taking into account patients' body mass index (BMI).

METHODS

CRT implantation was performed at two centers during SB in 92 and during CMV in 73 patients. Follow-up was carried out after 3 ± 5 and 36 ± 53 days. Functional lead parameters (FLP; pacing threshold and impedance), postoperative adverse events (A;  phrenic nerve stimulation [PNS] and lead malfunction), and patients' BMI were assessed. Delta values of FLP between baseline and follow-up visits were analyzed applying an analysis of covariance model to detect subclinical alterations in LV lead function.

RESULTS

AE occurred in a total of 36 (21%) patients. PNS was observed in 26 (15%) patients and LV lead repositioning due to malfunction was necessary in 10 (6%) patients. Both AE and FLP delta values between baseline and follow-up were not associated with intraoperative ventilation settings nor the patients' BMI.

CONCLUSIONS

This study demonstrates that there is no impact of the intraoperative ventilation setting (SB vs CMV) on postoperative FLP or the occurrence of AE. This is also the case taking into account the BMI. With respect to these findings both approaches-sedation only or general anaesthesia including CMV-can be safely implemented during CRT implantation.

Transvenous pacemaker placement: left lateral decubitus position and wireless digital radiography

A patient presented with symptomatic third degree atrioventricular block requiring emergency transvenous pacemaker placement. During the procedure, wireless digital radiographs tracked the position of the pacemaker electrode, which repeatedly missed the target right ventricle. The patient was then rolled to left lateral decubitus position and the electrode was advanced into the right ventricle, achieving electrical capture, hemodynamic stability, and symptom resolution. We review the published literature on transvenous pacemaker placement and identify two innovations: left lateral decubitus position to facilitate catheter placement and wireless digital radiography for procedure guidance.

Multipolar pacing by cardiac resynchronization therapy with a defibrillators treatment in type 2 diabetes mellitus failing heart patients: impact on responders rate, and clinical outcomes

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a multi factorial disease, affecting clinical outcomes in failing heart patients treated by cardiac resynchronization therapy with a defibrillator (CRT-d).

METHODS

One hundred and ninety-five T2DM patients received a CRT-d treatment. Randomly the study population received a CRT-d via multipolar left ventricle (LV) lead pacing (n 99, multipolar group), vs a CRT-d via bipolar LV pacing (n 96, bipolar group). These patients were followed by clinical, and instrumental assessment, and telemetric device control at follow up. In this study we evaluated, in a population of failing heart T2DM patients, cardiac deaths, all cause deaths, arrhythmic events, CRT-d responders rate, hospitalizations for HF worsening, phrenic nerve stimulation (PNS), and LV catheter dislodgment events (and re-intervention for LV catheter re-positioning), comparing multipolar CRT-d vs bipolar CRT-d group of patients at follow up.

RESULTS

At follow up there was a statistical significant difference about atrial arrhythmic events [7 (7%) vs 16 (16.7%), p value 0.019], hospitalizations for HF worsening [15 (15.2% vs 24 (25%), p value 0.046], LV catheter dislodgments [1 (1%) vs 9 (9.4%), p value 0018], PNS [5 (5%) vs 18 (18.7%), p value 0.007], and LV re-positioning [1 (1%) vs 9 (9.4%), p value 0.018], comparing multipolar CRT-d vs bipolar CRT-d group of patients. Multipolar pacing was an independent predictor of all these events.

CONCLUSIONS

CRT-d pacing via multipolar LV lead vs bipolar LV lead may reduce arrhythmic burden, hospitalization rate, PNS, LV catheters dislodgments, and re-interventions in T2DM failing heart patients. Clinical trial number NCT03095196.

Short-Term Availability of Viable Left Ventricular Pacing Sites with Quartet™ Quadripolar Leads

