Benefit and risks of long-term amiodarone therapy for sustained ventricular tachycardia/fibrillation: minimum of three-year follow-up in 145 patients.

Our experience with amiodarone therapy in 145 consecutively referred patients with medically refractory sustained ventricular tachycardia and/or fibrillation treated for at least 3 years was reviewed. Ninety-seven had sustained ventricular tachycardia; the remaining 48 patients were survivors of sudden cardiac death. The patients had a mean of 3.7 +/- 1.4 unsuccessful anti-arrhythmic drug trials before initiation of amiodarone. The initial doses of amiodarone averaged 845 +/- 258 mg for the first 2 weeks and 56% of all patients received a type I antiarrhythmic drug in addition to amiodarone during the initial phase of therapy. The average maintenance dose of amiodarone was 410 +/- 187 mg per day. All patients were followed for a minimum of 3 years or until death or withdrawal from therapy. The maximum follow-up was a period of 8 years. Thus, the average duration of amiodarone therapy was 39 +/- 26 months, representing 472 patient years of therapeutic time on amiodarone. The incidence of deaths either caused by a documented ventricular tachyarrhythmia or presumed to result from an arrhythmic cause was 5.5% in the first year and 3.4% in each of the second and third years of follow-up. During the entire period of follow-up, 56 patients died of all causes (38.6% of the study population). Survival over the follow-up period was influenced significantly by left ventricular function, as judged by either New York Heart Association Functional Class or objective assessment of left ventricular ejection fraction, which was available in 102 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Subthreshold atrial pacing in patients with a left-sided accessory pathway: an effective new method for terminating reciprocating tachycardia.

This study investigated the possibility of terminating reciprocating atrioventricular (AV) tachycardia using subthreshold atrial pacing. Ten patients with a left-sided accessory pathway and sustained AV tachycardia underwent subthreshold atrial pacing from the coronary sinus site closest to insertion of the accessory pathway. In seven of these patients, the tachycardia could be reliably terminated with subthreshold atrial overdrive pacing. When pacing at a cycle length of 80 +/- 23% of the tachycardia cycle length, the minimal subthreshold current that was effective in tachycardia termination was 64 +/- 14% of threshold current and the maximal ineffective current was 49 +/- 17% of threshold (p less than 0.05). In all cases, the tachycardia was terminated by one or two instances of atrial capture that resulted in a premature atrial impulse (20 +/- 4% advancement of the atrial cycle) that blocked the AV node limb of the tachycardia. Anterograde conduction over the accessory pathway never occurred, either during the tachycardia or during subthreshold pacing after a return to normal sinus rhythm. No instances of atrial fibrillation were provoked by subthreshold pacing. Possible explanations for the intermittent atrial capture with critically placed subthreshold impulses include supernormal atrial conduction or summation of impulses at the atrial insertion site of the accessory pathway. It is concluded that subthreshold pacing is effective in selected patients with AV tachycardia due to an accessory pathway. Furthermore, because neither atrial fibrillation nor anterograde conduction over the accessory pathway is seen with subthreshold pacing, this modality may hold significant promise for permanent antitachycardia pacing in these patients.

Utility of the signal-averaged electrocardiogram in patients presenting with sustained ventricular tachycardia or fibrillation while on an antiarrhythmic drug.

The utility of the signal-averaged electrocardiogram (SAECG) for predicting ventricular tachycardia (VT) induction in patients presenting with sustained VT or ventricular fibrillation (VF) while on an empirically chosen antiarrhythmic agent was assessed in 17 patients. At the time of presentation with a malignant arrhythmia, 12 patients were taking quinidine, three patients were taking procainamide, and two patients were taking flecainide. All patients underwent programmed ventricular stimulation when not taking antiarrhythmic drugs; 12 patients had no inducible sustained VT and five patients had inducible sustained monomorphic VT. The SAECG done in the control state without antiarrhythmic agents was negative for late potentials in 11 of 12 patients in the noninducible group and positive for late potentials in four of five patients in the inducible group (sensitivity = 80% and specificity = 92%). We conclude that in patients presenting with life-threatening ventricular arrhythmias while taking an antiarrhythmic drug, the SAECG distinguishes patients with possible proarrhythmic events from those who have the substrate for inducible sustained VT.

