Ventricular Capture Threshold Research Articles

Oral flecainide therapy and myocardial pacing: preliminary data from a prospective multicenter registry

Abstract Background Antiarrhythmic drugs, class I are widely used for prevention of atrial fibrillation recurrence. However, previous studies found that these drugs could affect pacing thresholds among pacemaker recipients. Aim of the study: evaluate short -term effect on myocardial pacing following therapy with oral flecainide (200 mg/daily). Methods 45 consecutive pacemaker recipients were prospectively enrolled in a multicenter registry. These patients had preserved left ventricular ejection fraction, a dual chamber pacemaker with symptomatic sustained high-rate atrial fibrillation episodes and stable output atrial and ventricular thresholds. Patients were followed with ambulatory and/or remote monitoring. Results mean age was 74±1 years, 48% pts were male and AF burden was 8±16%. Pacemaker implantation was performed 3.9±0.3 year before study enrollment. Three (6%) out of 45 patients were excluded due to drug sided effects including dyspnea (n=1), diplopia (n=1) and toxicity during acute renal insufficiency (n=1). Flecainide treatment was associated with a significant reduction of atrial fibrillation burden (from 8±16% to 5±12%, p<0.01). At 30 days follow-up since Flecainide starting therapy both atrial and ventricular sensing significantly decreased (3.6 ± 2.2 vs 3.4 ± 2.1mV p=0.01; 12.5±6.6 vs 11.8±6.3 mV p=0.01), while there was a slight increase of both atrial and ventricular capture thresholds (0.77±0.61V@0.4ms vs 0.80±0.42V@0.4ms p=0.01; 0.80±0.53V @0.4ms vs 0.83±0.33V @0.4ms p=0.01). No patient required pacemaker parameters reprogramming. Conclusions oral flecainide therapy among pacemaker recipients at 30 days follow-up seems to be safe and do not affect device function. Further studies with additional follow-up data are warranted.

Abstract 13000: Twiddler’s Syndrome - A Rare Cause of Pacemaker Malfunction

Description of Case: A 76-year-old female with a past medical history of chronic atrial fibrillation and symptomatic tachycardia and bradycardia status-post dual-chamber pacemaker with right atrial and ventricular leads who presented with dyspnea on exertion. TTE showed normal biventricular function and no significant valvular abnormalities. Upon further evaluation of her pacemaker, she was found to have a very high ventricular capture threshold suggesting RV lead failure. The patient underwent RV lead replacement. The inspection of the pacemaker pocket during the procedure showed manual dislodgement of both tie-down sleeves and the pacemaker leads required untangling. A new RV lead was subsequently placed. Upon further imaging review, displacement of the previous RV lead was evident from initial placement. In addition, the patient had previously had a history of interval diaphragmatic stimulation as well. Overall, the presentation was felt to be consistent with Twiddler’s Syndrome. Discussion: Twiddler’s or Reel Syndrome occurs when conscious or subconscious self-manipulation and spinning of the pulse generator result in lead dislodgement and loss of pacing and pacemaker malfunction. The reeling of the leads around the generator can also cause stimulation of the brachial plexus or phrenic nerve stimulation and subsequent rhythmic arm twitching or diaphragmatic pacing, respectively. It has previously been reported in cases of single- and dual-chamber ICDs, deep brain stimulators, and spinal nerve stimulators with varying presentation. The diagnosis requires clinical suspicion based on history, physical exam, imaging, or surgical inspection suggesting the displacement of leads with evidence of coiling of the wires around the pacemaker. Treatment often requires revision and focus should be maintained on patient education for both primary and secondary prevention of Twiddler’s Syndrome.

