Canadian Registry of ICD Implant Testing procedures (CREDIT): current practice, risks, and costs of intraoperative defibrillation testing.

BACKGROUND: There is uncertainty about the proper role of defibrillation testing (DT) at the time of implantable cardioverter defibrillator (ICD) insertion. METHODS: A prospective registry was conducted at 13 sites in Canada between January 2006 and October 2007. OBJECTIVES: To document the details of DT, the reasons for not conducting DT, and the costs and complications associated with DT. RESULTS: DT was conducted at implantation in 230 of 361 patients (64%). DT was more likely to be conducted for new implants compared with impulse generator replacements (71% vs 32%, P = 0.0001), but was similar for primary and secondary prevention indications (64% vs 63%, P = NS). Among patients not having DT, the reason(s) given were: considered unnecessary (44%); considered unsafe, mainly due to persistent atrial fibrillation (37%); lack of an anesthetist (20%); and, patient or physician preference (6%). When performed, DT consisted of a single successful shock > or = 10J below maximum device output in 65% of cases. A 10J safety-margin was met by 97% of patients, requiring system modification in 2.3%. Major perioperative complications occurred in 4.4% of patients having DT versus 6.6% of patients not having DT (P = NS). ICD insertion was $844 more expensive for patients having DT (P = 0.16), largely due to increased costs ($28,017 vs $24,545) among patients having impulse generator replacement (P = 0.02). CONCLUSIONS: DT was not performed in a third of ICD implants, usually due to a perceived lack of need or relative contraindication.

Differential entrainment distinguishes atrioventricular nodal reentry tachycardia from atrioventricular reentrant tachycardia.

BACKGROUND: Entrainment from the right ventricular (RV) apex and the base has been used to distinguish atrioventricular reentrant tachycardia (AVRT) from atrioventricular nodal reentry tachycardia (AVNRT). The difference in the entrainment response from the RV apex in comparison with the RV base has not been tested. METHODS: Fifty-nine consecutive patients referred for ablation of supraventricular tachycardia (SVT) were included. Entrainment of SVT was performed from the RV apex and base, pacing at 10-40-ms faster than the tachycardia cycle length. SA interval was calculated from stimulus to earliest atrial electrogram. Ventricle to atrium (VA) interval was measured from the RV electrogram (apex and base) to the earliest atrial electrogram during tachycardia. The SA-VA interval from apex and base was measured and the difference between them was calculated. RESULTS: Thirty-six AVNRT and 23 AVRT patients were enrolled. Mean age was 44 ± 12 years; 52% were male. The [SA-VA]apex-[SA-VA]base was demonstrable in 84.7% of patients and measured -9.4 ± 6.6 in AVNRT and 10 ± 11.3 in AVRT, P < 0.001. The difference was negative for all AVNRT cases and positive for all septal accessory pathways (APs). CONCLUSION: The difference between entrainment from the apex and base is readily performed and is diagnostic for all AVNRTs and septal APs.

Mapping and ablation of multiple atrial arrhythmias in a patient with persistent atrial standstill after remote viral myocarditis.

This is a case of multiple atrial arrhythmias (atrioventricular node reentry and two different focal atrial tachycardias) originating from the remaining atrial myocardium after global scarring of both atria following a remote viral myocarditis. All the induced arrhythmias were successfully treated with catheter ablation.

A technique for the rapid diagnosis of wide complex tachycardia with 1:1 AV relationship in the electrophysiology laboratory.

