Effect of an active abdominal pulse generator on defibrillation thresholds with a dual-coil, transvenous ICD lead system.

INTRODUCTION: Many patients with implantable cardioverter defibrillators (ICDs) have older lead systems, which are usually not replaced at the time of pulse generator replacement unless a malfunction is noted. Therefore, optimization of defibrillation with these lead systems is clinically important. The objective of this prospective study was to determine if an active abdominal pulse generator (Can) affects chronic defibrillation thresholds (DFTs) with a dual-coil, transvenous ICD lead system. METHODS AND RESULTS: The study population consisted of 39 patients who presented for routine abdominal pulse generator replacement. Each patient underwent two assessments of DFT using a step-down protocol, with the order of testing randomized. The distal right ventricular (RV) coil was the anode for the first phase of the biphasic shocks. The proximal superior vena cava (SVC) coil was the cathode for the Lead Alone configuration (RV --> SVC). For the Active Can configuration, the SVC coil and Can were connected electrically as the cathode (RV --> SVC + Can). The Active Can configuration was associated with a significant decrease in shock impedance (39.5 +/- 5.8 Omega vs. 50.0 +/- 7.6 Omega, P < 0.01) and a significant increase in peak current (8.3 +/- 2.6 A vs. 7.2 +/- 2.4 A, P < 0.01). There was no significant difference in DFT energy (9.0 +/- 4.6 J vs. 9.8 +/- 5.2 J) or leading edge voltage (319 +/- 86 V vs. 315 +/- 83 V). An adequate safety margin for defibrillation (> or =10 J) was present in all patients with both shocking configurations. CONCLUSION: DFTs are similar with the Active Can and Lead Alone configurations when a dual-coil, transvenous lead is used with a left abdominal pulse generator. Since most commercially available ICDs are only available with an active can, our data support the use of an active can device with this lead system for patients who present for routine pulse generator replacement.

Clinical predictors of atrial defibrillation thresholds with a dual-coil, active pectoral lead system.

OBJECTIVES: The purpose of this study was to identify clinical predictors of atrial defibrillation thresholds (DFTs) with standard implantable cardioverter-defibrillator (ICD) leads. BACKGROUND: Atrial defibrillation can be achieved with active pectoral, dual-coil transvenous ICD lead systems. If clinical predictors of atrial defibrillation efficacy with these lead systems were identified, they could be used to predict which patients may require more complex lead systems for atrial defibrillation, such as a coronary sinus electrode. METHODS: This was a prospective study of 135 consecutive patients undergoing initial ICD implant for standard indications. The lead system evaluated was a transvenous defibrillation lead with coils in the superior vena cava (SVC) and right ventricular apex (RV), and a left pectoral pulse generator emulator (CAN). The shocking pathway was RV-->SVC+CAN. Atrial DFT was measured using a step-up protocol. Clinical and echocardiographic parameters were evaluated as predictors of atrial DFT and multiple linear regression was performed. RESULTS: Mean atrial DFT was 4.6 +/- 3.8 J. Atrial DFT was < or =3 J in 70 patients (52%) and < or = 10 J in 97% of patients. The highest atrial DFT was 20 J (one patient). Left atrial size (r = 0.21, P = .01) and left ventricular end-diastolic diameter (r = 0.19, P = .02) were independent predictors of atrial DFT. However, these two predictors accounted for only 6% of the variability in atrial DFT. CONCLUSIONS: Clinical parameters are of limited use in predicting atrial DFT with a dual-coil, active pectoral ICD lead system. Because the RV--> SVC + CAN shocking pathway provides reliable atrial and ventricular defibrillation, this configuration should be preferred for combined atrial and ventricular ICDs.

Enhanced detection of arrhythmia vulnerability using T wave alternans, left ventricular ejection fraction, and programmed ventricular stimulation: a prospective study in subjects with chronic ischemic heart disease.

INTRODUCTION: In previous studies, the prognostic value of T wave alternans (TWA) was similar to that of programmed ventricular stimulation (PVS). However, presently it is unclear if TWA and PVS identify the same patients or provide complementary risk stratification information. In addition, the effects of left ventricular ejection fraction (LVEF) on the prognostic value of TWA are unknown. The aim of this study was to determine if combined assessment of TWA, LVEF, and PVS improves arrhythmia risk stratification. METHODS AND RESULTS: This was a prospective study of 144 patients with coronary artery disease and LVEF < or =40% who were referred for PVS for standard clinical indications. The endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator (ICD) therapy. TWA (hazard ratio 2.2, P = 0.03) and PVS (hazard ratio 1.9, P = 0.05) both were significant predictors of endpoint events, and TWA was the only independent predictor. LVEF markedly influenced the prognostic value of TWA, which was a potent predictor of events in subjects with LVEF between 30% and 40% (event rates: TWA+ 36%, TWA- 0%, P = 0.001) but did not predict events in subjects with LVEF <30% (hazard ratio 1.1, P > 0.5). PVS successfully identified additional low-risk patients within the cohort with negative or indeterminate TWA results (hazard ratio 4.7, P = 0.015) but did not provide incremental prognostic information for TWA+ patients (hazard ratio 0.9, P > 0.5). CONCLUSION: The combined use of TWA, LVEF, and PVS is a promising new approach to arrhythmia risk stratification that permits identification of high-risk and very-low-risk patients.

