The effects of propranolol on induction of A-V nodal reentrant paroxysmal tachycardia

Effects of pharmacological autonomic blockade on dual atrioventricular nodal pathways physiology in patients with slow-fast atrioventricular nodal reentrant tachycardia

The purpose of this study was to investigate the atrioventricular AV nodal physiology and the inducibility of AV nodal reentrant tachycardia (AVNRT) under pharmacological autonomic blockade (AB). Seventeen consecutive patients (6 men and 11 women, mean age 39 +/- 17 years) with clinical recurrent slow-fast AVNRT received electrophysiological study before and after pharmacological AB with atropine (0.04 mg/kg) and propranolol (0.2 mg/kg). In baseline, all 17 patients could be induced with AVNRT, 5 were isoproterenol-dependent. After pharmacological AB, 12 (71%) of 17 patients still demonstrated AV nodal duality. AVNRT became noninducible in 7 of 12 nonisoproterenol dependent patients and remained noninducible in all 5 isoproterenol dependent patients. The sinus cycle length (801 +/- 105 ms vs 630 +/- 80 ms, P < 0.005) and AV blocking cycle length (365 +/- 64 ms vs 338 +/- 61 ms, P < 0.005) became shorter after AB. The antegrade effective refractory period and functional refractory period of the fast pathway (369 +/- 67 ms vs 305 +/- 73 ms, P < 0.005; 408 +/- 56 ms vs 350 +/- 62 ms, P < 0.005) and the slow pathway (271 +/- 30 ms vs 258 +/- 27 ms, P < 0.01; 344 +/- 60 ms vs 295 +/- 50 ms, P < 0.005) likewise became significantly shortened. However, the ventriculoatrial blocking cycle length (349 +/- 94 ms vs 326 +/- 89 ms, NS) and effective refractory period of retrograde fast pathway (228 +/- 38 ms vs 240 +/- 80 ms, NS) remained unchanged after autonomic blockade. Pharmacological AB unveiling the intrinsic AV nodal physiology could result in the masking of AV nodal duality and the decreased inducibility of clinical AVNRT.

AV nodal reentrant tachycardia with unusual characteristics: lessons from radiofrequency catheter ablation

There are still some AV nodal reentrant tachycardias with unusual AV nodal properties that need further study to understand these complexities. Accordingly, the two-dimensional model with alpha and beta pathways in the AV nodal reentrant tachycardia circuit certainly is an oversimplification and does not explain adequately the anatomic and physiologic complexity of the AV junctional area. The modern concept suggests that this arrhythmia takes place in a highly complex three-dimensional model with nonuniform anisotropy and discontinuous conduction property in the AV junctional area. Application of radiofrequency energy within the AV junctional area should always be performed carefully to achieve a successful ablation procedure and to minimize possible injury of AV nodal conduction.

Isoprenaline and inducibility of atrioventricular nodal re-entrant tachycardia

OBJECTIVES

To examine the effect of isoprenaline on slow and fast pathway properties and tachycardia initiation.

DESIGN

Consecutive patients, prospective study.

SETTING

Referral centre for cardiology, academic hospital.

PATIENTS

24 patients suffering from common type atrioventricular nodal reentrant tachycardia (AVNRT).

INTERVENTIONS

Programmed electrical stimulation and radiofrequency catheter ablation of the slow pathway.

MEASUREMENTS AND MAIN RESULTS

AVNRT was induced before and after the administration of isoprenaline in nine patients (group 1), before isoprenaline only in five (group 2), and after isoprenaline only in 10 (group 3). The anterograde effective refractory period of the fast pathway was prolonged significantly during isoprenaline administration in group 1 (405 (31) v 335 (34) ms, p < 0.001) and shortened in group 2 (308 (57) v 324 (52) ms, p = 0.005). There was also significant shortening in group 3 (346 (85) v 395 (76) ms, p < 0.001). Isoprenaline administration did not result in a significant change of the anterograde effective refractory period of the slow pathway in groups 1 and 3, but eliminated slow pathway conduction in group 2. Isoprenaline significantly shortened the minimal and maximal atrial to His bundle conduction interval recording in response to each extrastimulus of the slow pathway (210 (24) v 267 (25) ms, p < 0.001 and 275 (25) v 328 (25) ms, p < 0.001, respectively) in group 1 and significantly prolonged these intervals (331 (34) v 274 (34) ms and 407 (33) v 351 (33) ms, respectively) in group 3. In all groups only minimal changes in the refractory period of the atrium occurred after isoprenaline administration. The effect of isoprenaline was also measured on the ventricular effective refractory period and on the minimal and maximal length of the ventriculoatrial (V2-A2) interval during ventricular pacing. Isoprenaline did not result in a significant change of the ventricular effective refractory period in groups 1 and 2 nor of the shortest and longest V2-A2 interval. In group 3, however, the ventricular effective refractory period and the shortest and longest V2-A2 interval shortened significantly after isoprenaline administration.

CONCLUSIONS

In group 1 isoprenaline did not affect inducibility of AVNRT because it prolonged the fast pathway refractory period without affecting slow pathway conduction. In group 2 isoprenaline shortened the fast pathway refractory period and appeared to abolish slow pathway conduction. Consequently, isoprenaline prevented induction of AVNRT. In group 3 isoprenaline facilitated induction of AVNRT. This effect seemed primarily to be the result of shortening of retrograde refractoriness of the fast pathway with prolongation of slow pathway anterograde conduction and refractory period.

Differential effects of adenosine on antegrade and retrograde fast pathway conduction in atrioventricular nodal reentry

Although adenosine depresses antegrade atrioventricular (AV) nodal conduction, the effects of adenosine on antegrade and retrograde fast pathway conduction in AV nodal reentry have not been determined. In 17 patients (five men, 12 women, mean age 49 +/- 12 years) with common slow-fast AV nodal reentrant tachycardia, the antegrade slow pathway conduction was selectively and completely ablated by radiofrequency catheter ablation while the antegrade and retrograde fast pathway conduction remained intact. During high right atrial pacing at a mean pacing cycle length of 474 +/- 36 msec, adenosine was rapidly injected intravenously at an initial dose of 0.5 mg followed by stepwise increases of 0.5 mg or 1.0 mg given at 5-minute intervals until second-degree AV block developed. During right ventricular apical pacing at the same pacing cycle lengths (mean 474 +/- 36 msec) as those in the study of antegrade conduction, intravenous injection of incremental doses of adenosine was repeated until ventriculoatrial (VA) block occurred. The adenosine-induced prolongation of VA conduction was also determined in the presence of verapamil (loading dose 0.15 mg/kg, maintenance dose 0.005 mg/kg/min) in seven of 17 patients. The dose of adenosine required to produce AV block, the increase in the atrio-His interval by 50% and the maximal response were 3.4 +/- 1.4 mg, 1.8 +/- 0.6 mg, and 58% +/- 5%, respectively. On the other hand, the dose of adenosine required to produce VA block, the increase in the VA interval by 50%, and the maximal response were 8.2 +/- 2.9 mg, 3.4 +/- 0.6 mg, and 20% +/- 5%, respectively, in the control and 3.7 +/- 0.5 mg, 3.5 +/- 0.7 mg, and 23% +/- 5%, respectively, in the presence of verapamil. In conclusion, adenosine has a differential potency to depress AV and VA conduction in patients with AV nodal reentry, with greater potency for slowing antegrade fast than retrograde fast pathway conduction. Verapamil had an additive effect to adenosine on slowing retrograde VA conduction, which further supports the evidence that the retrograde fast pathway in part involves an AV nodal-like structure.

