Catecholamine-dependent atrioventricular nodal reentrant tachycardia

The relationship between blood glucose and nocturnal supraventricular tachycardia attacks in non-diabetic patients

PURPOSE

Decrease in the blood glucose level may trigger the tachycardia or bradycardia because it has an arrhythmogenic effect on the heart. Our purpose in this study was to investigate whether the blood glucose level has an effect on patients who attended to the hospital with nocturnal supraventricular tachycardia (SVT).

METHODS

We included 151 patients in our study who have SVT history. Plasma glucose levels which were taken during night hours, electrolytes, and 12 lead electrocardiography were evaluated.

RESULTS

There were 105 patients without nocturnal SVT attack and 46 patients with nocturnal SVT attack. Patients with nocturnal SVT attack, blood glucose level, potassium, calcium, and hemoglobin levels were significantly lower, hs-CRP was significantly higher, basal cycle length (BCL) was significantly short, and QT interval was significantly longer. It was found that blood glucose (O.R. = 0.904, 95% GA 0.828-0.986, p = 0.023) and potassium levels (O.R. = 0.128, 95% GA 0.029-0.561, p = 0.006) and basal cycle length (BCL) (O.R. 0.988, 95% GA, 0.980-0.996, p = 0.005) values were in independently correlated with nocturnal SVT attacks.

CONCLUSION

The decrease in blood glucose level of the patients who are being followed with SVT diagnosis might trigger the nocturnal SVT attacks.

Synthesis and adrenolytic activity of new propanolamines

The synthesis of (2R,S)-1-(6-methoxy-4-(methoxymethyl)-1H-indol-5-yloxy)-3-(2-(2-methoxyphenoxy)ethylamino)propan-2-ol and (2R,S)-1-(4-methoxy-6-(methoxymethyl)-1H-indol-5-yloxy)-3-(2-(2-methoxyphenoxy)ethylamino)propan-2-ol is described. The compounds were tested for electrographic, antiarrhythmic, hypotensive, and spasmolytic activity, as well as for alpha(1)-, alpha(2)- and beta(1)-adrenoceptor binding affinity.

Synthesis and development of new 2-substituted 1-[3-(4-arylpiperazin-1-yl)propyl]-pyrrolidin-2-one derivatives with antiarrhythmic, hypotensive, and α-adrenolytic activity

A series of new 1-[3-(4-arylpiperazinyl-1-yl)-2-(N-alkylcarbamoyloxy)propyl]-pyrrolidin-2-one derivatives (4a-12a) were synthesised and tested for their electrocardiographic, antiarrhythmic and antihypertensive activity, as well as for the alpha1- and alpha2-adrenoceptor binding affinities. Of the newly synthesised derivatives, 1-{2-(N-2-methylethylcarbamoiloxy)-3-[4-(2-methoxyphenyl)piperazin-1-yl)]propyl}pyrrolidin-2-one dihydrochloride (10a) was the most active in prophylactic antiarrhythmic tests, its ED50 value equalling 2.7 mg kg(-1), and the therapeutic index being 75.2; moreover, compound 10a was also found to possess hypotensive activity. A preliminary molecular modelling study suggested that the selected alpha1-AR antagonist distances and angles between pharmacophoric features, estimated for the tested compounds, were in good agreement with the parameters evaluated for ligands.

Acute and Long-Term Results of Slow Pathway Ablation in Patients with Atrioventricular Nodal Reentrant Tachycardia-An Analysis of the Predictive Factors for Arrhythmia Recurrence

BACKGROUND

Predictors of atrioventricular nodal reentrant tachycardia (AVNRT) recurrence after radiofrequency ablation including the importance of residual slow pathway conduction are not known. The aim of this study was to report the acute and long-term results of slow pathway ablation in a large series of consecutive patients with AVNRT and to analyze the potential predictors of arrhythmia recurrence with a particular emphasis on the residual slow pathway conduction after ablation.

