Author + information
- Received September 4, 1997
- Revision received December 9, 1997
- Accepted December 22, 1997
- Published online March 15, 1998.
- Jiunn-Lee Lin, MDAB,
- Shoei K.Stephen Huang, MD, FACCAB,*,
- Ling-Ping Lai, MDAB,
- Wen-Chin Ko, MDAB,
- Yung-Zu Tseng, MDAB and
- Wen-Pin Lien, MD, FACCAB
- ↵*Dr. Shoei K. Stephen Huang, Department of Internal Medicine, National Taiwan University College of Medicine, Number 1, Section 1, Jen-Ai Road, Room 208, Taipei 10018, Taiwan.
Objectives. We sought to investigate the long-term efficacy of slow-pathway catheter ablation in patients with spontaneous, documented paroxysmal supraventricular tachycardia (PSVT) and dual atrioventricular (AV) node pathways but without inducible tachycardia.
Background. The lack of reproduction of clinical PSVT by programmed electrical stimulation, which is not uncommon in AV node reentrant tachycardia (AVNRT), is a dilemma in making the decision of the therapeutic end point of radiofrequency catheter ablation.
Methods. Twenty-seven patients (group A) with documented but noninducible PSVT and with dual AV node pathways were prospectively studied. Programmed electrical stimulation could induce a single AV node echo beat in 12 patients, double echo beats in 4 patients and none in 11 patients at baseline or during isoproterenol infusion. Of the patients in group A, 16 underwent slow-pathway catheter ablation and 11 did not. The clinical and electrophysiologic characteristics of the 27 patients were compared with those of patients with dual AV node pathways and inducible AVNRT (group B, n = 55) and patients with dual AV node pathways alone without clinical PSVT (group C, n = 47).
Results. During 23 ± 13 months of follow-up, none of the 16 patients with slow-pathway catheter ablation had recurrence of PSVT. However, 7 of the 11 patients without ablation had PSVT recurrence at 13 ± 14 months of follow-up (p < 0.03 by Kaplan-Meier analysis). Compared with groups B and C, group A consisted predominantly of men who had better retrograde AV node conduction and a narrower zone for anterograde slow-pathway conduction.
Conclusions. Slow-pathway catheter ablation is highly effective in eliminating spontaneous PSVT in which the tachycardia is not inducible despite the presence of dual AV node pathways.
The inability to induce clinical paroxysmal supraventricular tachycardia (PSVT) by programmed electrical stimulation often precludes the correct diagnosis of the arrhythmia and makes it difficult to judge the therapeutic end point of radiofrequency catheter ablation. This dilemma is not infrequently encountered in patients with atrioventricular (AV) node reentrant tachycardia (AVNRT) [1–3]. The application of radiofrequency catheter ablation to treat patients with spontaneous but noninducible PSVT and with demonstrated dual AV node pathways has not been well established . Furthermore, its long-term therapeutic benefit is not clear.
In the present study, we intended to test the hypothesis that slow-pathway catheter ablation by radiofrequency current is beneficial for long-term elimination of PSVT recurrence in patients with documented, spontaneous tachycardia with demonstrated dual AV node pathways but without inducible AVNRT.
1.1 Patient Group
Between March 1990 and March 1997, we prospectively studied 27 patients (group A) who had spontaneous, electrocardiographically documented PSVT with the presence of dual AV node pathways but without inducible tachycardia in the electrophysiology laboratory. Group A represented 5.2% of the overall 520 patients receiving radiofrequency catheter ablation for AVNRT at two institutions (National Taiwan University Hospital and University of Massachusetts Medical Center). There were 19 men and 8 women in group A (mean age 42 ± 19 years, range 14 to 74). The associated medical diagnosis was coronary artery disease in two patients and hypertension in three patients. None had accessory pathways, atrial flutter/fibrillation or ventricular tachycardia according to the patient’s history and electrophysiologic study. The clinical PSVT had a mean rate of 184 ± 28 beats/min (i.e., 333 ± 53 ms in cycle length). The frequency of PSVT attacks varied from once a month to twice a year, with most patients having them less than four times a year, for a duration of at least 1 year. All the clinical sustained PSVTs could be terminated by either carotid sinus massage or intravenous verapamil or adenosine. The clinical characteristics of these 27 patients are listed in Table 1.
