Left Ventricular Stimulation Research Articles

Abstract 17400: Catecholamine Release Triggered by Epicardial Absolute Refractory Period Stimulation Augments Global Left Ventricular Function

Background: Biventricular epicardial (Epi) pacing can augment left ventricular (LV) function in heart failure. We postulated that these beneficial effects could involve catecholamine release from local autonomic nerve activation. This hypothesis was tested by applying Epi pacing stimuli during the muscle’s absolute refractory period (ARP) thereby activating intrinsic nerves without altering activation sequence. Methods: Anesthetized farm pigs (n=5) were instrumented with a LV high-fidelity pressure transducer, left atrial and LV Epi pacing electrodes, and sonomicrometer segment length (SL) gauges placed proximal and distal to the LV stimulation site. A small catheter was placed into the great cardiac vein adjacent to the LV pacing site for blood sampling. During atrial pacing at constant rate, 3 electrical pulses (0.8ms, 2-3x threshold volts) were applied to the LV Epi electrodes during the ARP. An experimental run consisted of baseline measurements, with 10 minutes of stimulation followed by 5 minutes of recovery repeated 3 times before and with ß- receptor blockade (BB, metoprolol, 5 mg). Coronary venous blood was sampled at baseline and at 5 and 10 minutes of stimulation for norepinephrine analysis (NE by ELISA). Results: ARP stimulation produced a significant increase in coronary venous NE levels (p< 0.01) accompanied by a significant 10-15% increase in LV dP/dt max (p< 0.01). Segment length vs. LV pressure loop area proximal to the stimulus site was significantly decreased (29.8 ± 10.9 mmHg*mm) compared to baseline (92.6 ± 8.2 mmHg*mm) but was unchanged at the distal site. BB abolished the changes in segment function and blocked the increase in LV dP/dt despite continued NE release. Conclusion: These results demonstrate that ARP EPI pacing induces NE release and augments global LV function. This effect may contribute to the beneficial effect of biventricular Epi pacing in some patients with heart failure.

State of the art of leadless pacing.

Despite undisputable benefits, conventional pacemaker therapy is associated with specific complications related to the subcutaneous device and the transvenous leads. Recently, two miniaturized leadless pacemakers, Nanostim™ (St. Jude Medical) and Micra™ (Medtronic), which can be completely implanted inside the right ventricle using steerable delivery systems, entered clinical application. The WiCS™-cardiac resynchronisation therapy (CRT) system (wireless cardiac stimulation for CRT, EBR Systems) delivers leadless left ventricular endocardial stimulation for cardiac resynchronization. In addition to obvious cosmetic benefits, leadless pacing systems may have the potential to overcome some complications of conventional pacing. However, acute and long-term complications still remains to be determined, as well as the feasibility of device explantation years after device placement.

Cardiac memory in cardiac resynchronization therapy: A vectorcardiographic comparison of biventricular and left ventricular pacing

Introduction“Cardiac memory” (CM) refers to a change in repolarization induced by an altered pathway of activation, manifested after resumption of spontaneous ventricular activation (SVA). AimsTo investigate for the first time in humans the effects of left ventricular (LV) pacing on CM development through vectorcardiography (VCG). MethodsWe studied 28 patients with heart failure (HF) and left bundle branch block (LBBB) treated with cardiac resynchronization therapy (CRT). Fourteen patients underwent biventricular (BIV) stimulation; the other 14 underwent LV stimulation only. VCG was acquired during SVA at baseline and during AAI and DDD pacing immediately after and 7 and 90days after the implant. ResultsAt baseline, in both groups, the QRS and T vectors angles were those specific of LBBB pattern.During DDD pacing, QRS vector angle changed to the right and upward in BIV patients while no significant differences were observed in LV patients.During AAI pacing, T vector angle changed significantly in BIV patients, following the direction of the paced QRS and amplitude significantly increased. In LV patients no significant differences in T vector angles were observed. Only T vector amplitude significantly increased at 7days (p=0.03) and at 90days (p=0.008 vs baseline). ConclusionIn patients with LBBB, BIV pacing induces cardiac memory development as a significant change in T vector magnitude and angle, while LV pacing doesn’t induce significant modifications in QRS and T vector angles and CM is manifested only as a significant T vector amplitude change.