METHODS

The study included 506 consecutive patients with AVNRT (mean age 52.6 +/- 16 years, 315 women) who underwent slow pathway ablation using a combined electrophysiological and anatomical approach. The end point of ablation procedure was noninducibility of the arrhythmia. The primary end point of the study was the recurrence of AVNRT.

RESULTS

Acute success was achieved in 500 patients (98.8%). After ablation, 471 patients (93%) were followed up for a mean of 903 +/- 692 days. Of the 465 patients with successful ablation, 24 patients (5.2%) developed AVNRT recurrences during the follow-up. No significant differences in the cumulative rates of AVNRT recurrence were observed in groups with or without electrophysiological evidence of residual slow pathway conduction (P = 0.25, log-rank test). Multivariate analysis identified only age as an independent predictor of AVNRT recurrence (hazard ratio 0.96, 95% confidence interval 0.94-0.99, P = 0.004) with younger patients being at an increased risk for arrhythmia recurrence.

CONCLUSIONS

Our study demonstrated that only younger age, but not other clinical or electrophysiological parameters including residual slow pathway conduction predicted an increased risk for AVNRT recurrence after slow pathway radiofrequency ablation.

Atrioventricular nodal reentry tachycardia with multiple AH jumps: electrophysiological characteristics and radiofrequency ablation

This article describes the additional use of incremental atrial burst pacing (A1A1) and double atrial extrastimulation with a predefined fast pathway conducted A2 (A1A2A3), rather than single atrial extrastimulation (A1A2) only, to characterize typical atrioventricular nodal reentrant tachycardia (AVNRT). The authors noted an additional 32% of patients had multiple anterograde AV nodal physiology demonstrated when A1A1 or A1A2A3 protocols were deployed compared to more conventional A1A2 protocols. The A2H2max (449 +/- 147 vs 339 +/- 94 ms) and A3H3max (481 +/- 120 vs 389 +/- 85 ms) were higher in 31 patients where multiple jumps in the AV nodal conduction curve were obtained (group 1) compared to 192 patients where only single jump was obtained (group 2) (both P < 0.01). Postablation, the degree of reduction of A2H2max (49%) and A3H3max (50%) in group 1 was greater than in group 2 (38% and 42%, respectively, P < 0.05). In seven of group 1 patients in whom A1A2A3 stimulation was required to reveal multiple jumps, the A2H2max remained unchanged after ablation (237 +/- 89 vs 214 +/- 59, P > 0.05). A3H3max was the only parameter that shortened significantly after ablation. Generally, successful ablation resulted in loss of multiple discontinuities in A1A1/A1H1 or A2A3/A3H3 curves. In conclusion, a combination of A1A2, A1A1, and A1A2A3 are required to fully elucidate AVNRT. Significant shortening of AHmax or loss of multiple jumps after ablation indicates successful elimination of AVNRT in these patients.

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.

Effects of isoproterenol in facilitating induction of slow-fast atrioventricular nodal reentrant tachycardia

This study demonstrates that patients with poorer conduction properties of the anterograde slow and retrograde fast pathways usually need isoproterenol to facilitate induction of atrioventricular nodal reentrant tachycardia. Isoproterenol infusion usually facilitates induction of tachycardia by enhancing the retrograde ventriculoatrial conduction.

Initial onset of accessory pathway-mediated and atrioventricular node reentrant tachycardia after age 65: clinical features, electrophysiologic characteristics, and possible facilitating factors

OBJECTIVE

To evaluate the clinical features electrophysiologic characteristics, and possible facilitating factors in older patients (> or = 65 years) with initial onset of accessory pathway-mediated and atrioventricular (AV) node reentrant tachycardia.

DESIGN

Of the patients undergoing electrophysiologic study and radiofrequency catheter ablation of accessory pathway-mediated and AV node reentrant tachycardia at this institution, patients with initial tachyarrhythmia after age 65 years were compared with those presenting initially before age 30.

SETTING

A tertiary medical center for the general public.

PARTICIPANTS

Sixty-six patients had their initial symptoms after age 65: Group I, 32 patients with accessory pathway-mediated tachycardia, and Group II, 34 patients with AV node reentrant tachycardia. Four-hundred forty patients had their initial symptoms before age 30: Group III, 283 with accessory pathway mediated tachyarrhythmia, and Group IV, 157 with AV node reentrant tachycardia.