Exercise is superior to pacing for T wave alternans measurement in subjects with chronic coronary artery disease and left ventricular dysfunction.

INTRODUCTION: T wave alternans (TWA) is a heart rate-dependent marker of vulnerability to ventricular arrhythmias. Atrial pacing and exercise both are used as provocative stimuli to elicit TWA. However, the prognostic value of the two testing methods has not been compared. The aim of this prospective study was to compare the prognostic value of TWA measured during bicycle exercise and atrial pacing in a large cohort of high-risk patients with ischemic heart disease and left ventricular dysfunction. METHODS AND RESULTS: This was a prospective study of 251 patients with coronary artery disease and left ventricular dysfunction who were referred for electrophysiologic studies (EPS) for standard clinical indications. Patients underwent TWA testing using bicycle ergometry (exercise TWA, n = 144) and/or atrial pacing (pacing TWA, n = 178). The primary endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator therapy. The predictive value of exercise and pacing TWA for EPS results and for endpoint events was determined. Exercise and pacing TWA both were significant predictors of EPS results (odds ratios 3.0 and 2.9 respectively, P < 0.02). Kaplan-Meier survival analysis of the primary endpoint revealed that exercise TWA was a significant predictor of events (hazard ratio 2.2, P = 0.03). In contrast, pacing TWA had no prognostic value for endpoint events (hazard ratio 1.1, P = 0.8). CONCLUSION: TWA should be measured during exercise when it is used for clinical risk stratification. EPS results may not be an adequate surrogate for spontaneous events when evaluating new risk stratification tests.

Influence of QRS duration on the prognostic value of T wave alternans.

INTRODUCTION: T wave alternans (TWA) is a promising new noninvasive marker of arrhythmia vulnerability that quantifies beat-to-beat changes in ventricular repolarization. Secondary repolarization abnormalities are common in subjects with wide QRS complexes. However, the relationship between TWA and QRS prolongation has not been evaluated. The goal of this study was to determine if QRS prolongation influences the prevalence or prognostic value of TWA. METHODS AND RESULTS: The study consisted of 108 consecutive patients with coronary artery disease and left ventricular ejection fraction < or = 40% who were referred for electrophysiologic studies. Patients underwent TWA testing using bicycle ergometry in the absence of beta-blockers or antiarrhythmic drugs. The primary endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator therapy. The prognostic value of TWA was assessed in the entire cohort and in two subgroups: QRS < 120 msec (normal, n = 62) and QRS > or = 120 msec (prolonged, n = 46). TWA (hazard ratio 2.2, P = 0.03) and QRS prolongation (hazard ratio 2.2, P = 0.01) were both significant and independent predictors of arrhythmic events. QRS prolongation had no effect on the prevalence of positive TWA tests (QRS < 120 msec: 48%, QRS > or = 120 msec: 50%, P = NS). TWA was a highly significant predictor of events in patients with a normal QRS (hazard ratio 5.8, P = 0.02). In contrast, TWA was not useful for risk stratification in subjects with QRS prolongation (hazard ratio 1.1, P = 0.8). CONCLUSION: TWA is useful only for risk stratification in the absence of QRS prolongation. The presence of QRS prolongation and left ventricular ejection fraction < or = 40% may be sufficient evidence of an adverse prognosis that additional risk stratification is not useful or necessary.

Effects of selective autonomic blockade on T-wave alternans in humans.

BACKGROUND: T-wave alternans (TWA) is an important noninvasive measure of ventricular arrhythmia vulnerability. This study tested the hypothesis that the autonomic nervous system influences TWA measurement in high-risk subjects with coronary artery disease. METHODS AND RESULTS: T-wave alternans was measured in 60 patients with coronary artery disease, left ventricular dysfunction, and inducible sustained ventricular tachycardia during electrophysiological studies. All patients had TWA measured at baseline with atrial pacing at 100 bpm (600 ms), 109 bpm (550 ms), and 120 bpm (500 ms). After a 10-minute recovery period, TWA was measured again after sympathetic blockade (esmolol, n=20), parasympathetic blockade (atropine, n=20), or no intervention (control subjects, n=20). The prevalence of significant TWA was unchanged compared with baseline after atropine infusion and in the control group. In contrast, the amplitude of TWA in the vector magnitude lead was significantly reduced after esmolol infusion (P<0.001), and the number of positive TWA tests was reduced by 50% (70% versus 35%, P<0.05). CONCLUSIONS: Our findings have important implications for the use of TWA to risk-stratify patients for life-threatening ventricular arrhythmias and provide a new potential mechanism for the reduction in sudden cardiac death conferred by beta-blockers among patients with coronary artery disease and congestive heart failure.