Bachmann's Bundle's Unique Physiology: Reviewing How it Made an Atypical Flutter Even More Atypical.

A 69-year-old man with a history of previous ablation and cardiac surgery was found on cardiac electrophysiology study to have a macro-re-entrant left atrial flutter initially misdiagnosed as a micro-re-entrant right atrial tachycardia resulting from the unique conduction properties of Bachmann's bundle. (Level of Difficulty: Advanced.).

Idiopathic ventricular fibrillation in a 10-year-old boy: technical aspects of radiofrequency ablation and utility of antiarrhythmic therapy.

Idiopathic ventricular fibrillation (VF) is defined as spontaneous VF in the absence of structural heart disease. No prior reports exist addressing the technical aspects of idiopathic VF ablation in a child. We present the case of a 10-year-old boy with idiopathic VF, who presented a unique management challenge, particularly as regards the technical aspects of the ablation procedure. Ablation of idiopathic VF is feasible in a 10-year-old boy and oral quinidine seems more effective than other antiarrhythmic drugs in this condition.

Defibrillation threshold testing in patients with hypertrophic cardiomyopathy.

INTRODUCTION: Implantable cardioverter-defibrillators (ICDs) decrease sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). One of the vital aspects of ICD implantation is the demonstration that the myocardium can be reliably defibrillated, which is defined by the defibrillation threshold (DFT). We hypothesized that patients with HCM have higher DFTs than patients implanted for other standard indications. METHODS: We retrospectively reviewed the medical records of patients implanted with an ICD at the University of Maryland from 1996 to 2008. All patients with HCM who had DFTs determined were included. Data were compared to selected patients implanted for other standard indications over the same time period. All patients had a dual-coil lead with an active pectoral can system and had full DFT testing using either a step-down or binary search protocol. RESULTS: The study group consisted of 23 HCM patients. The comparison group consisted of 294 patients. As expected, the HCM patients were younger (49 ± 18 years vs 63 ± 12 years; P < 0.00001) and had higher left ventricular ejection fractions (66% vs 32%; P < 0.000001). The average DFT in the HCM group was 13.9 ± 7.0 Joules (J) versus 9.8 ± 5.1 J in the comparison group (P = 0.0004). In the HCM group, five of the 23 patients (22%) had a DFT ≥ 20 J compared to 19 of 294 comparison patients (6%). There was a significant correlation between DFT and left ventricle wall thickness in the HCM group as measured by echocardiography (r = 0.44; P = 0.03); however, there was no correlation between DFT and QRS width in the HCM group (r = 0.1; P = NS). CONCLUSIONS: Our results suggest that patients with HCM have higher DFTs than patients implanted with ICDs for other indications. More importantly, a higher percentage of HCM patients have DFTs ≥ 20 J and the DFT increases with increasing left ventricle wall thickness. These data suggest that DFT testing should always be considered after implanting ICDs in HCM patients.

Left-sided atrial flutter originating in the coronary sinus after radiofrequency ablation of atrial fibrillation.

We describe a case of atypical atrial flutter presenting 1 year after radiofrequency ablation for atrial fibrillation (AF). Electrophysiologic study showed a reentry circuit involving the inferolateral aspect of the mitral annulus and the coronary sinus (CS); however, a mitral isthmus line did not terminate the arrhythmia. Participation of the proximal CS musculature in the circuit suggested a possible target for ablation. Radiofrequency energy applications from within the CS terminated the tachycardia. Mapping and ablation within the CS should be considered in patients with post-AF ablation arrhythmias, particularly when the mitral annulus appears to be involved in the tachycardia circuit.

The influence of fat thickness on the human epicardial bipolar electrogram characteristics: measurements on patients undergoing open-heart surgery.