To distinguish the underlying electrophysiologic mechanism(s), two other groups of patients with dual AV node pathways and different clinical manifestations were included for comparative analysis. Group B consisted of 55 patients (18 men and 37 women; mean age 44 ± 14 years, range 16 to 70) randomly enrolled from the remaining 493 patients receiving radiofrequency catheter ablation for AVNRT in the present study. They all had clinically documented and electrically inducible AVNRT. Group C consisted of 47 patients with dual AV node pathways but without clinical or inducible AVNRT. They were randomly enrolled from a total of 365 patients receiving radiofrequency catheter ablation therapy for accessory pathways (n = 46) or atrial tachycardia (n = 1). None of the 47 patients in group C had any further clinical tachyarrhythmia in a follow-up period of 18 ± 9 months (range 6 to 36).
1.2 Electrophysiologic Study
After obtaining the informed, written consent, the patients were studied in a postabsorptive state. All antiarrhythmic drugs were discontinued for at least 5 half-lives. For the study, standard electrode catheters were positioned at the high right atrium, the His bundle region, the coronary sinus and the right ventricular apex for pacing and recording. Programmed electrical stimulation was performed from the high right atrium and the right ventricle at two driving cycle lengths at minimum (usually 600 and 400 ms) and up to double extrastimuli. If the tachycardia was not inducible, isoproterenol infusion was administered to increase the heart rate by at least 25%. The same stimulation protocol was repeated during isoproterenol infusion and during the washout phase. If the tachycardia was still not inducible, intravenous atropine (1.0 mg) and low right atrial pacing were used in some patients. The stimulation amplitude was two times the diastolic threshold with a pulse width of 2 ms delivered by a digitized stimulator (Bloom Associates). A surface electrocardiogram (ECG) (at least leads I, aVF and V1) and multiple intracardiac tracings were simultaneously displayed and recorded by a multichannel oscilloscope (EVR-110, PPG Biomedical or Cardiolab, Prucker Engineering Inc.). Intracardiac local electrograms were filtered between 30 and 500 Hz and printed at a paper speed of 100 or 200 mm/s.
The clinical tachycardia in the 27 patients in group A was suspected to be AVNRT according to two criteria [5, 6]: 1) a narrow QRS complex or QRS complex with rate-dependent aberrancy, with no discernible P wave (Fig. 1A) or with a small pseudo–S wave in the inferior leads and a pseudo–R′ wave in lead V1(Fig. 1B); and 2) the presence of dual AV node pathways. A single, rarely double, slow–fast AV node reentrant echo beat by atrial stimulation or a fast–slow AV node reentrant echo beat by ventricular stimulation was usually inducible. The presence of dual AV node pathways [1, 2]was defined as prolongation of the AH interval during atrial pacing or extrastimulus or the HA interval during ventricular pacing or extrastimulus for >50 ms with a 10-ms decrease of the coupling interval.
1.3 Radiofrequency Catheter Ablation
Radiofrequency catheter ablation of the slow pathway was attempted after discussion with the patients about the result of electrophysiologic study and the potential risk and benefit of the procedure. The ablation target was guided by both the anatomy and the characteristics of the local electrograms [7, 8]. During application of radiofrequency current, the surface ECG and intracardiac electrograms were continuously monitored. In case of the occurrence of junctional rhythm or tachycardia, atrial overdrive pacing was introduced for assessing AV conduction. The end point of catheter ablation was elimination of the slow-pathway conduction, demonstrated by the disappearance of dual AV node pathways and AV node echo beats. The radiofrequency current was delivered as an unmodulated sine wave of 500 Hz between the 4-mm distal electrode of the ablation catheter (Webster-Cordis or Dr. Osypka GmbH, Grenzach-Wyhlen, Germany) and a large, dispersive patch electrode on the back. Either power-controlled or temperature-monitored radiofrequency energy application was used for cardiac lesion formation. The radiofrequency generators (Radionics 3-C; HAT 200S, Dr. Osypka GmbH, Grenzach-Wyhlen, Germany) are commercially available and equipped with continuous display of power, voltage, current, impedance and temperature.
