Demonstration of dual atrioventricular nodal pathways utilizing a ventricular extrastimulus in patients with atrioventricular nodal re-entrant paroxysmal supraventricular tachycardia

Nonreentrant supraventricular tachycardia misdiagnosed as inappropriate sinus tachycardia

We report a case of a woman with incessant palpitations initially misdiagnosed as inappropriate sinus tachycardia that proved refractory to β-blockers. At the time of electrophysiologic testing, a sustained narrow-complex tachycardia with a 1:2 atrioventricular relationship was repeatedly initiated by a posterior fascicle depolarization induced by means of a timed ventricular extrastimulus. The tachycardia was repeatedly terminated with a timed atrial extrastimulus, which excluded junctional bigeminy and confirmed the diagnosis of nonreentrant supraventricular tachycardia. Catheter ablation of the slow pathway eliminated dual-pathway conduction and tachycardia.

The Electrophysiological Characteristics in Patients with Ventricular Stimulation Inducible Fast-Slow Form Atrioventricular Nodal Reentrant Tachycardia

BACKGROUND

Atrioventricular nodal reentrant tachycardia (AVNRT) can usually be induced by atrial stimulation. However, it seldom may be induced with only ventricular stimulation, especially the fast-slow form of AVNRT. The purpose of this retrospective study was to investigate the specific electrophysiological characteristics in patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation.

METHODS

The total population consisted of 1,497 patients associated with AVNRT, and 106 (8.4%) of them had the fast-slow form of AVNRT and 1,373 (91.7%) the slow-fast form of AVNRT. In patients with the fast-slow form of AVNRT, the AVNRT could be induced with only ventricular stimulation in 16 patients, Group 1; with only atrial stimulation or both atrial and ventricular stimulation in 90 patients, Group 2; and with only atrial stimulation in 13 patients, Group 3. We also divided these patients with slow-fast form AVNRT (n = 1,373) into two groups: those that could be induced only by ventricular stimulation (Group 4; n = 45, 3%) and those that could be induced by atrial stimulation only or by both atrial and ventricular stimulation (n = 1.328, 97%).

RESULTS

Patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation had a lower incidence of an antegrade dual AVN physiology (0% vs 71.1% and 92%, P < 0.001), a lower incidence of multiple form AVNRT (31% vs 69% and 85%, P = 0.009), and a more significant retrograde functional refractory period (FRP) difference (99 +/- 102 vs 30 +/- 57 ms, P < 0.001) than those that could be induced with only atrial stimulation or both atrial and ventricular stimulation. The occurrence of tachycardia stimulated with only ventricular stimulation was more frequently demonstrated in patients with the fast-slow form of AVNRT than in those with the slow-fast form of AVNRT (15% vs 3%, P < 0.001). Patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation had a higher incidence of retrograde dual AVN physiology (75% vs 4%, P < 0.001), a longer pacing cycle length of retrograde 1:1 fast and slow pathway conduction (475 +/- 63 ms vs 366 +/- 64 ms, P < 0.001; 449 +/- 138 ms vs 370 +/- 85 ms, P = 0.009), a longer retrograde effective refractory period of the fast pathway (360 +/- 124 ms vs 285 +/- 62 ms, P = 0.003), and a longer retrograde FRP of the fast and slow pathway (428 +/- 85 ms vs 362 +/- 47 ms, P < 0.001 and 522 +/- 106 vs 456 +/- 97 ms, P = 0.026) than those with the slow-fast form of AVNRT that could be induced with only ventricular stimulation.

CONCLUSION

This study demonstrated that patients with the fast-slow form of AVNRT that could be induced with only ventricular stimulation had a different incidence of the antegrade and retrograde dual AVN physiology and the specific electrophysiological characteristics. The mechanism of the AVNRT stimulated only with ventricular stimulation was supposed to be different in patients with the slow-fast and fast-slow forms of AVNRT.

Effects of adenosine triphosphate on ventriculoatrial conduction--usefulness and problems in assessment of catheter ablation of accessory pathways

The effects of adenosine triphosphate (ATP) on ventriculoatrial (VA) conduction were examined before and after accessory pathway (AP) ablation, with emphasis on assessment of the complication of dual atrioventricular (AV) node pathway. By evaluating the differences in the response to ATP of APs and other pathways, we assessed the usefulness and problems of this method. Of 59 patients who underwent AP ablation, 31 showed pre-excitation and 28 had concealed APs. A dual AV node pathway was found in 9 patients (15.3%) before ablation. After ablation, a dual AV node pathway was newly found in 9 patients. Thus, the total number of patients with a dual AV node pathway was 18 (30.5%). VA conduction over APs was not blocked in 26 of 29 patients, but the remaining 3 APs were blocked transiently by ATP. ATP caused VA block over the AV node in 15 of 16 patients and a dual AV node pathway in all 11 patients. In contrast, VA conduction over the retrograde fast pathway was blocked in 9 of 14 patients with AV node re-entrant tachycardia. ATP has little effect on APs, so observation of the response to ATP provides a more reliable and useful means of evaluating successful ablation. With this method, however, it is important to consider the possibility of the presence of ATP-sensitive APs and ATP-resistant retrograde fast pathways. The influence of ablation-induced injury has not been fully clarified. It is therefore essential to take into account various data, including the comparison between data obtained before and after ablation.

