Phrenic Nerve Stimulation Thresholds Research Articles

PO-707-08 ANTIDROMIC LEFT PERICARDIOPHRENIC VEIN ACCESS FOR DEPLOYMENT OF A PHRENIC NERVE STIMULATOR: LESSONS LEARNED FROM COMPLEX CORONARY SINUS LEAD IMPLANTATION

Left pericardiophrenic vein (PPV) access is required to deploy over-the-wire phrenic nerve stimulator leads for implantable sleep apnea therapy devices. Coursing along the left lateral aspect of the pericardium, the left PPV is accompanied by the left phrenic nerve and terminates superiorly at the left brachiocephalic vein (BCV) and inferiorly at the left inferior phrenic vein. A superior approach may be complicated by congenital atresia, tortuous anatomy, or iatrogenic dissection. We report a novel approach to PPV access using retrograde wire externalization and antidromic lead placement derived from complex coronary sinus (CS) access techniques. Recognize techniques for complex vascular access for phrenic nerve stimulators and cardiac implantable electronic devices (CIED). The right chest was prepared for subclavian vein access and pre-pectoral generator implant. A 7 French (Fr) delivery sheath and inner 5 Fr Merit CS vertebral vein selector were used to engage the left BCV. Contrast angiography and a 0.014 mm angioplasty wire were used to identify the PPV. Repeated attempts to engage the tortuous vein were associated with proximal dissection. An alternative approach with inferior PPV access was selected. The sheath and vein selector were positioned within the left hepatic vein and the left phrenic vein for angiography. The angioplasty wire was advanced retrogradely into the PPV and left subclavian vein followed by an additional support wire. A separate 7 Fr sheath was placed in the right subclavian vein and a 4 Fr snare was used to secure and externalize the distal angioplasty wire. The wire was used as a rail to advance the phrenic nerve stimulator anterogradely into the PPV. Lead deployment was successful and phrenic nerve stimulation thresholds were satisfactory. Antidromic posterolateral cardiac vein access has been well described for complex coronary sinus lead implantation. The technique may be applied to extracardiac vascular anatomy for challenging PPV lead implantation. This case highlights the technical expertise and anatomical familiarity needed to optimize cardiac implantable electronic device implantation.

B-AB03-02 BIPHASIC FOCAL MONOPOLAR PULSED ELECTRIC FIELD THERAPY: PRESERVED PHRENIC NERVE FUNCTION AND ANATOMY

Thermal cardiac ablation may cause phrenic nerve (PhN) palsy. Pulsed electric fields (PEF) induce cell death independently from thermal processes, potentially enabling cardiac ablation underlying the PhN without disrupting its function or morphology. This preclinical study evaluates cardiac-based PEF treatments on the morphology and function of the PhN. In the right atrium of 4 pigs a focal ablation catheter was maneuvered with pacing until the location and minimum PhN stimulation threshold was established, as determined by monitoring diaphragmatic movement while decreasing pacing amplitude until capture was lost. Biphasic monopolar PEF therapy was then delivered with the focal catheter either directly over, or in proximity to the PhN when electrically isolating the SVC and RSPV. Following treatment, the PhN stimulation threshold was re-evaluated. Pigs were survived acutely (n=1) and at 28 days (n=3), after which the PhN was examined grossly and histologically. The PhN stimulation threshold did not change following treatment. No clinical signs of PhN palsy nor diaphragmatic paralysis were observed during the 28-day recovery period. Gross and histological examination of the PhN did not indicate signs of macroscopic nor microscopic morphology, while SVC and RSPV electrical isolation was retained. The mechanisms underlying PEF ablation enable treatment to tissue adjacent to the PhN without adversely affecting its form or function. This suggests the ability to perform PEF-based cardiac ablation in regions typically associated with high risk for PhN injury without appreciable risk of PhN-associated morbidity.

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.

Phrenic nerve stimulation in cardiac resynchronization therapy.