Assessment of Cardiac Function and Ventricular Mechanical Synchronization in Left Bundle Branch Area Pacing by Speckle Tracking and Three-Dimensional Echocardiography

Real-time 3-dimensional echocardiography combined with speckle tracking was used in this study. A total of 90 patients with normal left ventricular ejection fraction were divided into 3 groups according to the pacing site: left bundle branch area pacing (LBBAP), right ventricular septal pacing (RVSP) or right ventricular apical pacing (RVAP). Procedure duration (90 ± 18 vs 61 ± 6.6 vs 58 ± 5.6 minutes, p=0.015), Fluoroscopy duration (15.5 ± 5.4 vs 4.8 ± 2.2 vs 4 ± 1.9 minutes, p=0.004), and ventricular capture threshold at implantation (0.8 ± 0.3 vs 0.6 ± 0.2 vs 0.6 ± 0.1 V, p=0.002) were significantly increased in patients that received LBBAP compared with RVSP or RVAP. At 4 weeks of follow-up, brain natriuretic peptide levels were significantly lower (22 [12 to 59] vs 135 [86 to 231] vs 235 [147 to 428] pg/ml, p=0.04), paced QRS duration was significantly shorter (115 ± 26 vs 134 ± 28 vs 157 ± 29 ms, p=0.012), and global longitudinal strain (-19.4 ± 2.4 vs -19.3 ± 3.4 vs -17.3 ± 3.5%, p=0.026) and systolic dyssynchrony index (2.5 ± 0.3 vs 5.9 ± 0.9 vs 7.7 ± 1.2, p=0.001), longitudinal absolute maximum difference of time to peak strain (17 [6 to 68] vs 117 [71 to 173] vs 126 [79 to 178] ms, p <0.0001), and circumferential absolute maximum difference of time to peak strain (76 [32 to 129] vs 148 [117 to 208] vs 161 [118 to 266] ms, p=0.005) were significantly lower in patients that received LBBAP compared with RVSP or RVAP. In conclusion, LBBAP can provide a more physiological ventricular activation pattern than RVSP or RVAP and results in good left ventricular electrical and mechanical synchronization.

Global left ventricular myocardial work efficiency in left bundle branch pacing versus right ventricular septal pacing: preliminary results of a randomized trial

Abstract Background Recently, the concept of left bundle branch pacing (LBBP) has emerged in clinical practice, in an attempt to prevent the deteriorating effects of right ventricular pacing (Vp). Purpose The aim of this study is to compare the effect of Vp on left ventricular (LV) dyssynchrony in patients with atrioventricular block (AVB) and preserved ejection fraction (EF), subjected to either LBBP or right ventricular septal pacing (RVSP). Methods Patients with AVB are randomized 1:1 to LBBP or RVSP. The effect of Vp is evaluated by echocardiographic indices of dyssynchrony, such as global myocardial work efficiency (GWE) and peak systolic dispersion (PSD). GWE represents the ratio of constructive work divided by the sum of constructive and wasted work [1]. Successful LBBP is defined by the presence of right bundle branch block paced QRS morphology in lead V1 and stim to LV activation time &amp;lt;75 msec [2]. No back-up right Vp lead was used in LBBP group. Results We conducted a preliminary analysis of the first 20 patients. Enrollment is still ongoing and total follow-up period is one year. We sought to investigate the acute effect of Vp on LV dyssynchrony 24 hours post procedure. Patients' baseline characteristics were similar in both groups and are presented in Table 1. One crossover was noted from LBBP to RVSP group, due to high ventricular capture threshold during implant. Implantation time was increased in LBBP arm (130±17.4 min in LBBP versus 47.7±4.5 min in RVSP group, p=0.004). Left bundle branch potential was recorded in 3 out of 10 LBBP patients. No statistically significant difference was demonstrated in GWE between the two groups (91.3% in LBBP versus 87.4% in RVSP group, p=0.052). PSD was numerically shorter in LBBP (53.3 msec) versus in RVSP (63.6 msec), p=0.114. There were no complications during both the acute perioperative phase and the running period of the follow-up. Moreover, no acute ventricular threshold capture rise, or lead dislodgement has been observed in neither group. The increased implantation time may be attributed to the more demanding technique, or the learning curve period required in the arm of LBBP. In the present analysis, a remarkable difference regarding GWE in favor of the LBBP group was demonstrated, although statistically not significant. However, even in this initial phase of the study, there is a trend of better LV synchrony and less wasted myocardial work in the LBBP group. The final difference of these indices will be assessed at the end of the one-year follow-up, when comparative results will be available. Conclusion LBBP is a novel, safe pacing method. Despite the longer procedural time and the risk of crossover, LBBP seems to offer better – without however statistical significance – LV synchrony even in the acute postoperative phase compared to RVSP. Longer follow-up studies are required to test whether LBBP compared to RVSP confers substantial clinical benefit. Funding Acknowledgement Type of funding sources: None.