Pharmacologic management of supraventricular tachycardias in children. Part 1: Wolff-Parkinson-White and atrioventricular nodal reentry

OBJECTIVE

To review the literature regarding the use of antiarrhythmic agents in the management of Wolff-Parkinson-White (WPW) syndrome and atrioventricular nodal reentry tachycardia (AVNRT) in infants and children, and to discuss the advantages and disadvantages of specific agents in each arrhythmia in an effort to develop treatment guidelines.

DATA SOURCES

A MEDLINE search encompassing the years 1966-1996 was used to identify pertinent literature for discussion. Additional references were found in the articles that were retrieved via MEDLINE.

STUDY SELECTION

Clinical trials that address the use of antiarrhythmic agents for the treatment of the supraventricular tachycardias WPW and AVNRT in children were selected. Literature pertaining to dosage, pharmacokinetics, efficacy and toxicity of antiarrhythmic agents in children were considered for possible inclusion in the review, and information judged to be pertinent by the authors was included in the discussion.

DATA EXTRACTION

Although there are numerous reports of antiarrhythmic use in children, very few large studies are designed to evaluate an individual antiarrhythmic agent for a specific arrhythmia. Controlled, comparison trials of antiarrhythmic agents in children are virtually nonexistent. Ideally, controlled clinical trials are used to develop clinical guidelines; however, in this situation, most data and information must be obtained from case series of children treated. Although the results from these type of studies may be useful in developing guidelines for the optimal use of these agents, controlled trials are required for establishing standard treatment guidelines for all patients.

DATA SYNTHESIS

Despite limited scientific evaluation of conventional agents in the treatment of WPW and AVNRT in children, they continue to be used as standard of care. Most information regarding the use of conventional agents in children has been extrapolated from the adult literature. Little justification for the use of agents or dosing in children is available. Controlled trials regarding the use of new antiarrhythmic agents (propafenone, amiodarone, flecainide) are available; however, the variance in dosing schemes, presence of structural heart disease, and patient age make the development of recommendations difficult.

CONCLUSIONS

Because of greater clinical experience with these conventional antiarrhythmic agents, they continue to be first-line therapy in the management of most supraventricular tachycardia (SVT) in children. The management of SVT in children with WPW syndrome should begin with the use of a beta-blocker with the addition of digoxin or procainamide for treatment failures. The use of digoxin monotherapy, although frequently used by many practitioners in infants and children with WPW, cannot be recommended. For failures to conventional agents, flecainide is the preferred agent, while therapy with propafenone, amiodarone, and sotalol remains to be elucidated. The management of AVRNT is similar to that of WPW; however, digoxin is the agent of first choice. Trials of beta-blockers and procainamide should follow for treatment failures with flecainide again being the preferred "newer" antiarrhythmic for use in resistant cases. Additional well-designed, controlled trials are needed to further evaluate the comparative efficacy of antiarrhythmics in the management of WPW and AVNRT in children, as well as to evaluate dosing and toxicity in various age groups.

Similar time-dependent recovery property of fast and slow atrioventricular nodal pathways

The purpose of this study was to determine whether fast and slow atrioventricular (AV) nodal pathways have the same recovery property. AV nodal recovery property is studied by delivering atrial extrastimuli coupled to atrial beats and plotting nodal coupling intervals against nodal conduction time. In patients with dual pathways the resultant curves will include a fast to fast (F-F) and a fast to slow (F-S) pathway coupled curves. Although fast pathway recovery property can be represented by the former, slow pathway recovery property requires further assessment by studying slow to slow (S-S) pathways coupled curve. In 9 patients with dual pathways F-F, F-S, S-F, and S-S curves were obtained by pacing protocols. In 8 patients (control) without dual pathways, F-F curve and atrial extrastimuli coupled to a preceding slowly conducted fast pathway beat (also designated as S-F curve) were obtained. (1) The S-S curve had a similar time constant as the F-F curve. (2) Although the S-S curve was markedly shifted upward and leftward from the F-F curve, the degree of leftward and upward shifts of the S-S curve from the F-F curve were both close to the difference of the basic fast and slow pathway conduction time (a constant). (3) Although the effective refractory period of the fast pathway in dual pathway patients was longer than that of the control patients, the slow pathway effective refractory period when corrected was close to that of fast pathway in control patients. These results suggest that the fast and slow AV nodal pathways have a similar time-dependent recovery property.

Effects of verapamil, propranolol, and procainamide on adenosine-induced negative dromotropism in human beings

Adenosine, verapamil, propranolol, and procainamide are widely used antiarrhythmic drugs. The interactions among them are still not known in human beings. Adenosine-induced negative dromotropic effects were assessed by rapid bolus injection of adenosine during constant high right atrial pacing in each patient. The initial dose of adenosine was 0.5 mg and was followed by a stepwise increment of 0.5 mg until atrioventricular (AV) nodal block occurred. The negative dromotropic actions of adenosine were examined in the control state and in the following three protocols in three groups of patients: (1) In 12 patients (group 1), intravenous verapamil, 0.15 mg/kg, was given; (2) In 12 patients (group 2), intravenous propranolol, 0.1 mg/kg, was given; and (3) in 10 patients (group 3), intravenous procainamide, 15 mg/kg, was given. The dose-response curves of adenosine on AV nodal conduction were almost identical in the control state and after verapamil, propranolol, or procainamide injection. However, verapamil, in contrast to propranolol, significantly reduced the dose of adenosine required to produce AV nodal block, from 4.4 +/- 0.7 mg to 2.7 +/- 0.3 mg (p < 0.01). Of note, procainamide exerted no significant effects on adenosine-induced negative dromotropism on AV nodal conduction or AV nodal block. In conclusion, the negative dromotropic effects of adenosine are preserved and independent even in the presence of verapamil, propranolol, or procainamide. Both verapamil and propranolol can exhibit additive effects with adenosine in prolonging AV nodal conduction time; however, only verapamil can reduce the dose of adenosine required to produce AV nodal block. This finding indicates that the dose of adenosine may be reduced for patients who have already been treated with verapamil.

PR/RR interval ratio during rapid atrial pacing: a simple method for confirming the presence of slow AV nodal pathway conduction

INTRODUCTION

Although the AV conduction curve in patients with AV nodal reentrant tachycardia (AVNRT) is usually discontinuous, many patients with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds the pacing cycle length when there is anterograde conduction over the slow pathway and AVNRT is induced. The purpose of this prospective study was to determine the diagnostic value of the ratio of the PR interval to the RR interval during rapid atrial pacing as an indicator of anterograde slow pathway conduction in patients undergoing electrophysiologic testing.