After the electrophysiologic study with or without concomitant radiofrequency catheter ablation, all 27 patients in group A were followed up monthly at the clinic. In case of recurrent palpitations, ECG documentation by an ambulatory event recorder (Heart Watch, Instromedix), 12-lead ECG or 24-h Holter monitor was required for arrhythmia confirmation. Electrophysiologic study and a possible repeat catheter ablation was performed when indicated clinically.
1.5 Data Analysis
The functional characteristics of the AV node and the fast and slow pathways in these 27 patients (group A) were analyzed before and after isoproterenol infusion and were compared retrospectively with the other two groups of patients (groups B and C). Continuous data are expressed as the mean value ± SD, compared by analysis of variance and the multiple comparison test. Categoric data were compared by the N×M chi-square test. Kaplan-Meier life-table analysis was applied to evaluate the actuarial PSVT-free rate in the 27 group A patients with (n = 16) or without (n = 11) slow-pathway catheter ablation. The difference between curves was analyzed by the log-rank test. For those patients with recurrence of PSVT, the follow-up ended at the time of recurrence. A p value < 0.05 was considered statistically significant.
2.1 Clinical Characteristics (Table 1)
Nineteen of the 27 patients in group A were men, which was in contrast to the dominance of women in group B (37 of 55 patients were women, p = 0.003 vs. group A) or the even distribution of men and women in group C (p = 0.09). Clinically, the PSVT was exercise-provocable in 14 of the 27 patients in group A and in 20 of the 55 patients in group B (p = 0.27). The frequency of PSVT attacks was 4 ± 3 (range 1 to 7) times a year for group A patients and 10 ± 11 (range 3 to 42) (p = 0.007) times a year for group B patients.
2.2 Electrophysiologic Characteristics
The electrophysiologic characteristics of the AV node and the fast and slow pathways in group A patients at baseline and during isoproterenol infusion are listed in Tables 2 and 3⇓and compared with the other two groups of patients with dual AV node pathways.
Compared with the group B patients who had dual AV node pathways and inducible AVNRT, group A patients were characterized by a narrow slow-pathway anterograde conduction zone. The anterograde slow-pathway effective refractory period was longer and the difference between the fast pathway and the slow pathway effective refractory periods was smaller. Also, the difference in the 1:1 AV conduction cycle length between the fast pathway and the slow pathway was narrower in group A patients at baseline and during isoproterenol infusion (Tables 2 and 3).
Compared with the group C patients who had dual AV node pathways without clinical or inducible AVNRT, group A patients had better retrograde ventriculoatrial (VA) conduction at baseline and during isoproterenol infusion (Tables 2 and 3).
Programmed electrical stimulation in the 27 group A patients induced a single AV node reentrant echo beat in 12 patients, double echo beats in 4 and none in 11. Slow-pathway catheter ablation was accepted in 16 patients (14 with single or double echo beats, 2 without an echo beat) and refused in 11 patients (2 with a single echo beat, 9 without an echo beat). There were no immediate or late complications after radiofrequency catheter ablation.
2.3 Long-term Effect of Slow-Pathway Catheter Ablation
During the follow-up period of at least 6 months (mean 23 ± 13, range 6 to 54), none of the 16 group A patients receiving the slow-pathway catheter ablation had recurrence of clinical tachycardia. In contrast, 7 of the remaining 11 group A patients without slow-pathway ablation had recurrence of PSVT during the mean follow-up period of 13 ± 14 months (range 1 to 45). Six of the 7 patients had the recurrence within 9 months (4 patients within 3 months). The benefit of slow-pathway catheter ablation with regard to prevention of PSVT recurrence is confirmed by the Kaplan-Meier life-table analysis (p < 0.03, between patients with slow-pathway ablation and those without it). Four patients with recurrent tachycardia consequently received slow-pathway catheter ablation and remained free of arrhythmia recurrence during subsequent follow-up of 43 ± 17 months (range 26 to 61). The other three patients who had recurrent tachycardia refused catheter ablation and were treated with calcium channel blockers or beta-blockers.
