Frequency of spontaneous and inducible atrioventricular nodal reentry tachycardia in patients with idiopathic outflow tract ventricular arrhythmias

OBJECTIVES: We sought to assess the frequency of spontaneous or inducible atrioventricular nodal reentry tachycardia (AVNRT) in patients referred for radiofrequency ablation (RFA) of idiopathic outflow tract ventricular arrhythmias. BACKGROUND: In patients with no obvious heart disease, AVNRT and outflow tract ventricular tachycardia (VT) are the most frequently encountered supraventricular and ventricular tachycardias, respectively. An increased coexistence of the two arrhythmias has been recently suggested. METHODS: In 68 consecutive patients referred for RFA of an idiopathic ventricular outflow tract arrhythmia, a stimulation protocol including repeated bursts of rapid atrial pacing, up to triple atrial extrastimuli during sinus rhythm and rapid ventricular pacing was performed before and after isoproterenol infusion following RFA of the ventricular arrhythmia. In patients with inducible AVNRT, RFA of the slow pathway was performed. RESULTS: Of the 68 study patients, 17 (25%) had either spontaneous AVNRT documented prior to RFA of the ventricular arrhythmia (n = 4) or inducible AVNRT at the time of RFA of the ventricular arrhythmia (n = 13). AVNRT was induced by atrial pacing in 15 (88%) of 17 patients: in 3 patients without isoproterenol and in 12 patients during isoproterenol infusion. Uncomplicated RFA of the slow pathway was successfully achieved in all patients with inducible AVNRT. CONCLUSION: Spontaneous or inducible AVNRT is relatively common in patients with idiopathic outflow tract ventricular arrhythmias. Atrial stimulation, especially when performed after isoproterenol infusion plays a major role in AVNRT inducibility. Although we performed RFA of the slow pathway in patients with inducible AVNRT and no prior tachycardia documentation, the question whether this is mandatory remains unsettled.     

Demonstration of Right and Left Atrial Dissociation by Atrial Rapid Pacing or Extrastimulation During Fast-Slow (Uncommon) Form of Atrioventricular Nodal Reentrant Tachycardia

Some recent works suggest that extranodal atrial fibers may form part of the reenlry circuit in the atrioventricular (AV) nodal reentrant tachycardia (AVNRT). This hypothesis is based on the fact that the perinodal dissection successfully abolished AVNRT while preserving intact AV conduction. Apart from the surgical success, the electrophysiological evidence supporting this hypothesis has not been demonstrated, especially in the uncommon (fast-slow) form of AVNRT. We present some electrophysiological evidence suggesting atrial participation in eight patients with the fast-slow form of AVNRT. During the tachycardia, rapid pacing or extrastimulation was done from the orifice of the coronary sinus (CS) and the right atrium (RA), while recording the electrograms of the CS and the low septal RA. In seven patients, right and left atrial dissociation was demonstrated during pacing from the RA, while in the remaining one this was demonstrated from the CS. The interatrial dissociation will be unlikely if the intranodal reentry circuit connects with the atria via a single upper common pathway. This suggests that the upper turnaround of the reentry circuit involves atrial tissue and that the extranodal accessory pathway with long conduction times may form the ascending limb of the circuit (atrionodal reentry). Alternatively, the reentry circuit is entirely intranodal and two or more connecting pathways are present between the atria and the circuit.     

Familial atrioventricular nodal reentry tachycardia

Dual atrioventricular nodal pathways, the substrate responsible for atrioventricular node reentry tachycardia (AVNRT), are thought to be randomly occurring congenital anomalies. This article describes 14 patients in six families, each with two or three first-degree relatives with paroxysmal supraventricular tachycardia. Electrophysiological evidence of dual atrioventricular nodal pathways was established in all 13 patients studied, AVNRT was induced in 12 (92%), and radiofrequency ablation of the slow pathway was curative in all cases. The data suggest a hereditary contribution to the development of atrioventricular nodal pathways and AVNRT. The pattern of inheritance appears to be autosomal dominant.     