In cardiac resynchronization therapy (CRT), the electrical impulse delivered by the left ventricular (LV) lead may incidentally cause phrenic nerve stimulation (PNS). The purpose of this state-of-the-art review is to describe the frequency, risk factors, and clinical consequences of PNS and to present the most recent options to successfully manage PNS. PNS occurs in 2 to 37% of implanted patients and is not always detected in the supine position during implantation. Lateral and posterior veins are at higher risk of PNS than anterior veins, and apical positions are at higher risk of PNS than basal positions. The management of PNS discovered during implantation may include mapping the course of the target vein in order to find a PNS-free site, targeting another vein if available, and pacing with alternative configurations before changing the lead location. Non-invasive options for management of post-operative PNS depend on the difference between PNS and LV stimulation thresholds and include reducing the LV pacing output, automatic determination of LV stimulation threshold and minimal output delivery by the device, increasing the pulse duration, and electronic repositioning. New quadripolar leads allow to pace from different cathodes, and the multiple pacing configurations available have proved superior to bipolar leads in mitigating PNS. This electronic repositioning addresses almost all of the clinically relevant PNS and should markedly reduce the need for invasive lead repositioning or CRT abandon, which is actually the last option for 2% of patients.

Left ventricular lead placement guided by coronary venous 3D electro-anatomic mapping

Purpose: Placement of the left ventricular (LV) lead in the latest activated region of the LV is an important determinant of successful application of cardiac resynchronization therapy (CRT). Technically, the final lead position depends on cardiac venous anatomy, performance and stability of the lead and absence of phrenic nerve stimulation (PS). Our aim was to optimize LV lead positioning guided by coronary venous mapping. Methods: In 16 CRT candidates (mean QRS duration 155 ms), the electrical activation of the coronary sinus (CS) and its tributaries was assessed intra-operatively using 3D electro-anatomic mapping (EnSite NavX, St. Jude Medical, St. Paul, MN, USA). Mapping and PS testing was performed with a Vision Wire (Biotronik SE & Co.KG, Berlin, Germany). Local activation time (LAT) was measured relative to QRS onset on the surface ECG. Results: The latest activated region was located lateral in 8 patients, infero-lateral in 7 patients and inferior in 1 patient. The figure illustrates a 3D electrical activation map of the CS branches of a patient. Eleven patients had a final lead position anatomically concordant with the latest activated region. In this group, mean LAT was 120.9±28.6 ms at the latest activated region and 114.4±27.6 ms at the final lead position (p=0.59). In 5 patients, lead placement in the latest activated region was hampered by PS (2 patients), lead instability (2 patients) or high pacing threshold (1 patient). In this subgroup, mean LAT was 107.0±22.6 ms at the latest activated region and 83.2±13.1 ms at the final lead position (p=0,08). ![Figure][1] 3D electrical activation map Conclusion: Coronary venous 3D electro-anatomic mapping can be used to guide LV lead placement in the region of latest electrical activation free of phrenic nerve stimulation during CRT implantation. [1]: pending:yes

Phrenic nerve stimulation in CRT patients and benefits of electronic lead repositioning: the ERACE trial

Despite novel left ventricular (LV) lead technologies, phrenic nerve stimulation (PNS) remains an adverse effect observed in many patients with cardiac resynchronization therapy (CRT). Beyond anatomic repositioning, modern CRT devices allow avoidance of PNS also by software-based adaption of the pacing configuration. The Electronic Repositioning With Acuity and Easytrak Leads study evaluated the incidence of PNS in a CRT population and examined how often LV lead relocation can be avoided by "electronic repositioning" (ER). Patients who had an indication for implantation of a first CRT defibrillator with the option of ER were enrolled. Primary endpoint was the efficiency of ER determined by the frequency of PNS with the standard pacing configuration (LV tip to RV coil) avoidable by ER. PNS and pacing parameters were evaluated during implant, predischarge, and first routine follow-up (FU) using four different pacing configurations available by ER. In total, 292 patients were enrolled and provided with a transvenous LV lead (82.2 % male, 65.5 ± 9.2 years old). The majority of the population was in NYHA III (84.2 %) with a LV ejection fraction of 25.3 ± 6.8 % and mean QRS width of 155 ± 27 ms, ischemic cardiomyopathy was present in 43.6 %. Median FU was 116 days. In the standard pacing configuration, PNS was inducible in 19.0/25.6/24.6 % at implant/predischarge/FU, respectively, resulting in 32.2 % of the patients presenting at least once with PNS. The safety margin for the standard pacing configuration between LV and PNS threshold was <1.0 V at 0.5 ms in 5.6/7.0/5.0 % of the patients, corresponding with a total rate of 11.6 % during the FU. In the finally chosen configuration, clinically relevant PNS occurred in 1.0/2.2/1.3 %. The four vector configurations allowed all but 6 of 292 (2 %) patients to be reprogrammed using ER without reoperation. The incidence of inducible PNS in CRT patients is considerable. In this study, PNS could be avoided in the majority of the patients by means of electronic repositioning. Thus, the use of ER should be considered for CRT patients.