The present study demonstrated that slow-pathway catheter ablation was highly effective in the long-term elimination of PSVT recurrence in patients with dual AV node pathways, who had spontaneous but noninducible supraventricular tachycardia. This specific group of patients consisted predominantly of men who characteristically had a narrow slow-pathway anterograde conduction zone and relatively better retrograde VA conduction, as compared with those with dual AV node pathways plus inducible AVNRT or those with only dual AV node pathways without clinical tachycardia.
3.1 Clinical Features
The presence of dual AV node pathways and spontaneous but noninducible tachycardia is an ambiguous indication for radiofrequency catheter ablation . The long-term benefit of catheter ablation in this group of patients is uncertain. Recently, Bogun et al. first reported the high efficacy of slow-pathway catheter ablation in prevention of PSVT recurrence in seven patients with spontaneous, documented but noninducible supraventricular tachycardia during a follow-up period of 15 ± 10 months. Our study, which has a larger patient group (n = 16) and a longer mean follow-up period (23 ± 13 months, range 6 to 54) largely confirms their observations. Furthermore, our patients are predominantly men and the tachycardias are often exercise provocable, in contrast to the features of patients with inducible AVNRT [7, 8, 10, 11]. Electrophysiologically, this group of patients has excellent anterograde and retrograde AV node conduction but a narrower anterograde slow-pathway conduction zone, which may disturb the initiation of sustained AVNRT by programmed electrical stimulation.
3.2 Noninducibility of AVNRT
The initiation of sustained, common AVNRT requires a critical interaction between the anterograde slow pathway and the retrograde fast pathway [1, 2, 12, 13]. The former determines the spontaneous rate of AVNRT, whereas the latter limits the fastest rate of AVNRT. A poor retrograde fast-pathway conduction generally predicts the low probability of initiating AVNRT . The present study compares the electrophysiologic characteristics between the three groups of patients with dual AV node pathways but variable AVNRT inducibility or spontaneous initiation, and suggests that the electrophysiologic mechanism for the noninducibility of AVNRT is most likely the result of a narrow slow-pathway anterograde conduction zone. The narrow gap in anterograde refractoriness between the fast pathway and the slow pathway, together with the longer anterograde slow-pathway effective refractory period, reduces the chance of sustaining slow-pathway conduction and inducing AVNRT, despite the functional integrity of retrograde fast-pathway conduction in this specific group of patients. The simple addition of isoproterenol or atropine , which mainly improves retrograde fast pathway conduction, is unlikely to recondition the slow-pathway anterograde conduction zone for initiation of AVNRT. Whether the functional heterogeneity of the AV junction in patients with dual AV node pathways is the result of anatomic variation or autonomic nervous imbalance remains unknown [17–19].
3.3 Study Limitations
First, intravenous atropine and pacing from other atrial sites were not routinely added to the stimulation protocol to facilitate AVNRT induction. However, our study used up to double atrial and ventricular extrastimuli at two or more driving cycle lengths before, during and after infusion of isoproterenol. Whether further perturbation of sympathovagal balance would help the induction is uncertain. Second, the majority of the group A patients with inducible single or double echo beats underwent slow-pathway catheter ablation, but few of those without echo beats had the procedure. The effect of the slightly uneven inclusion of the patients on the long-term benefit of the slow-pathway catheter ablation cannot be assessed.
Our study showed that slow-pathway catheter ablation appears beneficial in the elimination of PSVT recurrence in patients who have spontaneous, noninducible tachycardia and who have dual AV node pathways.
We thank Dr. Mei-Huan Wu, Ms. Ying-Hwa Lin and Ms. Yueh-Ju Liao for their assistance in the preparation of this manuscript.
This study was presented in part at the 46th Annual Scientific Session of the American College of Cardiology, Anaheim, California, March 1997.
- atrioventricular node reentrant tachycardia
- paroxysmal supraventricular tachycardia
- Received September 4, 1997.
- Revision received December 9, 1997.
- Accepted December 22, 1997.
- The American College of Cardiology
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