AIMS: Reference values exist for endocardial but not for epicardial (EPI) substrate mapping in cases of cardiomyopathy-associated ventricular tachycardia. We sought to establish such values for EPI electrogram voltage, including areas with overlying fat. METHODS AND RESULTS: Ten patients (six males) undergoing cardiac surgery were studied. After opening the pericardium, the distal bipole of an electrophysiology catheter was placed tangential to the EPI surface to obtain an electrogram recording. The bipole was tangentially rotated 90 degrees and the higher of the two amplitudes (mV) was taken as the local amplitude. Recordings were taken from normal left and right ventricular myocardium (n = 26 data points each), over thick (> or = 0.5 cm) fat at both ventricular bases (n = 16) and thin (<0.5 cm) fat at the mid-ventricular level (n = 32). A total of 100 recordings (mean 10/patient) were analysed. Four patients underwent valvular surgery, three bypass surgery, and three combined procedures. Mean age was 61.7 +/- 10.4 years and mean left ventricular ejection fraction was 46 +/- 12%. Electrogram amplitude was inversely related to EPI fat thickness. Over thick fat, 31% of recordings were <0.5 mV. CONCLUSION: Human EPI electrogram amplitude varies by ventricular chamber and significantly by EPI fat thickness. A cut-off of 0.5 mV to define 'scar' will include normal areas with thick overlying fat. EPI substrate maps should include data on EPI fat thickness for higher specificity.

A Tale of 2 Hearts: Simultaneous Dual Tachycardias Occurring 22 Years After Orthotopic Heart Transplantation.

At 22 years following heart transplantation, a patient presented with incessant atrial flutter. During electrophysiologic study, 2 simultaneous atrial arrhythmias were mapped, 1 from the donor and 1 from the recipient's heart. High-density mapping allowed for rapid identification of electrically abnormal areas, which were successfully ablated, thus restoring sinus rhythm. (Level of Difficulty: Advanced.).

Acute defibrillation performance of a novel, non-transvenous shock pathway in adult ICD indicated patients.

OBJECTIVES: The purpose of this study was to evaluate the efficacy of a totally subcutaneous, anteroposterior defibrillation shock pathway using a long time-constant shock waveform that emulates a proposed device having approximately twice the capacitance and thus twice the available energy of traditional transvenous devices. BACKGROUND: A non-transvenous defibrillation system potentially offers advantages over a transvenous system including simplification of the implant procedure and reduction of the impact of device complications by eliminating the need to place a lead within the heart. Previous non-transvenous defibrillation efficacy studies have been reported using anterolateral and anterior-anterior shock vectors. An external anteroposterior shock vector has demonstrated superior efficacy compared to anterolateral shock vectors but a prospective study on an anteroposterior shock vector with implanted electrodes has not been previously reported. METHODS: The non-transvenous shock vector consisted of an anterior low pectorally-placed active can emulator electrode and a posterior subcutaneous coil electrode. The shock waveform was a biphasic with 50% tilt per phase and a time constant of decay of 12 ms. Defibrillation efficacy was characterized using a step-down defibrillation threshold protocol (35 J, 25 J, 15 J). RESULTS: A total of 33 patients with standard ICD indications were enrolled in the study with 32 fully completing the protocol. The patient population was 69% male, with a mean age of 59 +/- 12 years. Mean ejection fraction was 27 +/- 12%. Of the 32 patients tested, 26 patients (81%) were successfully defibrillated at 35 J or less, 18 patients were defibrillated at 25 J or less and 9 patients were successfully defibrillated at 15 J. CONCLUSIONS: Defibrillation using a long time-constant waveform delivered through an anteroposterior non-transvenous pathway including a pectoral active can emulator electrode and a posterior subcutaneous coil electrode is feasible with over 80% of patients defibrillated successfully using 35 J or less.

Hibernating substrate of ventricular tachycardia: a three-dimensional metabolic and electro-anatomic assessment.