Short-spaced dipole for managing phrenic nerve stimulation in patients with CRT: The “phrenic nerve mapping and stimulation EP” catheter study

Phrenic nerve stimulation (PNS), occurring in 33%-37% of the patients with cardiac resynchronization therapy (CRT), is a limiting factor when implanting left ventricular (LV) leads from coronary veins. To test the hypothesis that PNS occurrence is related to bipolar electrode spacing. During standard CRT defibrillator implant procedures, a 5-F diagnostic electrophysiology catheter with 10 electrodes, spaced 2-5-2 mm, was positioned in a cardiac vein suitable for permanent LV lead placement. Pacing in the unipolar configuration identified the site with the lowest PNS threshold. PNS and left ventricular pacing (LVP) thresholds were then measured in different configurations at 0.5 ms: unipolar, each LV electrode served as the cathode in turn; and bipolar with different electrode spacing, cathode being the electrode with the lowest unipolar PNS threshold. From February to September 2010, 40 patients undergoing CRT implantation were enrolled in 4 centers in Italy. It was possible to identify PNS and perform a complete set of measurements in 23 patients. A bipolar electrode spacing of 2 mm resulted in higher PNS thresholds in bipolar configurations han did a bipolar electrode spacing of ≥ 5 mm. However, no significant increase in the LVP threshold was observed (P = ns). This experience suggests that LVP with a bipolar electrode spacing of 2 mm significantly increases the PNS threshold without affecting the LVP threshold, thereby increasing the possibility of delivering CRT when the LV lead is placed in proximity to the phrenic nerve.

442 Quadripolar LV Lead Provides Phrenic Nerve Stimulation Avoidance

Placement of an LV lead is often constrained by phrenic nerve stimulation (PNS). To address the challenge, the Left Ventricular Lead Acute Clinical Study (LILAC) was conducted to evaluate the ability of a new investigational quadripolar LV lead to map the PNS occurrence and mitigate it with single lead insertion at implant using multipolar configurations. This non-randomized study was conducted at 9 international centers and enrolled 54 patients indicated for CRT implantation. The lead design tested was intended to provide electrode contact in two different LV zones simultaneously (mid-apex (MA) and mid-base (MB)). Two lead models with short (S) and long (L) electrode spacing were included to provide the implanter with the ability to select an electrode spacing that matched the patient's individual anatomy. After acquiring a venogram, the implanter tested 1 or 2 lead models by wedging the lead in a selected target vein and recorded the lead testing positions via fluoro images. Unipolar pacing thresholds (PT) and PNS thresholds at each electrode were collected. Fifty patients were tested successfully with additional 2 attempts and 2 intents. The PNS occurrence and threshold are summarized in Table 1. By basing lead selection on individual venograms (no repositioning of the lead), 90% of cases demonstrated that at least one electrode in either zone had a PT ≤ 2.5V without PNS. In addition, 70% of patients achieved dual zone stimulation with a PT of ≤ 2.5V without PNS in MB and MA zones simultaneously. Mean thresholds from the best electrodes in MB and MA zones were 1.7±1.4V vs. 1.6±1.6V (p=ns) accordingly. Of the 24 patients with PNS, electrode switching resulted in no PNS in 20 patients at a PT of ≤ 2.5V and in 23 patients at ≤ 3.5V with unipolar pacing configuration only.Tabled 1 The LILAC quadripolar mapping data suggests PNS mostly occur in MA region with low stimulation threshold compared to MB region. Using this family of quadripolar leads, implanters would be able to achieve low PT and PNS avoidance at either MA or MB zone without repositioning the lead at implant.

Effect of Bipolar Electrode Spacing on Phrenic Nerve Stimulation and Left Ventricular Pacing Thresholds

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 &lt;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 &lt;0.05), whereas LV pacing thresholds did not change significantly ( P &gt;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 &lt;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 &lt;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.

Patients With New LV Leads Show a Bigger Change in Phrenic Nerve Stimulation Thresholds

Patients With New LV Leads Show a Bigger Change in Phrenic Nerve Stimulation Thresholds

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.