BACKGROUND: The differential diagnosis of wide complex tachycardia (WCT) with 1:1 atrioventricular (AV) relationship is broad. Accurate identification of the tachycardia mechanism is essential for successful ablation. We suggest a simple pacing maneuver that can immediately clarify the tachycardia mechanism in the electrophysiology laboratory. METHODS: Eight consecutive patients (four males, 32 +/- 14 years) demonstrating stable sustained WCT with persistent 1:1 AV relationship during electrophysiologic testing were included in this study. During the tachycardia, atrial overdrive pacing was performed. The following responses were observed: (1) a change of the QRS morphology during atrial pacing and (2) the first return electrogram of the tachycardia, whether occurring in the atrium (AVA response) or in the ventricle (AVVA response). RESULTS: Atrial overdrive pacing was successfully performed in all patients. It was associated with either a change or narrowing of the QRS in all ventricular tachycardia (VT) patients but not in supraventricular tachycardia (SVT) patients. All VT patients had an AVVA response upon cessation of atrial overdrive pacing as opposed to AVA response in SVT patients, P = 0.029. CONCLUSION: The response to atrial overdrive pacing during WCT with 1:1 AV relationship can rapidly diagnose or rule out VT as a mechanism of tachycardia.

Body-surface potential mapping to aid ablation of scar-related ventricular tachycardia.

We investigated whether body-surface potential mapping (BSPM) during catheter ablation of scar-related ventricular tachycardia (VT) could assist with the identification of VT exit sites. The study population consisted of 9 patients who underwent catheter ablation for VT, among whom 12 induced VTs with known exit sites were identified by entrainment criteria, pace mapping, or site of successful ablation. Paced activation was initiated at various intracardiac sites (20 +/- 4 sites per patient, a total of 180) documented by nonfluoroscopic electroanatomic mapping. During all episodes of VT and pacing, patients had a 120-lead electrocardiogram recorded, and we analyzed these electrocardiographic data--by means of a similarity coefficient (SC) calculated over 100 milliseconds after the initiation of depolarization--to assess the similarity between the BSPM sequences occurring during VTs and those induced by pacing. Based on 245 observations, the relationship between the SC and the distance of the pacing site from the VT exit site was then obtained for each individual VT by linear regression analysis: the distance D (in millimeters) from the VT exit site was related to SC by the regression equation D = slope (1 - SC2) + intercept. The parameters in this equation varied widely for the 12 VTs, but, in general, the nearer the pacing site was to the exit site, the better the goodness of match. This suggests that, although there is no universally applicable relationship between D and SC, BSPM could provide a useful adjunct to standard pace mapping, although additional processing--namely, an inverse calculation of epicardial potentials/isochrones--may be needed to reliably identify VT exit sites from body-surface electrocardiograms.

Use of primary prevention implantable cardioverter-defibrillators in a population-based cohort is associated with a significant survival benefit.

BACKGROUND: Underuse of implantable defibrillators has been previously noted in patients at risk for sudden cardiac death, as well as for survivors of sudden cardiac death. We sought to determine the utilization rates in a primary prevention implantable cardioverter-defibrillator (ICD)-eligible population and mortality in this group compared with a group that had undergone implantation of this therapy. METHODS AND RESULTS: A retrospective cohort of patients from April 1, 2006, to December 31, 2009, was used to define a primary prevention ICD-eligible population. Two groups were compared on the basis of ICD implantation (no-ICD versus ICD). The primary outcome measure was mortality. Of the 717 patients found to be potentially eligible for a primary prevention ICD, 116 (16%) were referred. The remaining cohort of 601 patients were compared with an existing cohort of primary prevention ICD patients (n=290). A significant survival benefit was associated with primary prevention ICD implantation (hazard ratio, 0.46; 95% CI [0.33-0.64]; P<0.0001). When adjusted for prespecified variables known to be associated with overall mortality and propensity score, a similar survival benefit was seen (hazard ratio, 0.59; 95% CI [0.40-0.87]; P=0.01). Appropriate ICD therapy occurred in 26% of those in the ICD group, during a mean follow-up of 2.7 years. CONCLUSIONS: A significant mortality benefit was observed for patients who underwent primary prevention ICD implantation compared with those who did not. Vigilance is required to ensure that patients eligible for primary prevention ICDs are appropriately referred and assessed to allow such patients to benefit from this life-saving therapy.

