Comparison of Two Antitachycardia Pacing Modes in Supraventricular Tachycardia

The comparative efficacy of two different antitachycardia pacing techniques was evaluated in 22 consecutive patients who received the pacemaker Intertach® with an atrial electrode for drug refractory, recurrent Supraventricular tachycardia (SVT). The Intertach® has two consecutive programmable primary and secondary termination modes. The termination programs investigated were adaptive autodecremental burst pacing and adaptive decremental scanning. Atrioventricular nodal reentrant tachycardia was present in 15 patients and atrioventricular reentrant tachycardia due to Wolff-Parkinson-White syndrome in seven patients. The prospective comparison was arranged in a randomized, cross-over study over a period of 12 months. To assess long-term efficacy, diagnostic data of the pacemakers were obtained in intervals of 3 months. In addition, noninvasive programmed stimulation was performed to compare the incidence of pacing-induced atrial fibrillation with both termination programs. During a follow-up of 12 months the overall success rate of autodecremental burst pacing and decremental scanning was 80% and 95%, respectively. Decremental scanning was more effective in 12 patients and less successful in two patients than autodecremental burst pacing. During noninvasive electrophysiological studies, pacing induced atrial fibrillation could be documented in three often patients (30%) using autodecremental burst pacing, compared to one often patients (10%) using decremental scanning. These data suggest that decremental scanning proved to be more successful in the long-term management of patients with recurrent S VT than autodecremental burst pacing. Furthermore, the occurrence of pacing-induced atrial fibrillation could be documented more frequently with autodecremental burst pacing compared to decremental scanning.     

Effects of Antiarrhythmic Drugs on Epicardial Defibrillation Energy Requirements and the Rate of Defibrillator Discharges

Antiarrhythmic drugs are commonly used with the implantable cardioverter/defibrillator to treat recurrent ventricular tachyarrhythmias. Since various antiarrhythmic drugs have been reported to alter defibrillation threshold, an important question is whether the device will provide adequate energy for defibrillation during long-term follow-up and to what extent antiarrhythmic drug treatment will affect defibrillation energy requirements. To answer these questions, the defibrillation thresholds were determined in 20 patients using an epicardial patch-patch lead configuration at the time of implantation and at the time of pulse generator replacement. During a mean follow-up period of 24 ± 6 months, the defibrillation threshold increased significantly from 14.2 ± 3.7 joules to 18.3 ± 5.5 joules in the entire group (P < 0.05). This increase in defibrillation threshold was due to a marked elevation of defibrillation energy requirements in the subgroup of patients taking amiodarone compared with patients receiving mexiletine. Based on these results it is mandatory to retest defibrillation threshold at any time of pulse generator replacement to guarantee continued effectiveness. In particular, if amiodarone treatment is initiated after implantation of a defibrillator, it is recommended to reevaluate defibrillation threshold to ensure an adequate margin of safety.     

Electrical Proarrhythmia: Induction of Inappropriate Atrial Therapies due to Far-Field R Wave Oversensing in a New Dual Chamber Defibrillator

R Wave Far-Field Sensing in Dual Chamber Defibrillators . This case report describes delivery of atrial therapies during a sinus tachycardia in a new dual chamber implantable cardioverter defibrillator inappropriately caused by far-field oversensing of ventricular beats in the atrial channel. Upon classification of the PR interval pattern, the rate criterion for an atrial tachycardia was fulfilled, and the device initiated high-frequency burst pacing as the first stage of programmed tiered atrial therapies. Atrial fibrillation subsequently was induced by high-frequency burst pacing, and eventually a programmed 10-J shock was delivered for successful termination of atrial fibrillation. The phenomenon of far-field oversensing of ventricular beats could be repeatedly observed during exercise testing and abolished by decreasing the atrial sensitivity.     

Alteration of Activities of Hepatic Antioxidant Defence Enzymes in Developing Chick Embryos After Glucocorticoid Administration - A Factor to Produce Some Adverse Effects?

