High altitude arrhythmias.

OBJECTIVE: To investigate the cause and nature of palpitations occurring at high altitude. METHODS: Implantable loop recorders were inserted subcutaneously in the left pectoral region of 9 healthy male volunteers. Subjects flew to Kathmandu (1,250 m) and then Lukla (2,800 m) before immediately commencing an identical ascent and descent profile to high altitude. The loop recorders were activated with any episode of palpitations and during exercise, rest and sleep. Arterial oxygen saturation was assessed concomitant with device activation. RESULTS: Above 5,000 m all subjects reported palpitations during exercise. All subjects demonstrated sinus tachycardia and marked sinus arrhythmia; one subject demonstrated atrial flutter; one subject had non-conducted p waves, and a further subject had marked ST segment depression. CONCLUSIONS: Significant arrhythmias occur at high altitude. In view of the increased risk of sudden cardiac death at high altitude, and considering that the elderly account for 15% of the 100 million visitors to altitude annually, further investigation is required.

Intravenous amiodarone for the pharmacological termination of haemodynamically-tolerated sustained ventricular tachycardia: is bolus dose amiodarone an appropriate first-line treatment?

OBJECTIVE: To examine the efficacy of bolus dose intravenous amiodarone for the pharmacological termination of haemodynamically-tolerated sustained monomorphic ventricular tachycardia (VT). DESIGN, SETTING AND PARTICIPANTS: Retrospective case series of consecutive emergency admissions with haemodynamically-tolerated sustained monomorphic VT administered bolus dose intravenous amiodarone 300 mg, according to current UK advanced life support practice guidelines. MAIN OUTCOME MEASURES: Pharmacological termination rates within 20 min and 1 h and incidence of hypotension requiring emergency direct current cardioversion (DCCV) during this period. RESULTS: 41 patients (35 men) of mean (SD) age 68 (10) years, the majority (85%) with ischaemic heart disease and impaired left ventricular function (mean (SD) ejection fraction 0.31 (0.11)), were enrolled in the study. The median VT duration was 70 min (range 15-6000), mean heart rate was 174 (34) bpm and systolic and diastolic blood pressures were 112 (22) and 73 (19) mm Hg, respectively. Pharmacological VT termination occurred within 20 min in 6/41 patients (15%; 95% CI 7% to 29%) and within 1 h in 12/41 patients (29%; 95% CI 18% to 45%). Haemodynamic deterioration requiring emergency DCCV occurred in 7/41 patients (17%; 95% CI 8% to 32%). CONCLUSIONS: Although advocated by advanced life support guidelines, bolus dose intravenous amiodarone was relatively ineffective for acutely terminating haemodynamically-tolerated sustained monomorphic VT with a significant incidence of haemodynamic destabilisation requiring emergency DCCV. Previous studies in the identical clinical setting suggest that alternative antiarrhythmic agents, particularly intravenous procainamide and sotalol, may be superior. A prospective randomised trial is required to determine the optimal drug treatment for stable sustained monomorphic VT in the emergency setting.

Treatment strategies in atrial fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice affecting up to 1% of the general population. There is a higher prevalence and incidence with increasing age and burden of chronic heart disease . Treatment for AF represents a significant healthcare cost, estimated to be about Euro 13.5 billion annually in the European Union. Manage-ment of AF remains challenging especially with new pharmacological and non-pharmacological approaches becoming readily available. This review article discusses the multitude of therapeutic options and how they may be applied to best effect.

Electrophysiological mapping and ablation of intra-atrial reentry tachycardia after Fontan surgery with the use of a noncontact mapping system.

BACKGROUND: Atrial tachyarrhythmias are a complication of Fontan surgery. Conventional electrophysiological mapping and ablation techniques are limited by the complex anatomic and surgical substrate and a high arrhythmia recurrence rate. This study investigates the use of noncontact mapping to identify arrhythmia circuits and guide ablation in Fontan patients. METHODS AND RESULTS: Eleven arrhythmias were recorded in 6 patients. Noncontact mapping improved recognition of the anatomic and surgical substrate and identified exit sites from zones of slow conduction in all clinical arrhythmias. Radiofrequency linear lesions were targeted across these critical zones in 5 patients. One patient underwent surgical cryotherapy. Although immediate success was achieved in 3 of 5 patients with radiofrequency ablation, 2 patients had a recurrence after a mean of 6.4 months of follow-up. The patient who underwent cryoablation remains free of arrhythmias. CONCLUSIONS: Noncontact mapping can identify arrhythmia circuits in the Fontan atrium and guide placement of ablation lesions. Arrhythmia recurrence is high, possibly because of inadequate lesion creation rather than inaccurate mapping and lesion targeting.

Comparison of coronary venous defibrillation with conventional transvenous internal defibrillation in man.