Progressive improvement of atrial and ventricular capture thresholds, sensing, and impedances in epicardial pacing leads in young adults undergoing Fontan conversion

Progressive improvement of atrial and ventricular capture thresholds, sensing, and impedances in epicardial pacing leads in young adults undergoing Fontan conversion

Chronic performance of subxiphoid minimally invasive pericardial Model 20066 pacemaker lead insertion in an infant animal model.

To describe chronic performance of subxiphoid minimally invasive pacemaker lead insertion in a piglet model. Minimally invasive pacemaker lead implantation was performed through a 10-mm incision under direct visualization using the PeriPath port. Epicardial access was obtained and the commercially available Medtronic Model 20066 pacemaker lead was inserted into the pericardial space and epicardial fixation was performed using the side-action helix. The lead was connected to a pacemaker generator in a para-rectus pocket. Animals underwent a 12-14-week observation period and lead impedances, R-wave amplitudes, and ventricular capture thresholds were tested biweekly. After the survival period, animals were euthanized and gross and histopathology were performed. Subxiphoid minimally invasive pacemaker lead placement was performed in 8 animals (median 4.9kg) with 100% acute success. Median procedure time was 65min (IQR 60.5-77). At implant, median lead impedance was 650Ω (IQR 244-984), R-wave amplitude 11.1mV (IQR 8-12.3), and ventricular capture threshold 1.5V @ 0.4ms (IQR 1-2.6). Over a median survival period of 13weeks, there was a median lead impedance change of + 262Ω (IQR 5.3-618.3), R-wave change of - 4.5mV (IQR - 7.1-- 2.7) and capture threshold change (1.0ms) of + 1.5V (IQR 0-3.3). At autopsy, epicardial fixation sites showed fibrovascular proliferation and minimal chronic inflammation. Subxiphoid pericardial pacemaker placement is safe and effective in a piglet model. Further study and development of leads designed for pericardial placement are warranted.

Safety of Magnetic Resonance Imaging in Patients with Cardiac Devices

BackgroundPatients who have pacemakers or defibrillators are often denied the opportunity to undergo magnetic resonance imaging (MRI) because of safety concerns, unless the devices meet certain criteria specified by the Food and Drug Administration (termed “MRI-conditional” devices).MethodsWe performed a prospective, nonrandomized study to assess the safety of MRI at a magnetic field strength of 1.5 Tesla in 1509 patients who had a pacemaker (58%) or an implantable cardioverter–defibrillator (42%) that was not considered to be MRI-conditional (termed a “legacy” device). Overall, the patients underwent 2103 thoracic and nonthoracic MRI examinations that were deemed to be clinically necessary. The pacing mode was changed to asynchronous mode for pacing-dependent patients and to demand mode for other patients. Tachyarrhythmia functions were disabled. Outcome assessments included adverse events and changes in the variables that indicate lead and generator function and interaction with surrounding tissue (device parameters).ResultsNo long-term clinically significant adverse events were reported. In nine MRI examinations (0.4%; 95% confidence interval, 0.2 to 0.7), the patient’s device reset to a backup mode. The reset was transient in eight of the nine examinations. In one case, a pacemaker with less than 1 month left of battery life reset to ventricular inhibited pacing and could not be reprogrammed; the device was subsequently replaced. The most common notable change in device parameters (>50% change from baseline) immediately after MRI was a decrease in P-wave amplitude, which occurred in 1% of the patients. At long-term follow-up (results of which were available for 63% of the patients), the most common notable changes from baseline were decreases in P-wave amplitude (in 4% of the patients), increases in atrial capture threshold (4%), increases in right ventricular capture threshold (4%), and increases in left ventricular capture threshold (3%). The observed changes in lead parameters were not clinically significant and did not require device revision or reprogramming.ConclusionsWe evaluated the safety of MRI, performed with the use of a prespecified safety protocol, in 1509 patients who had a legacy pacemaker or a legacy implantable cardioverter–defibrillator system. No long-term clinically significant adverse events were reported. (Funded by Johns Hopkins University and the National Institutes of Health; ClinicalTrials.gov number, NCT01130896.)