INTERVENTION

All patients underwent electrophysiological study to determine the mechanisms of tachyarrhythmia, and radiofrequency catheter ablation for treatment of tachycardia.

RESULTS

(1) Older patients with initial arrhythmia had incidence of critical clinical manifestations, including tachyarrhythmia-related syncope and cardioversion, similar to those with initial arrhythmia at a younger age. (2) Patients in Group III, showed anterograde effective refractory period (ERP) of the AV node (P = .432), longer anterograde ERP of the accessory pathway (P = .004), and greater difference of the anterograde ERP between the AV node and the accessory pathway (D-ERP) (P = .003) similar to patients in group I. In Group II, the ERP and Wenckebach cycle length of the retrograde fast pathway was significantly longer than in Group IV (P = .037 and P < .001, respectively), and a greater percentage of patients in Group II than in Group IV AV node reentrant tachycardia needed isoproteronol to facilitate the induction of reentrant tachycardia (P = .034). (3) Patients in Group I and Group II had a higher incidence of supraventricular and ventricular ectopic activity than those in Group III (P = .002 and P = .005, respectively) and Group IV (P = .024 and P = .012, respectively) in 24-hour ambulatory electrocardiograms.

CONCLUSION

The initial onset of accessory pathway-mediated tachycardia after age 65 may be caused by changes of electrophysiologic properties (greater D-ERP) as well as increased supraventricular and ventricular ectopic activity. Influence of the autonomic nervous system, rather than changes of conduction properties in the AV node, and increase in ectopic activity may contribute to the new onset of AV node reentrant tachycardia in older adults. The choice of antiarrhythmic drugs and radiofrequency ablation require attention to the clinical profile and facilitating factors of reentrant tachycardia in this group of patients.

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.

Efficacy of adenosine in terminating catecholamine-dependent supraventricular tachycardia

The purpose of this study was to determine if adenosine is equally effective in terminating catecholamine-dependent and independent supraventricular tachycardia (SVT). The effect of adenosine on termination of SVT was studied in 21 patients: 12 with atrioventricular (AV) reciprocating tachycardia, and 9 with AV node reentrant tachycardia. Group 1 comprised 13 patients who had SVT induced in the absence of exogenous catecholamines, whereas group 2 comprised 8 who needed isoproterenol (1.6 +/- 0.4 micrograms/min) for induction. There was no statistical difference between the 2 groups regarding age, weight, mean arterial pressure during sinus rhythm and SVT, cycle length of SVT, or norepinephrine and epinephrine levels during sinus rhythm and SVT. Cycle length during sinus rhythm was significantly decreased in group 2. The mean dose of adenosine needed to terminate SVT was 52 +/- 6 micrograms/kg of body weight in group 1, and 61 +/- 12 micrograms/kg in group 2 (p > 0.05). In addition to isoproterenol not altering the minimal dose of adenosine necessary to terminate SVT, there was also no correlation between the dose of adenosine (mean 55 +/- 6 micrograms/kg) of each patient, and the corresponding endogenous epinephrine (273 +/- 59 pg/ml) (r = -0.19) and norepinephrine (400 +/- 58 pg/ml) (r = 0.01) levels during SVT, or cycle length of SVT (323 +/- 9 ms) (r = -0.35). The results show that adenosine is equally effective in terminating catecholamine-dependent and independent SVT; higher adenosine doses should not be needed to manage catecholamine-dependent SVT.(ABSTRACT TRUNCATED AT 250 WORDS)

"AV nodal" reentry: Part I: "AV nodal" reentry revisited

This review is the first of a two-part series of articles on "atrioventricular [AV] nodal reentry." The early clinical literature as well as the experimental studies are reviewed, and more recent morphologic data are presented, with the aim of clarifying whether the reentrant circuit is confined to the AV node, or consists in part of extranodal components. Most of the evidence supports the concept that atrial tissue is an essential link in the reentrant pathway. Arguments will be presented to indicate that within the AV node, the separation between antegrade and retrograde pathways is functional, not anatomical, and that both pathways are in electrotonic contact.