Mechanisms of AV Node Reentrant Tachycardia in Young Patients With and Without Dual AV Node Physiology

Recent advances in electrophysiological mapping and radiofrequency catheter ablation have demonstrated the participation of perinodal atrial tissue or pathways in atrioventricular node reentrant tachycardia (AVNRT). Current concepts of the role of these pathways in the genesis of the various forms of AVNRT continue to evolve. In view of these recent advances, this study investigated the electrophysiology of AVNRT in young patients, and factors potentially associated with variant forms of this arrhythmia. Detailed programmed stimulation and catheter mapping were performed in 35 consecutive young patients with AVNRT. This group consisted of 15 male and 20 female patients, with a mean age of 12.1 ± 4.2 years (range 3–18 years). Of the 35 patients, 23 demonstrated dual AV node physiology, either in response to a critically timed extrastimulus (n = 17) or to rapid pacing (n = 6). The common form (antegrade slow-retrograde fast) of AVNHT was demonstrated in 21 of these 23 patients. Antegrade fast-retrograde slow (n = 1) and antegrade slow-retrograde slow (n = 1) forms of AVNRT were identified in the 2 other patients. In contrast, only 5 of the 12 patients who did not demonstrate dual AV node physiology had the common form of AVNRT (P = 0.03). Eive of these patients also had the slow-slow form of AVNRT, while 1 patient each had a fast-slow and fast-fast form of AVNRT. Patients with dual AV node physiology were older (14.2 ± 2.0 years) and more likely to be female (16 of 23) than patients in whom dual A V node physiology was not identified, where the mean age was 10.6 ± 4.2 years and only 4 of 12 patients were female (P = 0.02 for age and P = 0.07 for gender). These observations suggest that the physiology of AV node reentry may evolve as a function of age, with slow-fast AVNRT prevalent in adolescents. However, absence of dual AV node physiology should not preclude diagnosis of AVNRT in young patients with supraventricular tachycardia, in whom atypical forms of AVNRT may be common.     

房室折返性心动过速合并房室结双径路的射频消融治疗

目的:探讨房室折返性心动过速(AVRT)合并房室结双径路(AVNDP)的电生理特征和射频消融术式的选择。方法:对640例阵发性室上性心动过速(PSVT)进行电生理检查,观察PSVT发作时传导的顺序,然后进行消融治疗。结果:640例PSVT中检出AVRT AVNDP 68例,检出率为10.6%;有8例诱发房室结折返性心动过速,对此类患者进行慢径消融治疗。随访所有经治患者均无复发。结论:AVRT合并AVNDP者阻断房室旁道是消融成功的关键;房室旁道作为"旁观者"时也应作房室旁道消融;如仅有(AH)跳跃但无心动过速者无需接受房室结改良。     

Spontaneous Accelerated Junctional Rhythm: An Unusual but Useful Observation Prior to Radiofrequency Catheter Ablation for Atrioventricular Node Reentrant Tachycardia in Young Patients

Between May 1990 and March 1995, 5 of 29 young patients (ages 4.2–25 years; median 14.1 years) undergoing RF ablation for atrioventricular node reentrant tachycardia (AVNRT) presented with spontaneous accelerated junctional rhythm (AJR) (CL = 500–750 ms), compared to 0 of 58 age matched controls undergoing RF ablation for a concealed AV accessory pathway (P = 0.004). In 3 of the 5 patients with AVNRT and AJR, junctional beats served as a trigger for reentry. During attempted slow pathway modification in the five patients with AVNRT and AJR, AVNRT continued to be inducible until the AJR was entirely eliminated or dramatically slowed. These 5 patients are tachycardia-free in followup (median 15 months; range 6–31 months) with only 1 of the 5 patients continuing to experience episodic AJR at rates slower than observed preablation. Episodic spontaneous AJR is statistically associated with AVNRT in young patients and can serve as a trigger for reentry. Successful modification of slow pathway conduction may be predicted by the elimination of AJR or its modulation to slower rates, suggesting that the rhythm is secondary to enhanced automaticity arising near or within the slow pathway.     

Ten Year Follow-Up After Radiofrequency Catheter Ablation for Atrioventricular Nodal Reentrant Tachycardia in the Early Days Forever Cured,or a Source for New Arrhythmias?

