Relation Between Cellular Repolarization Characteristics and Critical Mass for Human Ventricular Fibrillation

INTRODUCTION: The critical mass for human ventricular fibrillation (VF) and its electrical determinants are unclear. The goal of this study was to evaluate the relationship between repolarization characteristics and critical mass for VF in diseased human cardiac tissues. METHODS AND RESULTS: Eight native hearts from transplant recipients were studied. The right ventricle was immediately excised, then perfused (n = 6) or superfused (n = 2) with Tyrode's solution at 36 degrees C. The action potential duration (APD) restitution curve was determined by an S1-S2 method. Programmed stimulation and burst pacing were used to induce VF. In 3 of 8 tissues, 10 microM cromakalim, an ATP-sensitive potassium channel opener, was added to the perfusate and the stimulation protocol repeated. Results show that, at baseline, VF did not occur either spontaneously or during rewarming, and it could not be induced by aggressive electrical stimulation in any tissue. The mean APD at 90% depolarization (APD90) at a cycle length of 600 msec was 227+/-49 msec, and the mean slope of the APD restitution curve was 0.22+/-0.08. Among the six tissues perfused, five were not treated with any antiarrhythmic agent. The weight of these five heart samples averaged 111+/-23 g (range 85 to 138). However, after cromakalim infusion, sustained VF (> 30 min in duration) was consistently induced. As compared with baseline in the same tissues, cromakalim shortened the APD90 from 243+/-32 msec to 55+/-18 msec (P < 0.001) and increased the maximum slope of the APD restitution curve from 0.24+/-0.11 to 1.43+/-0.10 (P < 0.01). CONCLUSION: At baseline, the critical mass for VF in diseased human hearts in vitro is > 111 g. However, the critical mass for VF can vary, as it can be reduced by shortening APD and increasing the slope of the APD restitution curve.     

Prospective Evaluation of Defibrillation Threshold and Postshock Rhythm in Young ICD Recipients

Background: Adaptation of implantable cardioverter defibrillator (ICD) systems to the needs of pediatric and congenital heart patients is problematic due to constraints of vascular and thoracic anatomy. An improved understanding of the defibrillation energy and postshock pacing requirements in such patients may help direct more tailored ICD therapy. We describe the first prospective evaluation of defibrillation threshold (DFT) and postshock rhythm in this population. Methods: We prospectively studied patients ≤60 kg at time of ICD intervention. DFTs were obtained using a binary search protocol with three VF inductions. Postshock pacing was programmed using a stepwise protocol, lowering the rate prior to each VF induction. Results: Twenty patients were enrolled: 11 had channelopathy, five congenital heart disease, and four cardiomyopathy. The median age was 16 years, median weight 48 kg. Twelve patients had a transvenous high‐voltage coil; eight had pericardial +/? subcutaneous coil(s). Median DFT was 7 J (range 3–31 J); 19/20 patients had DFT ≤15 J and all patients <25 kg had DFT ≤9 J (n = 6). There was no difference in DFT between patients with transvenous versus pericardial +/? subcutaneous coils (median 7 J vs 6 J, P = 0.59). No patient with normal atrioventricular conduction prior to defibrillation required postshock pacing (n = 16). There were no adverse events. Conclusions: These data suggest that many pediatric ICD patients have low DFTs and adequate postshock escape rhythm. This may help determine appropriate parameters for future design of pediatric‐specific ICDs. (PACE 2012;35:1487–1493)     

Outcomes in Patients Requiring Cardioversion Following Catheter Ablation of Atrial Fibrillation

Outcomes of Cardioversion Post AF Ablation.   Introduction: Early recurrence of atrial tachyarrhythmias is commonly noted after catheter ablation of atrial fibrillation (AF). The long-term outcomes of patients who require cardioversion for persistent AF after AF ablation is not known. This study reports the outcomes of patients who underwent cardioversion for persistent AF or atrial flutter following an AF ablation procedure.
Methods: The patient population comprised 55 patients (mean age 58 ± 10 years, 35% paroxysmal) who underwent catheter ablation of AF and subsequently required electrical cardioversion for persistent AF (45 patients) or atrial flutter (10 patients). Cardioversion was defined as early (within 90 days of the ablation procedure) or late (between 90 and 180 days following ablation).
Results: The mean follow-up duration was 15 ± 8 months. Forty-six of the 55 patients (84%) patients experienced recurrence during follow-up. The average time to recurrence after cardioversion was 37 days. Of the 55 patients, 8 (15%) patients had a complete success, 11 (20%) patients had a partial success and 36 patients (65%) had a failed outcome. Seven of the 43 patients (16%) who underwent early cardioversion had a complete success as opposed to one of 12 patients (8%) who underwent late cardioversion (P = 0.49).
Conclusions: This study shows that >80% of patients who undergo cardioversion for persistent AF or atrial flutter after AF ablation have recurrence. The timing of cardioversion did not affect the outcome. These findings allow clinicians to provide realistic expectations to patients regarding the long-term outcome and/or requirement for a second ablation procedure. (J Cardiovasc Electrophysiol, Vol. 21, pp. 27–32, January 2010)     

An Interesting Case of Infant Sudden Death: Severe Hypertrophic Cardiomyopathy in Pompe's Disease

Glycogen storage disease type II (Pompe's disease) is a rare inherited metabolic disorder, which often leads to infantile death from severe cardiomyopathy. This case of sudden death illustrates the features of the cardiac findings in the disorder, resulting from massive lysosomal accumulation of glycogen in the heart and other tissues. Pompe's disease should be considered in cases of unexplained infantile cardiomyopathy.     