BACKGROUND Whether quadripolar leads can provide sufficient viable left ventricular pacing sites (LVPSs) for device optimization and multipoint pacing remains unclear. This study aimed to evaluate the acute and 3-month availability of viable LVPSs provided by a quadripolar LV pacing lead. MATERIAL AND METHODS A single-center cohort study evaluated consecutive patients who underwent a CRT implant with the QuartetTM LV lead under local guidelines. The availability of viable LVPSs was assessed at the pre-discharge and 3-month follow-up visit. Bipolar lead configurations, which served as the control group, were modeled by eliminating the 2 proximal electrodes on the Quartet™ LV lead. RESULTS A total of 24 patients were enrolled and finished 3-month follow-up. The mean follow-up period was 93±3 days. At pre-discharge, the Quartet™ LV lead provided more viable LVPSs compared with the bipolar equivalents (median 3 [IQR 2-4] vs. median 2 [IQR 1-2], P<0.001). The percentage of patients with at least 1, 2, 3, and 4 viable LVPSs were 100% (24/24), 91.7% (22/24), 58.3% (14/24), and 33.3% (8/24) for Quartet™ leads and 91.7% (22/24), 70.8% (17/24), 0% (0/24), and 0% (0/24) for bipolar lead configurations, respectively. The median and IQR values of viable LVPSs provided by the Quartet™ LV lead remained the same (3 [IQR 2-4]) between pre-discharge and 3-month follow-up (P=0.45). CONCLUSIONS Compared with the bipolar equivalent, QuartetTM LV lead provides more viable LVPSs and opportunities for CRT optimization and multipoint LV pacing. The number of LVPSs provided by Quartet™ leads remained unchanged between pre-discharge and 3-month follow-up.

A Meta-Analysis Of Quadripolar Versus Bipolar Left Ventricular Leads On Post-Procedural Outcomes

Objective: We aimed to perform a meta-analysis from eligible studies to analyze the true impact of QL when compared with BL with regard to post-procedural outcomes including lead deactivation, revision or replacement. Background: Many observational and retrospective studies showed that quadripolar left ventricular leads (QL) are associated with better outcomes and fewer complications when compared with bipolar leads (BL). Methods: We performed a comprehensive literature search through June 30, 2015 using: quadripolar, bipolar, left ventricular lead and CRT in Pubmed, Ebsco and google scholar databases. Results: The analysis included 8 studies comparing QL and BL implantation. Post-procedural outcomes such as lead deactivation, revision or replacement were used as primary outcome and assessed with Mantel-Haenszel risk ratio (RR). Secondary outcomes included total fluoroscopy/procedure time, occurrence of phrenic nerve stimulation (PNS) and all-cause mortality on follow up. Follow-up duration for the studies ranged from 3 to 60 months. Compared with BL, the use of QL is associated with 52 % reduction (relative risk 0.48; 95% CI: 0.36-0.64, p=0.00001) in the risk of deactivation, revision or replacement of the LV lead. QL had significantly lower fluoroscopy/procedure time, PNS and all-cause mortality when compared with BL. Conclusion:Our meta-analysis shows that QL implantation was associated with decreased risk of LV lead deactivation, revision or replacement when compared with BL.

Bipolar left ventricular pacing is associated with significant reduction in heart failure or death in CRT-D patients with LBBB

BACKGROUND

There are limited data on the significance of left ventricular (LV) lead pacing polarity to predict clinical outcomes.

OBJECTIVES

We aimed to determine the association between the LV lead pacing polarity for heart failure (HF) or death and ventricular tachyarrhythmias (VTA) in patients enrolled in MADIT-CRT (Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy), receiving a cardiac resynchronization therapy device with implanted cardioverter-defibrillator (CRT-D).

METHODS

We retrospectively analyzed LV pacing polarity. Patients with LV bipolar leads paced between LV ring and LV tip were identified as True Bipolar, while those with LV bipolar leads paced between LV tip or LV ring and right ventricular coil or unipolar leads were identified as Unipolar/Extended Bipolar. Kaplan-Meier survival analyses and multivariate Cox proportional hazards regression models were used.

RESULTS

Of the 969 patients, 421 had True Bipolar pacing while the remainder (n = 548) had Unipolar/Extended Bipolar pacing. Among patients with left bundle branch block (LBBB), True Bipolar pacing was associated with lower cumulative incidence of death (P = .022) and HF/death (P = .046) compared to those with Unipolar/Extended Bipolar LV pacing. After adjustment for clinical covariates, bipolar LV pacing in LBBB patients was associated with 54% lower risk for death (HR: 0.46; 95% CI: 0.24-0.88; P = .020) and 32% lower risk for HF/death (HR: 0.68; 95% CI: 0.46-1.00; P = .048) compared to Unipolar/Extended Bipolar LV pacing, but not in those with non-LBBB. No association was seen with risk of ventricular tachyarrhythmia.

CONCLUSION

True Bipolar LV pacing configuration is associated with a significantly lower risk of HF/death and all-cause mortality in CRT-D patients with LBBB.