METHODS AND RESULTS

The PR and RR intervals were measured during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nodal reentry and the classical criterion for dual AV nodal pathways during atrial extrastimulus testing (AVNRT Group 1); (2) patients with inducible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2); (3) control subjects < or = 60 years of age without inducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with inducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pathway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 +/- 0.21) and 16 of 17 AVNRT Group 2 patients (mean 1.18 +/- 0.15, P = NS Group 1 vs Group 2). After slow pathway ablation, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 +/- 0.08, P < 0.00001 vs before ablation; Group 2 = 0.67 +/- 0.11; P < 0.00001 vs before ablation). Among both groups of control subjects, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relation to patient age.

CONCLUSION

The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This finding may be particularly useful in patients with inducible AV nodal reentry without dual AV nodal physiology on atrial extrastimulus testing.

Anatomic substrate of the experimentally-created atrioventricular node re-entrant tachycardia in the dog

Despite major success in the treatment of atrioventricular (AV) node reentrant tachycardia using either catheter ablation or surgery, the morphologic basis underlying AV node reentry is not yet clear. A canine model of AV node reentrant tachycardia was used to examine the histologic features of the reentry circuit. AV node reentrant tachycardia was created in 4 of 8 dogs by a right atrial division which divided the right atrial free wall and the atrial septum into upper and lower portions on a plane between the mid-right atrial free wall and the fossa ovalis. The AV junctional area of all dogs were serially sectioned on a plane that was perpendicular to the AV annulus and the septum. The slices were stained with Masson's trichrome technique. The connections between atrial fibers and the compact AV node and the common AV bundle were examined, and comparison of the histologic features between dogs with and without AV nodal re-entry was made. The histologic examinations showed that, in all dogs, the operation scar was remote from the AV junctional area leaving the Koch's triangle intact. The compact node received its atrial inputs mainly from the anterosuperior and posterior aspects of the Koch's triangle. However, both atrial inputs gave off superficial (subendocardial) fibers that by-passed the compact node to terminate at the base of tricuspid valve. These superficial fibers might function as the proximal link between the dual AV nodal inputs by means of lateral connections. There was no bypass connection between atrial fibers and the common AV bundle. The histologic features of the AV junctional area was not different between dogs with and without AV nodal reentry. In conclusion, AV nodal reentry involves the anterior and posterior atrio-nodal inputs which function as dual AV nodal pathways, and the superficial bypass fibers form the proximal linkage between the two inputs. These structures, together with the compact node, complete the reentry circuit.

Differential effect of esmolol on the fast and slow AV nodal pathways in patients with AV nodal reentrant tachycardia

INTRODUCTION

AV nodal reentrant tachycardia (AVNRT) usually involves anterograde conduction over a slowly conducting ("slow") pathway and retrograde conduction over a rapidly conducting ("fast") pathway. A variety of drugs, such as beta blockers, digitalis, and calcium channel blockers, have been reported to prolong AV nodal refractoriness in both the anterograde and retrograde limbs of the circuit. However, few data are available that address whether the fast and slow pathways respond in a quantitatively different manner to drugs such as beta-adrenergic antagonists. In addition, it is not known whether the effects of these agents on refractoriness parallel the effects on conduction in the fast and slow pathways. The present study was performed to measure the effect of the intravenous beta-adrenergic agent, esmolol, on refractoriness and conduction in both the fast and slow AV nodal pathways in patients with AVNRT.

METHODS AND RESULTS

Thirteen patients with discontinuous AV nodal conduction properties and typical AVNRT were studied. Anterograde and retrograde AV nodal functional assessment was performed at baseline and following steady-state drug infusion of intravenous esmolol at a dose of 500 micrograms/kg for 1 minute, 150 micrograms/kg per minute for the next 4 minutes, followed by a continuous maintenance infusion of 50 to 100 micrograms/kg per minute. The anterograde effective refractory period of the fast pathway increased from 381 +/- 75 msec at baseline to 453 +/- 92 msec during the infusion of esmolol (P = 0.003). The anterograde effective refractory period of the slow pathway was also prolonged by esmolol, from 289 +/- 26 msec to 310 +/- 17 msec (P = 0.005). However, the absolute magnitude of the change in the anterograde effective refractory period of the fast pathway (+72 +/- 59 msec) was significantly greater than the change in anterograde effective refractory period of the slow pathway (+21 +/- 16 msec, P = 0.01). The mean retrograde effective refractory period of the fast pathway increased from 276 +/- 46 msec to 376 +/- 61 msec during esmolol infusion (P = 0.03). Retrograde slow pathway conduction that could not be demonstrated at baseline became manifest in three patients during esmolol infusion. In contrast to the effects of esmolol on refractoriness, the AH interval during anterograde slow pathway conduction prolonged to a far greater extent (+84 msec) than the HA interval associated with retrograde fast pathway conduction (+5 msec, P = 0.04).

CONCLUSION

The beta-adrenergic antagonist, esmolol, has a quantitatively greater effect on anterograde refractoriness of the fast than the slow AV nodal pathway. However, the effects on conduction intervals during AVNRT are greater in the anterograde slow pathway than in the retrograde fast pathway. These observations suggest that the fast and slow pathways may have differential sensitivities to autonomic influences. This difference in the response to beta-adrenergic antagonists may be exploited as a clinically useful method for demonstrating slow pathway conduction in some individuals with AVNRT.

Dynamic behavior of the atrioventricular node: a functional model of interaction between recovery, facilitation, and fatigue

The wide variety of delays that the atrioventricular node can generate in response to an increased rate are explained by dynamic interactions between the three intrinsic properties of recovery, facilitation, and fatigue. The functional model presented suggests that any deviation of nodal conduction time from its minimum basal value represents, at any given time, the net sum of the effects produced by these properties. When a constant fast atrial rate is suddenly initiated, the node first "sees" a shortening in recovery time and responds by an increase in conduction time. This increase further shortens the recovery time of the ensuing beat, which is accordingly further delayed, and so on until a steady state is reached or a block occurs. However, these events do not occur alone. The second beat at the fast rate is conducted with a shorter conduction time than expected from the recovery time alone, and is therefore facilitated. These facilitatory effects develop within one short cycle and dissipate within one long cycle. They affect increasingly the conduction time of beats occurring with shorter cycle lengths. While steady-state effects of recovery and facilitation occur within seconds, nodal conduction time continues to increase slowly over several minutes when a rapid rate is maintained. This effect is attributed to fatigue, which develops and dissipates with a slow, symmetric time course. The dynamics of these properties can now be directly studied with selective stimulation protocols, and have many implications for the understanding of nodal behavior in the context of supraventricular tachyarrhythmias.

"AV nodal" reentry: Part II: AV nodal, AV junctional, or atrionodal reentry?

The classical model of "atrioventricular (AV) nodal" reentrant tachycardia suggests that the reentrant circuit is entirely within the compact AV node and that AV nodal tissue is present proximal and distal to the circuit. Recent evidence from mapping studies and from examination of the effects of curative procedures, however, suggests that the upper end of the circuit uses perinodal atrial or transitional tissue. Moreover, the anatomical substrate of dual "AV nodal" pathways is likely to be the multiple connections between compact AV node and atrium rather than discrete intranodal pathways. The antegrade slow pathway appears to be situated at the posteroinferior approaches to the AV node in the region between the coronary sinus orifice and the tricuspid annulus. The retrograde fast pathway appears to be situated in the anterior atrionodal connections at the apex of Koch's triangle, close to the His bundle. The lower turnaround point of the circuit is likely to be within the AV node.

