Electrophysiological effects of ibutilide in patients with accessory pathways.

BACKGROUND: Atrial fibrillation (AF) may cause life-threatening ventricular arrhythmias in patients with Wolff-Parkinson-White syndrome. We prospectively evaluated the effects of ibutilide on the conduction system in patients with accessory pathways (AP). METHODS AND RESULTS: In part I, we gave ibutilide to 22 patients (18 men, 31+/-13 years of age) who had AF during electrophysiology study, including 6 pediatric patients

Chemical cardioversion of atrial fibrillation or flutter with ibutilide in patients receiving amiodarone therapy.

BACKGROUND: Ibutilide is a class III drug that is used for the cardioversion of atrial arrhythmias, but it can cause torsade de pointes. Amiodarone also prolongs the QT interval but rarely causes torsade de pointes. There are no studies in which the concomitant use of the 2 agents was examined. The purpose of the present study was to assess the efficacy and safety of cardioversion with combination therapy in patients with atrial fibrillation or flutter. METHODS AND RESULTS: The study included 70 patients who were treated with long-term oral amiodarone and were referred for elective cardioversion of atrial fibrillation (57 of 70, 81%) or flutter (13 of 70, 19%). Patients were taking amiodarone (153+/-259 days, mean+/-SD) and were administered 2 mg intravenous ibutilide. Left ventricular ejection fraction was measured with echocardiography. The QT intervals were measured on 12-lead ECG. Fifty-five patients (79%) had structural heart disease. Patients were in arrhythmia for 196+/-508 days before cardioversion, with a left ventricular ejection fraction of 50+/-11%. In patients with atrial fibrillation, 22 (39%) of 57 and 7 (54%) of 13 patients with flutter converted within 30 minutes of infusion. Thirty-nine patients who did not convert after ibutilide were treated with electrical cardioversion, and 35 (90%) of 39 patients were successfully converted. The QT intervals were further prolonged after ibutilide for the group from 371+/-61 to 479+/-92 ms (P:<0.001). There was 1 episode of nonsustained torsade de pointes (1 of 70, 1.4%) after ibutilide. CONCLUSIONS: The use of ibutilide converted 54% of patients with atrial flutter and 39% of patients with atrial fibrillation who were treated with long-term amiodarone. Despite QT-interval prolongation after ibutilide, only 1 episode of torsade de pointes occurred. Our observations suggest that combination therapy may be a useful cardioversion method for chronic atrial fibrillation or flutter.

Quantitative effects of functional bundle branch block in patients with atrioventricular reentrant tachycardia.

Changes in the retrograde conduction time (ventriculoatrial [VA]) interval during functional bundle branch block (BBB) have been used to separate septal from free wall accessory pathways (APs), but different values of the VA interval prolongation (deltaVA) have been described in different reports. A total of 95 patients with single nondecremental APs who developed BBB during atrioventricular reentrant tachycardia were studied. Free wall APs were found in 60 patients, and 35 had septal APs. For patients with free wall APs, complete and incomplete BBB ipsilateral to the atrial insertion site of APs were observed in 39 of 60 patients (65%) and 31 of 60 patients (52%), respectively. For patients who had both complete (QRS > or = 120 ms) and incomplete (QRS <120 ms) BBB during atrioventricular reentrant tachycardia, deltaVA for patients with complete BBB was significantly greater than in those with incomplete BBB, 59 +/- 19 ms versus 30 +/- 11 ms, p <0.001. For patients with septal APs and complete and incomplete BBB during tachycardia, the mean deltaVA for those with complete BBB was 31 +/- 20 ms and was significantly longer than in patients with incomplete BBB (14 +/- 6 ms), p <0.001. There was no significant difference in deltaVA between those with free wall APs and incomplete BBB compared with those with septal APs and complete BBB. The criteria of QRS > or = 120 ms associated with deltaVA > or =40 ms served to best separate free wall from septal APs with a sensitivity of 88% and a specificity of 89%. Left anterior fascicular block was associated with marked lengthening of deltaVA for those with left free wall APs, whereas a left posterior fascicular block pattern resulted in a marked increase in the deltaVA for patients with posteroseptal APs. In the absence of fascicular block patterns, a deltaVA > or =40 ms provides strong evidence of a free wall AP, with a sensitivity of 95% and a specificity of 100%. The left posterior fascicle appears to provide predominant innervation of the posterior septum.

Electrophysiologic effects of adenosine in patients with supraventricular tachycardia.

