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.).

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.).

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.

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.

Automated vulnerability testing identifies patients with inadequate defibrillation safety margin.

BACKGROUND: Implantable cardioverter-defibrillator system efficacy is tested at implant by induction of ventricular fibrillation (VF). Defibrillation safety margin can be assessed without VF induction using upper limit of vulnerability methods, but these methods have required manual determination of T-wave timing. METHODS AND RESULTS: To test the feasibility of an inductionless system of implant testing, a multicenter prospective study of an automated vulnerability safety margin system was conducted, which measured T-wave timing using an intracardiac electrogram during a ventricular pacing train. The system delivered up to 4 T-wave shocks of 18 J. Lack of VF induction by all 4 shocks was considered evidence of defibrillation adequacy. Patients subsequently underwent conventional defibrillation testing to meet a standard implant criterion. The 95% lower CI for defibrillation success at 25 J for noninduced patients was found using Bayesian statistics. Sixty patients were enrolled at 6 centers. Vulnerability testing and defibrillation success results were obtained from 54 patients. Vulnerability testing induced VF in 10 (19%) patients, of whom 2 required system revision. All patients not induced by vulnerability testing were successfully defibrillated twice at ≤25 J. The Bayesian credible interval was 97% to 100% for the population success rate of defibrillation at 25 J for automated vulnerability safety margin noninduced patients. CONCLUSIONS: An automated system identified all patients who failed conventional safety margin testing, while inducing only 19% of patients. Although limited by sample size, this study suggests the feasibility of automated implant testing that substantially reduces the need for VF induction in patients receiving implantable cardioverter-defibrillators.

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.

Intermediate-term outcomes of surgical atrial fibrillation correction with the CryoMaze procedure.

BACKGROUND: Few studies have reported long-term outcomes of surgical atrial fibrillation (AF) correction. We perform the Cox-Maze III lesion set with argon-powered cryoenergy (CryoMaze procedure) on all patients with AF presenting for cardiac operations. This study reports long-term clinical results and heart rhythm status. METHODS: Between July 2002 and November 2005, 119 consecutive patients underwent surgical AF correction with the CryoMaze procedure. Mitral valve disease was the primary indication for operation in 66%. AF was continuous in 65%. Rhythm assessment was with 2-week continuous electrocardiographic (ECG) monitoring in 75% of patients and by noncontinuous ECG in the remainder. Median follow-up was 3.2 years and was 98% complete. RESULTS: There was one hospital (0.8%) death. Survival at 3 years was 84%. One perioperative stroke resolved completely. No late strokes occurred. In 4 of 119 patients (4 (3.4%), pacemakers were inserted during the index hospitalization. Median length of stay was 7 days. Overall freedom from AF more than 3 years after operation was 60%. Among patients with preoperative intermittent AF, 85% (28 of 33) were in normal sinus rhythm, and 47% (27 of 58) with continuous AF were in normal sinus rhythm (p < 0.001). CONCLUSIONS: CryoMaze AF correction is safe and is associated with a very low risk of stroke. Rates of normal sinus rhythm at more than 3 years postoperatively were high for patients with intermittent AF and acceptable for those with continuous AF. This experience supports wider application of the CryoMaze to all patients with AF who need cardiac operations.

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.

Cellular and molecular determinants of altered Ca2+ handling in the failing rabbit heart: primary defects in SR Ca2+ uptake and release mechanisms.

Myocytes from the failing myocardium exhibit depressed and prolonged intracellular Ca(2+) concentration ([Ca(2+)](i)) transients that are, in part, responsible for contractile dysfunction and unstable repolarization. To better understand the molecular basis of the aberrant Ca(2+) handling in heart failure (HF), we studied the rabbit pacing tachycardia HF model. Induction of HF was associated with action potential (AP) duration prolongation that was especially pronounced at low stimulation frequencies. L-type calcium channel current (I(Ca,L)) density (-0.964 +/- 0.172 vs. -0.745 +/- 0.128 pA/pF at +10 mV) and Na(+)/Ca(2+) exchanger (NCX) currents (2.1 +/- 0.8 vs. 2.3 +/- 0.8 pA/pF at +30 mV) were not different in myocytes from control and failing hearts. The amplitude of peak [Ca(2+)](i) was depressed (at +10 mV, 0.72 +/- 0.07 and 0.56 +/- 0.04 microM in normal and failing hearts, respectively; P < 0.05), with slowed rates of decay and reduced Ca(2+) spark amplitudes (P < 0.0001) in myocytes isolated from failing vs. control hearts. Inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a revealed a greater reliance on NCX to remove cytosolic Ca(2+) in myocytes isolated from failing vs. control hearts (P < 0.05). mRNA levels of the alpha(1C)-subunit, ryanodine receptor (RyR), and NCX were unchanged from controls, while SERCA2a and phospholamban (PLB) were significantly downregulated in failing vs. control hearts (P < 0.05). alpha(1C) protein levels were unchanged, RyR, SERCA2a, and PLB were significantly downregulated (P < 0.05), while NCX protein was significantly upregulated (P < 0.05). These results support a prominent role for the sarcoplasmic reticulum (SR) in the pathogenesis of HF, in which abnormal SR Ca(2+) uptake and release synergistically contribute to the depressed [Ca(2+)](i) and the altered AP profile phenotype.

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.

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.

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.

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.