Dual AV nodal paths leading to AV nodal reentrant tachycardia

A 27-year-old white female with a history of paroxysmal supraventricular tachycardia presented to the emergency department complaining of intermittent palpitations. Although no tachydysrhythmia was present, she was noted to have two distinct PR intervals during normal sinus rhythm while in the emergency department. The patient was referred for electrophysiologic study. This study demonstrated dual AV nodal paths, and AV nodal reentrant tachycardia was induced and terminated. She was placed on flecainide for outpatient management of her dysrhythmia. Dual AV nodal pathways leading to AV nodal reentrant tachycardia is discussed.

Electrophysiologic and clinical effects of oral encainide in paroxysmal atrioventricular node reentrant tachycardia

The electrophysiologic effects of oral encainide (75 to 150 mg daily) were evaluated in 14 patients (6 male and 8 female, aged 49 +/- 9 years) with atrioventricular (AV) node reentrant tachycardia of the slow-fast type. The patients were studied in control conditions and after 2 to 12 days of treatment. Encainide increased the AH interval from 67 +/- 10 to 82 +/- 23 ms (p less than 0.02). Anterograde Wenckebach cycle length was increased in three patients, reduced in four, unchanged in one; it was not measurable in the remaining patients because tachycardia was induced. Retrograde Wenckebach periodicity increased from 307 +/- 71 to 401 +/- 92 ms (p less than 0.005) in all nine patients in whom it was measurable; complete retrograde block was observed in one patient. At the control study, tachycardia was induced in all patients, with a mean cycle length of 341 +/- 50 ms; after encainide, tachycardia was inducible in only 1 patient, with an increase in cycle length from 270 to 320 ms; in the other patients, tachycardia was not inducible because of a lack of retrograde (11 patients) or anterograde (2 patients) conduction. The mean plasma concentrations of encainide and its metabolites O-demethyl-encainide and 3-methoxy-O-demethyl-encainide measured in 13 patients during the repeat study were 161 +/- 304, 128 +/- 100 and 95 +/- 85 ng/ml, respectively; three poor metabolizers who presented a high concentration of the parent compound were observed in this series. All patients were discharged on encainide at a mean daily dose of 112 +/- 39 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy and electrophysiologic effects of encainide for atrioventricular nodal reentrant tachycardia

To prospectively determine the clinical efficacy and electrophysiologic effects of encainide in atrioventricular nodal reentrant tachycardia (AVNRT), 49 patients refractory to 2.7 +/- 1.5 previous antiarrhythmic drug trials underwent electrophysiologic study before and 47 did so after administration of oral encainide (75 to 240 mg/day). Encainide prolonged the minimum atrial pacing cycle length maintaining 1:1 atrioventricular (AV) nodal conduction from 334 +/- 55 to 391 +/- 55 ms (p = 0.0001). Encainide induced ventriculoatrial (VA) block in 12 patients (25%) and slowed the minimum ventricular pacing cycle length maintaining 1:1 VA conduction from 315 +/- 46 to 485 +/- 89 ms (p = 0.0001) in the remaining 35 patients. After encainide, AVNRT was not inducible in 32 of 47 patients (68%) primarily because of the effects on retrograde AV nodal conduction. In the remaining 15 (32%) patients, AVNRT remained inducible; however, the tachycardia cycle length slowed from 397 +/- 86 to 492 +/- 90 ms (p = 0.0001). There was no significant difference in the baseline minimum ventricular pacing cycle length maintaining 1:1 VA conduction in patients whose inducible tachycardia was or was not suppressed. Forty-seven patients were treated for 18.9 +/- 12.9 months (range 1 to 50) with oral encainide. Encainide was completely effective in eliminating recurrences of supraventricular tachycardia in 26 of 47 patients (55%) and partially effective in an additional 42%. Recurrences of arrhythmia occurred in 15 of 32 patients (47%) whose inducible tachycardia was suppressed by encainide and 7 of 15 patients (47%) whose inducible tachycardia was not suppressed by encainide (p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of intracardiac recordings to determine the site of drug action in paroxysmal supraventricular tachycardia

Paroxysmal supraventricular tachycardia most often results from atrioventricular (AV) reentry using an accessory AV pathway (Wolff-Parkinson-White syndrome) or reentry within the region of the AV node. In AV reentry, using an accessory pathway, suppression of the tachycardia may be achieved by depressing either anterograde AV nodal conduction or retrograde accessory pathway conduction. Intracardiac recordings and programmed electrical stimulation have established that beta-adrenergic antagonists and calcium channel blockers principally affect AV nodal conduction (anterograde limb of the reentrant circuit), whereas class IA and IC agents principally affect the accessory AV pathway (retrograde limb). Pharmacologic therapy has been more effective when directed at the limb in which conduction is most marginal at the tachycardia rate (weak limb). In individual patients, intracardiac recordings and programmed electrical stimulation can be used to identify the weak limb, indicating the class of agents most likely to be effective. Specialized techniques allowing direct recording of accessory pathway activation suggest that limitations in accessory pathway conduction may be explained by anatomic impediments. Conduction is most limited at the atrial interface of the accessory pathway in some patients, whereas in others the ventricular interface may be the limiting factor. Class IA and IC agents appear to have the greatest effect at sites where conduction is most tenuous, i.e., at the anatomic impediments. Similar considerations apply to AV nodal reentry. Anterograde slow AV nodal pathway conduction is most often depressed by digitalis preparations, beta-adrenergic antagonists, and calcium channel blockers, whereas retrograde fast AV nodal pathway conduction is more often depressed by class IA and IC agents. Intracardiac recordings and programmed electrical stimulation can also be used in these patients to identify the weak limb and direct pharmacologic therapy. Direct catheter recordings of AV nodal conduction remain elusive, limiting knowledge of the different conduction properties of the anterograde and retrograde limbs and the site(s) of drug action. Studies in progress, comparing the retrograde AV nodal conduction time during tachycardia with that during ventricular pacing at the same rate, suggest that the His bundle may be incorporated in the reentrant circuit in some patients. It appears that verapamil more readily depresses retrograde fast pathway conduction in these patients than in those in whom the His bundle does not form part of the reentrant circuit, but the reasons for this are unknown.