Cardiac Resynchronization Therapy Delivered Via a Multipolar Left Ventricular Lead is Associated with Reduced Mortality and Elimination of Phrenic Nerve Stimulation: Long-Term Follow-Up from a Multicenter Registry

INTRODUCTION

Cardiac resynchronization therapy (CRT) using quadripolar left ventricular (LV) leads provides more pacing vectors compared to bipolar leads. This may avoid phrenic nerve stimulation (PNS) and allow optimal lead placement to maximize biventricular pacing. However, a long-term improvement in patient outcome has yet to be demonstrated.

METHODS

A total of 721 consecutive patients with conventional CRTD criteria implanted with quadripolar (n = 357) or bipolar (n = 364) LV leads were enrolled into a registry at 3 UK centers. Lead performance and mortality was analyzed over a 5-year period.

RESULTS

Patients receiving a quadripolar lead were of similar age and sex to those receiving a bipolar lead, although a lower proportion had ischemic heart disease (62.6% vs. 54.1%, P = 0.02). Both groups had similar rates of procedural success, although lead threshold, impedance, and procedural radiation dose were significantly lower in those receiving a quadripolar lead. PNS was more common in those with quadripolar leads (16.0% vs. 11.6%, P = 0.08), but was eliminated by switching pacing vector in all cases compared with 60% in the bipolar group (P < 0.001). Furthermore, LV lead displacement (1.7% vs. 4.6%, P = 0.03) and repositioning (2.0% vs. 5.2%, P = 0.03) occurred significantly less often in those with a quadripolar lead. All-cause mortality was also significantly lower in the quadripolar compared to bipolar lead group in univariate and multivariate analysis (13.2% vs. 22.5%, P < 0.001).

CONCLUSIONS

In a large, multicenter experience, the use of quadripolar LV leads for CRT was associated with elimination of PNS and lower overall mortality. This has important implications for LV pacing lead choice.

Profile of St. Jude Medical's Allure Quadra quadripolar pacemaker system for cardiac resynchronization therapy

Congestive heart failure is a major public health epidemic and economic burden in the USA and worldwide. Cardiac resynchronization therapy is an effective therapy for treating congestive heart failure in conjunction with pharmacologic therapy. The average congestive heart failure admission costs approximately US$ 8 billion annually. Current cardiac resynchronization therapy pacemaker systems from various manufacturers deliver therapy-utilizing bipolar leads including the left ventricle, with electrode spacing ranging from 8 to 22 mm. The Quartet LV™ lead model 1458Q (St. Jude Medical Sylmar, CA) is a quadripolar lead with a 4.0 Fr. tip electrode and three 4.7 Fr. ring electrodes located 20, 30 and 47 mm from the tip. The Quartet lead and Allure Quadra TM allows 14 pacing configurations, providing benefits, including reductions in phrenic nerve stimulation, reduced pacing thresholds, improved battery longevity and potential reductions, in non-responders to cardiac resynchronization therapy. In addition, there is cost benefit data from utilizing quadripolar technology compared with traditional bipolar cardiac resynchronization therapy.

Comparison of different pacing strategies to minimize phrenic nerve stimulation in cardiac resynchronization therapy

INTRODUCTION

Phrenic nerve (PN) stimulation (PNS) frequently limits cardiac resynchronization therapy (CRT). Yet, pacing strategies to minimize PNS have not been systematically compared. We propose to: (1) compare different pacing strategies to minimize PNS in CRT and (2) evaluate differences between PN and left ventricular (LV) capture thresholds among LV pacing configurations.

METHODS AND RESULTS

PN and LV thresholds were obtained using 6 LV configurations in 28 patients with any PNS during CRT implantation or replacement. Incidence of PNS was compared in all LV configurations by programming pacing output to (1) One Volt (V) above LV threshold, (2) triple pulse width (PW) at LV threshold, and (3) 1.5 times LV threshold for each patient. PN thresholds and PN strength-duration curves were statistically different between configurations (P < 0.05). Ring→RVcoil and Ring→Can had the largest difference between PN and LV thresholds. Pacing output programmed to 1.5 times LV threshold, 1 V above LV threshold, and triple PW at LV threshold had similar probability of PNS between LV configurations. However, 1 V above LV threshold and triple PW at LV threshold frequently resulted in poor (< 30%) LV capture safety margin (14-43% and 53-68%, respectively). Freedom from PNS (programmed output at twice LV threshold) was found in 88%, 84%, and 52% with 6, 3, or 2 available LV configurations, respectively.

CONCLUSION

Multiple LV pacing configurations marginally increase the probability of avoiding PNS by electronic reprogramming. Pacing output programmed to 1.5 times LV threshold is an additional alternative to minimize PNS when electronic reprogramming options are limited.