PURPOSE: Hibernating myocardium (HM) is associated with sudden cardiac death (SCD). Little is known about the electrophysiological properties of HM and the basis of its association with SCD. We aimed to electrophysiologically characterize HM in patients with ventricular tachycardia (VT). METHODS: Endocardial voltage mapping, metabolic 18FDG-positron emission tomography (PET) and perfusion 82Rb, 201Tl, or 99mTc scans were performed in 61 ischemic heart disease patients with VT. Hibernating areas were identified which was followed by three-dimensional PET reconstructions and integration with voltage maps to allow hybrid metabolic-electro-anatomic assessment of the arrhythmogenic substrate. RESULTS: Of 61 patients with ischemic heart disease and refractory VT, 7 were found to have hibernating myocardium (13%). A total of 303 voltage points were obtained within hibernating myocardium (8.2 points per 10 cm2) and displayed abnormal voltage in 48.5 and 78.3% of bipolar and unipolar recordings, respectively, with significant heterogeneity of bipolar (p < 0.0001) and unipolar voltage measurements (p = 0.0004). Hibernating areas in 6 of 7 patients contained all three categories of bipolar voltage-defined scar (<0.5 mV), border zone (0.5-1.5 mV), and normal myocardium (>1.5 mV). The characteristics of local electrograms were also assessed and found abnormal in most recordings (76.6, 10.2% fractionated, 5.3% isolated potentials). Exit sites of clinical VTs were determined in 6 patients, of which 3 were located within hibernating myocardium. CONCLUSIONS: Hibernating myocardium displays abnormal and heterogeneous electrical properties and seems to contribute to the substrate of VT. These observations may underlie the vulnerability to reentry and SCD in patients with hypoperfused yet viable myocardium.

Coronary sinus electrode does not reduce atrial defibrillation thresholds.

BACKGROUND: Atrial defibrillation can be achieved with a conventional dual-coil, active pectoral implantable cardioverter-defibrillator (ICD) lead system. Shocking vectors that incorporate an additional electrode in the CS have been used, but it is unclear if they improve atrial DFTs. OBJECTIVE: The objective of this prospective, randomized study was to determine if a coronary sinus (CS) electrode reduces atrial defibrillation thresholds (DFTs). METHODS: This was a prospective study of 36 patients undergoing initial ICD implant for standard indications. A defibrillation lead with superior vena cava (SVC) and right ventricular (RV) shocking coils was implanted in the RV. An active can emulator (Can) was placed in a pre-pectoral pocket. A lead with a 4 cm long shocking coil was placed in the CS. Atrial DFTs were determined in the following 3 shocking configurations in each patient, with the order of testing randomized: RV --> SVC + Can (Ventricular Triad), distal CS --> SVC + Can (Distal Atrial Triad), and proximal CS --> SVC + Can (Proximal Atrial Triad). RESULTS: The Proximal and Distal Atrial Triad configurations were both associated with significant reductions in peak current (p < 0.01), but this effect was offset by significant increases in shock impedance (p < 0.01), resulting in no net change in the peak voltage or DFT energy in comparison to the Ventricular Triad configuration (Ventricular Triad: 4.9 +/- 6.6 J, Proximal Atrial Triad: 3.3 +/- 4.1J, Distal Atrial Triad: 4.4 +/- 6.7 J, p > 0.2). CONCLUSION: Shocking vectors that incorporate a CS coil do not significantly improve atrial defibrillation efficacy. Since the Ventricular Triad shocking pathway provides reliable atrial and ventricular defibrillation, this configuration should be preferred for combined atrial and ventricular ICDs.

Management of arrhythmias in the emergency department.

The authors present practical and concise advice on initial diagnosis and management of arrhythmias, on arrhythmia devices, and on syncope. There is discussion of tachyarrhythmias, both wide and narrow, bradyarrhythmias, and management of pacemakers and defibrillators. Common pitfalls and concerns are addressed.

Inappropriate ICD discharges due to "triple counting" during normal sinus rhythm.

OBJECTIVE: To describe the clinical course of a patient with multiple ICD shocks in the setting of advanced renal failure and hyperkalemia. METHODS: The patient was brought to the Electrophysiology Laboratory where the ICD was interrogated. RESULTS: The patient was found to be hyperkalemic (serum potassium 7.6 mg/dl). Analysis of stored intracardiac electrograms from the ICD revealed "triple counting" (twice during his QRS complex and once during the T wave) and multiple inappropriate shocks. Correction of his electrolyte abnormality normalized his electrogram and no further ICD activations were observed. CONCLUSION: Electrolyte abnormalities can distort the intracardiac electrogram in patients with ICD's and these changes can lead to multiple inappropriate shocks.

