Effect of increased parasympathetic and sympathetic tone on internal atrial defibrillation thresholds in humans.

UNLABELLED: Although changes in autonomic tone affect ventricular defibrillation, little is known about the effect of increased parasympathetic or sympathetic tone on the atrial defbrillation threshold. METHODS: To evaluate the effect of reflexly increased parasympathetic and increase alpha- and beta-adrenergic tone on the atrial defibrillation threshold (ADFT), atrial fibrillation was induced in 14 patients. ADFTs, right atrial refractory period (RARP), and monophasic action potential duration (MAPD) were determined before and after autonomic intervention. ADFTs were determined with a step-up protocol using 3/3-ms biphasic shocks delivered through decapolar catheters in the right atrial appendage and coronary sinus. Two groups were studied. Group I (N = 8) had ADFTs determined at baseline, after receiving phenylephrine (PE), and with PE plus atropine (A). Group 2 (N = 6) had ADFTs determined at baseline and after receiving isoproterenol (ISO). RESULTS: Group I: PE significantly increased sinus cycle length (SR-CL) compared to baseline (742 +/- 123 to 922 +/- 233 ms) without significantly changing RARP, MAPD, or ADFT (2.3 +/- 1.3 J vs 2.3 +/- 0.8 J). With PE + A, SR-CL significantly decreased (529 +/- 100 ms vs 742 +/- 123 ms) and MAPD shortened (231 +/- 41 ms vs 279 +/- 49 ms) without altering RARP or ADFT (1.94 +/- 0.9 J vs 2.25 +/- 1.25 J). Group 2: ISO decreased SR-CL (486 +/- 77 ms vs 755 +/- 184 ms) and MAPD (169 +/- 37 ms vs 226 + 58 ms) but not RARP or ADFT (2.25 +/- 1.21 J vs 2.33 +/- 1.75 J). CONCLUSIONS: Increasing parasympathetic, alpha-, or beta-adrenergic tone does not affect the ADFT despite causing significant electrophysiological changes in the atria.

Safety of transvenous low energy cardioversion of atrial fibrillation in patients with a history of ventricular tachycardia: effects of rate and repolarization time on proarrhythmic risk.

The objective of this study was to assess the safety and efficacy of transvenous low energy cardioversion of atrial fibrillation in patients with ventricular tachycardia and atrial fibrillation and to study the mechanisms of proarrhythmia. Previous studies have demonstrated that cardioversion of atrial fibrillation using low energy, R wave synchronized, direct current shocks applied between catheters in the coronary sinus and right atrium is feasible. However, few data are available regarding the risk of ventricular proarrhythmia posed by internal atrial defibrillation shocks among patients with ventricular arrhythmias or structural heart disease. Atrial defibrillation was performed on 32 patients with monomorphic ventricular tachycardia and left ventricular dysfunction. Shocks were administered during atrial fibrillation (baseline shocks), isoproterenol infusion, ventricular pacing, ventricular tachycardia, and atrial pacing. Baseline shocks were also administered to 29 patients with a history of atrial fibrillation but no ventricular arrhythmias. A total of 932 baseline shocks were administered. No ventricular proarrhythmia was observed after well-synchronized baseline shocks, although rare inductions of ventricular fibrillation occurred after inappropriate T wave sensing. Shocks administered during wide-complex rhythms (ventricular pacing or ventricular tachycardia) frequently induced ventricular arrhythmias, but shocks administered during atrial pacing at identical ventricular rates did not cause proarrhythmia. The risk of ventricular proarrhythmia after well-synchronized atrial defibrillation shocks administered during narrow-complex rhythms is low, even in patients with a history of ventricular tachycardia. The mechanism of proarrhythmia during wide-complex rhythms appears not to be related to ventricular rate per se, but rather to the temporal relationship between shock delivery and the repolarization time of the previous QRS complex.

Ventricular tachycardia: pathophysiology and radiofrequency catheter ablation.

Limitations of pharmacological therapy for VT have led to great interest in alternative nonpharmacological therapies. The appeal of a curative therapy for VT initially led to the search for operative techniques to identify and destroy the underlying substrate, and more recently, has resulted in the development of catheter techniques to achieve the same goal in the electrophysiology laboratory. Investigations into the pathophysiology of VT have resulted in the recognition that this arrhythmia reflects a mechanistically and anatomically heterogeneous set of disorders. Recent growth in our understanding of these distinctions has both led to, and resulted from, simultaneous advances in catheter ablation techniques. The clinical electrophysiology laboratory has served as a testing ground for theories derived from in vitro and animal experiments while also providing its own set of human experimental data regarding the pathophysiology and treatment of VT. As a result of this process, several distinct forms of VT that are amenable to catheter ablation have been characterized. This article will summarize current knowledge of the pathophysiology of various VT subtypes and of techniques for catheter mapping and ablation.

Cost effectiveness of inpatient initiation of antiarrhythmic therapy for supraventricular tachycardias.