Cardiac resynchronization therapy in patients with permanent atrial fibrillation: results from the Resynchronization for Ambulatory Heart Failure Trial (RAFT).

BACKGROUND: Cardiac resynchronization (CRT) prolongs survival in patients with systolic heart failure and QRS prolongation. However, most trials excluded patients with permanent atrial fibrillation. METHODS AND RESULTS: The Resynchronization for Ambulatory Heart Failure Trial (RAFT) randomized patients to an implantable cardioverter defibrillator (ICD) or ICD+CRT, stratified by the presence of permanent atrial fibrillation. Patients with permanent atrial fibrillation were randomized to CRT-ICD (n=114) or ICD (n=115). Patients receiving a CRT-ICD were similar to those receiving an ICD: age (71.6±7.3 versus 70.4±7.7 years), left ventricular ejection fraction (22.9±5.3% versus 22.3±5.1%), and QRS duration (151.0±23.6 versus 153.4±24.7 ms). There was no difference in the primary outcome of death or heart failure hospitalization between those assigned to CRT-ICD versus ICD (hazard ratio, 0.96; 95% CI, 0.65-1.41; P=0.82). Cardiovascular death was similar between treatment arms (hazard ratio, 0.97; 95% CI, 0.55-1.71; P=0.91); however, there was a trend for fewer heart failure hospitalizations with CRT-ICD (hazard ratio, 0.58; 95% CI, 0.38-1.01; P=0.052). The change in 6-minute hall walk duration between baseline and 12 months was not different between treatment arms (CRT-ICD: 19±84 m versus ICD: 16±76 m; P=0.88). Patients treated with CRT-ICD showed a trend for a greater improvement in Minnesota Living with Heart Failure score between baseline and 6 months (CRT-ICD: 41±21 to 31±21; ICD: 33±20 to 28±20; P=0.057). CONCLUSIONS: Patients with permanent atrial fibrillation who are otherwise CRT candidates appear to gain minimal benefit from CRT-ICD compared with a standard ICD.

Predictors of implantable cardioverter-defibrillator use in patients with ischemic cardiomyopathy.

OBJECTIVES: The objective of this study was to identify and examine ICD utilization in a large group of eligible coronary artery bypass grafting (CABG) patients with impaired left ventricular function. METHODS: We conducted a retrospective study of ICD eligible patients who had previously undergone CABG surgery between March 1, 1995 and June 30, 2008 at a single tertiary care institution. All patients with a pre-operative left ventricular ejection fraction (LVEF) ≤ 35% were considered ICD eligible. The events of interest were ICD implantation and mortality, based on administrative data linkage. RESULTS: A total of 1,169 out of 11,931 CABG patients operated on during the same period had LVEF ≤ 35% and were defined as ICD eligible (mean EF = 27.3% +/- 6.4%). Of these eligible patients, only 101 received an ICD during follow-up (8.6%). The median time to implant was 255 days (14-1078). The single variable that independently predicted eventual ICD implantation was a history of arrhythmia (OR = 7.4; CI, 4.4-12.2). The variables that predicted not having an ICD implanted during follow-up included the need for urgent CABG (OR = 0.5; CI, 0.2-0.9), age > 70 years (OR = 0.5; CI, 0.3-0.8), female gender (OR = 0.2; CI,0.1-0.6), or having chronic obstructive lung disease (OR = 0.5; CI,0.3-0.8). As a data validation step, a series of consecutive patient records were reviewed (n=80) showing that fewer than 23% underwent appropriate follow-up EF assessment post revascularization. CONCLUSION: Our findings suggest that CABG patients with ischemic cardiomyopathy have low rates of ICD utilization. This is particularly evident among females and elderly patients. Furthermore our data suggests that few patients post-revascularization undergo follow-up EF assessment despite current guidelines likely contributing to the low rates of ICD utilization.