96-44: Atrial sensing stability in single-lead ICD with floating dipole: preliminary observations from the THINGS registry

Purpose of the study: The THINGS registry is an ongoing multicenter Italian Registry enrolling patients with single-chamber implantable defibrillators (ICD), including the DX system (BIOTRONIK BIOTRONIK SE & Co, Berlin, Germany) which consists of with a single-lead ICD provided with atrial sensing capability through a floating atrial dipole implemented in the lead body. The aim of this analysis was to evaluate the atrial sensing stability in this subgroup. Method used: DX systems were implanted according to standard procedures. Atrial and ventricular parameters were collected at implant and 1-year follow-up visit. The atrial sensitivity threshold was always programmed at 0.4 mV in all devices. Comparisons were performed with the paired Student's t-test. Summary of results: Sixty-eight patients (mean age 60.8 ± 14.6 years, 85% males) completed the 1-year follow up. Prevention indication was primary in 49 (72%) and secondary in 19 (28%); the mean left ejection fraction was 31 ± 14%. At implant atrial sensing amplitude was 5.4 ± 2.8 mV (13.5 times higher than the 0.4 sensing threshold) and did not change at 1-year follow-up (4.7 ± 2.8 mV; p = 0.18). Eighty percent statistical power was available to detect 1 mV variations or higher. The DX system also showed good stability of both ventricular sensing (15.1 ± 5.8 mV at implant Vs 15.7 ± 9.5 mV at 1 year; p = 0.56) and shock impedance (77 ± 12 Ohm at implant Vs 77 ± 10 Ohm at 1 year; p = 0.71). An expected though statistically significant increase of the ventricular capture threshold (0.58 ± 0.48 V Vs 0.75 ± 0.48 V; p = 0.036), as well as a ventricular pacing impedance decrease (633 ± 114 Ohm Vs 538 ± 115 Ohm; p < 0.01) were observed. A total of 118 episodes were found in the ICDs memory (87 sinus tachycardias in 12 patients, 3 atrial fibrillation episodes with high ventricular response in 3 patients and 28 ventricular tachycardias in one patient). All the recordings showed a correct detection of the atrial events on the signal provided by the floating dipole. Conclusion: The DX system provided stable atrial sensing during 1-year interval. The observed remarkable atrial sensing safety margin may favour undersensing prevention and rhythm discrimination

Full-Body MRI in Patients With an Implantable Cardioverter-Defibrillator: Primary Results of a Randomized Study

BackgroundMagnetic resonance imaging (MRI) of patients with conventional implantable cardioverter-defibrillators (ICD) is contraindicated. ObjectivesThis multicenter, randomized trial evaluated safety and efficacy of a novel ICD system specially designed for full-body MRI without restrictions on heart rate or pacing dependency. The primary safety objective was >90% freedom from MRI-related events composite endpoint within 30 days post-MRI. The primary efficacy endpoints were ventricular pacing capture threshold and ventricular sensing amplitude. MethodsSubjects received either a single- or dual-chamber ICD. In a 2:1 randomization, subjects either underwent MRI at 1.5-T of the chest, cervical, and head regions to maximize radiofrequency exposure up to 2 W/kg specific absorption rate and gradient field exposure to 200 T/m/s per axis (MRI group, n = 175), or they underwent a 1-h waiting period without MRI (control group, n = 88). A subset of MRI patients underwent ventricular fibrillation induction testing post-MRI to characterize defibrillation function. ResultsIn 42 centers, 275 patients were enrolled (76% male, age 60.4 ± 13.8 years). The safety endpoint was met with 100% freedom from the composite endpoint (p < 0.0001). Both efficacy endpoints were met with minimal differences in the proportion of MRI and control patients who demonstrated a ≤0.5 V increase in ventricular pacing capture threshold (100% MRI vs. 98.8% control, noninferiority p < 0.0001) or a ≤50% decrease in R-wave amplitude (99.3% MRI vs. 98.8% control, noninferiority p = 0.0001). A total of 34 ventricular tachyarrhythmia/ventricular fibrillation episodes (20 induced; 14 spontaneous) occurred in 24 subjects post-MRI, with no observed effect on sensing, detection, or treatment. ConclusionsThis is the first randomized clinical study of an ICD system designed for full-body MRI at 1.5-T. These data support that the system is safe and the MRI scan does not adversely affect electrical performance or efficacy. (Confirmatory Clinical Trial of the Evera MRI System for Conditionally-Safe MRI Access; NCT02117414)