OBJECTIVE: Animal studies have shown that defibrillation in coronary veins is more effective than in the right ventricle. We aimed to assess the feasibility of placing defibrillation electrodes in the middle cardiac vein (MCV) in man and its impact on defibrillation requirements. METHODS: A prospective randomised study conducted in a tertiary referral centre. 10 patients (9 male) undergoing ICD implantation (65 (12) yrs) for NASPE/BPEG indications were studied. Defibrillation thresholds (DFT) were measured, using a binary search and an external defibrillator after 10 seconds of ventricular fibrillation, for the following configurations in each patient (order of testing randomised): RV + MCV --> Can and RV --> SVC + Can. INTERVENTIONS: A dual coil defibrillation electrode was placed transvenously in the right ventricle (RV) in the conventional manner. Using a guiding catheter a 3.2 Fr (67.5 mm length) electrode was placed transvenously in MCV. A test-can was placed subcutaneously in the left pectoral region. RESULTS: Lead placement was possible in 8/10 pts. Time to perform a middle cardiac venogram and place the electrode was 21 (23) mins. No adverse events were observed. Defibrillation current was less (6.7 (2.7) A) with RV + MCV --> Can compared to the conventional RV --> SVC + Can configuration (8.9 (3.4) A, p = 0.03). There was no significant difference in defibrillation voltage or energy. However, shock impedance was higher in the former configuration (57 (10) v. 43 (6) Omega, p = 0.001). CONCLUSIONS: In the majority of cases placement of a defibrillation lead in MCV is feasible. Defibrillation current requirements are 25% less when the shock is delivered using a MCV electrode.

Single capacitive discharge utilizing an auxiliary shock in the coronary venous system reduces the defibrillation threshold.

UNLABELLED: Auxiliary shocks (AS) from electrodes sutured to the left ventricle (LV) prior to primary biphasic shocks (PS) have been shown to reduce defibrillation thresholds (DFT). Two capacitors are required to generate these waveforms. We investigate delivery of AS from one capacitor using a novel waveform. The epicardial surface of the LV is accessed transvenously via the middle cardiac vein (MCV) avoiding a thoracotomy. METHODS: A defibrillation electrode was placed in the right ventricle (RV) and superior vena cava (SVC) in 12 pigs (37+/-2 kg). A 50x1.8 mm electrode was inserted in the MCV through a guide catheter. A can was placed in the left pectoral region. A monophasic AS (100 microF, 1.5 J) was delivered along one pathway before switching to deliver a biphasic waveform (40% tilt, 2 ms phase 2) along another. DFTs (PS+AS) were assessed using a binary search. Two configurations not incorporating AS acted as controls. DFTs were compared using repeated measures analysis of variance. RESULTS: DFTs of the four novel configurations (AS/PS) were: RV-->Can/MCV-->Can=14.9+/-3.7 J, MCV-->Can/RV-->Can=17.2+/-5.7 J, RV-->SVC+Can/MCV-->SVC+Can=13.4+/-4.6 J, MCV-->SVC+Can/RV-->SVC+Can=17.1+/-5.9 J. Delivering AS in the RV followed by PS in the MCV reduced the DFT (RV-->Can (19.9+/-7.3 J, P<0.01) and RV-->SVC+Can (19.2+/-6.0 J, P<0.05)). CONCLUSIONS: Delivering AS prior to PS in the MCV reduces the DFT by up to a third compared to conventional configurations of RV-->Can and RV-->SVC+Can. This is possible using only a single capacitor and an entirely transvenous approach to the LV.

Rhythm control strategies for "symptomatic" persistent atrial fibrillation: is achieving sinus rhythm enough?

A significant proportion of symptomatic patients who undergo DC cardioversion for persistent atrial fibrillation are unable to correctly perceive their rhythm shortly afterwards. Restoration of sinus rhythm does not necessarily result in improvement in symptoms.

Regional survey of temporary transvenous pacing procedures and complications.

OBJECTIVE: A prospective regional survey was carried out to describe the current practice of temporary transvenous pacing in five hospitals in the Wessex region and identify factors that predispose to complications. METHODS: Data were collected on patient characteristics, pacing indication and setting, operator grade, training, experience and supervision, venous access, procedure time, duration of pacing, complications, and eventual outcome. RESULTS: A total of 144 procedures were performed on 111 patients (age 75 (12) years). Median procedure time was 30 (1-150) min. Trainees performed 129 (91.5%) procedures. The senior physician present was a cardiologist/cardiology trainee for 65/144 (45.1%), and had experience of >20 procedures for 81/144 (57.9%). Venous access was by the subclavian in 52 (46.8%), internal jugular in 37 (33.3%) and femoral in 22 (19.8%), requiring multiple stabs or multiple sites in 41(33.1%). Pacing wires remained in place for a median of 2 (0.04-20) days. Overall procedure times were shorter for cardiologists/cardiology trainees (24[1-90] v 45[10-150] min, p<0.0001), and experienced physicians (30[1-150] v 40[10-120] min, p<0.01). There were 50 complications in 46/144 (31.9%) procedures, affecting 31/111 (27.9%) patients. Immediate complications were less common with experienced physicians (1/81 v 5/59, p<0.05). Infection occurred more often with wires left in situ for >48 hours (17/86 v 2/55, p<0.01) and with longer procedure times (55[8-150] v 30[1-120] min, p<0.005). No factors predicted displacement, which occurred at a median time of 1 (0.04-8) day. Complications delayed permanent pacemaker insertion in 19/63 (22.9%) patients. CONCLUSIONS: Temporary pacemaker insertion is performed by physicians with variable experience and training. The presence of an experienced cardiologist/cardiology trainee and decreasing the time that pacing wires remain in situ may reduce complications.