Unusual resetting patterns in response to single atrial extrastimuli during AV junctional reentrant tachycardia

INTRODUCTION

Two unusual resetting patterns were observed in two patients with slow-fast AV junctional reentrant tachycardia (AVJRT) submitted to an electrophysiologic study.

METHODS AND RESULTS

After AVJRT induction, resetting was evaluated by introducing single extrastimuli at progressively shorter coupling intervals from the high right atrium (HRA) and the proximal coronary sinus (CS). An alteration in the return cycle length duration allowed demonstration of resetting. In the first patient, during and AVJRT with a large excitable gap, properly timed extrastimuli delivered both from the HRA and CS simultaneously reset the tachycardia and advanced the H electrogram of the preceding tachycardia beat. In the second patient, both HRA and CS stimulation apparently failed to reset AVJRT (return cycle length unchanged), but, at critical coupling intervals, the cycle length duration of the tachycardia beat following the return cycle was consistently shortened.

CONCLUSION

During slow-fast AVJRT, single atrial stimulation from sites remote to the reentrant circuit may result in unusual resetting patterns. Further studies are required to evidence the full spectrum of resetting in AVJRT.

Use of double ventricular extrastimulation to determine the preexcitation index in atrioventricular nodal reentrant tachycardia

The ability of single paced ventricular beats during tachycardia to penetrate the tachycardia circuit and reset the subsequent atrial depolarization (atrial preexcitation), enabling calculation of the "preexcitation index," can be helpful in analyzing supraventricular tachycardias. However, the ventricular refractory period often prevents ventricular capture of beats with the necessary prematurity to demonstrate atrial preexcitation, particularly in atrioventricular nodal reentrant tachycardia (AVNRT). We hypothesized that the use of double premature stimuli could overcome this limitation. In 25 consecutive patients with either AVNRT or atrioventricular reciprocating tachycardia (AVRT) we attempted to demonstrate atrial preexcitation with single and double ventricular extrastimuli. Whereas atrial preexcitation with a single extrastimulus could only be achieved in 3 of 11 patients with AVNRT, all but 1 patient demonstrated atrial preexcitation with the use of double ventricular extrastimuli. On the other hand, in all but 1 patient with AVRT, atrial preexcitation could be achieved with single and double extrastimuli. A formula was derived for obtaining a preexcitation index with double extrastimuli and shown to correspond closely with the preexcitation index obtained with a single extrastimulus in the 16 patients in whom atrial preexcitation could be achieved with single and double extrastimuli. Thus, this technique significantly enhances the ability to achieve atrial preexcitation and to calculate the preexcitation index in patients with AVNRT, and thus may be useful in deciphering tachycardia mechanism in some patients, as well as being a useful technique in studying the electrophysiological properties of the antegrade and retrograde limbs of AVNRT.

Systematic characterization of the reentrant circuit during atrioventricular nodal reentrant tachycardia

This study was conducted to systematically characterize the excitable gap and conduction properties of the reentrant circuit during atrioventricular nodal reentrant tachycardia (AVNRT). Previous studies have attempted to analyze these properties by introducing single ventricular extrastimuli during tachycardia. These studies have been limited, however, by the inability of single extrastimuli to engage the circuit in the majority of patients studied. Thus, in most cases, the nature of the excitable gap and the conduction properties of the anterograde and retrograde limbs of the circuit during tachycardia remain undefined. In this series, 11 patients with typical AVNRT were studied. During tachycardia, both single and double ventricular extrastimuli (the first extrastimulus acting as a conditioning stimulus) were used to scan diastole. The resetting response of the reentrant circuit, as well as the conduction properties of the retrograde fast and anterograde slow pathways, was recorded and analyzed. Whereas atrial preexcitation and resetting of the reentrant circuit could be demonstrated in only 1 patient with single ventricular extrastimuli, resetting was achieved in all 11 patients with closely coupled double ventricular extrastimuli. Over the full range of coupling intervals used, no retrograde delay in fast pathway conduction could be demonstrated before tachycardia termination or ventricular refractoriness. Penetration of the reentrant circuit resulted in a progressive increasing delay in the anterograde portion of the subsequent return cycle and an increasing resetting response pattern in all cases. Thus, the reentrant circuit during AVNRT demonstrates heterogeneous excitability. While the fast pathway remains fully excitable during tachycardia, the slow pathway uniformly demonstrates decremental conduction, resulting in an increasing resetting response pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic determinants of ventricular rate in human atrial fibrillation

INTRODUCTION

The mechanisms of the ventricular response during atrial fibrillation (AF) remain uncertain. The parameters obtained during an electrophysiologic study, including atrial rates during AF, were analyzed to clarify further the determinants of the ventricular rate during AF.

METHODS AND RESULTS

Thirty patients without manifest preexcitation in whom AF was induced during electrophysiologic study were divided into two groups. Group 1 consisted of 20 patients (ages 55 +/- 10 years) without a dual AV nodal pathway. Group 2 consisted of 10 patients (ages 53 +/- 13 years) having a dual AV nodal pathway. The correlation coefficient between the mean RR interval during AF (mRR) and the mean intra-atrial potential interval during AF (mff) was positive (0.05 [P < 0.05] in group 1 and 0.37 [P = NS] in group 2). The correlation coefficient of the mRR against the functional refractory periods of the AV node (AVFRP) was 0.73 (P < 0.001) in group 1. The correlation coefficients between mRR and the fast AV nodal pathway functional refractory periods and the slow AV nodal pathway effective refractory periods (SPERP) were 0.58 (P = NS) and 0.7 (P < 0.05) in group 2, respectively. The correlation coefficients between mRR against (mff x AVFRP)1/2 in group 1 and (mff x SPERP)1/2 in group 2 were 0.8 (P < 0.001) and 0.72 (P < 0.05), respectively.