Late onset atrioventricular nodal tachycardia

AV nodal tachycardia may present at any age, but onset in late adulthood is considered uncommon. To evaluate whether onset of AV nodal tachycardias at older age is related to organic heart disease (possibly setting the stage for re-entry due to degenerative structural changes) 32 consecutive patients with symptomatic AV nodal tachycardia were studied. The age at onset of attacks showed a bimodal pattern, with 2 peaks: one between 15 and 35 years (22 patients) and one around 55 years (10 patients). Significantly more older patients had an underlying heart disease (60% versus 14%, P < 0.01), with coronary artery disease in 4 and hypertensive heart disease in 3. Frequent supraventricular ectopic activity was seen during baseline 24-h ambulatory monitoring in all the older patients, versus in only half of the younger patients (P = 0.005). These results indicate that late onset AV nodal tachycardia (i.e. > age 45 years) is not infrequent (33%). The frequent supraventricular arrhythmias on one hand and age-related structural AV nodal changes, potentially enhanced by underlying heart disease on the other, both may contribute to the development of late onset re-entrant AV nodal tachycardia.

Proarrhythmic effects of reactive hypoglycemia

A patient with refractory atrioventricular nodal reentry tachycardia is reported in whom it was possible to document that reactive hypoglycemia was the trigger for aggravation of arrhythmia. Over a period of 6 years, a series of electrophysiological studies revealed that, when the patient was in a hypoglycemic state, initiation of tachycardia was easy and most importantly that tachycardla termination by extra-stimulus pacing always failed. Furthermore, atrial fibrillation was inducible or spontaneously occurred only when the blood glucose level was reduced by IV insulin administration.

Atrioventricular nodal reentrant tachycardia initiated by catecholamine-induced ventricular tachycardia. A case report

The authors describe a patient who experienced recurrent wide-complex and narrow-complex tachycardias during exercise. Electrophysiologic testing in the resting state revealed dual atrioventricular (AV) nodal pathways. AV nodal reentrant tachycardia was inducible by ventricular premature stimulation but was always nonsustained, terminating with block in the anterograde slow pathway. During isoproterenol infusion, runs of ventricular tachycardia occurred frequently, and spontaneously initiated sustained AV nodal reentrant tachycardia. Exercise testing also provoked ventricular tachycardia and sustained AV nodal reentrant tachycardia. The patient was effectively treated with a combination of atenolol and verapamil. This case is an unusual example of a catecholamine-induced arrhythmia, possibly due to triggered activity (exercise-induced ventricular tachycardia), initiating an arrhythmia due to reentry (AV nodal reentrant tachycardia).

Effects of standing on the induction of paroxysmal supraventricular tachycardia

To evaluate the effects of standing on induction of paroxysmal supraventricular tachycardia, electrophysiologic studies were performed in both the supine and standing positions in 22 patients with atrioventricular (AV) reciprocating tachycardia and in 11 with AV node reentrant tachycardia. AV reciprocating tachycardia was induced in 9 of the 22 patients with AV reciprocating tachycardia when they were in the supine position and in 17 when standing. The effective refractory period of the AV node markedly shortened, from 275 +/- 72 to 203 +/- 30 ms (n = 16, p less than 0.005) after standing. The effective refractory period of the accessory pathway shortened slightly, from 293 +/- 75 to 278 +/- 77 ms (n = 8, p less than 0.005), after standing. AV node reentrant tachycardia was induced in 3 of the 11 patients with AV node reentrant tachycardia when they were in the supine position and in 6 when standing. The effective refractory periods of the slow pathway and fast pathway shortened markedly, from 293 +/- 72 to 216 +/- 40 ms (n = 6, p less than 0.025) and from 416 +/- 85 to 277 +/- 50 ms (n = 10, p less than 0.005), respectively, after standing. Plasma norepinephrine levels increased during standing both in patients with AV reciprocating and in those with AV node reentrant tachycardia (n = 11, p less than 0.005, n = 8, p less than 0.005, respectively). In conclusion, standing, which is associated with increased sympathetic tone, changed the electrophysiologic properties of the reentrant circuits, facilitating induction of AV reciprocating tachycardia and AV node reentrant tachycardia.