Effect of Smaller Left Ventricular Capture Threshold Safety Margins to Improve Device Longevity in Recipients of Cardiac Resynchronization-Defibrillation Therapy

Device longevity in cardiac resynchronization therapy (CRT) is affected by the pacing capture threshold (PCT) and programmed pacing amplitude of the left ventricular (LV) pacing lead. The aims of this study were to evaluate the stability of LV pacing thresholds in a nationwide sample of CRT defibrillator recipients and to determine potential longevity improvements associated with a decrease in the LV safety margin while maintaining effective delivery of CRT. CRT defibrillator patients in the Medtronic CareLink database were eligible for inclusion. LV PCT stability was evaluated using ≥2 measurements over a 14-day period. Separately, a random sample of 7,250 patients with programmed right atrial and right ventricular amplitudes ≤2.5 V, LV thresholds ≤ 2.5 V, and LV pacing ≥90% were evaluated to estimate theoretical battery longevity improvement using LV safety margins of 0.5 and 1.5 V. Threshold stability analysis in 43,256 patients demonstrated LV PCT stability of <0.5 V in 77% of patients and <1 V in 95%. Device longevity analysis showed that the use of a 0.5-V safety margin increased average battery longevity by 0.62 years (95% confidence interval 0.61 to 0.63) compared with a safety margin of 1.5 V. Patients with LV PCTs >1 V had the greatest increases in battery life (mean increase 0.86 years, 95% confidence interval 0.85 to 0.87). In conclusion, nearly all CRT defibrillator patients had LV PCT stability <1.0 V. Decreasing the LV safety margin from 1.5 to 0.5 V provided consistent delivery of CRT for most patients and significantly improved battery longevity.

The Kora Pacemaker is Safe and Effective for Magnetic Resonance Imaging.

BACKGROUNDThe impact of magnetic resonance imaging (MRI) on pacemakers is potentially hazardous. We present clinical results from a novel MRI conditional pacing system with the capability to switch automatically to asynchronous mode in the presence of a strong magnetic field.AIMSThe IKONE (Assessment of the MRI solution: KORA 100™ and Beflex™ pacing leads system) study is an open-label, prospective, multicenter study aimed at confirming the safety and effectiveness of the system, when used in patients undergoing MRI of anatomical regions excluding the chest.METHODSPrimary eligibility criteria included patients implanted with the system, with or without a clinically indicated MRI. The primary endpoint was to confirm no significant change in pacing capture thresholds at 1 month after an MRI, with an absolute difference of ≤0.75 V between the pre- and 1-month post-MRI for both atrial and ventricular capture thresholds.RESULTSOut of 33 patients enrolled (mean age: 72.8 ± 11.4 years, 70% male, implant indication or device), 29 patients implanted with the MRI conditional system underwent an MRI 6–8 week postimplant. The study reached its primary endpoint: the mean absolute difference in pacing capture threshold at 1-month post-MRI versus pre-MRI was less than 0.75 V in the atrium (Δ = 0.18 ± 0.16 V, P-value < 0.001) and in the ventricle (Δ = 0.18 ± 0.22 V, P-value < 0.001). There were no adverse events related to the MRI procedure nor were there reports of patient symptoms or discomfort associated. MR image quality was of diagnostic quality in all patients.CONCLUSIONLead electrical performance as measured by difference in capture thresholds were not impacted by MRI. This first clinical evaluation of a novel MRI conditional system demonstrates it is safe and effective for use in out-of-chest, 1.5-T MR imaging.

MRI scanning in patients with new and existing CapSureFix Novus 5076 pacemaker leads: randomized trial results.