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.

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.

Repositioning of a dislodged and fibrosed ventricular lead.

UNLABELLED: This is a case of a 61 year old African American female with history of end stage renal disease on hemodialysis. She had a dual chamber permanent pacemaker implanted in 2003 for symptomatic bradycardia. Over the past several months the patient had problems with access for dialysis. The right arm AV fistula was occluded. The patient had multiple temporary central catheter placed for dialysis over the past 3 months. The patient was admitted for superior vena-cava syndrome. CT scan of the thorax and neck showed occluded right and left subclavian system. An incidental finding was the right ventricular (RV) lead been dislodged and the tip being in the inferior vena cava. Surgical and non-surgical options were discussed with the patient and she chose to go the less invasive route. The patient underwent a RV lead revision. Using different stylets the RV lead was repositioned in the RV with good pacing and sensing characteristics. CONCLUSIONS: Successful repositioning of an old dislodged RV pacing lead using stylets and eliminating the need for invasive procedure like lead extraction.

Effect of shock polarity on the efficacy of transthoracic atrial defibrillation.

BACKGROUND: The energy requirement for internal ventricular defibrillation is reduced by reversal of shock polarity. The influence of shock polarity on the efficacy of transthoracic atrial defibrillation is unknown. METHODS: This prospective, randomized study enrolled 110 consecutive patients who were referred for elective cardioversion of persistent atrial fibrillation (AF). The electrodes were placed in the anteroposterior position. The patients were randomized to receive either standard (anterior pad = cathode) or reversed polarity (anterior pad = anode) shocks with a damped sinusoidal monophasic waveform. A step-up protocol was used to estimate the cardioversion threshold. The initial shock energy was 50 J, with subsequent increments to 100, 200, 300, and 360 J in the event of cardioversion failure. RESULTS: Sixty-four percent of the patient population were men, with a mean age of 66 +/- 13 years and a mean duration of AF of 242 +/- 556 days. The overall success rates of cardioversion were 84% for standard polarity and 78% for reversed polarity (P not significant). Among the patients who were successfully cardioverted, the mean atrial defibrillation threshold was 198 +/- 103 J for standard polarity and 212 +/- 107 J for reversed polarity (P not significant). CONCLUSIONS: Reversal of shock polarity does not improve transthoracic cardioversion efficacy with a standard damped sinusoidal monophasic waveform. Alternate strategies should be considered for patients who fail external cardioversion, such as adjunctive pharmacologic treatment, use of a biphasic shock waveform, or internal cardioversion.

Efficacy of transthoracic cardioversion of atrial fibrillation using a biphasic, truncated exponential shock waveform at variable initial shock energies.

Biphasic shocks are more effective than damped sine wave monophasic shocks for transthoracic cardioversion (CV) of atrial fibrillation (AF), but the optimal protocol for CV with biphasic shocks has not been defined. We conducted a prospective, randomized study of 120 consecutive patients with persistent AF to delineate the dose-response curve for CV of AF with a biphasic truncated exponential shock waveform and to identify clinical predictors of shock efficacy. Our data suggest that the initial shock energy for CV with this waveform should be 200 J if the patient weighs <90 kg and 360 J if the patient weighs >/=90 kg.

Effect of shock polarity on defibrillation thresholds with a hybrid patch-coil lead system.

INTRODUCTION: Understanding the factors that affect defibrillation thresholds (DFTs) has important implications both for optimization of defibrillation efficacy and for the design of new lead systems. The objective of this prospective study was to evaluate the effect of shock polarity on defibrillation efficacy at the time of routine pulse generator replacement in patients with a hybrid patch-coil lead system. METHODS: Each patient underwent 4 assessments of DFT: monophasic or biphasic shock with standard or reversed polarity, with the order of testing with respect to polarity randomized. In standard polarity, the right atrial coil is the anode and the left ventricular patch is the cathode. RESULTS: The study population of 30 patients was 80% men with a mean age of 65 +/- 9 years and a mean left ventricular ejection fraction of 33 +/- 12%. There was a significant 21% decrease in the mean monophasic DFT with reversed polarity shocks (13.1 +/- 5.9 J vs. 16.6 +/- 6.5 J, p < 0.01). Reversal of shock polarity did not have a significant effect on the mean biphasic DFT (8.0 +/- 4.8 J vs. 8.5 +/- 4.3 J for reversed and standard polarity respectively, p = NS). However, when an elevated biphasic DFT (>or=15 J) was present in either standard or reversed polarity, a significant decrease in DFT was observed when the opposite polarity was used (16.7 +/- 2.5 J vs. 9.1 +/- 2.7 J, n = 9, p < 0.0001). CONCLUSION: Reversal of shock polarity markedly improves monophasic DFTs with the patch-coil lead configuration. The DFT should be determined with both shock polarities to optimize defibrillation efficacy for patients with high biphasic DFTs (>or=15 J).