This study assessed the cost effectiveness of inpatient antiarrhythmic therapy initiation for supraventricular tachycardias using a metaanalysis of proarrhythmic risk and a decision analysis that compared inpatient to outpatient therapy initiation. A MEDLINE search of trials of antiarrhythmic therapy for supraventricular tachycardias was performed, and episodes of cardiac arrest, sudden or unexplained death, syncope, and sustained or unstable ventricular arrhythmias were recorded. A weighted average event rate, by sample size, was calculated and applied to a clinical decision model of therapy initiation in which patients were either hospitalized for 72 hours or treated as outpatients. Fifty-seven drug trials involving 2,822 patients met study criteria. Based on a 72-hour weighted average event rate of 0.63% (95% confidence interval, 0.2% to 1.2%), inpatient therapy initiation cost $19,231 per year of life saved for a 60-year-old patient with a normal life expectancy. Hospitalization remained cost effective when event rates and life expectancies were varied to model hypothetical clinical scenarios. For example, cost-effectiveness ratios for a 40-year-old without structural heart disease and a 60-year-old with structural heart disease were $37,510 and $33,310, respectively, per year of life saved. Thus, a 72-hour hospitalization for antiarrhythmic therapy initiation is cost effective for most patients with supraventricular tachycardias.

Bundle branch reentry tachycardia and possible sustained interfascicular reentry tachycardia with a shared unusual induction pattern.

A case of bundle branch reentry tachycardia with an unusual induction pattern is presented. Unlike typical cases of this arrhythmia in which tachycardia is usually inducible with routine programmed ventricular stimulation and/or short-long sequences, tachycardia in this case was inducible only with atrial stimulation. It also arose spontaneously during atrial flutter and during isoproterenol administration. After ablation of the right bundle, possible interfascicular reentry tachycardia with a similar induction pattern was observed. This tachycardia was successfully ablated in the region of the posterior fascicle of the left bundle branch.

Utility of leg ultrasonography in suspected symptomatic isolated calf deep venous thrombosis.

PURPOSE: To evaluate the utility of duplex ultrasonography in patients with suspected symptomatic, isolated calf deep venous thrombosis. PATIENTS AND METHODS: Thirty patients with clinically suspected isolated calf deep venous thrombosis were examined with both duplex ultrasonography and contrast venography and the results were compared. RESULTS: Venography detected 7 cases of isolated calf deep venous thrombosis, all of which were also detected by ultrasonography. Ultrasound identified an additional 3 cases of soleal vein thrombosis, but venography did not visualize these veins. Of the 20 negative ultrasound studies, 11 were technically inadequate; however, no false-negative ultrasound studies were noted. CONCLUSIONS: Compression ultrasonography may be reliable for the evaluation of patients with suspected symptomatic infrapopliteal deep venous thrombosis. Its apparent superiority to contrast venography in visualizing muscular calf veins warrants further study; however, the high rate of technical inadequacy in ultrasound studies observed here, if confirmed in larger studies, may limit the usefulness of ultrasound in this setting.

Quantitative plasma D-dimer levels among patients undergoing pulmonary angiography for suspected pulmonary embolism.

OBJECTIVE: To test the hypothesis that a low D-dimer level has a high negative predictive value for acute pulmonary embolism (PE) among patients undergoing diagnostic pulmonary angiography. DESIGN: Blinded comparison of quantitative plasma D-dimer levels, measured using a monoclonal antibody assay, with pulmonary angiographic results from 173 patients with suspected acute PE. SETTING: Tertiary care setting at fur participating institutions. PATIENTS: Plasma samples were analyzed in 173 patients who underwent diagnostic pulmonary arteriography for suspected acute PE. MAIN OUTCOME MEASURES: Sensitivity, specificity, and predictive values of quantitative plasma D-dimer levels for the diagnosis of PE, using pulmonary angiographic data as the criterion standard test. RESULTS: Of 35 patients with D-dimer values less than 500 ng/mL, only three had abnormal pulmonary angiograms. The negative predictive value of a plasma D-dimer level less than 500 ng/mL for acute PE was 91.4% (95% confidence interval [CI], 76.9% to 98.2%). D-dimer levels were greater than 500 ng/mL in 42 of 45 patients with PE and in 96 of 128 patients without PE (P = .016). Sensitivity, specificity, and positive predictive value of a plasma D-dimer level greater than 500 ng/mL for acute PE were 93.3% (95% CI, 81.7% to 98.6%), 25.0% (95% CI, 17.5% to 32.5%), and 30.4% (95% CI, 22.8% to 38.1%), respectively. CONCLUSIONS: The results of our study indicate that quantitative plasma D-dimer levels can be useful in screening patients with suspected PE who require pulmonary angiography. Plasma D-dimer values less than 500 ng/mL may obviate the need for pulmonary angiography, particularly among medical patients for whom the clinical suspicion of PE is low. The plasma D-dimer value, assayed using a commercially available enzyme-linked immunosorbent assay kit, is a sensitive but nonspecific test for the presence of acute PE.

Ovarian vein thrombosis.

We report five cases of OVT and review the literature on this disease. Among our patients OVT was not suspected clinically and was diagnosed by CT scanning or MRI. Ultrasound imaging, utilized in three cases, failed to detect OVT. Although this disease usually occurs after delivery, in two cases it was diagnosed before delivery. Of the two postpartum cases, one had a typical presentation and the other was asymptomatic. The final case was diagnosed incidentally 5 months after removal of an ovarian carcinoma. Our experience suggests that this disease may be underdiagnosed. More widespread use of CT scanning and MRI may lead to more frequent diagnosis of OVT. The role that clinically silent OVT may play in peripartum pulmonary embolism should be clarified.