BACKGROUND: Radiofrequency (RF) catheter ablation is highly effective with a low complication rate. However, lesions created by RF energy are irreversible, inhomogeneous, and therefore potentially proarrhythmic. OBJECTIVES: The aim of this study was to examine the magnitude and importance of long-term proarrhythmic effects of RF energy. METHODS AND RESULTS: Between 1991 and 1995, 120 patients underwent RF ablation for atrioventricular nodal reentrant tachycardia (AVNRT). Patient data were collected by contacting patients and/or filling out a questionnaire, and medical files were screened for recurrent, documented arrhythmias, pharmacological treatment, and repeated EP study. Referring cardiologists were asked about recurrences of tachyarrhythmias. Fourteen patients (11%) were lost to follow-up. During a mean follow-up of 10 years, six patients died. Recurrences of AVNRT were not any more observed after 3 years after ablation. A total of 29 patients (24%) suffered from new arrhythmias, 6 from type 1 atrial flutter, 6 from atrial tachycardia, 9 from atrial fibrillation, and finally 16 from symptomatic premature atrial contractions (PACs), needing medical treatment or a combination of these arrhythmias. Nine patients underwent pacemaker implantation, 4 after developing procedural atrioventricular (AV) conduction disturbances, 2 after His ablation for permanent atrial fibrillation, 1 patient for sick sinus syndrome, and another 2 patients after developing late AV block, respectively, 7 and 9 years after ablation. CONCLUSION: During long-term follow-up after RF ablation for AVNRT, no AVNRT recurrences were observed, but 29 patients (24%) suffered from new arrhythmias or late AV block. This potential proarrhythmic effect of RF energy promotes the application of alternative energy sources for ablative therapies for cardiac arrhythmias.     

Inducible atrioventricular nodal reentrant echo behind organic 2:1 infra-hisian block during sinus rhythm

A 77-year-old male patient with an intermittent 2:1 infra-Hisian block during sinus rhythm was presented with dizziness and near-syncope. During electrophysiological (EP) study, dual atrioventricular (AV) nodal pathways and retrograde fast pathway were easily induced by atrial and ventricular programmed stimulation, respectively. A typical slow-fast AV nodal reentrant echo beat also could be demonstrated by single atrial extrastimulation. Atrioventricular nodal reentrant tachycardia (AVNRT) can occasionally exhibit 2:1 AV block. Conversely, AV nodal reentry property had been rarely reported behind 2:1 infra-Hisian block. The EP presentation from this case may support the notion that tissues below the His are not part of the reentrant circuit of AVNRT.     

aVR导联在阵发性室上性心动过速中的鉴别诊断价值

目的分析心电图aVR导联形态在阵发性室上性心动过速中的鉴别诊断价值。方法选取泰达国际心血管病医院行射频消融的室上性心动过速患者157例,男69例,女88例,年龄13~74岁,平均（41.9±19.2）岁,以心内电生理检查结果为金标准,分为慢快型房室结折返性心动过速组（SF-AVNRT组,n=89）和左侧房室旁路参与的房室折返性心动过速组（AVRT组,n=68）,入选者在窦性心律和室上性心动过速时无束支传导阻滞。结果与窦性心律时相比,SF-AVNRT组aVR导联QRS波终末部形态改变（假性r波或粗顿）的发生率73.0%,AVRT组aVR导联QRS波终末部形态改变（假性r波或粗顿）的发生率为1.5%,差异有统计学意义（P〈0.01）;与窦性心律时相比,SF-AVNRT组aVR导联ST段抬高、水平型移行或T波降支切迹的发生率为2.2%,AVRT组aVR导联ST段抬高、水平型移行或T波降支切迹的发生率为89.7%,差异有统计学意义（P〈0.05）。结论与窦性心律时相比,SF-AVNRT和AVRT在aVR导联具有不同的心电图特点,aVR导联QRS波终末部形态和ST段形态对判断室上性心动过速的类型具有重要意义,需高度重视aVR导联在室上性心动过速中的鉴别诊断价值。     

Ablation of Atrioventricular Nodal Reentrant Tachycardia in a Patient with Reversal of Slow and Fast Pathways Inputs into the Atrioventricular Node

We report a case of atrioventricular nodal reentrant tachycardia (AVNRT) coexistent with His bundle anomaly and atrial septal defects. The His‐bundle potential was recorded at the coronary sinus (CS) ostium. Fractionated atrial potentials and an A:V electrogram ratio 1:3 were recorded at the anterior septum of the tricuspid annulus approximately 2 cm from CS ostium. Radiofrequency catheter ablation at the anterior septum of the tricuspid annulus effectively eliminated AVNRT. (PACE 2012; 35:e17–e19)     

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.     