Networked multielectrode left ventricular pacing lead for avoidance of phrenic nerve stimulation in a canine model

In cardiac resynchronization therapy, left ventricular stimulation may lead to concomitant phrenic nerve stimulation (PNS). To evaluate a new networked multielectrode lead with 16 electrode segments (SEGs) configured into groups of 4, forming a virtual band (VBAND) around the lead. Each electrode is individually programmable using an embedded integrated circuit. In 8 anesthetized dogs, the lead was positioned in a left ventricular coronary vein. The voltage thresholds for cardiac stimulation and PNS were measured for different electrode configurations, including "VBAND-VBAND" (∼conventional bipolar pacing), "SEG-VBAND", and "SEG-SEG" (anode and cathode within the same VBAND). The measurements were performed (1) with closed chest and (2) after opening the chest and repositioning the phrenic nerve to above the lead, simulating a worst-case scenario. Compared with the conventional VBAND-VBAND stimulation, the SEG-SEG stimulation increased the PNS threshold and raised the difference between phrenic and cardiac thresholds from 6.2 ± 2.3 to 9.5 ±0.3 V in the closed chest condition and from 1.4 ± 1.6 to 9.0 ± 1.0 V in the worst-case scenario (both P < .001). Both SEG-VBAND and SEG-SEG stimulations reduced the cardiac threshold and increased pacing impedance, thus reducing the required cardiac pacing power by 77%-80% (P <.001 and P <.01 for closed and open chest, respectively). This novel multielectrode pacing lead achieves low cardiac and high extracardiac stimulation thresholds during left ventricular pacing in a canine model. The virtual elimination of PNS may facilitate and improve the application of cardiac resynchronization therapy.

Elimination of phrenic nerve stimulation occurring during CRT

Phrenic nerve stimulation (PNS) occurs at follow-up in approximately 20% of patients with bipolar leads. The quadripolar Quartet model 1458Q (St. Jude Medical, Sylmar, CA, USA) left ventricular lead (LV) has four electrodes (one distal tip and three ring) capable of ten different pacing vectors which may allow reprogramming to eliminate PNS. Forty patients underwent attempted CRT-D implantation between October 2009 and October 2010 with the Quartet lead. Pacing parameters, lead position, complications and presence of PNS were collected at implant, pre-discharge and at 3 and 6 months follow-up. A quadripolar LV lead was successfully implanted in 95% (38/40) of patients. During follow-up, one patient (3%) had a lead displacement requiring reposition. LV pacing parameters remained stable at 6 months follow-up (mean threshold 1.3 V at 0.6 ms and impedance 948 Ω). PNS at the time of implant was observed in 12 patients (32%) all of which were overcome by using the additional vectors available on the quadripolar LV lead or by repositioning the lead at the time of index implant. During 6 months follow-up there were five (13%) cases of PNS, all of which were successfully treated by reprogramming to a different vector. No cases required reintervention, surgical epicardial lead placement, or that lead be turned off. The quadripolar Quartet lead is associated with a high implant success rate, stable pacing parameters and a low displacement rate during the first 6 months after implant. The ten LV pacing vectors available with this lead allowed PNS and capture threshold problems to be overcome at implant, and importantly at follow-up, thus obviating the need for lead reposition.

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

AimsProblems 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 resultsFour 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).ConclusionThe 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.

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.

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

Phrenic nerve stimulation (PNS) can affect, and in some cases considerably limit, the long-term success of cardiac resynchronization therapy (CRT) therapy. To address this common problem, the manufacturers of CRT devices offer a range of configurations aimed at preventing high left ventricular pacing thresholds (LVPTs) and PNS. In 101 consecutive patients who had undergone implantation of a CRT system, we investigated prospectively the parameters LVPT and PNS threshold in relation to coronary sinus (CS) lead position, CS lead configuration, body position, and body mass index. With the configurations LV tip to right ventricular (RV) coil, LV tip to LV ring, and LV ring to RV coil, the LVPT and PNS threshold of patients with LV pacing were measured in the supine and left lateral body positions. The overall mean LVPT was lowest in LV tip to RV coil and highest in LV ring to RV coil configurations. The lowest PNS thresholds were measured in LV tip to RV coil and the highest in LV tip to ring configurations. The LVPT was not affected by body position and was stable in the standard supine and left lateral positions. Flexible LV pacing configurations are a useful feature of CRT systems for preventing PNS. The optimal LV pacing configuration should be determined on the basis of individual patient testing.