CONCLUSIONS

This clinical study did not indicate an inverse relation between the atrial and ventricular rates that had been reported by the previous experimental study. The ventricular rate during AF appeared to be quantitatively related to the atrial rate via AV node function. The importance of the slow pathway in determining the ventricular rate during AF was observed.

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.

Complexities of junctional tachycardias

The atrioventricular junction is a compact area in which most of the known electrophysiologic substrates and mechanisms play a role in the genesis and maintenance of tachyarrhythmias. The purpose of this review is to summarize the data on normal atrioventricular junction anatomy and electrophysiologic function and correlate that information with surface electrocardiographic recordings, intracardiac electrophysiologic data, and interventional data from surgical and catheter techniques. Models of tachycardia mechanisms are proposed for typical and atypical atrioventricular nodal reentrant tachycardia, permanent junctional reciprocating tachycardia, and orthodromic supraventricular tachycardias utilizing "intermediate septal" accessory connections.

Anterograde and retrograde decremental conduction over left-sided accessory atrioventricular pathways in the Wolff-Parkinson-White syndrome

The electrophysiologic properties of left-sided accessory pathways (APs) were examined by cardiac stimulation in 55 patients with Wolff-Parkinson-White syndrome. Atrioventricular and ventriculoatrial conduction times were assessed at the coronary sinus level nearest to the AP and then plotted graphically as a function of coupling interval (for atrial and ventricular refractory period determinations). Of 29 patients with anterograde conduction over the AP, 10 (34%) exhibited decremental conduction. However, only two (7%) had a maximal decrement equal to or more than 30 msec. In the other eight (27%) patients the maximal decrement ranged from 10 to 20 msec. The longest coupling interval at which anterograde decremental conduction was demonstrated ranged from 260 to 440 msec (346 +/- 52 msec). The shortest coupling interval ranged from 240 to 320 msec (265 +/- 24 msec). The anterograde decremental conduction zone was 91 +/- 55 msec. Of 51 patients with retrograde conduction over the AP, 23 (45%) exhibited decremental conduction. However, only eight (15%) had a maximal decrement equal to or greater than 30 msec. In the other 15 (29%) patients the maximal decrement ranged from 10 to 25 msec. The longest coupling interval was 338 +/- 70 msec. The shortest coupling interval was 275 +/- 42 msec. The retrograde decremental conduction zone was 72 +/- 47 msec. There was a significant inverse correlation between the AP effective refractory period and the maximal decrement (r = -0.42; p < 0.05). The comparison of maximal ventriculoatrial conduction time with the maximal decrement revealed a positive correlation (r = 0.63; p < 0.01). These data reveal that minimal decremental conduction over left-sided APs is not an uncommon finding and stress that care should be taken in evaluation of conduction over these connections.

Flecainide single oral dose for management of paroxysmal supraventricular tachycardia in children and young adults

The efficacy of a single oral dose of flecainide to terminate paroxysmal supraventricular tachycardia (PSVT) was evaluated in 25 children and young adults. The subjects were selected from a group of 35 patients with recurrent attacks of PSVT evaluated by means of electrophysiologic study and intravenous electropharmacologic testing with flecainide. In all 25 patients the induced PSVT was stopped by intravenous flecainide and was then no longer inducible or nonsustained. All patients had normal hearts. At least 48 hours after acute intravenous testing, 25 patients underwent electrophysiologic study with a transesophageal catheter and PSVT was induced in all of them: atrioventricular reentrant tachycardia in 16 and atrioventricular nodal reentrant tachycardia in nine. During stable tachycardia, a single oral dose of flecainide (2.9 +/- 0.3 mg/kg; 2.5 to 3.3 mg/kg) was administered. This approach was effective for termination of PSVT in 22 patients. The mean plasma level of flecainide at cessation of tachycardia was 277 +/- 92 ng/ml (150 to 500 mg/ml). All 22 patients who responded were given a single oral dose of flecainide for recurrences of PSVT during follow-up. During a period of 12 +/- 7 months (2 to 27 months) a total of 134 spontaneous episodes of PSVT were reported, and 127 of these episodes were terminated with periodic management. Thus oral periodic flecainide seems useful for management of PSVT in selected patients.

Recovery of retrograde fast pathway excitability in the atrioventricular node reentrant circuit after concealed anterograde impulse penetration

The recovery of the retrograde fast pathway excitability in atrioventricular (AV) node reentry has been difficult to assess with ventricular extrastimulation because of difficulty in achieving sufficiently short intranodal coupling intervals and the potential interposition of "lower common pathway" nodal tissue. To circumvent these methodologic obstacles in 10 patients with inducible AV node reentrant tachycardia, a fixed atrial extrastimulus (A2) coupled to a basic atrial drive (A1) at a cycle length of 500 ms was utilized to reproducibly initiate AV node reentrant echoes. A ventricular extrastimulus (V3) was then introduced after A2 at progressively shorter coupling intervals (A2V3) in an attempt to pre-excite the retrograde fast pathway after concealed anterograde penetration by A2. In six patients, retrograde fast pathway pre-excitation was achieved at critical A2V3 intervals, as evidenced by the appearance of A3 by up to 28 +/- 6 ms in advance of the expected first AV node reentrant echo. In five of the six cases, the V3A3 interval was virtually unaltered (less than or equal to 5 ms decrease) when A2 was omitted. In seven patients, at a critically short A2V3 coupling interval (195 +/- 27 ms ), V3 abruptly failed to elicit A3 and concomitantly abolished all AV node echoes; yet when A2 was omitted, an A3 response returned, with V3A3 identical to previous values.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic and clinical effects of flecainide for recurrent paroxysmal supraventricular tachycardia