Entrainment to Distinguish Orthodromic Reciprocating Tachycardia from Atrioventricular Nodal Reentry Tachycardia in Children

Background : Studies in adults suggest that after entrainment from the right ventricle, a post‐pacing interval (PPI) minus tachycardia cycle length (TCL), when corrected for atrioventricular node delay (cPPI‐TCL), is useful to distinguish atrioventricular nodal reentry tachycardia (AVNRT) from orthodromic reciprocating tachycardia (ORT), but this has not been evaluated in children. Methods : In 100 children undergoing catheter ablation, entrainment of ORT or AVNRT was performed from the right ventricular apex. The atrial‐His (AH) interval was measured on the return cycle (post‐AH) and during tachycardia just prior to pacing (pre‐AH). The cPPI‐TCL was calculated as (PPI‐TCL) ? (post‐AH ? pre‐AH). In the first 50 children, the best cutoff was identified and then validated in the next 50 children. Results : In the first 50 children, cPPI‐TCL was longer in AVNRT compared with ORT (122 ± 19 ms vs 63 ± 23 ms, P < 0.001). Furthermore, cPPI‐TCL exceeded 95 ms in all AVNRT patients, but was less than < 95 ms in 28 of 29 ORT patients. In the next 50 children, a cPPI‐TCL < 95 ms was 100% specific for ORT; a cPPI‐TCL > 95 ms was 95% specific for AVNRT. There was even greater separation of cPPI‐TCL values comparing AVNRT with ORT utilizing a septal accessory pathway. Conclusions : The cPPI‐TCL is a useful technique to distinguish AVNRT from ORT in children. Our data suggest that in children a cPPI‐TCL < 95 ms excludes AVNRT, while a value > 95 ms is rarely observed in ORT. This technique is particularly useful to distinguish AVNRT from ORT utilizing a septal accessory pathway. (PACE 2010; 469–474)     

Differential Entrainment Distinguishes Atrioventricular Nodal Reentry Tachycardia from Atrioventricular Reentrant Tachycardia

Background: Entrainment from the right ventricular (RV) apex and the base has been used to distinguish atrioventricular reentrant tachycardia (AVRT) from atrioventricular nodal reentry tachycardia (AVNRT). The difference in the entrainment response from the RV apex in comparison with the RV base has not been tested. Methods: Fifty‐nine consecutive patients referred for ablation of supraventricular tachycardia (SVT) were included. Entrainment of SVT was performed from the RV apex and base, pacing at 10–40‐ms faster than the tachycardia cycle length. SA interval was calculated from stimulus to earliest atrial electrogram. Ventricle to atrium (VA) interval was measured from the RV electrogram (apex and base) to the earliest atrial electrogram during tachycardia. The SA‐VA interval from apex and base was measured and the difference between them was calculated. Results: Thirty‐six AVNRT and 23 AVRT patients were enrolled. Mean age was 44 ± 12 years; 52% were male. The [SA‐VA]apex–[SA‐VA]base was demonstrable in 84.7% of patients and measured ?9.4 ± 6.6 in AVNRT and 10 ± 11.3 in AVRT, P < 0.001. The difference was negative for all AVNRT cases and positive for all septal accessory pathways (APs). Conclusion: The difference between entrainment from the apex and base is readily performed and is diagnostic for all AVNRTs and septal APs. (PACE 2010; 1335–1341)     