Electrophysiologic characteristics of manifest and latent retrograde conduction in dogs

Atrioventricular (AV) nodal reentry requires intact retrograde ventriculoatrial (VA) conduction. The purpose of this study was to assess the contribution of various pacing and pharmacologic techniques to uncover VA conduction during apparent unidirectional VA block, and to evaluate the role of several biologic and electrophysiologic factors in concealment of retrograde conduction. Forty healthy dogs underwent catheter-electrophysiologic studies of AV and VA conduction. Group I (20 animals) had intact VA conduction. Group II (six animals) had VA dissociation with ventricular pacing initiated during sinus rhythm, but the presence of VA conduction was confirmed by isoproterenol infusion or by premature ventricular stimulation. In group III (14 animals), the above techniques failed to uncover VA conduction. Eight of 14 group III animals underwent thoracotomy and crushing or freezing of the sinoatrial (SA) node. Ventricular pacing initiated during sinus standstill was associated with 1:1 VA conduction in each experiment. VA conduction time and retrograde Wenckebach cycle length, both in the baseline state and during isoproterenol infusion, were significantly longer in the eight animals in group III than in those in group I. Age, gender, weight, breed, sinus cycle length, and anterograde AV conduction properties were not significantly different between groups I, II, and III. The data suggest that (1) in normal dogs, complete unidirectional VA block probably does not exist; (2) in the presence of anterograde input to the AV node, even sophisticated pacing and pharmacologic maneuvers may fail to uncover the presence of VA conduction; (3) although anterograde input is essential for concealment of VA conduction, the phenomenon is more closely associated with depressed retrograde than with anterograde AV nodal characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of intravenous isoproterenol in the electrophysiologic induction of atrioventricular node reentrant tachycardia in patients with dual atrioventricular node pathways

To assess the role of intravenous isoproterenol for the facilitation of electrophysiologic induction of atrioventricular (AV) node reentrant tachycardia, 20 patients with dual AV node pathways who lacked inducible AV node reentrant tachycardia at control study had a constant isoproterenol infusion administered and underwent repeat study. Six (30%) of 20 patients (group I) had inducible AV node reentrant tachycardia during isoproterenol infusion whereas the other 14 (70%) patients (group II) did not. Paroxysmal supraventricular tachycardia was clinically documented in all 6 group I patients compared to 3 (21%) of 14 group II patients (p = 0.002). The sensitivity and specificity of isoproterenol-facilitated induction of AV node reentrant tachycardia were 67 and 100%, respectively. The isoproterenol-facilitated induction of sustained AV node reentry was mediated by resolution of the weak link in anterograde slow pathway in 2 (33%) patients, in retrograde fast pathway in 3 (50%) and in both anterograde slow and retrograde fast pathways in 1 (17%) patient. Four group I patients were given intravenous propranolol, 0.2 mg/kg body weight, and had complete suppression of isoproterenol-facilitated induction of AV node reentry. Thus, intravenous isoproterenol is a rather sensitive and highly specific adjunct to electrophysiologic induction of AV node reentrant tachycardia in patients with dual AV node pathways but without inducible sustained AV node reentry.