Synchronization of repolarization by mechano-electrical coupling in the porcine heart.

The aim of this study was to evaluate the effect of increase in left ventricular (LV) pressure on repolarization and activation-recovery intervals. Six pig hearts were Langendorff-perfused. A compliant liquid-filled balloon, connected with a pressure transducer, inserted through the mitral orifice, could be filled until the required LV systolic pressure was obtained. A grid of 121 electrodes (11 × 11; 5 mm interelectrode distance) was sutured on the LV free wall. Ventricular pacing at 600 ms and at 400 or 450 ms was either performed from the LV wall or from the ventricular septum. Under all these four conditions, the pressure wave occurred at the same moment relative to the onset of the QRS complex. Consequently, the time relation between local repolarization and the pressure wave differed between the various pacing sites. Repolarization times (RTs) at a cycle length (CL) of 600 ms were prolonged by increased pressure. With stimulation from the LV, when the pressure wave coincides with the action potentials (APs) late in their phase (sites with relatively early repolarization), an increase in pressure from 0 to 100 mmHg delayed repolarization more than with stimulation from the septum, when the pressure wave occurs at a relatively earlier phase of the AP (sites with relatively late repolarization). At pacing at CL 400/450 ms, an increase in pressure caused RT prolongation at the LV free wall during LV stimulation, but less RT prolongation or even shortening during septal stimulation. The effect of increased LV pressure is synchronization of repolarization.

Acute hemodynamic effects of single- and dual-site left ventricular pacing employing a dual cathodal coronary sinus lead.

We studied the acute hemodynamic effect of left ventricular (LV) pacing from a dual cathodal coronary sinus (CS) lead in a both single- and dual-site electrode configuration. In 17 patients who underwent implantation of a cardiac resynchronization therapy-defibrillator system with dual cathodal CS leads, LV stimulation was performed from the distal and proximal electrode separately and from both electrodes simultaneously. The acute hemodynamic response was evaluated by invasive measurement of LVdP/dtmax. Timing of LV electrical activation time measured from onset QRS to LV sense during intrinsic rhythm at both electrodes were determined from simultaneous intracardiac recordings. The latter results were compared to those of an additional group of 26 patients in whom no hemodynamic effects were evaluated. Baseline LVdP/dtmax was 897 ± 222 mm Hg/s. Single-site LV pacing resulted in a rise of LVdP/dtmax to 1,053 ± 266 mm Hg/s (+17.4%) taking the best of the two sites and 1,020 ± 254 mm Hg (+13.7%) at the worst site (P = 0.0001). In the dual-site pacing configuration LVdP/dtmax was 1,026 ± 243 mm Hg/s (+14.1%). P value for single best versus dual site was 0.005, and for dual site versus worst single site was 0.18 (n.s.). Even with a relatively small distance of 20-21 mm between stimulation electrodes, there is a significant difference in acute hemodynamic effect from the single best and worst site. Dual-site LV pacing offers no hemodynamic benefit over the best single pacing site. The short electrode distance may have been a limitation and results may not be applicable to other forms of multisite pacing.

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.

Long Pacing Pulses Reduce Phrenic Nerve Stimulation in Left Ventricular Pacing

Phrenic nerve stimulation is a major obstacle in cardiac resynchronization therapy (CRT). Activation characteristics of the heart and phrenic nerve are different with higher chronaxie for the heart. Therefore, longer pulse durations could be beneficial in preventing phrenic nerve stimulation during CRT due to a decreased threshold for the heart compared with the phrenic nerve. We investigated if long pulse durations decreased left ventricular (LV) thresholds relatively to phrenic nerve thresholds in humans. Eleven patients, with indication for CRT and phrenic nerve stimulation at the intended pacing site, underwent determination of thresholds for the heart and phrenic nerve at different pulse durations (0.3-2.9 milliseconds). The resulting strength duration curves were analyzed by determining chronaxie and rheobase. Comparisons for those parameters were made between the heart and phrenic nerve, and between the models of Weiss and Lapicque as well. In 9 of 11 cases, the thresholds decreased faster for the LV than for the phrenic nerve with increasing pulse duration. In 3 cases, the thresholds changed from unfavorable for LV stimulation to more than a factor 2 in favor of the LV. The greatest change occurred for pulse durations up to 1.5 milliseconds. The chronaxie of the heart was significantly higher than the chronaxie of the phrenic nerve (0.47 milliseconds vs. 0.22 milliseconds [P = 0.029, Lapicque] and 0.79 milliseconds vs. 0.27 milliseconds [P = 0.033, Weiss]). Long pulse durations lead to a decreased threshold of the heart relatively to the phrenic nerve and may prevent stimulation of the phrenic nerve in a clinical setting.