Effect of flestolol on ventricular rate during atrial fibrillation in Wolff-Parkinson-White syndrome

The ultrashort-acting beta blocker flestolol was studied during atrial pacing and atrial fibrillation (AF) in 10 patients with Wolff-Parkinson-White syndrome. Flestolol was given as a 100-micrograms/kg bolus followed by a 10-micrograms/kg/min infusion for 15 minutes. The drug did not alter the antegrade effective refractory period of the accessory pathway or the atrial paced cycle length at which block occurred in the accessory pathway. After flestolol, the percent of preexcited QRS complexes during AF increased (60 +/- 10 vs 87 +/- 5%, p = 0.01). Despite this, the ventricular rate slowed, with increases in mean RR interval (382 +/- 20 vs 416 +/- 22 ms, p = 0.02) and in the shortest interval between preexcited QRS complexes (251 +/- 18 vs 270 +/- 17 ms, p less than 0.01). The effect of isoproterenol 3 to 5 micrograms/min was studied in 5 patients. During atrial pacing, isoproterenol decreased the antegrade refractory period and the atrial paced cycle length of block in the accessory pathway (p less than or equal to 0.05). During AF, it decreased the percent of preexcited QRS complexes, mean RR interval and shortest interval between preexcited QRS complexes (p less than 0.05). Flestolol reversed the effects of isoproterenol both during atrial pacing and AF. Thus, flestolol does not alter conduction over the accessory pathway during atrial pacing, but during AF it slows conduction over the accessory pathway and prevents isoproterenol-mediated increases in ventricular rate. This suggests that in patients with Wolff-Parkinson-White syndrome sympathetic stimulation after the onset of AF enhances conduction over the accessory pathway and is an important determinant of ventricular rate.

Usefulness of isoproterenol in facilitating atrioventricular nodal reentry tachycardia during electrophysiologic testing

In some patients with documented atrioventricular (AV) nodal supraventricular tachycardia (SVT), the arrhythmia is not inducible during a standard stimulation protocol. In these patients the level of sympathetic activity may be an important factor. This study evaluates the influence of isoproterenol on anterograde and retrograde pathway properties in patients with AV nodal SVT and the mechanism by which this SVT is facilitated. Group 1 consisted of 8 consecutive patients, ages 23 to 85 years (mean +/- standard error, 57 +/- 8) who had no inducible AV nodal SVT during electrophysiologic testing until isoproterenol (0.5 to 3.0 micrograms/min) was infused. These patients were compared with 6 patients in the same age range (45 to 78 years, mean +/- standard error, 64 +/- 5) who had inducible AV nodal SVT without isoproterenol and who comprised group 2. In comparing group 1 (before isoproterenol) with group 2, there was no significant difference in the refractory periods of the anterograde slow and fast pathways, although the anterograde block cycle length was longer in group 1 patients (421 +/- 18 vs 362 +/- 14 ms, p less than 0.05). The retrograde block cycle length was also longer in 7 of the 8 group 1 (before isoproterenol) patients in whom it could be measured versus those in group 2 (411 +/- 14 vs 318 +/- 27 ms, p less than 0.05). During isoproterenol, the anterograde and retrograde block cycle lengths in group 1 were not different from group 2. Therefore, AV nodal SVT may not be inducible in some patients during routine electrophysiologic testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium antagonists and their potential for antihypertensive therapy

Calcium antagonists are potent arterial vasodilators devoid of relevant chronic sympathetic reflex activation and sodium and volume retention. This favorable hemodynamic profile of action renders them suitable for monotherapy of hypertension where they act to reduce an enhanced, calcium-influx-dependent vasoconstrictor mechanism which may be brought about by altered smooth muscle cation handling and increased intracellular free calcium concentrations. Clinical studies have proved their efficacy, safety, and good tolerability alone or in combination with other drugs in uncomplicated hypertension where they are particularly effective in older and low-renin and possibly black patients. These properties and their efficacy in the treatment of severe and accelerated hypertension or hypertensive emergencies make them a valuable addition to already available drug therapy.

Electropharmacology of flestolol for supraventricular tachycardia without associated structural heart disease

Flestolol is an ultrashort-acting beta-blocking drug with a half-life of 6.9 minutes. Its antiarrhythmic efficacy was studied in 21 patients with spontaneous and inducible supraventricular tachycardia: atrioventricular (AV) nodal tachycardia in 6 patients and orthodromic AV reciprocating tachycardia in 15. It increased the effective refractory period of the AV node in all patients with AV nodal tachycardia (fast pathway, p less than 0.02; slow pathway, p less than 0.01), but did not alter the anterograde (n = 8) or retrograde (n = 9) refractory periods of accessory pathways. Flestolol prevented initiation of tachycardia by causing block in anterograde AV nodal conduction. It was more effective in patients with AV nodal tachycardia (5 of 6) than in those with AV reciprocating tachycardia (4 of 15, p less than 0.03). In patients in whom it was ineffective, the mean tachycardia cycle length increased by 54 ms because of an increase in AH interval (p less than 0.0001, n = 11). The cycle length of tachycardia induced 30 minutes after infusion was similar to the cycle length in the control state (354 vs 355 ms, n = 16). Flestolol's kinetics permitted clinically indicated electropharmacologic testing of a second antiarrhythmic drug in 8 patients and control of ventricular rate until arrhythmia surgery in 1 patient with incessant tachycardia. No hypotension or toxicity occurred. Our findings indicate that flestolol's principal antiarrhythmic effects are on the AV node, similar to the effects of other beta-blocking drugs. Its ultrashort duration of action is an advantage during electropharmacologic testing.

Pirmenol in the termination of paroxysmal supraventricular tachycardia

The effects of pirmenol in terminating paroxysmal supraventricular tachycardia were studied in 25 patients. Pirmenol was administered as 1 or 2 injections of 50 mg to 17 patients during a spontaneous attack, or as a 50-mg bolus followed by steady infusion of 2.5 mg/min in 8 patients during a tachycardia that was induced electrophysiologically. Termination was successful in 11 of 17 patients who had a spontaneous attack and in 3 of 8 patients who had induced tachycardia. Pirmenol was effective in 3 of 5 patients with atrioventricular nodal reentrant mechanism, but in none of 3 patients with a reentrant tachycardia with a retrogradely conducting atrioventricular bypass tract. Conversion to sinus rhythm was achieved in 14 of 25 patients (56%). No hemodynamic adverse effects occurred. Pirmenol increased the atrial effective refractory period, but had little effect on conduction in the atrioventricular node and His-Purkinje system. Reentry was abolished through a block in the retrograde part of the dual atrioventricular nodal pathway, which is typical of class I antiarrhythmic agents.

Noncardiac surgery in the patient with heart disease

Optimal care of the patient with heart disease undergoing noncardiac surgery requires that the members of the surgical team, including anesthesiologist, internist-cardiologist, and surgeon, be familiar with the cardiovascular response to surgery, preoperative cardiac risk stratification, and the unique pathogenesis of cardiac complications that may occur in the perioperative period. Preoperative evaluation and computation of cardiac risk, anesthetic considerations, along with perioperative care of the patient with ischemic heart disease, valvular heart disease, congestive heart failure, arrhythmias and conduction disorders, and hypertension is discussed.

A matrical approach to the basic and clinical pharmacology of antiarrhythmic drugs

In summary, the lethal cardiac arrhythmias remain a major public health problem and their treatment is a major challenge to the clinician. We possess rapidly increasing knowledge of the electrophysiologic events which underly arrhythmogenesis and the antiarrhythmic as well as the proarrhythmic actions of drugs. Much of this electrophysiologic knowledge is irrelevant to the practicing physician. While complex, we believe that the matrical approach provides the clinician with a useful intellectual framework within which to consider the actions of arrhythmogenic influences and antiarrhythmic drugs. The matrical approach is scientifically sound, reflects clinical realities, and serves as a rational guide to the treatment of cardiac arrhythmias. The traditional classifications of antiarrhythmic drugs have served a useful purpose, but they are clearly outmoded.