The Use of a Quadripolar Left Ventricular Lead Increases Successful Implantation Rates in Patients with Phrenic Nerve Stimulation and/or High Pacing Thresholds Undergoing Cardiac Resynchronisation Therapy with Conventional Bipolar Leads

Background

Phrenic nerve stimulation (PNS) and high pacing thresholds (HPT) hinder biventricular stimulation in patients (pts) undergoing cardiac resynchronization therapy (CRT). A new quadripolar left ventricular (LV) lead (Quartet 1458Q, St. Jude Medical) with increased number of pacing configuration, might overcome this problem.

Methods

All consecutive pts in whom a standard bipolar lead intraoperatively resulted in PNS and/or HPT (≥4.00V/1mV), received, during the same implant, a quadripolar LV lead. Aim of the study was to evaluate acute and short term outcome.

Results

26 pts [24 (92%) male, mean age 74±6 years)] with PNS (22 pts; 85%) and HPT (4 pts; 15%) were included. Permanent right ventricular pacing was the reason for broad QRS complex in 4 (15%) pts, whereas all other pts had a left bundle branch block. Severely symptomatic (NYHA Class ≥3) heart failure with reduced ejection fraction (EF 31±9%) was mostly caused by ischemic heart disease (14 pts; 54%). Idiopathic dilated cardiomyopathy and valvular heart disease were diagnosed in 6 (23%) pts each. In most (24/26, 92%) pts the use of the Quartet lead led to successful biventricular pacing due to a significant reduction in intraoperative pacing threshold (5.2V/1.0ms vs. 1.4V/0.8ms; p=0.03), which was maintained (1.2V/0.7ms) at follow-up. PNS never represented reason for failed LV pacing, neither acutely nor during follow-up.

Conclusion

Excessively HPT and/or PNS are frequently encountered when conventional bipolar leads are used for CRT. A new quadripolar LV lead increases the rate of successful biventricular stimulation. Lower pacing threshold and freedom from PNS are maintained at follow-up.

Occurrence of phrenic nerve stimulation in cardiac resynchronization therapy patients: the role of left ventricular lead type and placement site

AIMS

Unwanted phrenic nerve stimulation (PNS) has been reported in ∼1 in 4 patients undergoing left ventricular (LV) pacing. The occurrence of PNS over mid-term follow-up and the significance of PNS are less certain.

METHODS AND RESULTS

Data from 1307 patients enrolled in pre-market studies of LV leads manufactured by Medtronic (models 4193 and 4195 unipolar, 4194, 4196, 4296, and 4396 bipolar) were pooled. Left ventricular lead location was recorded at implant using a common classification scheme. Phrenic nerve stimulation symptoms were either spontaneously reported or identified at scheduled follow-up visits. A PNS-related complication was defined as PNS resulting in invasive intervention or the termination of LV pacing. Average follow-up was 14.9 months (range 0.0-46.6). Phrenic nerve stimulation symptoms occurred in 169 patients (12.9%). Phrenic nerve stimulation-related complications occurred in 21 of 1307 patients (1.6%); 16 of 738 (2.2%) in the unipolar lead studies, and 5 of 569 (0.9%) in the bipolar lead studies (P = 0.08). Phrenic nerve stimulation was more frequent at middle-lateral/posterior, and apical LV sites (139/1010) vs. basal-posterior/lateral/anterior, and middle-anterior sites (20/297; P= 0.01). As compared with an anterior LV lead position, a lateral LV pacing site was associated with over a four-fold higher risk of PNS (P= 0.005) and an apical LV pacing site was associated with over six-fold higher risk of PNS (P= 0.001).

CONCLUSION

Phrenic nerve stimulation occurred in 13% of patients undergoing LV lead placement and was more common at mid-lateral/posterior, and LV apical sites. Most cases (123/139; 88%) of PNS were mitigated via electrical reprogramming, without the need for invasive intervention.

Effect of bipolar electrode spacing on phrenic nerve stimulation and left ventricular pacing thresholds: an acute canine study

BACKGROUND

Phrenic nerve stimulation (PNS) is a common complication of cardiac resynchronization therapy when left ventricular (LV) pacing occurs via a coronary vein. The purpose of this study was to evaluate the effects of bipolar electrode spacing on PNS and LV pacing thresholds.