Liver tissue is one of the principal targets of glucocorticoids, therefore changes in the balance between hepatic oxidative and reductive capacity may greatly influence adverse effects of glucocorticoid therapy. In this study, effects of glucocorticoid on the activities of hepatic antioxidant defence enzymes were examined by using developing chick embryos. After the administration of 0.25 μmol hydrocortisone sodium succinate, a typical glucocorticoid, to 15-day-old chick embryos, glutathione peroxidase, glutathione reductase, catalase and superoxide dismutase in the liver generally began to decrease at around 4 h, reaching 60–70% of control levels between 24 and 48 h. These changes were observed much earlier than the elevation of the hepatic thiobarbituric acid reacting substance (TBARS) level which began to increase from 20 h, reaching about six times the control level at 48 h after hydrocortisone administration. Conversely, the elevated TBARS level decreased back to the normal level with the recoveries of these enzyme activities. Furthermore, it was found that the aniline hydroxylase activity, measured as a marker of oxidative activity, began to increase after around 12 h. These results suggested that TBARS levels were possibly produced by the suppression of antioxidant defence abilities and the significant induction of oxidative activity in the liver by glucocorticoid. As the elevated TBARS in the liver can be distributed to tissues, TBARS will be involved in the occurrence of some of the glucocorticoid-induced adverse effects such as cataract formation.     

Histometric and Histochemical Analysis of the Effect of Trichloroacetic Acid Concentration in the Chemical Reconstruction of Skin Scars Method

BACKGROUND: Atrophic scars can be induced by various causes, including severely inflamed acne, chicken pox, and trauma. Many treatment modalities are used for reconstructing and improving the appearance of scars with various treatment results. OBJECTIVE: A recent report shows the clinical efficacy of the chemical reconstruction of skin scars (CROSS) method, which consists of the focal application of trichloroacetic acid (TCA) in a higher concentration. Histometric analysis of the CROSS method, however, has not yet been established. METHODS: In this study, five hairless mice were used to evaluate the effect of the CROSS method and to analyze the difference between the CROSS method and simple TCA application. RESULTS: Similar histologic changes were observed in the two methods, including epidermal and dermal rejuvenation with new collagen deposition. These changes, however, were more prominent in the CROSS method-treated areas, particularly when 100% TCA was used. CONCLUSION: The results of this study suggest that treatment of atrophic scars using the CROSS method is more effective than simple application of TCA in activating fibroblasts in the dermis and increasing the amount of collagen.     

Efficacy and Safety of Combination Therapy with Amiodarone and Type I Agents for Treatment of Inducible Ventricular Tachycardia

In a prospective study the efficacy of amiodarone in combinalion with the three Class I drugs mexiletine, fiecainide, orencainide was evaluated consecutively in 12 patients with recurrent venlriculav tachycardias (VT) by programmed stimulation. None of the tested drug combinations suppressed induction of sustained VT. The combination of amiodarone with Class IC drugs fJecainide and encainide prolonged the cycle length of VT significantly, whereas the combination with mexiletine did not hove the same degree of slowing on the VT cycle length. Several proarrhythmic effects occurred during the combination therapy with encainide: (1) frequent, spontaneous recurrences of hemodynamically well tolerated VT in four patients; (2) enhanced inducihilily of VT in three patients; (3) impaired termination of VT in three patients. Though a marked increase in QRS and QTc intervals was observed by combined treatment with encainide, no significant correlation could be established between aggravation of arrhythmia and plasma levels of encainide, degree of QRS widening, JT or QTc prolongation. The only predictor for the occurrence of proarrhythmic events was found in left ventricular ejection fraction. These findings suggest that in patients refractory to amiodarone alone or a combination with mexiletine, the combined treatment of amiodarone with other Class IC drugs prolongs the VT cycle length but does not suppress induction of VT during programmed stimulation. Combination therapy of amiodarone with encainide was associated with a high incidence of proarrhythmic effects.