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Notes: VF is induced during ICD implantation to determine efficacy of therapy. Establishing the best clinical method of induction of VF would potentially be beneficial in reducing the number of induction attempts and reducing the frequency of inadvertent induction of VT. Commonly used methods to induce VF include shock in the T wave vulnerable period (T shock) and high frequency stimulation. This study compared the efficacy of T shock with a new induction method using a 9-V DC pulse. The study was a randomized, prospective, case crossover trial in patients receiving ICDs. VF was induced by T shock and DC in a randomized sequence during an ICD implant. VF was induced at least four times in each patient (two T shocks and two DC inductions) and with each induction; attempts were continued with modifications until successful. A paired evaluation between the T shock/DC induction was performed in 37 patients (28 men, age 64 ± 12 years) with a left ventricular ejection fraction of 0.40 ± 0.20. Arrhythmia indications were VT (n = 23), VF (n = 10), and VT/VF (n = 4). Drug therapy included amiodarone (n = 10), metoprolol (n = 6), digoxin (n = 1), and lidocaine (n = 1). The average T shock voltage was 207.0 ± 16.1 V. The S1 cycle drive length was consistently 400 ms, and the mean S2 coupling interval was 317.8 ± 19.6 ms. The length of time DC applied averaged 3.8 ± 1.4 seconds. A total of 148 episodes of VF were included in the analysis. T shock induced VF with a cycle length of 213.5 ± 35.1 ms, and DC induced VF with a cycle length of 214.6 ± 34.5 ms (P = 0.86). Although VF was eventually induced for each randomization, the number of attempts required were dependent on the method of induction. The successful DC first attempt VF induction rate was 96%, with three patients requiring two attempts during one of the DC inductions. T shock had a 68% first attempt success rate with 21 patients requiring multiple T shocks to induce VF. All nine female patients had at least one unsuccessful first attempt T shock, which contributed to an overall unsuccessful first attempt induction rate significantly higher in women then men (36.1% vs 12.5%, P = 0.001). A constant DC voltage induction of VF may be more effective than T shock for induction of VF in a clinical setting because it reduces the number of attempts required to induce VF. By either method, VF appears to be more difficult to induce in women. DC induction has the advantage of simple programming of only duration of stimulation. These findings have implications particularly for ICD implantation with conscious sedation. (PACE 2004; 27:89–94)

Notes: Radiofrequency catheter ablation has been used to treat idiopathic left ventricular tachycardia with high success rates. The majority of reported cases have exhibited the typical findings of right bundle branch block morphology with left axis deviation and originate from within or near the left posterior fascicle. We report a case of idiopathic left ventricular tachycardia originating from within or near the left anterior fascicle, which was successfully ablated using a local Purkinje potential as a guide.

Notes: Tachycardia-Induced Cardiomyopathy. Introduction: Two years after orthotopic cardiac transplantation, a 60-year-old man presented with unexplained congestive heart failure and an incessant atrial tachycardia. Methods and Results: Electrophysiologic evaluation identified the underlying arrhythmia as automatic atrial tachycardia with site of origin at the high anterior lateral right atrial wall. Radiofrequency catheter ablation successfully eliminated the tachycardia, which resulted in prompt improvement of this patient's congestive heart failure. Conclusion: This is the first reported case of tachycardia-induced cardiomyopathy in a cardiac transplant patient. Radiofrequency catheter ablation can he used successfully in this patient population.

Notes: Stimulus Intensity Effect on SA Tissue. Introduction: Prior studies of sinus node function in man stated that the stimulus intensity of overdrive pacing has no effect on (he response of the sinus node to overdrive suppression; however, data documenting these statements were lacking. Previous studies have also suggested that drive train stimulus intensity can alter ventricular refractoriness, but similar studies have not been performed on the human atrium. The purpose of this study was to evaluate the effects of drive train stimulus intensity on atrial effective refractory period and sinus node recovery time. Methods and Results: The effect of drive train stimulus intensity on atrial effective refractory period and sinus node recovery time was studied in 42 patients undergoing clinical electrophysiologic tests. The atrial effective refractory period was shorter at 10 mA (221 ± 20 msec) and 5 mA (232 ± 25 msec) than at a drive train stimulus intensity of 1.5 times late diastolic threshold (248 ± 24 msec, P 〈 0.05 for pairwise comparison). The sinus node recovery time did not demonstrate a similar effect in the baseline state, following beta-adrenergic blockade, or following combined parasympathetic and beta-adrenergic blockade. However, following isolated parasympathetic blockade with atropine, the corrected sinus node recovery time shortened from 88 ± 51 msec at 1.5 times late diastolic threshold to 48 ± 55 msec at 10 mA (P 〈 0.05). Significant variability was present in sinus node recovery time measurements a(baseline and following beta blockade; this variability decreased following parasympathetic blockade. Conclusion: These data suggest that drive train stimulus intensity can affect the electrophysiologic properties of sinus node and atrial tissue. This effect appears to he mediated by local catecholamine and acetylcholine release and provides further evidence that the interaction between pacing stimuli and the cardiac autonomic system may need to be considered in evaluating electrophysiologic effects.