Magnetic resonance imaging (MRI) can be safely performed in patients with magnetic resonance (MR)-conditional pacemaker systems but remains relatively contraindicated with non-MR-conditional pacemaker systems. The purpose of this study was to evaluate the safety of MRI without positioning restrictions in patients with an MR-conditional pacemaker and currently a non-MR-conditional Medtronic CapSureFix Novus 5076 lead(s). The study randomized 266 patients in a 2:1 ratio to the MRI group (177 patients) or to the control group (89 patients). At 9-12 weeks postimplant, the MRI group underwent MRI at 1.5 T. Primary end points were MRI-related complication-free rate and noninferiority of the MRI group compared to the control group with regard to the proportion of patients with an increase of ≤0.5 V in right atrial (RA) and right ventricular (RV) pacing capture thresholds from immediately before MRI to 1-month after MRI. No MRI-related complications occurred in 156 MRI-scanned patients who were followed through 1-month post-MRI. Differences in the proportion of patients with ≤0.5 V pacing capture threshold changes from pre-MRI to 1-month post-MRI were minimal between the groups for RA (proportions of 100% in both groups; a P value cannot be calculated) and RV leads (proportions of 99.3% in the MRI group and 100% in the control group; noninferiority test, P < .0001). Proportions of patients with acceptable sensing amplitude changes from pre-MRI to 1-month post-MRI were also similar between the 2 groups for RA and RV leads (noninferiority test, P < .0001 and P = .0004, respectively). No arrhythmias occurred during MRI. MRI scans can be performed safely without positioning restrictions in patients with Medtronic CapSureFix Novus 5076 leads connected to an MR-conditional pacemaker.

Short- and long-term electrical performance of the 5086MRI pacing lead

Owing to potential patient harm, magnetic resonance imaging (MRI) in patients with cardiac implantable electronic devices has traditionally been contraindicated. Following the EnRhythm MRI SureScan Study, an MR conditional pacemaker with modified leads was approved by the Food and Drug Administration. Electrical and handling characteristics of MR conditional pacing leads compared with those of traditional leads have not been established. To compare short- and long-term performance of the Medtronic 5086MRI lead with that of the Medtronic 5076 lead. Patients (n = 466) implanted with 2 5086MRI leads (EnRhythm MRI Study) and 316 patients implanted with 2 5076 leads in 2 prospective clinical investigations were analyzed. Electrical characteristics were stable in both groups at implant and at 12 months and were clinically acceptable throughout. Ventricular capture thresholds were slightly higher at 12 months for the 5086MRI lead than for the 5076 lead (0.93 ± 0.47 V vs 0.74 ± 0.42 V; P < .001). Ventricular sensing amplitudes for the 5086MRI lead were lower at implant (9.0 ± 4.7 mV vs 13.9 ± 6.9 mV; P < .001) and 12 months (9.8 ± 4.8 mV vs 15.4 ± 7.5 mV; P < .001) than for the 5076 lead. There was no statistical difference in lead handling. At 12 months, the estimated right atrial lead-related complication-free survival rate was 99.3% for the 5086MRI lead and 99.6% for the 5076 lead (log-rank P = .65), and the estimated right ventricular lead-related complication-free survival rates were 98.5% and 100% (log-rank P = .03). Acute lead dislodgments occurred in 12 patients with the 5086MRI leads (2.6%) compared with 2 patients with 5076 leads (0.6%) (p = .05) than in 0.6% of the patients with the 5076 lead (P = .05). The 5086MRI lead demonstrates clinically acceptable electrical characteristics while providing safe access to MR-guided diagnostics. However, compared with the 5076 lead, the 5086MRI lead exhibits lower ventricular sensing, slightly higher ventricular capture thresholds, and higher acute lead dislodgement rate.

Comparison of Different Pacing Strategies to Minimize Phrenic Nerve Stimulation in Cardiac Resynchronization Therapy

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. 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. 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.

Left ventricular pacing in persistent left superior vena cava: a case series and potential application

Persistent left superior vena cava (PLSVC) is found in 0.3-2% of the population. Pacemaker implant in PLSVC can be technically challenging. Most operators have hitherto manipulated ventricular leads through the coronary sinus (CS) into the right ventricle (RV). In this case series, we describe the use of standard passive tined ventricular leads implanted into the left ventricular (LV) epicardial veins in PLSVC. Three patients with PLSVC underwent pacemaker implantation for bradycardia. Contrast injection in the dilated CS identified LV coronary veins. Standard passive tined pacing leads were manoeuvred into these branches using hand-shaped stylets without need for additional equipment. Atrial leads were actively fixed to the anterolateral right atrial wall. There were no procedural complications. Chronic ventricular capture threshold at 6 months of follow-up was 1.0 mV@ 0.4 ms. Implanting standard leads into the LV veins in PLSVC is safe, effective, and simple without the need for special tools. This is easier than manipulating leads into the RV in PLSVC. Longer-term follow-up and dedicated clinical trials are needed to evaluate the efficacy and safety of this approach.

