A blended sensor restores chronotropic response more favorably than an accelerometer alone in pacemaker patients: the LIFE study results.

BACKGROUND: Adaptive rate sensors used in permanent pacemakers incorporate an accelerometer (XL) to increase heart rate with activity. Limited data exists regarding the relative benefit of a blended sensor (BS) (XL and minute ventilation) versus XL alone in restoring chronotropic response (CR) in chronotropically incompetent (CI) patients. METHODS: One thousand five hundred thirty-eight patients from the limiting chronotropic incompetence for pacemaker recipients (LIFE) study were implanted with a pacemaker and 1,256 patients had data collected at 1 month. Patients performed a treadmill test 1-month postimplant while programmed in nonrate responsive mode (DDD-60) to determine CI. Only patients who completed at least three exercise stages and achieved a peak perceived exertion >or=16 were included in the analyses. The metabolic chronotropic relationship (MCR) slope was used to evaluate CR in 547 patients. Patients were randomized to XL or BS with a conservative fixed rate response factor (XL = 8, MV = 4). CI patients performed a follow-up 6-month treadmill test. RESULTS: CI prevalence in this patient population (n = 547) was 34%. No differences in baseline characteristics existed between groups. Although both groups showed significant within-group improvements in MCR slope from 1 to 6 months (both P < 0.001), the BS group had a significantly higher MCR slope at 6 months compared to the XL group (P = 0.011). Improvement in quality of life (QOL) did not differ between groups. CONCLUSIONS: In this general pacemaker population with CI, a BS programmed empirically restores CR more favorably than an XL sensor programmed nominally. Further studies are needed to determine if individual sensor optimization would lead to improvement in functional capacity, higher MCR slopes, and QOL.

Long-term retention of cardiac resynchronization therapy.

OBJECTIVES: The purpose of this study was to determine the frequency and causes of intermittent and permanent loss of cardiac resynchronization therapy (CRT) in patients who have undergone the successful implantation of a transvenous defibrillator that delivers CRT (CRT-D). BACKGROUND: The causes of loss of CRT have not been described. METHODS: The records of 512 patients who underwent an attempt at implantation of a transvenous CRT-D device as part of the VENTAK CHF/CONTAK CD Biventricular Pacing study were analyzed. RESULTS: Device implantation was successful in 443 of 512 (87%) of patients. Among these 443 patients, CRT was interrupted in 161 (36%) patients during a mean follow-up of 2.5 +/- 1.1 years. Reasons included the development of an atrial tachyarrhythmia (18%), loss of left ventricular capture (10%), diaphragmatic stimulation (2%), loss of right ventricular capture (2%), infection (1%), intentional discontinuation of CRT (1%), loss of right atrial sensing (1%), and ventricular oversensing (0.2%). Most patients underwent an intervention that permitted the reinstitution of CRT, such that only 20 of the 443 patients (5%) experienced the permanent loss of CRT. Using an intention-to-treat analysis, the long-term retention of CRT was 83% during the course of 2.5 years. CONCLUSIONS: Cardiac resynchronization therapy is interrupted in more than one-third of patients after the successful implantation of a CRT-D device. However, CRT can be reinstituted in most patients and has a high long-term retention rate. Because patients with slower heart rates were more likely to develop atrial tachyarrhythmias, a dual-chamber rate-modulated pacing mode (DDDR) may reduce interruptions of CRT.

Magnetic resonance imaging and cardiac pacemaker safety at 1.5-Tesla.

OBJECTIVES: The study was done to determine whether patients with pacemakers could safely undergo magnetic resonance imaging (MRI) at 1.5-Tesla (T). BACKGROUND: Because of theoretical risks, it is an absolute contraindication for a patient with a pacemaker to undergo MRI. However, there are times when an MRI is needed to provide valuable clinical information. METHODS: Fifty-four patients underwent a total of 62 MRI examinations at 1.5-T. The type of MRI examination was not limited and included cardiac, vascular, and general MRI studies using various whole-body averaged specific absorption rate (SAR) of radiofrequency power. Restrictions were not placed on the type of pacemaker present in the patient. All pacemakers were interrogated immediately before and after MRI scanning, and patients were continuously monitored. Before and after MRI, interrogation was done, and pacing and sensing thresholds, as well as lead impedances, were all measured. RESULTS: A total of 107 leads and 61 pulse generators were evaluated. No adverse events occurred. Forty (37%) of the leads underwent changes, whereas 10 (9.4%) leads underwent a significant change. Only 2 of the 107 (1.9%) leads required a change in programmed output. Threshold changes were unrelated to cardiac chamber, anatomical location, peak SAR, and time from lead implant to the MRI examination. Electrocardiographic changes and patient symptoms were minor and did not require cessation of MRI. CONCLUSIONS: Safety was demonstrated in this series of patients with pacemakers at 1.5-T.

Defibrillation energy requirements using a left anterior chest cutaneous to subcutaneous shocking vector: implications for a total subcutaneous implantable defibrillator.