BACKGROUND: We correlated the electrophysiologic (EP) effects of adenosine with tachycardia mechanisms in patients with supraventricular tachycardias (SVT). METHODS AND RESULTS: Adenosine was administered to 229 patients with SVTs during EP study: atrioventricular (AV) reentry (AVRT; n=59), typical atrioventricular node reentry (AVNRT; n=82), atypical AVNRT (n=13), permanent junctional reciprocating tachycardia (PJRT; n=12), atrial tachycardia (AT; n=53), and inappropriate sinus tachycardia (IST; n=10). There was no difference in incidence of tachycardia termination at the AV node in AVRT (85%) versus AVNRT (86%) after adenosine, but patients with AVRT showed increases in the ventriculoatrial (VA) intervals (13%) compared with typical AVNRT (0%), P<0.005. Changes in atrial, AV, or VA intervals after adenosine did not predict the mode of termination of long R-P tachycardias. For patients with AT, there was no correlation with location of the atrial focus and adenosine response. AV block after adenosine was only observed in AT patients (27%) or IST (30%). Patients with IST showed atrial cycle length increases after adenosine (P<0.05) with little change in activation sequence. The incidence of atrial fibrillation after adenosine was higher for those with AVRT (15%) compared with typical AVNRT (0%) P<0.001, or atypical AVNRT (0%) but similar to those with AT (11%) and PJRT (17%). CONCLUSIONS: The EP response to adenosine proved of limited value to identify the location of AT or SVT mechanisms. Features favoring AT were the presence of AV block or marked shortening of atrial cycle length before tachycardia suppression. Atrial fibrillation was more common after adenosine in patients with AVRT, PJRT, or AT. Patients with IST showed increases in cycle length with little change in atrial activation sequence after adenosine.

Sustained volume expansion and [Na,K]ATPase inhibition in chronic renal failure.

Hypotheses regarding the pathogenesis of volume-dependent hypertension have invoked an endogenous sodium pump inhibitor or digitalis-like factor (DLF) to link altered sodium homeostasis to the rise in blood pressure. Our goal was to develop a clinical protocol that achieved predictable, sustained volume expansion, with the premise that renal failure patients on peritoneal dialysis would increase intravascular volume, gain weight, and raise blood pressure (BP) in relation to measured increases in DLF. In a 5-day protocol, dialysis was kept constant but dietary NaCl and fluids were modified in 7 patients. DLF was measured as inhibition of [Na,K]ATPase. Likewise, the first 2 L of daily peritoneal dialysate (PD) was processed on HPLC and the eluate analyzed for DLF. The group achieved significant weight gain (WT) by day 3 (delta WT = 4.1 +/- 1.2 kg, P < .05). Likewise, mean arterial pressure (MAP) and plasma DLF activity increased significantly. All variables were highly correlated (DLF v WT: R = 0.88, P = .004; MAP v DLF: R = 0.82, P = .01; MAP v WT: R = 0.90, P = .003). Although a number of HPLC fractions contained agents that interacted with the assay, only one PD HPLC fraction (at 19.5 min) contained DLF activity that correlated with changes in MAP (R = 0.60, P = .002), and body weight (R = 0.67, P = .0003). We conclude that candidate DLF responds to sustained volume expansion and the relationship suggests that it could influence blood pressure. Moreover, the application of stringent criteria to the confusing array of factors in plasma that may affect assays for DLF appears to reduce the field dramatically, to a single candidate in this setting.

Volume expansion in renal failure patients: a paradigm for a clinically relevant [Na,K]ATPase inhibitor.

A volume-sensitive inhibitor of [Na,K]ATPase, termed the digitalis-like factor (DLF), is postulated to participate in hypertension. To test this hypothesis, end-stage renal failure patients on peritoneal dialysis were placed on a clinical protocol that brought about a gradual, sustained volume expansion. This was accompanied by significant increases in body weight (4.1 +/- 1.2 kg, p < 0.05), mean arterial pressure (18.2 +/- 6.4 mm Hg, p < 0.05), and serum DLF activity (4.7 +/- 1.9% inhibition, p < 0.05). Processing these patients' daily dialysates by ultrafiltration and high-performance liquid chromatography allowed for the identification of a single elution fraction having volume-sensitive [Na,K]ATPase inhibitory activity. This factor in turn was correlated with serum DLF activity (R = 0.60, p = 0.002), weight gain (R = 0.67, p = 0.0003), and mean arterial pressure (R = 0.59, p = 0.003). This factor was readily distinguished from ouabain and digoxin but was similar to the DLF isolated from amniotic fluid. These results suggest that volume expansion in renal failure patients on peritoneal dialysis gives rise to a unique volume-sensitive DLF that may contribute to these patients' increase in blood pressure.