Prospective assessment of the CryoMaze procedure with continuous outpatient telemetry in 136 patients.

BACKGROUND: Only 40% of patients with atrial fibrillation (AF) undergoing cardiac surgery are treated with surgical AF correction. We prospectively studied endocardial cryoablation of the Cox-maze III lesion set following prespecified rhythm assessment with outpatient telemetry. METHODS: Between 2007 and 2011, 136 patients underwent surgical AF correction using an argon-powered cryoablation device. Patients wore continuous electrocardiogram monitoring prior to and at 6, 12, and 24 months after surgery. The average length of monitoring was 6.5±1 days prior to surgery and 11±4 days at each time point after surgery. Patients were assessed for cardiac rhythm, interval cardioversion or ablation procedures, pacemaker placement, and the use of warfarin or antiarrhythmic medications. The primary endpoint of this study was freedom from AF at 1 year. RESULTS: Mean patient age was 66±12 years, 50% (69 of 138) were male and 41% (55 of 134) had persistent AF. CryoMaze was done in conjunction with mitral valve operation in 95% (131 of 138) and other procedures in 41% (56 of 138). Follow-up was 96% complete at 1 year and 90% at 2 years. Freedom from AF was 76% at 1 year. Perioperative mortality and stroke rates were both 1.5% (2 of 138). Perioperative pacemaker implantation was required in 7% (9 of 136). In univariate analysis, younger age, female gender, decreased height and weight, smaller preoperative and postoperative left atrial diameter, intermittent AF, and freedom from AF at discharge were associated with freedom from AF at 1 year. Actuarial 2- and 4-year (Kaplan-Meier) survival were 93% and 80%, respectively. CONCLUSIONS: The CryoMaze procedure is safe and is associated with 76% freedom from AF at 1 year.

Safety of computed tomography in patients with cardiac rhythm management devices: assessment of the U.S. Food and Drug Administration advisory in clinical practice.

OBJECTIVES: To assess the safety of computed tomography (CT) imaging in patients with cardiac rhythm management (CRM) devices, which was subject to an advisory from the U.S. Food and Drug Administration (FDA) in 2008. BACKGROUND: The FDA warned about potential interference of CT imaging with CRM devices and made recommendations for clinical practice despite only limited evidence. METHODS: All 516 CT scans that involved direct radiation exposure of CRM devices (332 defibrillators, 184 pacemakers) at 2 large-volume centers between July 2000 and May 2010 were included. The primary outcome was a composite endpoint of death, bradycardia or tachycardia requiring termination of the scan or an immediate intervention, unplanned hospital admission, reprogramming of the device, inappropriate defibrillator shocks, or device replacement/revision thought to be due to CT imaging. Significant changes in device parameters were sought as a secondary outcome (control group 4:1 ratio). RESULTS: The main finding was that none of the CTs were associated with the primary outcome. With serial device interrogations, there were no differences in changes in battery voltage or lead parameters between devices exposed to radiation and their controls. Potentially significant changes in device parameters were observed in a small group of devices (both the CT group and control group), but no definitive link to CT was confirmed, and there were no associated clinical consequences. CONCLUSIONS: The findings suggest that the presence of CRM devices should not delay or result in cancellation of clinically indicated CT imaging procedures, and provide evidence that would be helpful when the FDA advisory is re-evaluated.