Multipoint pacing: Can we connect the dots to improve resynchronization therapy?

The utility of cardiac resynchronization therapy (CRT) for patients with congestive heart failure and electromechanical dyssynchrony is well established. This form of therapy has a salutary effect on both quality of life and survival. Nevertheless, approximately one-third of the patients may not experience clinical benefit. Furthermore, if reverse remodeling, defined as a 415% reduction in end systolic volume, is used as a marker of response, then as many as half of the patients may be considered nonresponders. 1 Several techniques have been used in an attempt to improve the efficacy of CRT. The optimization of AV and VV intervals has been used with marginal benefit. Large studies have suggested that simultaneous vs sequential activation of the ventricles has little effect on the vast majority. 2 Left ventricular (LV) stimulation alone has also been evaluated, and it demonstrated clinical outcomes similar to those demonstrated by biventricular stimulation. 2,3 However, it should be noted that an individual not responding to LV stimulation may benefit from a change to biventricular pacing. 3 Optimizing lead placement by either electrical or hemodynamic parameters has been investigated. Identifying sites of late LV activation and targeting such

Different brain activation under left and right ventricular stimulation: an fMRI study in anesthetized rats.

BackgroundMyocardial ischemia in the anterior wall of the left ventricule (LV) and in the inferior wall and/or right ventricle (RV) shows different manifestations that can be explained by the different innervations of cardiac afferent nerves. However, it remains unclear whether information from different areas of the heart, such as the LV and RV, are differently processed in the brain. In this study, we investigated the brain regions that process information from the LV or RV using cardiac electrical stimulation and functional magnetic resonance imaging (fMRI) in anesthetized rats because the combination of these two approaches cannot be used in humans.Methodology/Principal FindingsAn electrical stimulation catheter was inserted into the LV or RV (n = 12 each). Brain fMRI scans were recorded during LV or RV stimulation (9 Hz and 0.3 ms width) over 10 blocks consisting of alternating periods of 2 mA for 30 sec followed by 0.2 mA for 60 sec. The validity of fMRI signals was confirmed by first and second-level analyses and temporal profiles. Increases in fMRI signals were observed in the anterior cingulate cortex and the right somatosensory cortex under LV stimulation. In contrast, RV stimulation activated the right somatosensory cortex, which was identified more anteriorly compared with LV stimulation but did not activate the anterior cingulate cortex.Conclusion/SignificanceThis study provides the first evidence for differences in brain activation under LV and RV stimulation. These different brain processes may be associated with different clinical manifestations between anterior wall and inferoposterior wall and/or RV myocardial ischemia.

Narrow QRS Is Not the Right Substrate for Cardiac Resynchronization Therapy

The physiological underpinning for cardiac resynchronization therapy (CRT) began with Carl Wiggers in 1925. He showed that when contraction of the heart was induced by direct cardiac electric stimulation, the early phase of contraction of the heart was slowed and myocardial tension developed more gradually.1 Wiggers explained these findings by differences in the order of excitation of the ventricle. Subsequent studies by a number of investigators highlighted the fact that a left bundle-branch block conduction pattern was associated with dyssynchronous contraction that exacerbated left ventricular systolic dysfunction. Few people appreciate the fact that Dr Morton Mower, who was involved in the development of the implantable cardioverter defibrillator,2,3 also developed the patent for cardiac resynchronization therapy in 19904 that was assigned to CPI/Guidant and subsequently licensed to Medtronic. In 1994, Cazeau et al5 reported 1 patient with widened QRS and advanced heart failure who achieved dramatic improvement with biventricular pacing. Various short-term animal and clinical hemodynamic studies showed significant improvement in cardiac function when both right and left ventricles of a diseased heart with conduction disturbance were preexcited (biventricular pacing),6 and similar findings were observed recently with univentricular left ventricular stimulation in the compromised heart …

