Novel use of atrial overdrive pacing to rapidly differentiate junctional tachycardia from atrioventricular nodal reentrant tachycardia.

BACKGROUND: Distinguishing between junctional tachycardia (JT) and atrioventricular nodal reentrant tachycardia (AVNRT) is essential to minimize unnecessary catheter ablation and the risk of heart block during treatment of AVNRT. OBJECTIVE: The purpose of this study was to investigate whether the tachycardia response to atrial overdrive pacing at a cycle length (CL) slightly shorter than tachycardia CL can differentiate between JT and AVNRT. We hypothesized that atrial overdrive pacing would transiently suppress JT but would entrain AVNRT. METHODS: Twenty-one patients in whom AVNRT was induced and atrial overdrive pacing during either AVNRT or JT was attempted were included in the study. We predicted that, upon cessation of atrial overdrive pacing, an atrial-His-His-atrial (AHHA) response would identify JT and an atrial-His-atrial (AHA) response would identify AVNRT. RESULTS: A total of 8 JT and 21 typical AVNRT were induced. Atrial overdrive pacing was attempted in all cases of JT and in 16 cases of AVNRT. An AHHA response was observed in 100% (8/8) of JT cases. In 2 cases of AVNRT, atrial overdrive pacing repetitively terminated the tachycardia. In the remaining patients with AVNRT, an AHA response was observed in 100% (14/14) of cases. When a response was able to be elicited, atrial overdrive pacing was 100% sensitive and 100% specific for differentiating JT from AVNRT. CONCLUSION: Atrial overdrive pacing during tachycardia can rapidly differentiate JT from AVNRT, which can improve the safety and efficiency of catheter ablation of these arrhythmias.

Electrophysiological effects of late percutaneous coronary intervention for infarct-related coronary artery occlusion: the Occluded Artery Trial-Electrophysiological Mechanisms (OAT-EP).

BACKGROUND: The Occluded Artery Trial-Electrophysiological Mechanisms (OAT-EP) tested the hypothesis that opening a persistently occluded infarct-related artery by percutaneous coronary intervention and stenting (PCI) after the acute phase of myocardial infarction compared with optimal medical therapy alone reduces markers of vulnerability to ventricular arrhythmias. METHODS AND RESULTS: Between April 2003 and December 2005, 300 patients with an occluded native infarct-related artery 3 to 28 days (median, 12 days) after myocardial infarction were randomized to PCI or optimal medical therapy. Ten-minute digital Holter recordings were obtained before randomization, at 30 days, and at 1 year. The primary end point was the change in alpha1, a nonlinear heart rate variability parameter, between baseline and 1 year. Major secondary end points were the changes in the filtered QRS duration on the signal-averaged ECG and variability in T-wave morphology (T-wave variability) between baseline and 1 year. There were no significant differences in the changes in alpha1 (-0.04; 95% CI, -0.12 to 0.04), filtered QRS (2.2 ms; 95% CI, -1.4 to 5.9 ms), or T-wave variability (3.0 microV; 95% CI, -4.8 to 10.7 microV) between the PCI and medical therapy groups (medical therapy change minus PCI change). Multivariable analysis revealed that the results were unchanged after adjustment for baseline clinical variables and medication treatments during the Holter recordings. CONCLUSIONS: PCI with stenting of a persistently occluded infarct-related artery during the subacute phase after myocardial infarction compared with medical therapy alone had no significant effect on changes in heart rate variability, the time-domain signal-averaged ECG, or T-wave variability during the first year after myocardial infarction. These findings are consistent with the lack of clinical benefit, including no reduction in sudden death, with PCI for stable patients with persistently occluded infarct-related arteries after myocardial infarction in the main OAT.

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.

Improved defibrillation efficacy with an ascending ramp waveform in humans.

OBJECTIVES: The purpose of this study was to compare an ascending ramp waveform (RAMP) with a standard, clinically available biphasic truncated exponential waveform (BTE) for defibrillation in humans. BACKGROUND: In animal studies, RAMP had a lower defibrillation threshold (DFT) than BTE. METHODS: We studied 63 patients at implantable cardioverter-defibrillator placement using a dual-coil lead and left pectoral active can. The subjects were divided into two groups, one with a 12-ms ascending first phase and one with a 7-ms ascending first phase. Phase 2 of RAMP for both groups was a truncated exponential decay with 65% tilt and reversed polarity. The BTE had a 50% tilt in each phase. DFT and upper limit of vulnerability (ULV) were measured for both waveforms using a binary search protocol. RESULTS: The patient population was 77% male, with a mean age of 63 +/- 10 years and ejection fraction of 33 +/- 13%. Delivered energy at DFT was lower with the 7-ms RAMP vs BTE (5.4 +/- 2.6 J vs 6.5 +/- 3.4 J; P < .01) but unchanged with the 12-ms RAMP (7.4 +/- 4.5 J vs 7.1 +/- 4.9 J). Maximal voltage at DFT was significantly lower with either RAMP compared to BTE (P < .01). There was a strong correlation between ULV and DFT for both RAMP and BTE (P < .01). CONCLUSIONS: The 7-ms ascending ramp waveform significantly reduced delivered energy (18%) and voltage (24%) at DFT, whereas the 12-ms RAMP reduced only DFT voltage. This is the first report of a waveform that is superior to a BTE for defibrillation in humans. ULV correlates with DFT for RAMP, supporting the use of ULV testing for implantation of devices.

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.

Safety of a single successful conversion of ventricular fibrillation before the implantation of cardioverter defibrillators.

UNLABELLED: Multiple successful conversions of ventricular fibrillation (VF) at 10 J below the maximum output of implantable cardioverter defibrillator (ICD) have been recommended as a minimum device implantation criterion. This recommendation is based on the probabilistic properties of defibrillation that necessitates multiple shocks to establish an adequate safety margin for the conversion of subsequent spontaneous arrhythmias. We hypothesized that a single successful shock at a 14 J may suffice. METHODS AND RESULTS: The Low Energy Safety Study (LESS) enrolled 720 patients undergoing initial ICD implantation with a dual-coil transvenous lead and active pulse generator. At implant, an enhanced defibrillation threshold (DFT++) was determined by a rigorous protocol beginning at 14 J, and requiring at least 4 shocks. Fifty percent of all patients were then randomized to full output shock energy and the conversion rates for spontaneous ventricular tachyarrhythmias at rates > 200 beats/min were measured. There were 318 patients randomized to 31 J, of whom 254 were successfully defibrillated by an initial 14 J shock. During a mean follow-up of 24 +/- 12 months, 112 spontaneous VF episodes occurred in 31 patients. The combined conversion success of the first and second shock (when needed) did not differ between the subgroup of patients who were successfully defibrillated by an initial 14 J shock, regardless of the results of additional testing, and the whole cohort who underwent more systematic testing (97% vs 97%). All spontaneous episodes of VF were successfully treated during long-term follow-up. CONCLUSIONS: A first successful shock of 14 J may be a sufficient endpoint to allow the implantation of ICDs with the Triad lead configuration, when programming all shocks to 31 J.

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.