Atrial Oversensing and Mode Switching Caused by Lead Polarization Artifact During an Automatic Ventricular Capture Threshold Test

This article presents the case of a 41-year-old woman with a dual-chamber pacemaker who complained of palpitations. Mode-switching episodes demonstrated a repeated pattern of atrial sensed events associated with ventricular stimulation during automatic capture threshold testing (ACTT). Recognition of potential ACTT problems is important in preventing unnecessary treatment and in guiding appropriate device programming.

A Prospective Evaluation of a Protocol for Magnetic Resonance Imaging of Patients With Implanted Cardiac Devices

Magnetic resonance imaging (MRI) is avoided in most patients with implanted cardiac devices because of safety concerns. To define the safety of a protocol for MRI at the commonly used magnetic strength of 1.5 T in patients with implanted cardiac devices. Prospective nonrandomized trial. (ClinicalTrials.gov registration number: NCT01130896) SETTING: One center in the United States (94% of examinations) and one in Israel. 438 patients with devices (54% with pacemakers and 46% with defibrillators) who underwent 555 MRI studies. Pacing mode was changed to asynchronous for pacemaker-dependent patients and to demand for others. Tachyarrhythmia functions were disabled. Blood pressure, electrocardiography, oximetry, and symptoms were monitored by a nurse with experience in cardiac life support and device programming who had immediate backup from an electrophysiologist. Activation or inhibition of pacing, symptoms, and device variables. In 3 patients (0.7% [95% CI, 0% to 1.5%]), the device reverted to a transient back-up programming mode without long-term effects. Right ventricular (RV) sensing (median change, 0 mV [interquartile range {IQR}, -0.7 to 0 V]) and atrial and right and left ventricular lead impedances (median change, -2 Ω [IQR, -13 to 0 Ω], -4 Ω [IQR, -16 to 0 Ω], and -11 Ω [IQR, -40 to 0 Ω], respectively) were reduced immediately after MRI. At long-term follow-up (61% of patients), decreased RV sensing (median, 0 mV, [IQR, -1.1 to 0.3 mV]), decreased RV lead impedance (median, -3 Ω, [IQR, -29 to 15 Ω]), increased RV capture threshold (median, 0 V, IQR, [0 to 0.2 Ω]), and decreased battery voltage (median, -0.01 V, IQR, -0.04 to 0 V) were noted. The observed changes did not require device revision or reprogramming. Not all available cardiac devices have been tested. Long-term in-person or telephone follow-up was unavailable in 43 patients (10%), and some data were missing. Those with missing long-term capture threshold data had higher baseline right atrial and right ventricular capture thresholds and were more likely to have undergone thoracic imaging. Defibrillation threshold testing and random assignment to a control group were not performed. With appropriate precautions, MRI can be done safely in patients with selected cardiac devices. Because changes in device variables and programming may occur, electrophysiologic monitoring during MRI is essential.

Clinical use of automatic pacemaker algorithms: results of the AUTOMATICITY registry

Follow-up of the ever-increasing numbers of patients with implantable cardiac devices places a heavy burden on clinical departments. Device automaticity may alleviate the follow-up burden by minimizing the time for physician involvement. The aim of the prospective, multicentre AUTOMATICITY registry was to examine the performance of a subset of programmed automatic algorithms during patient follow-up and their acceptance by implanting physicians. The clinical use of automatic algorithms from the Insignia pacemakers (PM; Boston Scientific, St Paul, MN, USA) was evaluated: atrial and ventricular AutoSense (sensitivity adjustment), ventricular Automatic Capture (threshold verification and output setting), AutoLifeStyle (sensor settings adjustment). The objective of the study was to assess the reprogramming rates within 12 months of implant, the reasons for reprogramming and relationship to adverse events. A total of 960 patients were enrolled in the study. The proportion of patients free from any algorithm reprogramming at 12 months was 86.1%. A total of 2736 algorithms were activated at enrolment, with 156 (5.7%) being reprogrammed in 115 patients at 12 months for any reason. Forty-nine reprogrammings (1.8%) were unintentional or related to changes in device settings such that the algorithm was no longer available, 33 (1.2%) were due to suspected sensing issues, and 22 (0.8%) were assumed related to the algorithm. The individual 12-month reprogramming-free rates were: ventricular AutoSense 94.3%, Atrial AutoSense 93.3%, AutoLifeStyle 93.9%, and Automatic Capture 95.9%. The results of the AUTOMATICITY registry show that automatic measurement of key settings and automatic adjustment to optimal programming is feasible and safe. The simplicity of PM follow-up and avoidance of frequent reprogramming may contribute to a more effective use of hospital time and resources.