Hemodynamic influences on sinus node recovery time: effects of autonomic blockade.

Ten patients with normal sinus node function were evaluated prospectively, to determine whether the decrease in blood pressure during rapid atrial pacing shortens the corrected sinus node recovery time. All patients had 30 seconds of atrial pacing at cycle lengths from 600 to 300 ms, with continuous arterial pressure monitoring, before and after intravenous administration of propranolol (0.2 mg/kg body weight) and atropine (0.04 mg/kg). In the control state, a decrease in corrected sinus node recovery time was recorded with faster atrial pacing rates, which was significantly related to the initial drop in systolic blood pressure at the onset of atrial pacing. Specifically, as the initial pressure drop increased from 15 mm Hg or less to 16 to 45 and 45 to 100 mm Hg, corrected sinus node recovery time decreased from 272 +/- 79 to 205 +/- 70 ms (p less than 0.04) and to 134 +/- 120 ms (p less than 0.04), respectively. In contrast, after autonomic blockade, the corrected sinus node recovery time was prolonged, in a near linear fashion, as atrial pacing rates increased. The magnitude of blood pressure drop with atrial pacing did not differ significantly from that in the control state at similar pacing rates. These findings suggest that hypotension during rapid atrial pacing activates autonomic reflexes that significantly shorten the corrected sinus node recovery time. Autonomic blockade negates this effect and the corrected sinus node recovery time prolongs with faster atrial pacing.

The yield of programmed ventricular stimulation in mitral valve prolapse patients with ventricular arrhythmias.

A high-risk subset of patients with mitral valve prolapse (MVP) and a predisposition to sudden cardiac death (SCD) has been proposed. We analyzed the results of programmed ventricular stimulation (PVS) in 20 patients with MVP and ventricular arrhythmias (ventricular premature depolarization in 6, ventricular couplets in 2, nonsustained ventricular tachycardia [VT] in 7, ventricular fibrillation [VF] in 5) and in 12 "normal" control subjects. With the use of an identical stimulation protocol from the right ventricular apex (twice diastolic threshold, three extrastimuli), 9 of 20 MVP patients and 1 of 12 normal subjects had inducible ventricular arrhythmias (p less than 0.05). When more aggressive attempts at ventricular stimulation were used, an additional five MVP patients had positive responses to PVS while no normal subjects did. In the MVP group, the following arrhythmias were induced: nonsustained polymorphic VT in 10, VF in three, and ventricular flutter in one. In all but two patients, triple ventricular extrastimuli were required to elicit this response. Two of the 10 MVP patients undergoing electropharmacologic testing had a successful antiarrhythmic regimen identified, while 13 patients were discharged on empiric antiarrhythmic therapy. At a follow-up of 19.8 +/- 13.1 months, all 19 MVP patients who could be contacted were alive. Five patients had symptomatic recurrences at follow-up including two SCD survivors (VT in one and VF in one). In conclusion, it was found that the majority of MVP patients with ventricular arrhythmias have inducible ventricular tachyarrhythmias during PVS and are more susceptible to this than patients without structural heart disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Electropharmacologic testing in sustained ventricular tachycardia associated with coronary heart disease: value of the response to intravenous procainamide in predicting the response to oral procainamide and oral quinidine treatment.

Twenty patients with inducible, sustained ventricular tachycardia (VT) were prospectively evaluated to determine whether the response to intravenous procainamide administration, as assessed by programmed ventricular stimulation, predicted the response to oral procainamide and oral quinidine treatment. Six patients (30%) responded to intravenous procainamide (fewer than 10 beats of inducible VT). Ten of 20 patients (50%) responded to oral quinidine and 5 (25%) responded to oral procainamide. Mean drug serum levels were 11.3 +/- 2.1 micrograms/ml for intravenous procainamide, 5.4 +/- 0.8 micrograms/ml for oral quinidine and 11.7 +/- 3.4 micrograms/ml for oral procainamide. There was no significant difference in serum levels between those who responded and those who did not. Fifteen patients (75%) had a concordant drug response for intravenous and oral procainamide. Ten patients (50%) had a concordant response for intravenous procainamide and oral quinidine. Fifteen patients (75%) had a concordant drug response for oral procainamide and oral quinidine. Thus, in patients with sustained VT, the response to intravenous procainamide does not reliably predict the response to oral quinidine or oral procainamide, and serial day drug testing with these agents is necessary. Furthermore, high-dose quinidine therapy may be more effective in controlling VT in these patients than procainamide.