The mechanisms of exercise provocation of supraventricular tachycardia

Treadmill exercise tests, electrophysiologic studies, and isoproterenol infusions were performed in 14 patients with exercise provocable supraventricular tachycardia to delineate the mechanisms of exercise provocation of paroxysmal supraventricular tachycardia. Treadmill exercise tests reproducibly provoked supraventricular tachycardia in all patients. Supraventricular tachycardia similar to that provoked by exercise occurred spontaneously during isoproterenol infusions in 9 of 11 patients tested. The specific supraventricular tachycardia diagnoses of all patients were atrial reentrant tachycardia (two patients), automatic atrial tachycardia (three), atrial flutter-fibrillation (one), atypical junctional tachycardia (two), and orthodromic atrioventricular (AV) reentrant tachycardia (six) as defined by electrophysiologic studies. Various mechanisms of exercise or isoproterenol induction of supraventricular tachycardia were identified. A critical heart rate and/or appropriate sympathetic state was found to provoke all instances of reentrant or automatic atrial tachycardia and atypical junctional tachycardia. A properly timed atrial premature beat provoked five of six cases of AV reentrant tachycardia and the only case of atrial flutter-fibrillation. The remaining case of AV reentrant tachycardia was induced by a ventricular premature beat. In conclusion, the mechanisms of exercise provocation of reentrant or automatic supraventricular tachycardia are multiple and include a critical sinus rate, increased sympathetic tone, and properly timed atrial or ventricular premature beats.

Isoprenaline as an aid to the induction of catecholamine dependent supraventricular tachycardias during programmed stimulation

The effects of isoprenaline on the induction of supraventricular tachycardia by programmed stimulation were studied in 67 patients to see whether they correlated with spontaneous catecholamine mediated symptoms during exercise testing and Holter monitoring. Thirty seven control patients (group 1) did not have spontaneous arrhythmias either during exercise testing or Holter monitoring. Thirty patients (group 2) had documented exercise or stress related supraventricular tachycardias--that is paroxysmal junctional tachycardia (24) or atrial arrhythmia (6). Programmed electrical stimulation was performed before and during the infusion of isoprenaline. No group 1 patient developed sustained supraventricular tachycardia during isoprenaline infusion. In 21 patients with paroxysmal junctional tachycardia and all the patients with atrial arrhythmias electrical stimulation during isoprenaline infusion produced the same tachycardia that had been seen during exercise testing and Holter monitoring. Changes in electrophysiological variables and the concentrations of serum potassium were not associated with the induction of supraventricular tachycardia by isoprenaline. Infusion of isoprenaline safely facilitated the induction of supraventricular tachycardia by programmed stimulation in patients who had spontaneously occurring catecholamine mediated symptoms.

Electrophysiological study of young patients with exercise related paroxysms of palpitation: role of atropine and isoprenaline for initiation of supraventricular tachycardia

Electrophysiological studies were performed in eight patients (four men and four women, mean (SD) age 24 (5) years with paroxysmal attacks of palpitation during or immediately after exercise. Five patients were competitive athletes at college. In two patients spontaneous supraventricular tachycardia during exercise was recorded by ambulatory electrocardiographic monitoring and in another it was induced by treadmill exercise testing. Two had dual atrioventricular nodal pathways, three had manifest atrioventricular accessory pathways, and three had concealed atrioventricular pathways. Programmed stimulation induced sustained supraventricular tachycardia in six patients--in two after intravenous injection of atropine sulphate (1 mg) and in four during infusion of isoprenaline (0.01 microgram/kg/min). In one patient, non-sustained atrioventricular nodal reentrant tachycardia was induced during isoprenaline infusion. In the remaining patient, who had dual atrioventricular nodal pathways, tachycardia was not inducible. AH block prevented maintenance of reentry in five patients. In five patients shortening of the effective refractory period of the atrioventricular node with atropine (one patient) and isoprenaline (four patients) caused sustained supraventricular tachycardia. The present study indicates that treatment with atropine and isoprenaline may be an important factor in the initiation of supraventricular tachycardia in patients with exercise related paroxysms of palpitation.