Relationship between left ventricular stimulation characteristics at implantation and echocardiographic response after 6 months of cardiac resynchronization therapy

Although the electrical stimulation of an ischaemic tissue adversely affects the left ventricular (LV) systolic function, the optimal stimulation site in patients with non-ischaemic cardiomyopathy has not been systematically studied. We hypothesized that the local stimulation characteristics at the time of device implantation predict the response to cardiac resynchronization therapy (CRT). We measured the impedance, sensing, and capture threshold of a bipolar LV lead in 138 patients with non-ischaemic cardiomyopathy undergoing first implantation of CRT device for drug refractory heart failure. All patients underwent echocardiography at baseline and at 6 months post-implantation. An absence of favourable response to CRT was defined as <15% decrease in echocardiographic LV end-systolic volume (LVESV) at 6 months. Echocardiographic response to CRT was observed in 70% of patients. The LV lead measurements predicted neither the optimal stimulation site nor the response to CRT. Left ventricular capture threshold (1.50 ± 1.1 vs. 1.32 ± 0.8 V) and impedance (725 ± 287 vs. 720 ± 261 Ω) were similar between the responders and the non-responders. Independent of baseline LV ejection fraction or ESV, the LV R-wave amplitude at implantation was significantly higher (P = 0.0038) in responders (12.7 ± 5.2 mV) than in non-responders (9.7 ± 6.3 mV), with an area under the receiver operating characteristic curve of 0.7. Response to CRT, as determined by decrease in LVESV at 6 months, was associated with significantly higher LV R-wave amplitude at the time of device implantation.

The Effects of Temperature on Cardiac Pacing Thresholds

Human core body temperature can fluctuate between 36 degrees C (sleep) and 42 degrees C (intense exercise). Also, efforts are underway to develop implantable pacing systems that minimize heating during magnetic resonance imaging (MRI) scans (i.e., MRI safe). Concerns exist that ventricular pacing capture thresholds (VPCT) are modified by changing cardiac temperatures. This project was designed to assess the effects of temperature on VPCT of the mammalian heart. Fresh ventricular specimens were obtained from healthy canine, healthy swine, and diseased human hearts. Isolated trabeculae were suspended in temperature-controlled tissue baths containing oxygenated Krebs buffer. Small active fixation pacing leads delivered pacing pulses to each specimen. Baseline strength-duration curves were determined at 37 degrees C, then at randomized temperatures ranging from 35 degrees C to 42 degrees C. Final thresholds were repeated at 37 degrees C to confirm baseline responses. All threshold data were normalized to a baseline average. Both canine and swine trabeculae elicited significant decreases in thresholds (10-14%) at pacing stimulus durations (pulsewidths) of 0.02 ms (P < 0.01) and 0.10 ms (P < 0.05) between the temperatures of 38 degrees C and 41 degrees C, compared to baseline. Thresholds at 42 degrees C trended back to baseline for both canine (NS) and swine trabeculae (P < 0.05 compared to 38 degrees C-41 degrees C). Human trabeculae thresholds increased >35% (P < 0.05) at 42 degrees C relative to baseline with no significant differences at other temperatures. Temperature is a significant factor on pacing thresholds for mammalian ventricular myocardium. Our data for the diseased human trabeculae indicate that cases where cardiac heating may occur (e.g., radiofrequency energy due to MRI scans, febrile events), patients without adequate VPCT safety margin may be at higher risk of loss of proper function of an implanted pacing or defibrillation system.