Pirmenol in termination of paroxysmal supraventricular tachycardia

An assessment was made of the effect of pirmenol in the termination of paroxysmal supraventricular tachycardia (SVT). Sinus rhythm was restored by intravenous administration in 11 of 17 patients during a spontaneous attack. Another 8 patients were studied electrophysiologically. Pirmenol terminated an induced SVT in 3 of 5 patients having an atrioventricular (AV) intranodal re-entry mechanism but in none of 3 patients having an atrioventricular bypass tract as one re-entrant limb. The overall success in restoring sinus rhythm was 14 of 25 patients (56%). The drug was hemodynamically well tolerated even in cases of continued SVT. Pirmenol increased the atrial effective refractory period and had no obvious effect on AH and HV intervals. The functional refractory period of the AV node was decreased, probably by an anticholinergic effect. The effective and functional refractory periods of retrograde atrioventricular conduction via the AV node and bypass tract were increased in some patients. The mechanism terminating the AV intranodal SVT was a block in the retrograde part of the dual AV nodal pathway, a typical antiarrhythmic Class I effect.

Influence of the site of stimulation on atrioventricular nodal refractory periods and the effect of verapamil

The refractory periods of the atrioventricular (AV) node appear dependent on the pattern of AV nodal input. In 21 superfused AV rabbit heart preparations stimulated from each of the 2 principal input regions, crista terminalis or atrial septum, the effect of changing the site of stimulation of the AV nodal refractoriness and the relative effect of verapamil on AV nodal refractoriness was determined. In 6 of 21 preparations the functional AV refractory curve became discontinuous only when stimulation was applied at the atrial septum and suggested dual AV nodal pathways (dual pathways group). In the 15 other preparations no interruption of the curve occurred with either crista terminalis or atrial septal stimulation (normal conduction group). In the normal conduction group, the difference in the effective refractory period of the AV node obtained by crista terminalis vs atrial septal stimulation was not significant (154 +/- 25 vs 150 +/- 28 ms). However, the functional refractory period was significantly longer with crista terminalis vs atrial septal stimulation (232 +/- 19 vs 239 +/- 19 ms, p less than 0.001). After verapamil administration, the effective and functional refractory periods during crista terminalis vs atrial septal stimulation were prolonged to 270 +/- 49 vs 285 +/- 55 ms (p less than 0.01) and 335 +/- 43 vs 351 +/- 41 ms (p less than 0.001), respectively. Thus, the difference in refractory periods associated with changing the stimulation site was exaggerated with verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute electrophysiologic effects of pirmenol in normal subjects and in patients with Wolff-Parkinson-White syndrome

The acute electrophysiologic effects of pirmenol are reported in 8 normal subjects and in 8 patients with Wolff-Parkinson-White (WPW) syndrome. Standard electrophysiologic testing was performed before and after a 50-mg intravenous bolus and a 60-minute infusion of 150 mg of pirmenol. After pirmenol administration, AH interval, atrial refractory period, atrioventricular (AV) nodal functional refractory period and Wenckebach cycle length did not change; however, sinus cycle length decreased from 743 +/- 169 to 650 +/- 133 ms (p less than 0.001), sinoatrial conduction time from 103 +/- 35 to 78 +/- 37 ms (p less than 0.05) and AV nodal effective refractory period from 308 +/- 51 to 272 +/- 23 ms (p less than 0.01). Pirmenol increased the HV interval from 43 +/- 5 to 48 +/- 6 ms (p less than 0.05) and ventricular functional refractory period from 247 +/- 21 to 260 +/- 21 ms (p less than 0.005). Anterograde effective refractory period of the accessory AV pathway increased in 4 of 6 patients with ventricular preexcitation and retrograde effective refractory period increased in all patients. Pirmenol treatment prolonged the shortest preexcited RR interval from 253 +/- 38 to 459 +/- 19 ms (p less than 0.05) and the average RR interval from 354 +/- 26 to 421 +/- 60 ms (p less than 0.01) during atrial fibrillation in all 6 patients with preexcitation. Pirmenol did not influence the inducibility or cycle length of AV reciprocating tachycardia in the patients with WPW syndrome. The pirmenol infusions were well tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Diltiazem and propranolol in combination: hemodynamic effects following acute intravenous administration

Diltiazem and propranolol are independently useful antianginal agents with common negative chronotropic, dromotropic, and inotropic properties. Concern over the safety of the concurrent use of these two drugs led to an investigation of their intravenous combination in 19 patients with suspected coronary artery disease. Hemodynamics were recorded in both a sinus and atrial paced rhythms at baseline and again following administration of a loading dose of diltiazem (0.25 mg/kg) followed by continuous infusion (0.002 mg/kg/min). Propranolol was then added by intravenous bolus (0.07 mg/kg) and continuous infusion (0.0012 mg/kg/min), with reassessment of hemodynamics once steady state was achieved. Patients were stratified by left ventricular ejection fraction (LVEF): group 1 (LVEF = 62% to 69%), group 2 (LVEF = 49% to 59%), and group 3 (LVEF = 20% to 47%). The combination of drugs resulted in a 15% drop in heart rate (p less than 0.01) and a 15% prolongation in the PR interval (p less than 0.01) for the group of 19 patients. Left ventricular end-diastolic pressure (LVEDP) was not significantly changed by diltiazem or its combination except in group 3. Cardiac output was lowered in all groups following diltiazem and propranolol (p less than 0.05). Untoward reactions included marked vasovagal reactions at the conclusion of the procedure in six patients. The combination of drugs resulted in profound sinus bradycardia with attendant 2:1 atrioventricular (AV) block in one patient. Diltiazem and propranolol were hemodynamically well tolerated in patients with preserved left ventricular function. Because of the additive negative dromotropic activities of these two drugs, ECG monitoring is warranted when they are acutely combined.

Cardiac electrophysiologic testing: its role in the selection of antiarrhythmic drug regimens for supraventricular and ventricular arrhythmias

Cardiac electrophysiology studies use intracardiac recording and programmed stimulation to define the mechanisms and most appropriate therapy for supraventricular and ventricular arrhythmias. Using these techniques, the majority of clinical tachycardias can be reproducibly initiated and terminated in the electrophysiology laboratory, thereby allowing the most appropriate therapy to be selected. With this approach, antiarrhythmic agents can be tested in a systematic, serialized fashion for efficacy, safety and patient tolerance. With both supraventricular and ventricular tachycardias, suppression of arrhythmia induction predicts freedom from recurrence, whereas inducibility carries a poor prognosis in clinical follow-up. Electrophysiology studies provide a safe and effective approach to the treatment of selected patients with cardiac arrhythmias.

Basic understanding of the electrophysiologic actions of antiarrhythmic drugs. Sources, sinks, and matrices of information

The author creates an intellectual framework consisting of key electrophysiologic principles, basic mechanisms of arrhythmogenesis, and important drug reactions that will allow the rational use of antiarrhythmic drugs. Basic principles have been emphasized because current understanding requires it.