The antiarrhythmic effects of flecainide acetate were evaluated in 9 patients with paroxysmal atrioventricular (AV) nodal tachycardia and 17 patients with AV tachycardia. An electrophysiologic study was performed before and after intravenous flecainide acetate, 2 mg/kg body weight, was infused over 15 minutes and was followed by a maintenance infusion of 1.6 mg/kg given over 1 hour to 26 patients and during oral treatment to 15. Treatment with oral flecainide acetate was continued for 14 +/- 5 months. Intravenous flecainide acetate terminated AV nodal tachycardia by blocking the retrograde fast pathway conduction in 7 of 7 patients and AV tachycardia by blocking retrograde conduction in the extranodal pathway in 10 of 10 patients. AV nodal tachycardia and AV tachycardia were noninducible in 8 of 9 patients (90%, p less than 0.001) and 11 of 17 patients (65%, p less than 0.001), respectively. Long-term treatment with oral flecainide acetate suppressed AV nodal tachycardia and AV tachycardia in 8 of 9 patients (90%, p less than 0.001) and 11 of 17 patients (65%, p less than 0.001), respectively. A favorable outcome was associated with block in the accessory pathway after intravenous flecainide acetate and noninducibility during oral treatment. Recurrences preferentially occurred in the younger patients. Flecainide acetate is effective in the acute and long-term management of paroxysmal supraventricular reentry tachycardia by suppressing conduction through the retrograde fast limb of the tachycardia circuit. The clinical effect can be predicted by electrophysiologic testing.

Electrophysiologic effects and clinical efficacy of flecainide in children with recurrent paroxysmal supraventricular tachycardia

The electrophysiologic effects of intravenous flecainide were evaluated in 16 patients aged 9 +/- 4 years: 15 with recurrent paroxysmal supraventricular tachycardia (SVT) and 1 with overt accessory pathway and history of syncope. Eleven patients had an accessory pathway; it was concealed in 2, overt in 9 and in 10 of these patients an orthodromic atrioventricular reentrant tachycardia was induced. Five patients without accessory pathway had an atrioventricular nodal reentrant tachycardia. After intravenous flecainide (1.5 mg/kg) the effective refractory period of the atrium and ventricle increased significantly; the anterograde and retrograde effective refractory periods of the atrioventricular node did not. Flecainide blocked retrograde conduction in the accessory pathway in 4 patients (effective refractory period 245 +/- 41 ms) and anterograde conduction in 8 of 9 patients (effective refractory period 284 +/- 57 ms). The mean cycle length of orthodromic reciprocating tachycardia and atrioventricular nodal reentrant tachycardia increased significantly. After flecainide tachycardia was noninducible in 6 patients with orthodromic reciprocating tachycardia and in 1 with atrioventricular nodal reentrant tachycardia. It was inducible but nonsustained (less than or equal to 30 seconds) in 1 patient with orthodromic reciprocating tachycardia and in 3 with atrioventricular nodal reentrant tachycardia. Fifteen patients continued oral flecainide treatment for 19 +/- 11 months.(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.

Determinants of tachycardia induction using ventricular stimulation in dual pathway atrioventricular nodal reentrant tachycardia

Factors determining tachycardia induction using ventricular stimulation in atrioventricular (AV) nodal reentrant tachycardia utilizing the slow pathway for anterograde and the fast pathway for retrograde conduction were analyzed in 53 patients. Sixteen patients had tachycardia induced by ventricular stimulation. In 15, tachycardia was inducible with incremental ventricular pacing. In 4 of these 15 patients, the tachycardia was also induced with V1V2 testing, while in 11 patients, the tachycardia was not induced with V1V2 testing. In 9 of the latter 11 patients, tachycardia could be induced with V1V2V3 testing, suggesting that the retrograde effective refractory period (ERP) of the right bundle (RB) or the relative refractory period of the His-Purkinje system (HPS) was the limiting factor for tachycardia induction during V1V2 testing. In the remaining one patient, tachycardia was induced with V1V2V3 testing, which provoked a premature ventricular beat, leading to tachycardia induction. Tachycardia was not induced by ventricular stimulation in 37 patients. Factors deterring tachycardia induction in these patients may be related to the retrograde ERP or functional refractory period (FRP) of the HPS, the retrograde ERP of the fast pathway, and an insufficient conduction delay of the circuit (retrograde fast and anterograde slow pathway) to allow anterograde conduction of the slow pathway. In conclusion, AV nodal reentrant tachycardia can be induced by ventricular stimulation in approximately 30% of patients with incremental ventricular pacing and/or ventricular extrastimulus testing. Induction of tachycardia with ventricular stimulation, nevertheless, is frequently limited by the retrograde FRP or ERP of the HPS, the retrograde ERP of the fast pathway, and possibly by an insufficient conduction delay of the circuit.