Left ventricular endocardial leadless pacing brings new hope to patients with heart failure

Cardiac resynchronization therapy (CRT) provides prognostic and symptomatic benefits for patients with heart failure and left ventricular (LV) dyssynchrony. It requires the implantation of an LV lead, usually placed in a tributary of the coronary sinus. Despite important progress made in the development of dedicated instrumentation, challenges still remain, and the procedure may even be unsuccessful for various reasons, including CS occlusion, dissection, abnormal ostium of the CS, coronary vein stenosis, lead instability, high threshold, or phrenic nerve stimulation. Even if the procedure is successful, about 30% of patients receiving CRT do not respond to treatment [1]. Although the underlying reasons for the lack of CRT response in some patients are undoubtedly multifactorial, some problems have been identified and may have the potential to be ameliorated. Firstly, limitations imposed by coronary venous anatomy on the selection of the site for LV stimulation are thought to be a major contributor to the lack of CRT response. Secondly, stimulation is epicardial, which leads to delayed electrical activation of the LV in comparison to endocardial stimulation, and has been shown to provide less hemodynamic benefit [2]. Additionally, pacing leads are the most frequent cause of complications related to permanent pacing systems and CRT complication rates for coronary vein leads are ~11–12% [3]. An alternative approach of delivering left ventricular endocardial leadless pacing (LVELP) offers a number of potential advantages, including greater choice of LV lead position, possibly more rapid LV activation, and reducing lead-related complications. The feasibility of a new technology using energy transfer from an ultrasound transmitter to a receiver electrode to achieve cardiac stimulationwithout theuseof apacing leadhas been reportedpreviously [4]. A novel implantable cardiac pacing systembased on this concept has recently been developed for the treatment of heart failure (Wireless Cardiac Stimulation-LVSystem,WiCS®-LV, EBRSystems, Inc., Sunnyvale, CA, USA) and a clinical trial using the WiCS®-LV system is ongoing in Europe. The study titled Wireless Stimulation Endocardially for CRT (WiSE-CRT) is evaluating the safety and feasibility in specific subsets of patients with CRT-eligible heart failure. LVLEPwill maybe become an effective approach for LV pacing in CRT. In this letter we discuss the potential advantages and disadvantages of this method. LVLEP provides several potential advantages, including:

Benefits of Endocardial and Multisite Pacing Are Dependent on the Type of Left Ventricular Electric Activation Pattern and Presence of Ischemic Heart Disease

Background— There is considerable heterogeneity in the myocardial substrate of patients undergoing cardiac resynchronization therapy (CRT), in particular in the etiology of heart failure and in the location of conduction block within the heart. This may account for variability in response to CRT. New approaches, including endocardial and multisite left ventricular (LV) stimulation, may improve CRT response. We sought to evaluate these approaches using noncontact mapping to understand the underlying mechanisms. Methods and Results— Ten patients (8 men and 2 women; mean [SD] age 63 [12] years; LV ejection fraction 246%; QRS duration 161 [24] ms) fulfilling conventional CRT criteria underwent an electrophysiological study, with assessment of acute hemodynamic response to conventional CRT as well as LV endocardial and multisite pacing. LV activation pattern was assessed using noncontact mapping. LV endocardial pacing gave a superior acute hemodynamic response compared with conventional CRT (26% versus 37% increase in LV dP/dt max , respectively; P <0.0005). There was a trend toward further incremental benefit from multisite LV stimulation, although this did not reach statistical significance ( P =0.08). The majority (71%) of patients with nonischemic heart failure etiology or functional block responded to conventional CRT, whereas those with myocardial scar or absence of functional block often required endocardial or multisite pacing to achieve CRT response. Conclusions— Endocardial or multisite pacing may be required in certain subsets of patients undergoing CRT. Patients with ischemic cardiomyopathy and those with narrower QRS, in particular, may stand to benefit.

CARDIAC RESYNCHRONISATION THERAPY EFFECTS COMPARE OF THE SURGERY EPICARDIAL LEAD VERSUS CORONARY SINUS LEAD PLACEMENT

ObjectivesCardiac resynchronisation therapy (CRT) with biventricular pacing has demonstrated cardiac function improvement. Two strategies (coronary sinus vs epicardial) for left ventricular (LV) pacing were compared.Methods33 patients with ejection fraction <35%,...

