Selected Abstracts

Title: Biventricular pacing in patients with bradycardia and normal ejection fraction

Yu et al (N Engl J Med 2009;361:2123-2134; PMID: 19915220) evaluated whether biventricular (BiV) pacing is superior to right ventricular apical (RVA) pacing in preventing deterioration of left ventricular (LV) systolic function and cardiac remodeling in patients with bradycardia and a normal ejection fraction (EF). In this prospective, double-blind, multicenter study, 177 patients with implantation of a BiV pacemaker were randomized to BiV pacing (89 patients) or RVA pacing (88 patients). The primary end points were the LVEF and LV end-systolic volume. At 12 months, the mean LVEF was significantly lower with RVA pacing than in the BiV pacing (54.8_/-9.1% vs. 62.2_/-7.0%, P_0.001).The LV end-systolic volume was significantly higher in the RVA pacing group than in the BiV group (35.7_/-16.3 ml vs. 27.6_/-10.4 ml, P_0.001). The authors conclude that in patients with normal LVEF, RVA pacing resulted in adverse LV remodeling and in a reduction in the LVEF. These effects were prevented by biventricular pacing.

Title: Cardiac Resynchronization Therapy in Patients with Right Ventricular Pacing-Induced Cardiomyopathy

Background: It is not known whether patients with normal baseline left ventricular (LV) function who develop right ventricular (RV) pacing-induced cardiomyopathy as a result of dual-chamber pacing can benefit from cardiac resynchronization therapy (CRT). We retrospectively assessed the effect of a CRT upgrade on RV pacing-induced cardiomyopathy.
Methods and Results: We reviewed the charts of patients who received a CRT device for RV pacing induced cardiomyopathy. We assessed the effects of CRT on LV function, recovery, and other response parameters. From September 2005 through February 2009, 21 patients (13 men; aged 63 ± 9 years) underwent a treatment upgrade to a CRT system. Before the dual-chamber pacemaker was implanted, the LV ejection fraction (LVEF) was 53 ± 2.3%. After pacing, the LVEF was 31.2 ± 3.8%, the LV end-diastolic dimension (LVEDD) was 5.8 ± 0.5 cm, and B-type natriuretic peptide (BNP) levels were 426 ± 149 pg/mL. The duration of pacing before documentation of pacing-induced cardiomyopathy was 3.8 ± 1.5 months.
All the patients had been on a stable medical regimen for at least 2 months. After the upgrade to CRT, the follow-up time was 4.9 ± 0.9 months. Sixteen patients (76%) reported a significant improvement in their symptoms. After the CRT upgrade, the LVEF increased to 37.4 ± 9.0% (P < 0.01 vs pre-CRT). The LVEDD decreased to 5.0 ± 1.0 cm (P = 0.03 vs pre-CRT), and BNP levels decreased to 139 ± 92 pg/mL (P = 0.08 vs pre-CRT).
Conclusion: A CRT upgrade is an effective treatment for RV pacing-induced cardiomyopathy and should be implemented as soon as the diagnosis is established. Unfortunately, about 24% of our patients did not respond to the upgrade. (PACE 2010; 33:37-40)

Title: Permanent Pacemaker Implantation Following Aortic Valve Replacement: Current Prevalence and Clinical Predictors