Feasibility of a left atrial electrical disconnection procedure for atrial fibrillation using transcatheter radiofrequency ablation.

INTRODUCTION: An effective, catheter-based treatment for persistent atrial fibrillation (AF) remains elusive. This study assessed the feasibility of transcatheter left atrial (LA) electrical disconnection and its effect on AF inducibility. METHOD AND RESULTS: Thirteen anesthetized swine underwent noncontact mapping of the right atrium (RA) during coronary sinus (CS) pacing. Sites of earliest RA activation were identified using isopotential maps. An ablation catheter was navigated to these sites and a cluster of radiofrequency (RF) lesions applied until earliest activation shifted to a new site. The procedure was repeated until the atria were electrically disconnected. AF induction was attempted before and after ablation. Earliest RA activation was the CS os during proximal CS pacing and Bachmann's bundle during distal CS pacing. These two sites were successfully ablated in all 13 animals. Earliest activation then shifted to the fossa ovalis. RF energy was applied at a median of 2.5 sites (range 1 to 5) around the fossa, then at sites in the triangle of Koch, septum, cavotricuspid isthmus, and posterior wall. Atrial electrical disconnection was achieved in 10 of 13 animals (5 LA electrical disconnection, 3 RA electrical disconnection, 2 biatrial electrical disconnection with complete heart block). After atrial electrical disconnection, the LA became electrically silent. Before ablation, AF was inducible in every animal. After atrial electrical disconnection, AF was inducible in 3 of 10 animals. CONCLUSION: Atrial electrical disconnection is feasible using noncontact mapping and RF ablation. Successful electrical disconnection of the atria reduces AF inducibility. This approach is worthy of further evaluation as a management strategy for persistent AF, combined with device therapies.

Runaway in a modern "soft top" pacemaker.

Although runaway pacemaker was a relatively common occurrence, modern pacemaker design has made it extremely rare. We report a case occurring with a modern "soft-top" pacemaker that resulted from a loss of hermeticity. Although the different treatment options are discussed, the definitive maneuvre is explantation of the faulty pacemakers

Inappropriate shock therapy in a heart failure defibrillator.

A 63-year-old male with dilated cardiomyopathy underwent implantation of a "heart failure" defibrillator capable of biventricular pacing. He received an inappropriate shock 5 hours after the procedure. Stored electrograms revealed that during each sinus beat the ventricular channel recorded up to three separate events. These resulted from far-field atrial sensing by the coronary venous lead, appropriate right ventricular sensing, then delayed left ventricular sensing (the result of left bundle branch block). As a consequence of far-field left atrial sensing the two subsequent ventricular electrograms fell within the VF zone. Following an atrial premature beat, VF detection criteria were satisfied and shock therapy delivered. Although coronary venous lead repositioning eliminated far-field atrial sensing, double counting of the widely split right and left ventricular electrograms still occurred during sinus rhythm. Shortening the programmed AV delay resulted in constant biventricular pacing with a single electrogram.

Radiofrequency ablation of idiopathic left ventricular tachycardia at the site of earliest activation as determined by noncontact mapping.

INTRODUCTION: The most effective method for guiding radiofrequency (RF) ablation of idiopathic left ventricular tachycardia (ILVT) has yet to be determined. We investigated the use of noncontact mapping in five patients with this condition. METHODS AND RESULTS: The multielectrode array was positioned in the left ventricular apex via the retrograde approach. Isopotential color maps of ILVT were examined to determine the site of earliest endocardial activation. The ablation catheter was steered to the target site using the locator signal. Pace mapping was performed and contact electrograms examined for diastolic potentials. RF energy was applied to the target site. Sustained ventricular tachycardia was induced in 2 patients and nonsustained ventricular tachycardia in 3. The site of earliest activation was at the apical septum in 3, the inferior apex in 1, and the base of the inferior wall in 1. Mean timing was 21 +/- 10 msec before onset of the surface QRS. Diastolic activity was visualized with noncontact mapping at the base of the septum in 1 patient. A Purkinje potential was seen at the ablation site in only 1 patient. No diastolic activity was seen in the remaining 3 patients. Tachycardia was successfully terminated in all 5 patients with a median of four RF applications. No patient suffered a recurrence after 9.6 +/- 4.7 months of follow-up. CONCLUSION: By identifying the precise site of earliest activation during ILVT, noncontact mapping has been shown to be an effective and safe method for guiding RF ablation.