The effect of ibutilide on retrograde accessory pathway conduction

Ibutilide is a compound with Class III effects marketed for rapid conversion of atrial fibrillation and atrial flutter. The Class III effect is primarily mediated by blockade of the rapid component of the cardiac delayed rectifier of potassium current, Ikr. Ibutilide was used in three patients with concealed accessory pathways during electrophysiological evaluation for ablation of symptomatic atrioventricular reentry tachycardia. Each pathway (mid-septal, left posterior, and left lateral) exhibited a mean retrograde effective refractory period of 240 +/- 20 ms. Each patient had atrioventricular reentry tachycardia that consistently degenerated to recurrent sustained atrial fibrillation. One to two milligrams of intravenous ibutilide converted atrial fibrillation to sinus rhythm and maintained sinus rhythm throughout the procedure. Retrograde accessory pathway conduction was unchanged. Maintenance of sinus rhythm allowed for successful mapping and catheter ablation of the concealed accessory pathways. No direct current cardioversion was needed. In these patients, ibutilide was effective in converting and controlling atrial fibrillation induced by atrioventricular reentry tachycardia without masking retrograde pathway conduction. Antegrade accessory pathway conduction could not be assessed in this study.     

Sustained Slow Pathway Conduction: Superior to Dual Atrioventricular Node Physiology in Young Patients with Atrioventricular Nodal Reentry Tachycardia?

BACKGROUND: Young patients with atrioventricular nodal reentry tachycardia (AVNRT) frequently do not display discrete dual AV node physiology (DAVNP) as classically defined. The purpose of the study was to investigate the prevalence of sustained slow pathway conduction (SSPC; PR > RR during atrial pacing) in young patients with AVNRT and compare it to dual atrioventricular node physiology. METHODS: The presence of SSPC and DAVNP was prospectively assessed before and after radiofrequency catheter ablation in 61 young patients (age 4-23 years) with typical AVNRT. RESULTS: Prior to ablation, 32 (52%) displayed DAVNP, while 46 (75%) displayed SSPC; 7 patients (11%) had neither marker. Patients with DAVNP were older than those without (15 +/- 3 vs 13 +/- 4, P = 0.027) and the prevalence increased with age (38% <13 years, 50% 13-15, 70% >15, P = 0.041), while SSPC showed no age predilection. Patients under 13 years displayed SSPC more commonly than DAVNP (81% vs 38%, P = 0.004). DAVNP persisted after ablation in 10/32 (31%) patients, compared to 6/46 (13%) with persistent SSPC after ablation. The ability to use loss of the marker (present before, absent after ablation) as a surrogate for successful ablation was greater for SSPC than for DAVNP (66% vs 36%, P = 0.001). CONCLUSION: SSPC is more common than DAVNP in young patients with AVNRT. SSPC is eliminated more frequently than DAVNP after acutely successful ablation, and appears to be a better indicator of the substrate for AVNRT. Elimination of SSPC may serve as a useful surrogate endpoint for slow pathway ablation.     

Acute effects of simvastatin to terminate fast reentrant tachycardia through increasing wavelength of atrioventricular nodal reentrant tachycardia circuit

Simvastatin (SV) leads to reduction of ventricular rhythm during atrial fibrillation on rabbit atrioventricular (AV) nodes. The aim of our study was (i) to determine the frequency‐dependent effects of SV in a functional model, and (ii) to assess the effects of SV to suppress experimental AV nodal reentrant tachycardia (AVNRT). Selective stimulation protocols were used with two different pacing protocols, His to atrial, and atrial to atrial (AA). An experimental AVNRT model with various cycle lengths was created in three groups of perfused rabbit AV nodal preparations (n = 24) including: SV 3 μm , SV 7 μm , and verapamil 0.1 μm . SV increased nodal conduction time and refractoriness by AA pacing. Different simulated models of slow/fast and fast/slow reentry were induced. SV caused inhibitory effects on the slow anterograde conduction (origin of refractoriness) more than on the fast anterograde conduction time, leading to an increase of tachycardia cycle length, tachycardia wavelength and termination of slow/fast reentrant tachyarrhythmia. Verapamil significantly suppressed the basic and frequency‐dependent intrinsic nodal properties. In addition, SV decreased the incidence of gap and echo beats. The present study showed that SV in a concentration and rate‐dependent manner increased the AV effective refractory period and reentrant tachycardia wavelength that lead to slowing or termination of experimental fast AVNRT. The direction‐dependent inhibitory effect of SV on the anterograde and retrograde dual pathways explains its specific antireentrant actions.     

