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.     

DDIR Versus VVIR Pacing in Patients with Paroxysmal Atrial Tachyarrhythmias

Patients with sinus node dysfunction (SND) in particular those with tachycardia-bradycardia syndrome and patients undergoing atrioventricular nodal ablation procedures for refractory paroxysmal atrial tachyarrhythmias (PAT), are candidates for single chamber (VVIR mode) or dual chamber rate responsive (DDIR mode) systems. To evaluate the benefits and disadvantages of each pacing mode we retrospectively analyzed 33 patients with a history of frequent PAT who received a VVIR (22 patients); or a DDDR pacemaker (11 patients) programmed to the DDIR mode. The mean follow-up time was 25 and 18 months, respectively. Preimplant left atrial diameter was significantly smaller in the DDIR group. Chronic atrial fibrillation developed in 54% of the VVIR patients and 27% of the DDIR group, but this difference was not significant. Complications of patients with VVIR pacemakers included new mitral and tricuspid insufficiency, stroke, pacemaker inlolerance and aggravated congestive heart failure. Patients with DDIR pacemakers had a lower incidence of symptoms and complications. However, this group received more antiarrhythmic medication, required a closer follow-up, and their pacemakers needed frequent reprogramming. Our findings suggest that VVIR is a poor choice for patients with SND, congestive heart failure, and PAT, and that DDIR may be an acceptable alternative.     

Nonsurgical Electrical Ablation of Tachycardias: Importance of Prior in Vitro Testing of Catheter Leads

Nonsurgical electrical ablation of tachycardia pathways or foci has been attempted or carried out using a variety of temporary pacing catheter leads. To determine the ability of such leads to withstand the high energies used in such procedures, 34 leads were suspended in saline, and subjected to repeated electrical shocks. Small (4 French) temporary pacing leads made by a variety of manufacturers tolerated multiple shocks up to 100 joules; above this level, failures became increasingly common, although usually the failure mode was benign with respect to patient care implications. Testing of 6, 7, and 8 French leads revealed considerable inter-and intra-manufacturer differences in the ability to withstand higher energy shocks, reflecting differences in materials and fabrication techniques. It is concluded that careful in vitro lead testing is required prior to using identical models in humans for arrhythmia ablation procedures.     

In Vivo Ventricular Lesion Growth in Radiofrequency Catheter Ablation

While radiofrequency catheter ablation has proved highly effective in the treafment of various supravenfricular tQchyarrhythmias, resulls in the trentment of ventricular tachycardia invite improvement. Knowledge of lesion growth in vivo might improve understanding of this discrepancy. So far only information from in vitro and in vivo studies using a small 2 mm tip eiectrode is available. Growlh of ventricular radiofrequency lesions created with a 4 mm ahlalion electrode was studied in 11 closed-chest dogs. Endocardia] ablations were performed at 31 left and 35 right ventricuiar sites at a power setting of 25 Watts and 5, 10, 20, 30 or 60 seconds pulse duration. Macroscopic and histopathologic lesion examination were performed after one week survival. Mean lesion volume increased from 52 mm³ after 5 seconds pulse duration to a maximum 388 mm³ and approximately 7 mm depth after 30 seconds. Lesions were prolate spheroid in form, with a sparing of subendocardial myocardium and maximum lesion diameter at some millimeters depth. Results indicate that catheter positioning at no more tlian 7 mm from the target is required for successful ablation. Due to lesion geometry, subendocardial targets demand even more exact catheter positioning, while subepicardial substrates may not be ammenable to ablation if ventricular wall thickness exceeds 7 mm at the ablation site. Repeated pulses at adjacent sites may be required for ablation of extended arrhytbmogenic areas. Volume at 5 seconds was only approximately 15% of mature lesions. Therefore, the use of a short'test pulse after careful mapping may be useful to pinpoint the most appropriate site for ablation in discrete pathways.     

Lead Extraction in Young Patients With and Without Congenital Heart Disease Using the Subclavian Approach

Pacemaker lead removal using interlocking stylets and dilator sheaths has greatly reduced the need for major surgical intervention when lead extraction is required. Previous reports have shown the utility of this method in older patients, most of whom have anatomically normal hearts. The purpose of this study is to report the results of this technique in young patients with and with-out congenital heart disease. There were 13 patients (M:F = 7:6) aged 9–26 years (median 13). Congenital heart disease was present in 8 of 13 patients. A total of 17 leads required removal; they had been implanted for 54 ± 24 months (range 19–94). Leads were removed from the left subclavian vein (13) or right subclavian vein (4) only. Seventeen of 18 leads were completely removed and one partially retained in the left subclavian vein. New leads were implanted from the same vein in 11 of 13 patients. Interlocking stylets and metal or flexible dilator sheaths were used in all cases except two. There was one surgical complication: a late wound dehiscence, which was easily managed. No patient required a transfusion, and there was no structural damage noted in any patient on the postoperative echocardiogram. We conclude that lead removal using interlocking stylets and dilator sheaths from the subclavian approach is an effective technique that can be used in young patients, including those with congenital heart disease.     