From the Division of Cardiology, Providence Hospital and Medical Center/Wayne State University School of Medicine, Southfield, Michigan
Background: The incidence of conduction disease requiring permanent pacemaker (PPM) implantation following aortic valve replacement (AVR) ranges from 3% to 6%. Data concerning the potential risks for PPM requirement associated with certain valve types have been conflicting and controversial. We sought to evaluate the prevalence, predictors for PPM implantation, and PPM dependency during follow-up in patients undergoing AVR.
Methods: A total of 214 consecutive patients undergoing AVR were studied retrospectively. A total of 207 patients were included in the statistical analysis. Clinical variables including valve size and types were catalogued and the incidence of PPM evaluated. Cardiac rhythm device clinic records were examined and PPM dependency status was catalogued. Multivariate analyses were performed to determine predictors of PPM implantation and PPM dependency during follow-up.
Results: Fifteen patients (7.2%) required PPM postoperatively. After controlling for clinical and surgical characteristics, predictors for PPM included preoperative first-degree atrioventricular block with and without left anterior fascicular block or intraventricular conduction delay [odd ratios (OR) = 12.5, P = 0.001], cardiac arrest postoperatively (OR = 9.4, P = 0.012), and combined aortic and mitral valve surgery (OR = 11.5, P = 0.027). Aortic valve types did not predict complete heart block (CHB) and PPM implantation. Of those patients who underwent PPM implantation, 70% were classified as PPM dependent
during long-term follow-up.
Conclusion: CHB and PPM implantation continue to be common complications of AVR. Preexisting atrioventricular with intrafascicular or intraventricular conduction disease along with cardiac arrest and dual valve surgery are the most important significant predictors of PPM implantation and PPM dependency during follow-up. The selection of valve types did not predict conduction disease requiring PPM implantation. (PACE 2009; 32:1520-1525)

Title: Atrial vs. dual-chamber cardiac pacing in sinus node disease: a register-based cohort study

Aim: In patients with sinus node disease, dual-chamber pacing (DDD) possibly results in adverse effects on the ventricular function. We have compared the incidence of cardiovascular morbidity and mortality in patients with sinus node disease and with atrioventricular (AV) synchronous pacemakers, DDD vs. atrial pacing (AAI).

Methods and results :A nation-wide population-based cohort of 8777 patients with AAI- or DDD-mode pacemakers was followed during 12 years. The cohort was linked to national healthcare and census registers. Patients with DDD pacing and without any pre-implant admission for atrial fibrillation or flutter had an increased risk of post-implant fibrillation or flutter, in relation to corresponding AAA patients [hazard ratio (HR) ¼ 1.30; 95% confidence interval (CI) 1.10-1.52]. A slight increase in the risk of any cardiovascular disease (HR ¼ 1.07; CI, 1.00-1.15), and all-cause mortality (HR ¼ 1.12; CI, 1.00-1.25), was seen among DDD patients, in relation to AAI patients, but there was no significant difference in the risk of ischaemic or unspecified stroke (HR ¼ 1.14; CI, 0.94-1.37). Among DDD patients, the all cause mortality did not differ from the general population [standardized mortality ratio (SMR) ¼ 1.04; CI, 0.98-1.11]. Patients with AAI, however, had a decreased all-cause mortality risk (SMR ¼ 0.89; CI, 0.82-0.97).

Conclusion: Our results support AAI as the preferred mode of pacing in patients with sinus node disease, and a normal AV node function.

Title: Magnetic Resonance Imaging of Implantable Cardiac Rhythm Devices at 3.0 Tesla

Background: A relaxation of the prohibition of scanning cardiac rhythm device patients is underway,largely because of the growing experience of safe scanning events at 1.5T. Magnetic resonance imaging (MRI) at 3T is becoming more common and may pose a different risk profile and outcome of MRI of cardiac device patients.

Methods: No restrictions were placed on pacemaker dependency, region scanned, device type, or manufacturer.Sixteen scans at 3T were performed with an electrophysiologist present on 14 patients with a variety of devices from various manufacturers. An "MRI-S" strategy was used. Multimodal monitoring was required. Device interrogation was performed prior to, immediately after, and 1-3 months after the MRI.For nonpacemaker-dependent device patients, attempts were made to turn all device features off (with OOO programming the goal) conceptually rendering the device "invisible." In pacemaker-dependent patients,the device was programmed to asynchronous mode at highest output for the duration of the scan with the goal of rendering the device conceptually "invulnerable" to MRI effects. The specific absorption rate (SAR) was limited to 2W/kg.

Results: All patients were successfully scanned. No arrhythmias were noted. No significant change in the programmed parameters, pacing thresholds, sensing, impedance, or battery parameters was noted.The insertable loop recorder (ILR) recorded prolonged artifactual asystole during MRI. One patient noted chest burning during the scan.