Diaphragm Pacing with a Quadripolar Phrenic Nerve Electrode: An International Study

We sought to determine the international experience with the quadripolar diaphragm pacer system and to test two hypotheses: the incidence of pacer complications would be (1) increased among pediatric as compared to adult patients; and (2) highest among active pediatric patients with idiopathic congenital central hypoventilation syndrome (CCHS). Data were collected via a questionnaire coupled with the Atrotech Registry data for a total of 64 patients (35 children and 29 adults) from 14 countries. Thoracic implantation of electrodes and bilateral pacer use each occurred in 94% of all subjects. Tetraplegic (vs pediatric CCHS) patients were more typically paced 24 hours/day (P = 0.001). Pacing duration averaged 2.0 ± 1.0 years among children and 2.2 ± 1.1 years among adults. Infections occurred among 2.9% of surgical procedures, all in pediatric CCHS patients (vs pediatric tetraplegic patients, P = 0.01). The incidence of mechanical trauma was 3.8%, without significant differences among patient groups. The incidence of presumed electrode and receiver failure were 3.1% and 5.9%, respectively, with internal component failure greater among pediatric CCHS than pediatric tetraplegic patients (P < 0.01). Intermittent or absent function of 0–4 electrode combinations occurred among 19% of all patients, with increased frequency among pediatric CCHS than pediatric tetraplegic patients (P < 0.03). Complication- free successful pacing occurred in 60% of pediatric and 52% of adult patients. In all, 94 % of the pediatric and 86% of the adult patients paced successfully after the necessary intervention. Although pacer complications were not increased among pediatric as compared to adult patients, the incidence of complications was highest among the active pediatric patients with CCHS. Longitudinal study of these patients will provide invaluable information for modification and improvement of the quadripolar system.     

Menetrier''s Disease and Adenoearcinoma of the Pancreas and

A 74-year old woman with abdominal pain and edema was diagnosed to have Menetrier's disease on surgical full thickness gastric wall biopsy. Two months later, she complained of increasing severe abdominal pain radiating to the back, unusual in Menetrier's. Work-up showed classic Menetrier's disease with large gastric folds, achlorhydria, gastrointestinal protein loss and hypoalbuminemia. A celiac arteriogram, however, suggested a pancreatic neoplasm and adenocarcinoma of the body of the pancreas was confirmed at laparotomy. This is the first report of the concurrence of these two diseases. The difficulty of differentiating Menetrier's from occult gastrointestinal cancer is discussed.     

Questions in Gastroenterology

The Last Page appears as a regular feature in each issue of THE AMERICAN JOURNAL OF GASTROENTEROLOGY
The questions that follow have been prepared exclusively from material in the current issue of the Journal and the page on which the article can be found is indicated with each question.
One way for regular readers of the Journal to utilize this feature is to scan The Last Page and attempt to answer the questions before reading the Journal. Then, when the articles have been read, return to The Last Page. again try to answer the questions and finally refer to the page locutions that are provided in order to confirm your answers.
For each question, one or more responses may be correct, or none may be correct.     

Computerized Pacemaker Patient Analysis

BYRD, C.B., ET AL.: Computerized Pacemaker Patient Analysis. We have developed computer hardware and software that imports analog waveforms and other measured data from a patient into the PaceBase database system supported by any IBM PC/AT compatible. The programmable AID converter has the capacity to acquire the pacemaker artifact from the surface ECG leads. Analysis of the pacemaker artifact permits confirmation of pulse width as well as programmability and facilitates discovery of pacemaker hardware failures otherwise undetectable. Continuous recording of real-time surface ECG can be made as other measurements or storing functions are being performed. In this way, sporadic or infrequent intrinsic events are automatically recorded and can be selected to be played back and reviewed or stored on the permanent record. Pacemaker spike detection enhances identification of paced and intrinsic complexes by emphasizing the paced artifact. Even bipolar atrial spikes with pulse widths as short as 0.05 ms are easily identified; myopotential muscle noise is rejected. Enhancement of pacemaker spikes takes the guesswork out of interpretation of ECGs, especially for bipolar systems and when testing or troubleshooting for myopotential tracking or inhibition.     

Overview: The treatment of drug dependence

Addictive disorders resemble other chronic medical disorders in that they are characterized by relapses and remissions. This central feature of the addictions is addressed by many of the contributors in their individual chapters. There are also several specific points raised in the chapters which merit further discussion. For instance, any assumption that long–term anti–anxiety treatment with benzodiazepines implies a form of dependence that requires treatment could be set against an alternative view that there may be appropriate medical/psychiatric indications for such prolonged treatment. There are also interesting questions which deserve discussion surrounding the debate over treatment setting for opiate dependence treatments. The paper by Johns presents a case for inpatient treatment whereas in the United States long–term methadone maintenance is seen as one of the most effective treatments. Given the complexity of the bio–psycho–social mechanisms involved in Addiction a combination of therapeutic approaches tailored to individual needs should probably continue to be the guiding principle.