Vitamin D metabolites in post-menopausal women and their relationship to the myopathic electromyogram

Proximal muscular weakness is a feature of many metabolic bone diseases but is not well recognized in spinal osteoporosis. Thirty-six post-menopausal women presenting with back pain, with or without osteoporosis, were therefore studied in order to define the relationship between abnormal electromyographic findings and disturbed vitamin D metabolism, as both low plasma 1,25 dihydroxy vitamin D concentrations and malabsorption of calcium have been reported in osteoporosis. Patients with abnormal electromyograms had lower concentrations of plasma 1,25 dihydroxy vitamin D (mean 78.3 pmol/l, SD 20.5, n = 15) than normal subjects of similar age (mean 110.4 pmol/l, SD 39.4, n = 21; P less than 0.01), but electromyographic abnormality was not associated with changes in radiocalcium absorption, plasma 25 hydroxy vitamin D, plasma calcium or phosphate or urinary calcium or hydroxy-proline excretion or impaired renal function. There was no relationship between abnormal electromyography and osteoporosis assessed by spinal radiographs and iliac crest biopsy. These findings are consistent with our previous suggestion that muscle weakness in many unrelated bone disorders is related to low plasma 1,25 dihydroxy vitamin D concentrations, but suggest that there is no relationship between proximal myopathy and spinal osteoporosis in post-menopausal women.     

Laparoscopic Hernia Repair of an Incisional Hernia Secondary to Placement of an Implantable Cardioverter Defibrillator

We present the lapamscopic repair of a large incisional hernia secondary to placement of a subcostal ICD pulse generator. Laparoscopic repair of large incisional hernias provides a unique and technically feasible form of repair in the 2%–13% of patients who will develop an incisional hernia following an abdominal surgery. This form of hernia repair is associated with minimal morbidity and prompt resumption of patient activities and work.     

Left Heart Pacing and Cardioembolic Stroke

Three patients with inadvertently positioned left heart pacemaker leads were admitted for neurological symptoms consistent with embolic stroke. In one of them, the pacemaker lead crossed the interatrial septum, the mitral valve, and entered the left ventricle. In another it was erroneously placed through the subclavian artery, across the aortic valve, and into the left ventricular chamber In the third patient, the right ventricular lead of a DDD pacemaker was placed in the coronary sinus and the right atrial lead crossed the interatrial septum, and intermittently entered the left ventricular cavity. Once anticoagulation was initiated, symptoms resolved; they recurred when the level of anticoagulation dropped leading to a major stroke in one of the patients. Two of the patients were on aspirin at the onset of symptoms. We believe that every approach must be considered to remove the malpositioned lead. Otherwise, full dose anticoagulation must be initiated since antiplatelet therapy alone does not confer adequate protection against stroke.     

Electrophysiologic Basis for T Wave Alternans as an Index of Vulnerability to Ventricular Fibrillation

Electrophysiologic Basis for T Wave Alternans. Substantial evidence indicates that T wave alternans is an intrinsic property of ischemic myocardium. The electrophysiologic basis appears to be spatial and temporal heterogeneity of repolarization resulting from changes in action potential morphology rather than in activation sequence. Ischemia-induced changes in postrepolarization refractoriness and depressed electrical restitution of action potential duration have also been implicated. The main underlying ionic basis for T-wave alternans during coronary occlusion appears to be derangements in intracellular cycling of calcium. Accumulation of potassium in the extracellular space adjoining ischemic cells and disruption in electro-genie sodium-calcium exchange may also be involved. In humans, T wave alternans has been observed in Prinzmetal's and classical angina, angioplasty, and bypass graft occlusion. Under these conditions associated with acute myocardial ischemia, alternans is restricted to the ischemic zone, and alternation in action potential morphology is an underlying factor. Recently, repolarization alternans has been shown to be a statistically significant predictor of the results of electro physiologic testing and arrhythmia-free survival in individuals with and without organic heart disease. Collectively, these observations provide a rationale for quantitation of T-wave alternans magnitude for assessment of vulnerability to life-threatening ventricular arrhythmias both in response to and independent of the effects of myocardial ischemia.