Effect of verapamil on retrograde conduction in atrioventricular nodal reentrant tachycardia

Using His bundle electrograms, incremental ventricular pacing and the ventricular extrastimulus (V2) technique, the effects of intravenous verapamil, 0.2 mg/kg, on retrograde atrioventricular (AV) nodal conduction during ventricular pacing, premature ventricular stimulation (H2A2 interval) and paroxysmal supraventricular tachycardia (SVT) (H-Ae interval) were evaluated in 11 patients with AV nodal reentrant tachycardia. During the control study, SVT could be induced in all 11 patients. After verapamil administration, SVT or atrial echo beats could be induced in 5 patients. Verapamil produced ventriculoatrial (VA) block at a longer cycle length than that during the control study in 10 of 11 patients (295 +/- 27 vs 352 +/- 40 ms, p less than 0.01), but prolonged H2A2 interval in only 5 of 11 patients (37 +/- 6 vs 60 +/- 31 ms, p less than 0.05). In all 5 patients with persistence of inducible SVT or atrial echo beats after verapamil treatment, the H-Ae interval remained unchanged even though in 4 of these 5 patients VA conduction time or H2A2 interval was prolonged. Correlation between the paced cycle length which induced VA block, the shortest V1H2 interval achieved during premature ventricular stimulation and the cycle length of SVT revealed that in all instances in which verapamil induced VA block at a longer cycle length than in controls but did not prolong H2A2 or H-Ae interval, the shortest V1H2 interval and the cycle length of SVT (H-H interval) were significantly longer than the ventricular paced cycle length which produced VA block.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethmozin. II. Effects of intravenous drug administration on atrioventricular nodal reentrant tachycardia

Electrophysiologic studies were performed in 11 patients with atrioventricular (AV) nodal reentrant tachycardia (SVT) before and after intravenous administration of 1.5 to 2 mg/kg ethmozin. Initially, 9 of 11 patients had induction of sustained SVT, and two remaining patients had nonsustained SVT and atrial echoes, respectively. Ethmozin terminated induced SVT in six of nine patients. In six of nine patients ethmozin prevented the development of sustained SVT, indicating that ethmozin depressed retrograde fast pathway AV nodal conduction. In four of these patients atrial echoes were abolished. In the two remaining cases ethmozin prevented the induction of nonsustained SVT. In only three of these nine patients was sustained SVT induced. Anterograde fast and slow pathway properties did not significantly change with ethmozin administration. Effective refractory period (ERP) of the ventriculoatrial (VA) conduction system and ventricular paced cycle length producing VA block was 305 +/- 40 (mean +/- SEM) and 347 +/- 38 msec before and 424 +/- 105 and 475 +/- 71 msec after ethmozin administration, respectively (p less than 0.01, n = 8), suggesting depression of retrograde pathway with ethmozin administration. Ethmozin significantly (p less than 0.05) lengthened PA, AH, HV, and PR intervals (36 +/- 11 to 45 +/- 14 msec, 84 +/- 21 to 93 +/- 17 msec, 42 +/- 8 to 50 +/- 7 msec, and 163 +/- 23 to 190 +/- 31 msec, respectively). No significant change was observed in sinus rate, QRS and QT intervals, or ERP of atrium and ventricle. Thus, a single intravenous dose of ethmozin terminated induced SVT and prevented induction of sustained SVT in most patients, reflecting depression of retrograde fast pathway conduction.

Carotid sinus baroreflex influence on electrophysiologic properties of the canine atrioventricular node and ventricle

This study examines the efferent mechanisms of carotid sinus baroreflex influence on ventricular repolarization and refractory period compared with effects on atrioventricular (AV) nodal conduction. Pressure was controlled in both carotid sinuses by the Moisejeff technique in 16 chloralose-anesthetized dogs. Increases in carotid sinus pressure during pacing produced graded prolongation of AV nodal conduction, ventricular repolarization and refractory period with a threshold at a carotid sinus pressure of 120 mm Hg and a peak response at 200 mm Hg. Atropine, 0.4 mg/kg, attenuated the peak percent change in ventricular repolarization interval by only 12 +/- 14% (+/- standard error of the mean) despite a significantly greater attenuation (48 +/- 11%, p less than 0.05) in peak percent change in AV nodal conduction. However, stellate ganglionectomy attenuated the peak percent change in ventricular repolarization (42 +/- 19%), similar to effects on AV nodal conduction (59 +/- 21%, p greater than 0.25). Changes in mean arterial pressure, ventricular end-diastolic segment length or segment length shortening with systole (sonomicrometer technique) did not account for the electrophysiologic responses. Latency to peak effect on ventricular repolarization (43 +/- 7 seconds) was slower than that on AV nodal conduction (23 +/- 6 seconds, p less than 0.05). This difference in time course was not abolished by atropine. Thus, the carotid sinus baroreflex prolongs ventricular repolarization and refractoriness mainly by withdrawal of sympathetic influence; AV nodal conduction is prolonged by both vagal activation and sympathetic withdrawal. In addition, differences in time course between ventricular and AV nodal electrophysiologic responses are not explained by different efferent autonomic mechanisms.

Atrioventricular nodal reentrant tachycardia

This entity represents the most common type of recurrent, regular, narrow QRS tachycardia in the absence of preexcitation syndrome. Electrophysiologic basis for the arrhythmia is reentry within the AV node resulting from dissociation between intranodal pathways. A better understanding of these intranodal pathways helps in the selection of a rational approach to management of these cases.

Differential effects of sotalol and metoprolol on induction of paroxysmal supraventricular tachycardia

Seventeen patients with recurrent paroxysmal supraventricular tachycardia (SVT) underwent serial electrophysiologic studies to compare the effects of i.v. sotalol (1.5 mg/kg) and i.v. metoprolol (0.15 mg/kg). The plasma concentrations of sotalol (2.1 +/- 1.1 microgram/ml) and metoprolol (67 +/- 15 ng/ml) were within the therapeutic range. Before drug administration, sustained SVT could be reproducibly induced in all patients. Sotalol prevented induction of sustained SVT in 10 of 17 patients (59%) and metoprolol in 4 (28%) (p less than 0.05). In 6 of 8 patients with atrioventricular (AV) nodal reentrance, the site of action of sotalol was the anterograde or the retrograde limb, reflecting an increase in refractoriness in both pathways of the circus movement. In 4 of 9 patients with AV reentrance, the site of action of sotalol was exclusively the AV nodal pathway; conduction through the extranodal accessory tract appeared to be unchanged, but its anterograde effective refractory period was prolonged (from 285 +/- 25 to 322 +/- 28 ms, p less than 0.001; mean +/- standard deviation). In the 7 patients in whom sotalol did not prevent sustained SVT, the tachycardia cycle length increased from 347 +/- 42 to 392 +/- 45 ms (p less than 0.01). Compared with sotalol, metoprolol had qualitatively similar but quantitatively less potent effects on the AV nodal pathways; however, different from sotalol, metoprolol had no effect on extranodal accessory tracts. The study suggests that at therapeutic plasma concentrations, sotalol would be effective in preventing clinical SVT in a significant proportion of patients refractory to metoprolol; because sotalol not only has beta-blocking properties but also results in acute prolongation of the action potential duration, this combination of class II and III activity may contribute to its superior prophylactic efficacy compared with pure beta blockade.

