Shane Kimber

Multisite Pacing as a Supplemental Treatment of Congestive Heart Failure: Preliminary Results of the Medtronic Inc. InSync Study

This report describes the initial results of the “InSync” study, a European and Canadian multicenter trial that examines the safety and efficacy of a multisite pacemaker (Medtronic InSync) and of left ventricular pacing leads (Medtronic 2187 and 2188) implanted via a cardiac vein as a supplemental treatment of refractory congestive heart failure. Over a 10‐month period, the system was implanted successfully in 68 of the 81 (84%) patients who had been enrolled in the study. The 68 patients were, on average, 66 ± 10 years old, had a mean left ventricular ejection fraction (LVEF) = 21 %± 9%, and 63% were in NYHA functional Class III and 37% were in Class IV. No system implant related complication occurred. During follow‐up, 7 of 10 patients who exited the study had died, 4 suddenly. There was a clinical benefit among surviving patients, which was corroborated by a significant improvement in NYHA functional class and in the Minnesota Living with Heart Failure Quality of Life Questionnaire Score (MLS) and by a longer distance covered during a 6‐minute walk test. This clinical improvement was associated with a significant narrowing of the paced QRS complex during biventricular pacing, a significant decrease in the interventricular mechanical delay, and a trend towards an increase in the duration of ventricular filling. These encouraging preliminary results confirm the feasibility and reliability of this new multisite pacing system in the management of dilated cardiomyopathy and support the continuation of further evaluations of this complementary treatment of refractory congestive heart failure.

Complications associated with defibrillation threshold testing: The Canadian experience

BACKGROUND Defibrillation threshold (DFT) testing has traditionally been a routine part of implantable cardioverter-defibrillator (ICD) implantation, despite a lack of compelling evidence that it predicts or improves outcomes. In the past, when devices were much less reliable, DFT testing seemed prudent; however, modern ICD systems have such a high rate of successful defibrillation that many electrophysiologists now question whether DFT testing is still worthwhile, particularly since DFT testing may now be the highest acute risk component of ICD implantation. OBJECTIVE The purpose of this study was to systematically document complications directly attributable to intraoperative DFT testing. METHODS We obtained data on DFT-related complications from all 21 adult ICD implant centers in Canada, covering the period from January 1, 2000, to September 30, 2006. RESULTS There were a total of 19,067 ICD implants in Canada during the study period. There were three DFT testing-related deaths, five DFT testing-related strokes, and 27 episodes that required prolonged resuscitation. Two patients had significant clinical sequelae after prolonged resuscitation. CONCLUSIONS The risk of severe complications from intraoperative DFT testing appears small, even allowing for the underestimation of its true rate with the current study methodology. These slight but measurable risks must be considered when assessing the risk-benefit ratio of the procedure. Additional data from ongoing prospective ICD registries and/or clinical trials are required.

Circadian variation of paroxysmal atrial fibrillation

The circadian variation of paroxysmal atrial fibrillation (AF) was studied in 67 patients who received a dual-chamber pacemaker 3 months before a planned atrioventricular node ablation. A distinct circadian variation of AF was observed with 2 time peaks in initiation (1 in the early morning and 1 in the early evening hours), which was modulated by atrial pacing, the duration of AF, and the use of beta-adrenergic blocking agents.

Contemporary Utilization of Digoxin in Patients with Atrial Fibrillation

OBJECTIVE: To define the contemporary practice patterns of digoxin utilization for the management of patients with atrial fibrillation (AF). METHODS: A retrospective medical records audit of 2490 patients with documented AF, from 12 Canadian hospitals and six outpatient clinics, during fiscal year 1993–1994, was conducted. RESULTS: There were 1158 women and 1332 men, with a mean age of 72 years; 956 patients were <70 years of age and 1534 were ≥70 years old. The majority of patients had nonvalvular AF (75% of those with a documented etiology). Paroxysmal AF (PAF) was documented in 800 patients, 936 had chronic AF, and 754 had new-onset AF. While the prescribing patterns were heterogeneous, the predominant strategy pursued in all subgroups appeared to be that of achieving rate control. Digoxin was the most commonly prescribed medication (79%) and was prescribed for the majority of patients in all subgroups, including patients with PAF (74%) and patients with a history of chronic AF who were currently in sinus rhythm (83%). Only 10% of the patients with PAF who were prescribed digoxin had congestive heart failure. Similarly, less than 25% of the patients with chronic AF who were prescribed digoxin after conversion to sinus rhythm had evidence of heart failure. CONCLUSIONS: In the absence of clinical trial evidence supporting either a strategy of antiarrhythmic therapy or rate control with anticoagulation, the appropriateness of the observed prescribing practices cannot be judged. However, digoxin is not the best rate-controlling agent for all patients and may be overused in certain subgroups of patients, such as those with PAF and those successfully converted to sinus rhythm.