METHODS AND RESULTS

Electrophysiology catheters with standard (2 mm-5 mm-2 mm) or modified (1 mm-5 mm-1 mm) interelectrode spacing was, respectively, inserted in a posterior/lateral cardiac vein in a randomized order in 6 anesthetized dogs via jugular access. The phrenic nerve was dissected via a left minithoracotomy and repositioned over the vein as close as possible to one of the electrodes. The presence of PNS was verified (ie, PNS threshold <2 V at 0.5 ms in unipolar configuration). Bipolar pacing was delivered using the electrode closest to the phrenic nerve as the cathode, and multiple bipolar electrode spacing configurations were tested. During bipolar pacing, PNS threshold increased as bipolar electrode spacing was reduced (P<0.05), whereas LV pacing thresholds did not change significantly (P>0.05). Compared with a standard bipolar electrode spacing of 20 mm for LV leads, 1 and 2 mm bipolar electrode spacing resulted in a PNS threshold increase of 5.5±2.2 V (P=0.003) and 2.8±1.7 V (P<0.001), respectively. Similarly, PNS threshold increased by 6.5±3.7 V with 1 mm and by 3.8±1.9 V with 2 mm bipolar pacing (both P<0.001), compared with unipolar pacing.

CONCLUSIONS

This study suggests that reducing LV bipolar electrode spacing from the standard 20 mm to 1 or 2 mm may significantly increase the PNS threshold without compromising LV pacing thresholds.

Disparity in left ventricular stimulation among different pacing configurations in cardiac resynchronization therapy

BACKGROUND

Cardiac resynchronization therapy (CRT) demands high energy utilization due to continuous biventricular pacing. Current technology allows 6 pacing configurations for a bipolar left ventricular (LV) lead. Understanding the energy requirements for each configuration will allow optimization of pacing output.

METHODS AND RESULTS

Pacing impedance, LV voltage threshold at 1.5 ms (rheobase) and 0.4 ms and chronaxie were obtained in 6 LV configurations in 49 consecutive patients undergoing CRT implantation or replacement. Strength-duration curves were derived using the Lapicque formula. Pacing impedances and voltage thresholds at 1.5 and 0.4 ms, calculated minimum threshold energy at chronaxie, current drain, energy thresholds at 0.4 ms, and strength-duration curves were statistically different between LV configurations (P<0.05). The lowest threshold energy requirements were found in Tip→right ventricular (RV) coil and Tip→Can configuration. Energy strength-duration curves involving the ring as the cathode (Ring→RV, Ring→Can, and Ring→Tip) had the highest LV thresholds. The pacing configuration with the lowest energy threshold correlated 89% of the time with the lowest voltage threshold at 0.4 ms. The probability to reach LV thresholds <1.5 V at 0.4 ms was increased from 51% with 2 LV configurations to 67% with 6 LV configurations.

CONCLUSIONS

Pacing impedance, LV thresholds, minimum threshold energy at chronaxie, current drain, voltage, and energy strength-duration curves were statistically different between LV pacing configurations. LV pacing configuration with the lowest voltage threshold does not always reflects the lowest energy threshold, particularly in the presence of a low impedance configuration. The availability of 6 LV configurations increases the probability of optimizing LV pacing output.

[Technical innovations and limitation in cardiac electrotherapy]

Coronary sinus (CS) lead positioning is one of the main determinants of cardiac resynchronization therapy (CRT). The implantation of the CS lead is faced with several technical difficulties that may prevent the achievement of a stable position and good performance of the CS lead without phrenic nerve stimulation (PNS). New developments in catheter and lead technology to overcome these difficulties are presented.

Use of a quadripolar left ventricular lead to achieve successful implantation in patients with previous failed attempts at cardiac resynchronization therapy

Aims

Problems with implanting a left ventricular (LV) lead during cardiac resynchronization therapy (CRT) procedures are not uncommon and may occur for a variety of reasons including phrenic nerve stimulation (PNS) and high capture thresholds. We aimed to perform successful CRT in patients with previous LV lead problems using the multiple pacing configurations available with the St Jude Quartet model 1458Q quadripolar LV lead to overcome PNS or high capture thresholds.

Methods and results

Four patients with previous failed attempts at LV lead implantation underwent a further attempt at CRT using a Quartet lead. In all four cases, successful CRT was achieved using a Quartet lead placed in a branch of the coronary sinus. Problems with PNS or high capture thresholds were seen in all four patients but were successfully overcome. Satisfactory lead parameters were seen at implant, pre-discharge, and at short-term follow-up (8.5 ± 5 weeks).

Conclusion

The Quartet lead allows 10 different pacing vectors to be used and may overcome common pacing problems because of the multiple pacing configurations available. Problems with either PNS or unsatisfactory pacing parameters experienced during CRT may be resolved simply by changing the pacing configuration using this quadripolar lead system.