Entrainment of atrioventricular nodal reentrant tachycardias during overdrive pacing from high right atrium and coronary sinus. With special reference to atrioventricular dissociation and 2:1 retrograde block during tachycardias

Entrainment was attempted during electrophysiologic evaluation of 8 patients with atrioventricular (AV) nodal reentrant tachycardia. Entrainment could be performed while pacing from the high right atrium in 35 of 35 episodes, from proximal coronary sinus in 9 of 21 episodes and from distal coronary sinus in 10 of 20 episodes. The minimal rates required were 8 to 40 beats/min faster than those of the tachycardias. That the atria (as defined in electrophysiologic studies) were not a necessary component of the reentry circuit was suggested by the occurrence, during tachycardia, of short episodes of AV dissociation and of 1 episode of 2:1 retrograde block. For the tachycardia to be interrupted, the pacing rate usually had to be slightly faster than that required to entrain, as well as sufficiently rapid to produce anterograde block of an atrial impulse in the slow AV nodal pathway. Moreover, termination of tachycardia apparently was a function of the pacing site. In some episodes, either because of a proximity effect or because of a preferential input into the upper common pathway, coronary sinus pacing terminated the tachycardia at slower rates or with fewer stimuli than high right atrial pacing. Thus, patients with drug-resistant AV nodal reentrant tachycardias may benefit from recently introduced pacing techniques for termination of tachycardia through entrainment.

Initiation of atrioventricular nodal reentrant tachycardia in patients with discontinuous anterograde atrioventricular nodal conduction curves with and without documented supraventricular tachycardia: observations on the role of a discontinuous retrograde conduction curve

To evaluate factors playing a role in initiation of atrioventricular (AV) nodal reentrant tachycardia utilizing anterogradely a slow and retrogradely a fast conducting AV nodal pathway, 38 patients having no accessory pathways and showing discontinuous anterograde AV nodal conduction curves during atrial stimulation were studied. Twenty-two patients (group A) underwent an electrophysiologic investigation because of recurrent paroxysmal supraventricular tachycardia (SVT) that had been electrocardiographically documented before the study. Sixteen patients (group B) underwent the study because of a history of palpitations (15 patients) or recurrent ventricular tachycardia (one patient); in none of them had SVT ever been electrocardiographically documented before the investigation. Twenty-one of the 22 patients of group A demonstrated continuous retrograde conduction curves during ventricular stimulation. In 20 tachycardia was initiated by either a single atrial premature beat (18 patients) or by two atrial premature beats. Fifteen of the 16 patients of group B had discontinuous retrograde conduction curves during ventricular stimulation, with a long refractory period of their retrograde fast pathway. Tachycardia was initiated by multiple atrial premature beats in one patient. Thirteen out of the remaining 15 patients received atropine. Thereafter tachycardia could be initiated in three patients by a single atrial premature beat, by two atrial premature beats in one patient, and by incremental atrial pacing in another patient. In the remaining eight patients tachycardia could not be initiated. Our observations indicate that the pattern of ventriculoatrial conduction found during ventricular stimulation is a marker for ease of initiation of AV nodal tachycardia in patients with discontinuous anterograde AV nodal conduction curves.

Pathophysiology of arrhythmias: clinical electrophysiology

We have endeavored to relate known electrophysiologic mechanisms of arrhythmia development to clinically occurring arrhythmias, realizing that definitive conclusions can only be surmised at present. Arrhythmias that may be due to disorders of impulse formation include slow atrial, junctional, and ventricular escape rhythms, certain types of atrial tachycardias (such as those produced by digitalis), accelerated junctional (nonparoxysmal junctional tachycardia) and idioventricular rhythms, and parasystole. Arrhythmias that may be due to disorders of impulse conduction include flutter and fibrillation, atrioventricular nodal reentrant tachycardia, reciprocating tachycardias associated with an accessory pathway, sinus nodal reentry, some atrial tachycardias, and many ventricular tachycardias. Understanding the mechanism of the tachycardia, in some instances, helps direct rational therapeutic approaches.

Selective blockade of retrograde fast pathway by intravenous disopyramide in paroxysmal supraventricular tachycardia mediated by dual atrioventricular nodal pathways

Electrophysiological effects of 2 to 2.5 mg/kg iv disopyramide were studied in 10 patients with dual nodal pathways who used a slow pathway for anterograde and a fast pathway for retrograde conduction during paroxysmal supraventricular tachycardia (mean cycle length 308.5 +/- 37 ms; range 260-370 ms). Disopyramide terminated the tachycardia in six cases by production of ventriculoatrial block in five and by sinus overdrive in one. In the remaining four patients cycle length of the paroxysmal supraventricular tachycardia increased significantly from 270 +/- 8 ms to 377.5 +/- 28 ms. In all 10 patients disopyramide depressed retrograde fast pathway conduction manifest by an increase in mean ventricular paced cycle length producing ventriculoatrial block from less than or equal to 296.5 +/- 25 ms to 358 +/- 60 ms, and increase in retrograde fast pathway effective refractory period from less than or equal to 246 +/- 34 ms to 325 +/- 36 ms; the drug abolished ventriculoatrial conduction in two cases. Anterograde slow pathway and fast pathway conduction properties were unchanged after disopyramide (atrial paced cycle length producing AH block 292 +/- 30 to 306.5 +/- 30 ms; effective refractory period of anterograde fast pathway less than or equal to 274 +/- 56 to 284 +/- 44 ms, before and after the drug, respectively) suggesting that anterograde conduction was not crucial either for sustainment or for failure to initiate paroxysmal supraventricular tachycardia after the drug. Paroxysmal supraventricular tachycardia could not be reinduced in six cases after disopyramide. In the other four the ventricular paced cycle lengths producing ventriculoatrial block (318 +/- 41 ms) and effective refractory period of retrograde fast pathway (320 +/- 28 ms) were shorter than the cycle length of reinduced paroxysmal supraventricular tachycardia (367.5 +/- 35 ms) allowing perpetuation of the tachycardia. We conclude that disopyramide breaks atrioventricular nodal re-entrant tachycardia by specific blockade of the retrograde fast pathway though the effect on anterograde atrioventricular nodal conduction is variable.