Worldwide evaluation of a defibrillation lead with a small geometric electrode surface for high-impedance pacing

Abstract Background Pacing leads with a small electrode surface for high-impedance stimulation have been shown to prolong pacemaker longevity, but no sufficient data is available on the safety and feasibility of a defibrillation lead with this novel design. Methods We evaluated the clinical performance of a tined, steroid-eluting defibrillation lead with a small electrode surface area (model 6944) in a prospective multicenter study. A total of 542 patients with conventional indications for an implantable cardioverter defibrillator were randomized 1:1 to receive either the model 6944 or a tined, steroid-eluting defibrillation lead with a conventional sized electrode surface area (model 6942). Device performance and electrical parameters were evaluated at implant and 1, 3, 6, and 12 months thereafter (mean follow-up 11.3 ± 5.6 months). Results Baseline characteristics, lead implant success rates, and defibrillation thresholds did not differ significantly between the 2 groups. While pacing thresholds did not differ significantly during follow-up, pacing impedance was approximately twice as high in the model 6944 as in the model 6942 lead (P Conclusions The use of a defibrillation lead with a small electrode surface for high-efficiency pacing is safe and feasible and increases pacing impedance without significantly compromising clinical performance.

Fibrillation Complexity as a Predictor of Successful Defibrillation

A major focus of implantable cardioverter defibrillator (ICD) research has been to reduce the defibrillation shock energy to prolong battery life and provide an enhanced quality of life for the patient. We investigated whether the degree of disorganization (complexity) of the electrogram is correlated with defibrillation shock outcome. The study data sets were recorded using the high voltage leads of an ICD during device implantation. A total 57 data segments from 19 patients were analyzed. Beat cycles were identified using a novel wavelet based method. Two algorithms were proposed and implemented to quantify the disorganization of the electrogram signals: approximate entropy and cross correlation. Entropy Index based on the ApEn method, was able to discriminate successful episodes from failure ones with a specificity of 93% and sensitivity of 100%. Similarity index based on cross correlation method, obtained a specificity of 72% and sensitivity of 66%. We conclude that the organization of a VF episode is related to the minimum energy required for successful defibrillation

Inappropriate shocks by subcutaneous implantable cardioverter-defibrillator due to T-wave oversensing in hyperkalemia leading to ventricular fibrillation

Introduction The implantable cardioverter-defibrillator (ICD) has reduced mortality in survivors of sudden cardiac arrest and patients at high risk of sudden cardiac death. This benefit comes at the cost of device-related complications, including those related to transvenous leads. The subcutaneous ICD (S-ICD) is an alternative to the conventional transvenous ICD (TV-ICD) system and has no transvenous leads, thereby avoiding endocardial lead–related complications. However, with only subcutaneous electrodes, rhythm detection and discrimination is a much more challenging task for the S-ICD. We describe a case of ventricular fibrillation induced by inappropriate shocks from the S-ICD owing to T-wave oversensing (TWOS) in the setting of hyperkalemia and dialysisdependent chronic renal failure.

Defibrillation Success Is Not Associated With Near Field Electrogram Complexity or Shock Timing

BACKGROUND It has been suggested that more-complex fibrillation requires higher energy shocks to terminate. Furthermore, animal studies have demonstrated that shock timing also plays a role. The objective of this study was to test these assertions in a clinical context. METHODS Near- and far-field electrograms were collected during defibrillation threshold testing. Fibrillation complexity was measured by quantifying the organization in the signals with wavelet-based methods, scaling exponent, and cross-correlation analysis. Receiver operator characteristic curves were used to determine predictive value. The effect of the phase at which defibrillation shocks were applied was also determined. RESULTS No measure was able to classify whether a particular shock would be successful. All performed very poorly. Shock timing played no role in defibrillation outcome. CONCLUSIONS Signal organization of a local electrogram and phase of shock delivery do not relate to minimum defibrillation shock energy immediately after ventricular fibrillation onset.

Predicting defibrillation outcome based on phase of ventricular activity during ICD implantation

Implantable cardioverter-defibrillaters (ICDs) are well known medical device for patients who are at a risk of sudden cardiac death caused by ventricular fibrillation (VF). The relationship between VF mechanisms and successful ICD therapy to terminate of VF is still not well understood. The purpose of this work is to evaluate the timing of ICD therapy as a predictor of successful VF termination. Clinical data sets were recorded from the patients who underwent ICD implantation in 6 Canadian centers. Timing of the defibrillation attempt (phase) was analyzed by using the ICD Marker Channel which monitors and displays cardiac events sensed by ICD. Phase, based on the VF period, was divided into 10 equally distributed bins and number of successful defibrillation episodes in each bin was compared. A total of 187 defibrillation attempts were identified from the 65 subjects. 126 of the defibrillation attempts were successful, while 61 failed. The optimal case was observed at a phase value of 1.2π with 2 successful attempts. The lowest performance rate was found at a phase value of 1.4π and 1.8π with 50% (3 and 2 successful attempts, respectively). The probability of success was analyzed by using generalized estimating equations (GEE) approach with an exchangeable correlation structure. The results of the GEE logistic regression model indicate no correlation between successful defibrillation attempts and phase of ventricular activity during VF (p-value = 3D 0.78). From our results, timing of defibrillation shock attempt is not a factor in successful termination of VF for patients undergoing ICD implantation.