Active fixation pacing leads in the distal coronary venous system in patients with prosthetic tricuspid valve

Permanent pacemaker implantations in patients requiring ventricular pacing is usually accomplished by the placement of endocardial pacing lead in the right ventricle. In the presence of prothestic tricuspid valve, this method has the potential of causing complications to the lead or the prosthetic valve and thus not recommended. Pacing options for this group of patients include epicardial lead implantation or the placement of lead in the coronary sinus. We describe the use of active fixation lead mechanism in the coronary sinus to improve stability in this group of patients. Between July 2010 until September 2011, we implanted 4F active fixation leads (SelectSecure Model 3830, Medtronic, Minneapolis, MN, USA) in three patients with prosthetic tricuspid valve who required ventricular pacing. Active fixation leads were used in view of lead instability with conventional coronary sinus pacing leads. The lead was positioned and actively fixed at its optimal at the distal coronary sinus. The performances of the leads and its related complications were then monitored. The leads were successfully implanted in all three patients. The peri implantation pacing parameters were within acceptable limits with pacing thresholds of 2.3, 1.2 and 0.5 V, respectively and pacing impedances of 1450, 817 and 1384 Ω. Follow up interrogation revealed stable pacing parameters. No immediate complications were observed. A 4F active fixation lead placement at the distal coronary sinus to deliver left ventricular stimulation in patients with prosthetic tricuspid valve showed stable and consistent delivery of acceptable pacing performances.

Temporary left ventricular stimulation in patients with refractory cardiogenic shock and asynchronous left ventricular contraction: A safety and feasibility study

Despite modern treatment strategies, cardiogenic shock (CS) is still associated with high mortality. To evaluate the feasibility and safety of temporary percutaneous left ventricular (LV) stimulation as rescue therapy in patients with CS refractory to standard clinical care. Consecutive patients with deteriorating CS without further treatment options received transjugular placement of a temporary LV lead if they exhibited signs of asynchronous LV contraction. To maintain atrioventricular synchronous contraction, an additional right atrial lead was placed in patients with sinus rhythm. The leads were externally connected to a conventional pacemaker. Hemodynamic course, clinical outcome, and adverse events were assessed. A total of 15 patients [ischemic cardiomyopathy (n = 8), dilated cardiomyopathy (n = 6), and acute myocarditis (n = 1)] underwent successful lead placement. Median procedure and fluoroscopy times measured 60 minutes (interquartile range [IQR] 55-90) and 12 minutes (IQR 7-34), respectively. Ten patients (67%) acutely responded by improvement of hemodynamic parameters with simultaneous reduction of catecholamine support. Catecholamine therapy was discontinued after a median of 28 hours (IQR 16-60). The temporary leads were removed after a median of 6 days (IQR 3-10). Total in-hospital mortality was 47%, measuring 80% in nonresponders and 30% in responders (P = .119). There was no therapy-related serious adverse event. Our data indicate that there may be a role for temporary LV stimulation as rescue therapy in selected patients with refractory CS. In clinical situations where aggressive therapies are used for urgent hemodynamic stabilization, temporary LV stimulation may evolve as a further and less invasive treatment option.

Unusual cause of desynchronization in a cardiac resynchronization device

This report describes a new cause of desynchronization encountered in a cardiac resynchronization device functioning in the VVIR mode. Left ventricular stimulation was inhibited when the sensor-driven rate exceeded the programmed left ventricular (LV) maximum trigger rate. With these devices, it is important to program the LV maximum trigger interval (essentially equivalent to a LV upper interval) to a value equal or faster than the sensor-driven upper rate.