BACKGROUND: Subcutaneous implantable defibrillators (ICDs) are being developed to facilitate ICD implantation. OBJECTIVE: The purpose of this study was to estimate the human defibrillation energy requirement (DER) using a left chest cutaneous (Q) to subcutaneous (SQ) shocking vector. METHODS: Twenty patients undergoing implantation of an indicated ICD were enrolled (15 males, age = 63 +/- 12 years; ejection fraction = 0.27 +/- 0.14). Defibrillation testing was performed using an investigational system consisting of an external defibrillator and a constructed connector to deliver a shock between a pectoral SQ can and a cardiac apical Q electrode. Two attempts at defibrillation using this configuration were allowed. Stage 1 testing started at 70 J with a step-down/step-up to 50 or 100 J, respectively. Stage 2 testing began at 50 J with a step-down/step-up to 30 or 70 J. RESULTS: During stage 1, a 70-J shock was successful in 7/9 (78%) patients. A second attempt was successful in 7/7 patients using a 50-J shock. In the two remaining patients, a second attempt using a 100-J shock was successful. During stage 2, a 50-J shock was successful in 10/11 (91%) patients. The protocol could not be completed in 2/11 patients. Of the remaining nine patients, a second defibrillation was successful in seven (78%) using a 30-J shock. CONCLUSIONS: The defibrillation energy requirement (DER) of this study vector was 50 J or less in most patients. This low DER supports further investigation of a totally SQ-ICD. However, the DER of 100 J in two patients indicates that further investigation is needed regarding DER variability and safety margins.

Performance of a new single-chamber ICD algorithm: discrimination of supraventricular and ventricular tachycardia based on vector timing and correlation.

AIMS: Interval- and morphology-based algorithms have been used in modern implantable cardioverter defibrillators (ICDs) to discriminate supraventricular tachycardia (SVT) from other rhythms. A newly developed ICD discrimination algorithm, Rhythm ID (Guidant Corporation, St Paul, MN, USA), uses both interval-based metrics and an electrogram vector timing and correlation (VTC) algorithm in a dual-chamber ICD. In a single-chamber ICD, Rhythm ID contains only the VTC component. This study conducted a retrospective analysis of the performance of Rhythm ID for the detection of induced and spontaneous rhythms in a single-chamber ICD. METHODS AND RESULTS: This study gathered the data from a prospective, multicentre clinical trial. Ninety-six patients were implanted with a dual-chamber ICD. For this study, each episode was analysed to determine the performance of the single-chamber ICD Rhythm ID algorithm. The mean age of the patients implanted with the device was 67+/-11 years. Seventy-eight patients were male. The primary cardiovascular disease was coronary artery disease and the primary tachyarrhythmia was monomorphic ventricular tachycardia (VT). The mean follow-up time was 11.4 months. A total of 369 induced and spontaneous ventricular arrhythmias was analysed. The algorithm detected 100% of ventricular arrhythmias. Four hundred and forty-two SVT episodes were analysed, including 145 induced and 297 spontaneous. The SVTs were atrial fibrillation (n=199), atrial flutter (n=135), and 1:1 SVT (n=108). The single-chamber ICD Rhythm ID algorithm successfully discriminated 403 SVT episodes and achieved a specificity of 91%. CONCLUSION: The single-chamber version of Rhythm ID demonstrated high specificity without compromising sensitivity.

Clinical results of an advanced SVT detection enhancement algorithm.

INTRODUCTION: Supraventricular tachycardia (SVT) has many characteristics that are similar to ventricular tachycardia (VT). This presents a significant challenge for the SVT-detection algorithms of an implantable cardioverter defibrillator (ICD). A newly developed ICD, which utilizes a Vector Timing and Correlation algorithm as well as interval-based conventional SVT discrimination algorithms (Rhythm ID), was evaluated in this study. MATERIALS AND METHODS: This study was a prospective, multicenter trial that evaluated 96 patients implanted with an ICD at 21 U.S. centers. All patients were followed at 2 weeks, 1 month, and every 3 months post implant. A manual Rhythm ID reference vector was acquired prior to any arrhythmia induction. During testing, atrial tachyarrhythmias were induced first, followed by ventricular arrhythmia induction. Induced and spontaneous SVT and VT/ventricular fibrillation (VF) episodes recorded during the trial were annotated by physician investigators. RESULTS: The mean age of the patients implanted with an ICD was 67.3 +/- 10.8 years. Eighty-one percent of patients were male. The primary cardiovascular disease was coronary artery disease, and the primary tachyarrhythmia was monomorphic VT. Implementation of the Rhythm ID algorithm did not affect the VT/VF detection time. There were a total of 370 ventricular tachyarrhythmias (277 induced and 93 spontaneous) and 441 SVT episodes (168 induced and 273 spontaneous). Sensitivity for ventricular tachyarrhythmias was 100%, and specificity for SVT was 92% (94% and 91% for induced and spontaneous SVT, respectively). All patients had a successful manual Rhythm ID acquisition prior to atrial tachyarrhythmia induction. At the 1-month follow-up, the Rhythm ID references were updated automatically an average of 167.8 +/- 122.7 times. Stored Rhythm ID references correlated to patients' normally conducted rhythm 100% at 2 weeks, and 98% at 1 month. CONCLUSIONS: The Rhythm ID algorithm achieved 100% sensitivity for VT/VF, and 92% specificity for SVT. The manual and automatic Rhythm ID update algorithms successfully acquired references, and the updated references were highly accurate.