Conclusions: Device patients may undergo carefully tailored 3T MRI scans when pre-MRI reprogramming of the device occurs in conjunction with extensive monitoring, supervision, and follow-up. (PACE 2008; 31:795-801)

Title: Rate Responsive Pacemakers: A Rapid Assessment Protocol

Background: Rate responsive (RR) pacemakers are commonly implanted with nominal conservative factory-set responsiveness, which is usually accepted because established exercise protocols are timeconsuming.We aimed for efficient assessment of RR pacemaker settings.

Methods: We tested exercise heart rates in controls and paced patients using a brief exercise test that approximates real-life levels of exertion. The test used a nonmotorized treadmill: 30 seconds walking at patient-determined speed followed by 15 seconds brisk exertion. Subjects totaled 110: 26 with RR pacemakers; 22 with non-RR pacers; 27 "sick" nonpaced control patients; and 35 healthy controls. Heart rate (HR) was measured prior to exercise, after 30 seconds of casual walk, after 15 seconds of brisk walk,and 1 minute into recovery. Testing required <5 minutes from set-up to recovery.

Results: The 26 RR pacer patients had a mean HR at rest = 74 ± 10 beats per minute (bpm), walk = 87 ± 14, and brisk = 94 ± 18 (increase 27%). Non-RR pacer patients (n = 22): rest = 73 ± 12 bpm, walk = 88 ± 14, and brisk = 94 ± 17 (increase 24.3%, P = 0.60 vs RR patients). "Sick" controls (n = 27): rest = 78 ± 14 bpm, walk = 102 ± 17, and brisk = 117 ± 18 (increase 51.9%, P< 0.001 vs RR pts). For the healthy controls, HRs were at rest 83+/11 bpm, walk = 104 ± 12, and brisk = 117 ± 13 (P< 0.001 compared to both paced groups; P = NS vs sick controls).

Conclusions: Nominal RR settings may be suboptimal for many patients. The nonmotorized treadmill test allows quick and inexpensive assessment of RR programming, with the potential for efficient RR optimization.

Title: Comparison of Two Strategies to Reduce Ventricular Pacing in Pacemaker Patients

Background: Managed Ventricular Pacing (MVP) and Search AV+ (SAV+) are two pacing algorithms designed to reduce ventricular pacing.MVPpromotes conduction by operating in AAI/R mode with backup ventricular pacing during atrioventricular block (AVB). SAV+ operates in DDD/R mode with a nominal AV extension of 290 ms during atrial sensing and 320 ms during atrial pacing. The reduction in ventricular pacing was compared with these two algorithms in pacemaker patients.

Methods: The EnRhythm and EnPulse clinical studies assessed the percentage of ventricular pacing (%VP) after 1 month. Each patient's AVB status was assigned using the following hierarchical categories: persistent third-degree AVB (p3AVB), episodic third-degree AVB (e3AVB), second-degree AVB (2AVB),first-degree AVB (1AVB), and no AVB (nAVB). The%VP was tabulated for each AVB status category.

Results: Data were available from 322 patients of whom 129 received DDD(R) pacing with the MVP algorithm activated and 193 patients with DDD(R) pacing and the SAV+ function activated, each for a month period. MVP resulted in a significantly lower median%VP than SAV+ in all AVB categories except for p3AVB: nAVB (0.3 vs 2.9, P < 0.0001), 1AVB (0.9% vs 80.6%, P < 0.0001), 2AVB (37.6 vs 99.3, P<0.002), e3AVB (1.2 vs 42.2, P = 0.02), p3AVB (98.9 vs 100, P = 1.00).

Conclusion: MVP resulted in a greater reduction in%VP than SAV+ across all patient groups except persistent third-degree AV block. The greatest reduction in%VP was observed in patients with mildly impaired AV conduction.

Title: Conventional and dedicated atrial overdrive pacing for the prevention of paroxysmal atrial fibrillation: the AFTherapy study


Title: Evaluation of pacemaker dependence in patients on ablate and pace therapy for AF

Aims In patients with atrial fibrillation (AF) and uncontrolled ventricular rate, radiofrequency (RF) ablation of the atrioventricular (AV) node and pacemaker (PM) implantation (ablate and pace) is a valid therapeutic approach, especially in elderly patients. The aim of our study was to evaluate the PM dependence and the incidence of correlated clinical phenomena in a patients population with AV block induced by RF ablation of the AV junction.