Effects of upright posture on atrioventricular nodal reentry and dual atrioventricular nodal pathways

The electrophysiologic effects of upright posture (45 degrees upright tilt) were studied in 17 patients with dual atrioventricular (AV) nodal pathways, AV nodal reentry or both. Discontinuous AV nodal conduction curves were observed in 16 patients while supine, but in only 11 patients while upright. Fast pathway refractoriness was shortened: the anterograde fast pathway effective refractory period decreased from 360 +/- 22 to 275 +/- 14 ms (mean +/- standard error of the mean), the anterograde fast pathway block cycle length shortened from 448 +/- 28 to 348 +/- 20 ms and the retrograde fast pathway block cycle length shortened from 425 +/- 29 to 338 +/- 24 ms (all p less than 0.01). The anterograde slow pathway block cycle length shortened from 378 +/- 29 to 316 +/- 17 ms (p less than 0.05). AV nodal reentrant tachycardia was induced in 5 patients while supine (2 sustained, 3 nonsustained) and in 6 patients while upright (4 sustained, 2 nonsustained). Tachycardia cycle length shortened during upright posture, from 413 +/- 30 to 345 +/- 22 ms (p less than 0.01), primarily due to shortened anterograde slow pathway conduction time, from 322 +/- 23 to 268 +/- 20 ms (p less than 0.05). Upright posture thus enhances conduction in patients with dual AV nodal pathways, facilitating AV nodal reentry. Electrophysiologic testing in the upright position may yield additional clinical important information in patients with dual AV nodal pathways.

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)

Unidirectional retrograde atrioventricular nodal block in man: determinants of reversibility by vagal antagonism

The mechanism of unidirectional retrograde atrioventricular (AV) nodal block remains largely unknown. In this study, factors determining the reversal of the unidirectional block by atropine were evaluated in 12 patients who had no demonstrable ventriculoatrial (VA) conduction during ventricular pacing. Six patients demonstrated 1:1 VA conduction after atropine (group I), while the remaining six patients continued to show VA block (group II). During the control study there was no significant difference in the sinus cycle length and AH interval between the two groups. The percent decrease in sinus cycle length after atropine was also similar in groups I and II (i.e., 23 +/- 12 and 26 +/- 6, respectively). The effect on antegrade AV nodal conduction (i.e., the percent decrease in AH interval), however, was significantly greater in group I (24 +/- 9) as compared to group II (9 +/- 5) (p less than 0.004). The onset of VA conduction appeared to correlate with the improvement of antegrade conduction. The ratio of these two effects of atropine (i.e., percent decrease in AH interval to percent decrease in sinus cycle length) was higher when VA conduction was first demonstrated in group I (2.3 +/- 1.1) than at the maximal effect of atropine (1.2 +/- 0.3), reflecting a relatively greater decrease in sinus cycle length. Three of six group I patients redeveloped VA block at maximal effect of atropine. The results suggest a functional and dynamic nature of the unidirectional AV nodal block, possibly caused by vagal influence exaggerating the well-known directional asymmetry of AV nodal conduction in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of inducible tachycardia in patients with syncope of unknown origin: a long-term follow-up

The frequency of inducible tachycardia was assessed in patients presenting with syncope whose noninvasive evaluation did not reveal a cause for syncope. It was also determined whether treatment of tachyarrhythmias during programmed electrical stimulation would prevent recurrence of syncope. One hundred five patients were studied and 97 were followed up for a mean period of 25.8 months. Sixty-eight patients (65%) did not have inducible tachycardia. Sixty of these 68 patients could be followed up; 12 (20%) had recurrent syncope. Ventricular or supraventricular tachycardia was inducible in 37 patients (35%). The frequency of organic heart disease was not higher in this group or in those with inducible ventricular tachycardia as compared with those with inducible supraventricular tachycardia. Three patients with inducible ventricular tachycardia died suddenly or were resuscitated from cardiac arrest, and an additional seven had recurrent syncope; thus, the total recurrence rate was 27%. Of 23 patients undergoing effective therapy as predicted by electrophysiologic testing, 3 (14%) had a recurrent event. Results were significantly different in patients receiving ineffective therapy as judged by electrophysiologic testing. Of 13 patients in this latter category, 7 patients (54%) had recurrence of syncope or cardiac arrest (p less than 0.05). In three patients, recurrence took place a mean of 5 months after cessation of therapy; on resumption of effective therapy, no syncope recurred for 15.6 months (p less than 0.025). Tachycardia is frequently induced in patients with syncope of unknown origin, whether or not organic heart disease is present. Treatment of inducible tachycardia may prevent recurrence of syncope.