Vectorcardiography as a Tool for Easy Optimization of Cardiac Resynchronization Therapy in Canine Left Bundle Branch Block Hearts

Background— In cardiac resynchronization therapy (CRT), optimization of left ventricular (LV) stimulation timing is often time consuming. We hypothesized that the QRS vector in the vectorcardiogram (VCG) reflects electric interventricular dyssynchrony, and that the QRS vector amplitude (VA QRS ), halfway between that during left bundle branch block (LBBB) and LV pacing, reflects optimal resynchronization, and can be used for easy optimization of CRT. Methods and Results— In 24 canine hearts with LBBB (12 acute, 6 with heart failure, and 6 with myocardial infarction), the LV was paced over a wide range of atrioventricular (AV) delays. Surface ECGs were recorded from the limb leads, and VA QRS was calculated in the frontal plane. Mechanical interventricular dyssynchrony (MIVD) was determined as the time delay between upslopes of LV and right ventricular pressure curves, and systolic function was assessed as LV dP/dt max . VA QRS and MIVD were highly correlated ( r =0.94). The VA QRS halfway between that during LV pacing with short AV delay and intrinsic LBBB activation accurately predicted the optimal AV delay for LV pacing (1 ms; 95% CI, –5 to 8ms). Increase in LV dP/dt max at the VCG predicted AV delay was only slightly lower than the highest observed ∆LV dP/dt max (–2.7%; 95% CI, –3.6 to –1.8%). Inability to reach the halfway value of VA QRS during simultaneous biventricular pacing (53% of cases) was associated with suboptimal hemodynamic response, which could be corrected by sequential pacing. Conclusions— The VA QRS reflects electric interventricular dyssynchrony and accurately predicts optimal timing of LV stimulation in canine LBBB hearts. Therefore, VCG may be useful as a reliable and easy tool for individual optimization of CRT.

Left Ventricular Versus Biventricular for Cardiac Resynchronization Therapy

The primary mechanism of benefit associated with cardiac resynchronization therapy (CRT) is attributed to improvement in left ventricular (LV) function resulting from restoration of LV contractile synchrony.1,2 The vast majority of implanted CRT-capable devices are programmed to provide the therapy by simultaneous pacing of the right ventricle and LV (biventricular stimulation). This mode of CRT delivery has been the mode best tested in large-scale clinical trials that have demonstrated improvement in functional, anatomic, and event-driven outcomes.3–6 The reasons for the more thorough evaluation of biventricular stimulation compared with LV stimulation alone are largely practical in nature. Early studies of CRT systems were designed to demonstrate the safety and efficacy of CRT. Long-term transvenous epicardial LV stimulation was not an established therapy, and LV lead performance was unknown. Biventricular stimulation allowed backup pacing and sensing if the LV lead failed. Additionally, all bradycardia pacing and defibrillating lead timing and therapy delivery are determined by right ventricular lead–based sensing. These considerations necessitated the presence of a right ventricular lead in long-term studies of CRT. There was also the early short-term observation that short-term stimulation results in similar mechanical synchrony with …

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.

Multi-site left ventricular pacing as a potential treatment for patients with postero-lateral scar: insights from cardiac magnetic resonance imaging and invasive haemodynamic assessment

Multi-site left ventricular (LV) pacing may be superior to single-site stimulation in correcting dyssynchrony and avoiding areas of myocardial scar. We sought to characterize myocardial scar using cardiac magnetic resonance imaging (CMR). We aimed to quantify the acute haemodynamic response to single-site and multi-site LV stimulation and to relate this to the position of the LV leads in relation to myocardial scar. Twenty patients undergoing cardiac resynchronization therapy had implantation of two LV leads. One lead (LV1) was positioned in a postero-lateral vein, the second (LV2) in a separate coronary vein. LV dP/dtmax was recorded using a pressure wire during stimulation at LV1, LV2, and both sites simultaneously (LV1 + 2). Patients were deemed acute responders if ΔLV dP/dtmax was ≥ 10%. Cardiac magnetic resonance imaging was performed to assess dyssynchrony as well as location and burden of scar. Scar anatomy was registered with fluoroscopy to assess LV lead position in relation to scar. LV dP/dtmax increased from 726 ± 161 mmHg/s in intrinsic rhythm to 912 ± 234 mmHg/s with LV1, 837 ± 188 mmHg/s with LV2, and 932 ± 201 mmHg/s with LV1 and LV2. Nine of 19 (47%) were acute responders with LV1 vs. 6/19 (32%) with LV2. Twelve of 19 (63%) were acute responders with simultaneous LV1 + 2. Two of three patients benefitting with multi-site pacing had the LV1 lead positioned in postero-lateral scar. Multi-site LV pacing increased acute response by 16% vs. single-site pacing. This was particularly beneficial in patients with postero-lateral scar identified on CMR.