Electrophysiologic studies of supraventricular tachycardia in children. I. Clinical-electrophysiologic correlations

We investigated the clinical features, surface ECG findings, associated with congenital heart disease (CHD), and status at follow-up in 103 children who underwent intracardiac electrophysiologic evaluation of supraventricular tachycardia (SVT). Age at catheterization ranged from 2 days to 17 years (mean 4.2 years). Diagnosis of the mechanism was based upon standard electrophysiologic techniques. Of the 103 patients, 37 had reentry without a bypass tract (10 sinoatrial node, two atrial muscle, and 25 atrioventricular node); 51 had reentry with a bypass tract (28 manifest Wolff-Parkinson-White [WPW], 18 unidirectional retrograde accessory pathway [URAP], an five Lown-Ganong-Levine); and 15 had an ectopic focus (11 atrial, four junctional). Distinguishing features among the common types are depicted in Table III. We conclude that in children the various mechanisms of SVT (1) are likely to be found in different clinical situations, (2) have a different potential for surgical cure, and (3) have a different prognosis for long-term treatment. Since curative surgery was theoretically possible in 57% of our patients (WPW, concealed WPW, atrial, and junctional ectopic), we recommend electrophysiologic study in any patient who has had frequent recurrences of SVT for longer than 1 year and who requires drugs in addition to digoxin for treatment.

Determinants of sustained slow pathway conduction and relation to reentrant tachycardia in patients with dual atrioventricular nodal transmission

In 24 patients with dual atrioventricular (AV) nodal pathways, multiple incremental atrial pacing studies were performed to obtain atrial (A) to His (H) basic driven (A1 and H1) and extrastimulus (A2 and H2) intervals. Discontinuous A1-A2 and H1-H2 intervals were analyzed for relations between initial coupling times and subsequent A-H responses, and to examine curves of sequential paced cycle lengths (A-A intervals) versus A-H intervals. Seventeen patients showed sustained slow pathway (SP) conduction with demonstration of discontinuous A-A and A-H curves. Sustained SP conduction occurred at critical atrial paced rates when the first paced beat was blocked in the fast pathway (FP) with conduction via the SP. Eleven of these 17 patients had inducible sustained supraventricular tachycardia (SVT). A-H interval during SVT in these 11 patients was closely related to SP A-H interval during atrial pacing at the paced rate comparable to SVT rate (r = +0.89, p less than 0.001). The seven remaining patients showed continuous A-A and A-H curves. In three of these seven patients, sustained SVT was inducible, suggesting ability to sustain SP conduction. All of these three patients had continuous A1-A2 and H1-H2 curves during sinus rhythm so that the first atrial paced beat could not be blocked in the FP for subsequent SP conduction. In the other four of the remaining seven patients, despite block of the first atrial paced beat in the FP with SP conduction, the second paced beat was blocked in the SP so that all subsequent beats resumed FP conduction. In conclusion, sustained SP conduction in patients with dual AV nodal pathways requires (1) an initiating beat being blocked in the FP, (2) a critical rate cycle length, and (3) the ability of SP for repetitive conduction at critical rates.

Observations on spontaneous termination of atrioventricular nodal reentrant tachycardia

Unusual mechanisms of spontaneous termination of atrioventricular (A-V) nodal reentrant tachycardia were observed in two patients during programmed electrical stimulation of the heart. In both patients the mechanism of termination was based on the use of another reentrant pathway than the use used during tachycardia. This pathway was located extranodally in one patient and intranodally in the other. The observations illustrate some of the complexities of reentry in the human heart and how they can play a role in spontaneous termination of A-V nodal tachycardia.

Simultaneous anterograde fast-slow atrioventricular nodal pathway conduction after procainamide

Three patients with paroxysmal supraventricular tachycardia underwent electrophysiologic studies that included His bundle recordings, incremental atrial and ventricular pacing and extrastimulation before and after intravenous infusion of 500 mg of procainamide. In all three patients the tachycardia was induced during atrial pacing or premature atrial stimulation, or both. Two of the three patients had discontinuous atrioventricular (A-V) nodal curves with induction of a slow-fast tachycardia during failure in anterograde fast pathway conduction and one patient had a smooth A-V nodal curve with induction of a slow-fast tachycardia at critical A-H interval delays. After procainamide: (1) in all three patients atrial pacing induced A-V nodal Wenckebach periodicity (cycle length 300 to 400 ms) resulting in simultaneous anterograde fast and slow pathway conduction (one atrial beat resulting in two QRS complexes) and retrograde fast pathway conduction initiating an echo response or a slow-fast tachycardia, or both; (2) in all three patients there was enhanced conduction and shortening of refractoriness of the anteriograde fast pathway and depressed conduction and lengthening of refractoriness of the retrograde fast pathway; and (3) in two patients there was inability to sustain tachycardia because of selective block within the retrograde fast pathway.