Combined verapamil and propranolol for supraventricular tachycardia

The electrophysiologic effects of intravenous verapamil and propranolol were compared alone and in combination in 14 patients (aged 21 to 69 years) with paroxysmal supraventricular tachycardia (SVT). Ten patients had atrioventricular (AV) reentry utilizing a manifest (7 patients) or concealed (3 patients) accessory pathway. Four patients had AV nodal reentry. Electrophysiology studies were performed using standard techniques in the control state and after verapamil (0.15 mg/kg intravenous bolus and 0.005 mg/kg/min). The next day, studies were repeated after propranolol (0.1 mg/kg) and a combination of verapamil and propranolol. No adverse effects occurred with the drug combination. Each drug intervention prolonged anterograde functional refractory period of the AV node (control, 370 +/- 50 ms; verapamil, 446 +/- 90 ms; propranolol, 436 +/- 92, p less than 0.05), with the greatest increase occurring after the drug combination (502 +/- 103 ms, p less than 0.001). In 2 patients prolonged sinus node recovery time developed after the drug combination. Verapamil or propranolol prevented SVT induction in 7 patients (50%). However, only the drug combination prevented reinduction of sustained SVT in 6 patients. These 6 patients were treated chronically with verapamil and propranolol, with no recurrence of SVT in any patient after 2 to 26 months.

Electrophysiologic effects and mechanisms of termination of supraventricular tachycardia by intravenous amiodarone

Electrophysiologic studies were performed in nine patients with reentrant paroxysmal supraventricular tachycardia (PSVT) during a control period and following 5 mg/kg body weight of intravenous amiodarone (Cordarone, Labaz) administered as a slow continuous infusion over 15 to 20 minutes. All nine patients had induction of sustained PSVT during control studies. In seven of nine patients (group 1) the tachycardia was due to atrioventricular (AV) nodal reentry, and in two of nine patients (group 2) a concealed retrograde bypass tract was incorporated in the reentrant process. In group 1, following amiodarone, all seven patients lost the ability to sustain PSVT with either absence of atrial echoes (one patient) or induction of less than or equal to 3 echo beats (six patients) with termination of PSVT in the antegrade pathway (three patients) or retrograde pathway (two patients) or both (one patient). In group 2, following amiodarone, both patients lost the ability to sustain PSVT with absence of atrial echoes (one patient) on induction of a single echo beat (one patient) with block in the retrograde pathway (i.e., the concealed retrograde bypass tract). Amiodarone significantly increased (1) atrial cycle length for AV nodal Wenckebach block, (2) antegrade functional refractory period of the AV node, (3) antegrade effective refractory period of the AV node, (4) ventricular paced cycle length for ventricular atrial block, and (5) the retrograde functional refractory period of the ventricular-atrial conducting system.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intravenous and oral disopyramide on paroxysmal atrioventricular nodal tachycardia

The effect of intravenous and oral disopyramide on the mechanisms of the arrhythmia were studied in 11 patients with the common type of atrioventricular (AV) nodal paroxysmal reentrant tachycardia. Programmed electric stimulation of the heart was used to initiate and terminate tachycardia and to evaluate the effect of disopyramide on mode of initiation and termination of tachycardia. Disopyramide was given intravenously to all patients during tachycardia. This resulted in termination of tachycardia, by block in the anterograde slow pathway in 1 and in the retrograde fast pathway in 3 patients. In all 4 patients, reinitiation of tachycardia was no longer possible. In these 4 patients, oral disopyramide prevented spontaneous and pacing-induced AV nodal tachycardia. In 4 of the remaining 7 patients in whom tachycardia was not terminated by intravenous disopyramide, reinitiation of the arrhythmia during programmed stimulation was prevented by the drug. In these 4 patients, oral disopyramide was also effective in preventing spontaneous occurrence of tachycardia. In 3 patients, tachycardia was not terminated and its reinitiation was not prevented by intravenous disopyramide. Only 1 of these 3 patients received disopyramide by mouth, and it failed to prevent reinitiation and spontaneous tachycardia. In conclusion, disopyramide is an effective drug in patients with AV nodal paroxysmal reentrant tachycardia. A good correlation was found between intravenous and oral effect of disopyramide on the mechanisms of the arrhythmia. The study of the effect of intravenous disopyramide predicted the outcome of oral disopyramide therapy.

Nadolol and supraventricular tachycardia: an electrophysiologic study

To assess antiarrhythmic efficacy of oral nadolol, 15 patients with recurrent supraventricular tachycardia were studied. Eight patients had atrioventricular (AV) nodal reentrant tachycardia and seven had AV reciprocating tachycardia involving an accessory AV pathway. Electrophysiologic studies were performed before and after intravenous infusion of propranolol (0.20 mg/kg), and were repeated 5 to 8 days after oral nadolol therapy at a daily dose of 80 to 160 mg. Both intravenous propranolol and oral nadolol induced significant prolongation of the sinus cycle length from 741 +/- 73 ms to 834 +/- 97 and 1,029 +/- 95 ms, respectively (p less than 0.001 and p less than 0.0001, respectively). Both intravenous propranolol and oral nadolol depressed AV nodal but not accessory AV pathway conduction, and shifted the dual AV nodal pathway conduction curves (A1A2, A2H2; A1A2, H1H2) upward and to the right by prolonging the conduction time and increasing the refractory period. Ten patients (seven with AV nodal reentry and three with AV reciprocation) who responded to intravenous propranolol also responded to oral nadolol with loss of the inducibility of sustained tachycardia; the remaining five patients (one with AV nodal reentry and four with AV reciprocation) who did not respond to intravenous propranolol also failed to respond to oral nadolol with persistence of the inducibility of sustained tachycardia. Thus, in conclusion, intravenous propranolol testing predicts the therapeutic efficacy of oral nadolol therapy and oral nadolol in once-daily doses may be used for long-term prophylaxis of recurrent supraventricular tachycardia.

Role of electrophysiologic testing in the therapy of ventricular arrhythmias

The past decade has witnessed important advances in the understanding of the mechanism underlying ventricular arrhythmias. It has become clear that sustained ventricular arrhythmias can generally be reproduced with programmed ventricular stimulation in the clinical electrophysiology laboratory. False positive results may, however, occur with very vigorous stimulation techniques, particularly in patients without documented arrhythmias. False negative results are not infrequent in victims of cardiac arrest. Ability or inability to initiate ventricular tachycardia during acute and chronic drug testing has predicted clinical failure or success, at least for conventional antiarrhythmics. Patients with sustained ventricular tachycardia and cardiac arrest occurring outside the peri-infarction period are those most likely to benefit from study. Conventional antiarrhythmic agents are successful in about one-third of patients with a high degree of concordance among these drugs. Amiodarone is frequently effective in patients with drug-refractory ventricular arrhythmias. However, its efficacy cannot be predicted by programmed stimulation. This is in striking contrast to Type 1A anti-arrhythmic agents.