Mode of stimulation versus response: validation of a protocol for induction of ventricular tachycardia.

Electrophysiologic studies were prospectively performed in 91 consecutive patients referred for evaluation of sustained ventricular tachycardia or sudden cardiac death. Fifty-two patients had a history of sustained ventricular tachycardia and 39 patients had a history of sudden cardiac death. The identical stimulation protocol was used in all patients. The stepwise protocol involved atrial pacing, burst ventricular pacing, single, double, and triple extrastimuli during ventricular pacing. Stimulation was performed at the right ventricular apex at two and five times diastolic threshold. Using this protocol, ventricular tachycardia was inducible in 48 (92%) of the 52 patients with a history of sustained ventricular tachycardia and in 28 (72%) of 39 patients with a history of sudden cardiac death (p less than 0.02). The use of a third extrastimulus increased the yield of inducible ventricular tachycardia by 37% in patients with a history of sustained ventricular tachycardia and by 25% in patients with a history of sudden cardiac death. Stimulation at five times diastolic threshold and stimulation from the right ventricular outflow tract added a 15% increment in overall yield of inducible ventricular tachycardia in patients with a history of sustained ventricular tachycardia, and a 26% increment in yield in patients with a history of sudden cardiac death. Forty-four (92%) of the 48 inducible patients in the sustained ventricular tachycardia group had inducible monomorphic ventricular tachycardia as compared to 19 (68%) of 28 patients in the sudden cardiac death group (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Rate-dependent effects of procainamide on His-Purkinje conduction in man.

Microelectrode studies in isolated cardiac tissues have shown that the depressant effect of several antiarrhythmic drugs on the maximal upstroke velocity of the cardiac action potential is rate-dependent. To determine whether this effect of antiarrhythmic drugs is seen in humans, 14 patients undergoing atrial pacing at several rates were prospectively studied before and after the infusion of procainamide (15 mg/kg). The HV interval (His-Purkinje conduction rate) and the QRS duration (intraventricular conduction rate) were measured. Before procainamide infusion, atrial pacing did not significantly prolong the maximal HV interval (from 54 +/- 15 to 58 +/- 13 ms). After procainamide infusion (mean serum level 10.0 +/- 3 micrograms/ml) atrial pacing at an average of 5 pacing rates significantly prolonged the HV interval (from 67 +/- 18 to 80 +/- 20 ms, p less than 0.001). The extent of HV prolongation with atrial pacing after procainamide infusion was independent of the HV interval at rest before procainamide. The duration of the QRS complex also tended to prolong with atrial pacing after procainamide infusion, but this prolongation was not statistically significant. Thus, procainamide produces a rate-dependent depressant effect on His-Purkinje and intraventricular conduction, confirming observations made in isolated tissue preparations.

Sinus node electrogram in patients with the hypersensitive carotid sinus syndrome.

Sinus node electrograms were obtained in two patients with unexplained syncope and the cardioinhibitory form of the hypersensitive carotid sinus syndrome. Direct recordings of sinus node potentials were obtained using a transvenous electrode catheter. Sinus node function was normal in both patients during standard electrophysiologic evaluation. Carotid sinus massage was performed in both patients and the sinus node electrogram was continuously recorded. After the onset of carotid sinus massage, prolongation of sinoatrial time, slowing of sinus rate of depolarization, sinoatrial exit block and finally sinus node arrest were recorded. After termination of carotid sinus massage, sinus node potentials did not precede the first atrial impulse; subsequent beats showed markedly prolonged sinoatrial times as well as changes in the P wave on the surface electrocardiogram. Sinus rate and sinoatrial time returned to control values gradually, as did the P wave configuration. Intravenous atropine (1.0 mg) abolished the abnormal response to carotid sinus massage. It is concluded that the application of carotid sinus massage in patients with the hypersensitive carotid sinus syndrome produces profound changes in sinoatrial conduction including sinoatrial exit block, as well as shifts in primary pacemaker site and sinus node arrest. These alterations in conduction and automaticity are reversible with atropine and may be secondary to denervation sensitivity to acetylcholine.