IN CONCLUSION

(1) procainamide altered conduction and refractoriness of the anterograde fast and slow pathways so that simultaneous conduction could occur during atrial pacing, resulting in a double ventricular response and a slow-fast echo or tachycardia, or both; and (2) the differential effects of procainamide on anterograde fast and retrograde fast pathways suggests two functional A-V nodal fast pathways, oine for anterograde and the other for retrograde conduction.

Incidence, determinants and significance of fixed retrograde conduction in the region of the atrioventricular node. Evidence for retrograde atrioventricular nodal bypass tracts

Of 104 consecutive patients studied in our laboratory with His bundle electrograms, atrial and ventricular pacing and the atrial and ventricular extrastimulus techniques, 18 patients in whom the existence and utilization of ventriculoatrial (V-A) bypass tracts were excluded demonstrated evidence for fixed and rapid retrograde conduction in the region of the atrioventricular node (A-V) as suggested by the following: (1) short (36 +/- 2 msec [mean +/- standard error of mean]) and constant retrograde H2-A2 intervals during retrograde refractory period studies; (2) significantly (P less than 0.025) better V-A than A-V conduction; (3) significantly (P less than 0.025) shorter retrograde functional refractory period of the V-A conducting system than of the A-V conduction system; and (4) the retrograde effective refractory period of the A=V nodal region was not attainable in any of the 18 patients. Fourteen of the 18 patients (77 percent) had a history of palpitations and 10 (51 percent) had documented paroxysmal supraventricular tachycardia; in 13 (72 percent) single echoes or sustained reentrant supraventricular tachycardia, or both, could be induced during atrial pacing or atrial premature stimulation studies, or both. During tachycardia all these 13 patients had a short (37 +/- 2.4 msec) and constant conduction time in the retrograde limb (H-Ae interval) of the reentrant circuit that was identical to the H2-A2 interval. In conclusion, fixed and rapid retrograde conduction in the region of the A-V node (1) is seen in approximately 17 percent of patients, (2) is associated with a large incidence of reentrant paroxysmal supraventricular tachycardia, and (3) suggests the presence of A-V nodal bypass tracts (intranodal or extranodal functioning in retrograde manner).

The fast-slow form of atrioventricular nodal reentrant tachycardia in children

An unusual form of atrioventricular (A-V) nodal reentry is described as the underlying mechanism for incessant tachycardia in two children. During tachycardia a fast pathway was utilized for anterograde conduction and a slow pathway for retrograde conduction. This is the reverse of the usual form of A-V nodal reentrant tachycardia, in which the slow pathway is utilized for anterograde conduction and the fast pathway for retrograde conduction. One patient had a smooth ventriculoatrial (V-A) conduction curve demonstrating exclusive utilization of the slow pathway for retrograde conduction. The other had a discontinuous V-A conduction curve demonstrating failure of retrograde fast pathway conduction with resultant slow pathway conduction. In both cases the retrograde effective refractory period of the fast pathway was longer than that of the slow pathway, resulting in the establishment of this unusual reentry circuit. Both patients had a superior P axis with a P-R interval shorter than the R-P interval during tachycardia, features described in a significant number of children with incessant tachycardia. This unusual form of reentrant tachycardia can be suggested by its electrocardiographic pattern and is another mechanism for reentrant tachycardia not previously documented in children.

Paroxysmal nonreentrant tachycardias due to simultaneous conduction in dual atrioventricular nodal pathways

Electrophysiologic studies were performed in a 41 year old man for analysis of paroxysmal tachycardias appearing in various electrocardiographic patterns of supraventricular and ventricular bigeminy, junctional and ventricular tachycardia and atrial fibrillation, among others. All these arrhythmias were due to dual atrioventricular (A-V) nodal pathways with simultaneous dual fast and slow conduction of single atrial beats at a normal basic sinus rate. Moderate changes in sinus rate and in fast or slow pathway conduction times, or both, changed the position of the slowly conducted beats between the neighboring two fast conducted beats and resulted in various electrocardiographic manifestations of the conduction disturbance. Different blocks, such as second degree type 1, 2:1, 3:1 and possibly also type II, in one of the two pathways and occasionally aberrant conduction induced even more unusual tracings. After intravenous injection of 25 mg of ajmaline, unexpected lengthening and shortening of the A-H interval occurred, suggesting variable shifts between fast and slow pathway conduction. The incidence of dual A-V nodal pathways is discussed; it was documented in 17 (4.2 percent) of 405 patients studied. A theoretical model of A-V nodal conduction is proposed to explain its normal properties and abnormal patterns.

Retrograde block during dual pathway atrioventricular nodal reentrant paroxysmal tachycardia

There are limited reported data regarding the occurrence of retrograde block during dual pathway atrioventricular (A-V) nodal reentrant paroxysmal tachycardia. This study describes two patients with this phenomenon. The first patient had 2:1 and type 1 retrograde ventriculoatrial block during the common variety of A-V nodal reentrance (slow pathway for anterograde and fast pathway for retrograde conduction). Fractionated atrial electrograms suggested that the site of block was within the atria. The second patient had type 1 retrograde block (between the A-V node and the low septal right atrium) during the unusual variety of A-V nodal reentrance (slow pathway for retrograde and fast pathway for anterograde conduction). The abolition of retrograde block by atropine suggested that the site of block was within A-V nodal tissue. Both cases demonstrate that intact retrograde conduction is not necessary for the continuation of A-V nodal reentrant paroxysymal tachycardia. Case 2 supports the hypothesis that the atria are not a requisite part of the A-V nodal reentrant pathway.

Clinical, electrocardiographic and electrophysiologic observations in patients with paroxysmal supraventricular tachycardia

Seventy-nine patients without ventricular preexcitation but with documented paroxysmal supraventricular tachycardia were analyzed. Electrophysiologic studies suggested atrioventricular (A-V) nodal reentrance in 50 patients, reentrance utilizing a concealed extranodal pathway in 9, sinus or atrial reentrance in 7 and ectopic automatic tachycardia in 3. A definite mechanism of tachycardia could not be defined in 10 patients (including 7 whose tachycardia was not inducible). The three largest groups with inducible tachycardias were compared in regard to age, presence of organic heart disease, rate of tachycardia, functional bundle branch block during tachycardia and relation of the P wave and QRS complex during tachycardia. A-V nodal reentrance was characterized by a narrow QRS complex and a P wave occurring simultaneously with the QRS complex during tachycardia. Reentrance utilizing a concealed extranodal pathway was characterized by young age, absence of organic heart disease, fast heart rate, presence of bundle branch block during tachycardia and a P wave following the QRS complex during tachycardia. Sinoatrial reentrance was characterized by frequent organic heart disease, a narrow QRS complex and a P wave in front of the QRS complex during tachycardia. In conclusion, a mechanism of paroxysmal supraventricular tachycardia could be defined in most patients. Observations of clinical and electrocardiographic features in these patients should allow prediction of the mechanism of the tachycardia.

Dissociation of the atrioventricular node in acute inferior wall myocardial infarction. 2. Longitudinal dissociation (dual atrioventricular nodal pathways)

Four cases of longitudinal dissociation of the atrioventricular node, with dual pathways developing during the acute phase of an inferior wall myocardial infarction (three cases) or during acute ischemia (one case), are presented. In all four cases, two grossly different P-R intervals were recorded, and in two cases, studies of the His bundle confirmed the location of the dissociation within the atrioventrcular node. In one case, premature atrial depolarization caused a bidirectional shifting of P-R intervals, while in the remaining three cases, premature ventricular depolarization (spontaneous or pacemaker-induced) was responsible for this phenomenon. In all cases, evidence of longitudinal dissociation of the atrioventricular node appeared during the acute phase of the infarction or ischemia, and in all of them the phenomenon was transient. This favors the assumption that this phenomenon is of a functional nature, most probably related to the ischemic lesion of the atrioventricular node.

Paroxysmal supraventricular tachycardia with unusual induction. Concealed reentry or automaticity?

In a patient with documented paroxysmal supraventricular tachycardia, earlier atrial extrastimuli consistently induced His-ventricle (H-V) block and "atrioventricular junctional" beats, which were always followed by an echo or paroxysmal supraventricular tachycardia. In "atrioventricular junctional" beats, a V wave was preceded by an H deflection with the same intervals as that of the sinus beat. As for the underlying mechanism of paroxysmal supraventricular tachycardia, two possibilities were considered: (1) concealed atrioventricular nodal reentry, and (2) "triggered automaticity."

Demonstration of bidirectional dual A-V nodal pathways in the same patient

In a patient with documented paroxysmal junctional tachycardia (PJT) electrophysiologic studies were performed using an extrastimulus technique. At an A1-A2 interval of 360 msec, atrial extrastimulus revealed sudden prolongation of an A2-H2 interval from 370 to 540 msec and PJT ensued. This finding was consistent with antegrade dual A-V nodal pathways. On the other hand, at a V1-V2 interval of 540 msec, ventricular estrastimulus showed a jump in ventriculo-atrial (V-A) conduction time with evidence of delay in the A-V node from 285 to 565 msec and a ventricular echo followed. This finding was consistent with retrograde dual A-V nodal pathways. Mechanisms of bidirectional dual A-V nodal pathways are discussed.

Dual effects of concealed A-V nodal conduction in man

An interpolated premature ventricular contraction (PVC) may produce either complete block of the next sinus impulse or depression of A-V nodal conduction with a prolonged A-H interval. When a PVC results in partial depression of a A-V nodal conduction, the effect on subsequent premature atrial stimuli is unknown. The authors have recently observed three patients in which the effect of a premature ventricular stimulus with interpolation on the functional refractory period of the A-V node could be measured. In case one an interpolated PVC sufficient to prolong the A-H interval from 80 to 120 msec was followed by programmed premature atrial stimuli which resulted in no additional A-V nodal delay, and the apparent functional refractory period of the A-V node was reduced from 420 to 330 msec when compared with the atrial extrastimulus technique. In case two a programmed ventricular extrastimulus prolonged the A-H interval in the following sinus beat from 120 to 240 msec; atrial extrastimuli then resulted in only minimal increments in A-V nodal delay and the apparent functional refractory period of the A-V node was reduced from 590 msec. A ventricular extrastimulus in case three increased the resting A-H interval from 60 to 115 msec; conduction of atrial extrastimuli then resulted in a reduction in the functional refractory period of the A-V node from 465 to 400 msec. In each case an interpolated premature ventricular stimulus produced (1) depression of A-V nodal conduction in the ensuing sinus beat A1 and (2) relative facilitation of A-V nodal conduction of a subsequent premature atrial stimulus (A2). The functional refractory period of the A-V node was reduced when compared with the atrial extrastimulus technique alone.