Cryoablation of Typical Atrioventricular Nodal Reentrant Tachycardia in Children: Six Years’ Experience and Follow‐Up in a Single Center

Background: Cryoablation is an effective and safe treatment for children with supraventricular tachycardias when the reentry circuit is located near the atrioventricular (AV) junction. We retrospectively reviewed consecutive cryoablation procedures for the treatment of atrioventricular nodal reentrant tachycardia (AVNRT) in children and young adults in a single pediatric center. Methods: From October 2002 to October 2008, cryoablation was attempted in 76 pediatric patients (mean age 11.3 ± 2.4 years, range: 6–16.4 years) with symptomatic typical AVNRT. Cryomapping, used to identify the tissue site for safe arrhythmia ablation, was performed at ?30°C for a maximum of 60 seconds. The efficacy of the cryomapping procedure was assessed in terms of disappearance of dual‐AV node physiology and noninducibility of AVNRT. Results: Cryoablations were from 4 to 8 minutes long at ?75°C. A single “bonus” cryoapplication (?75°C for minimum 6 minutes) was delivered to consolidate the acutely successful cryoablation for 64 consecutive patients. After the cryoablation procedure, patients were assessed at 1, 3, 6, 12, 18, and 24 months (and then every year thereafter) by a clinical evaluation and standard electrocardiogram, Holter monitoring, and exercise stress testing. No permanent cryo‐related complications were reported. Seventy‐four (97.4%) patients were successfully acutely ablated. During a mean follow‐up of 29.5 months (range 2–74 months), five (6.8%) acutely successful pediatric patients experienced arrhythmia recurrence. We did not identify any predictive factors of AVNRT recurrence. Conclusions: Acute and long‐term results demonstrate that cryoablation of AVNRT can be considered a safe and effective procedure in pediatric patients. (PACE 2010; 475–481)     

Clinical Experience with a New Software-Based Antitachycardia Pacemaker for Recurrent Supraventricular and Ventricular Tachycardias

The Intermedics Intertach 262-12 tachycardia reversion pulse generator was implanted in 14 patients (six male, eight female, mean age at implantation 45 +/- 16 years) with recurrent symptomatic tachycardias. Six patients had atrioventricular (AV) nodal reentrant tachycardia, three patients had orthodromic tachycardia with Wolff-Parkinson-White syndrome, two had circus movement tachycardia via a concealed bypass tract, two had ventricular tachycardia, one patient had atrial flutter. Mean duration of symptoms before implantation was 8 +/- 4 years and mean number of antiarrhythmic drug trials was 3.5 +/- 1. The primary tachycardia response made consisted of autodecremental pacing in one patient, burst pacing in two patients, and adaptive scanning of the initial delay or burst cycle length in eleven patients. The secondary tachycardia response mode consisted of autodecremental pacing in four patients, burst pacing in three patients and burst scanning in four patients. Tachycardia response was automatic in all but one patient with ventricular tachycardia. During a follow-up period of 30.5 +/- 10.6 months, one patient with ventricular tachycardia died from a nonarrhythmic cause. Reinterventions were necessary due to electrode fracture in one patient and due to pacemaker software defect in another one. Two patients underwent surgical cure of their arrhythmia: one patient with atrial flutter and one patient with AV nodal reentry tachycardia, 24 months and 11 months postpacemaker implantation, respectively. Four patients required digitalis to prevent pacing induced atrial fibrillation. Other proarrhythmic effects were not encountered. The pacemaker proved to be a versatile system with reliable tachycardia detection and termination functions. It provided a valuable adjunctive therapy in these selected patients.     

Variable Effects of Adenosine on Retrograde Conduction in Patients with Atrioventricular Nodal Reentry Tachycardia

Adenosine has been demonstrated to reliably produce transient block of atrioventricular nodal (AVN) conduction, and has been advocated as a method of differentiating retrograde conduction via the atrioventricular node from accessory pathway conduction. However, the response of retrograde AVN to adenosine in patients with typical atrioventricular nodal reentry tachycardia (AVNRT) remains unclear. We evaluated 13 patients (mean age 45 ± 20 years) with typical AVNRT prior to AVN modification. During right ventricular pacing, a rapid bolus of adenosine (0.2 mg/kg; maximum 18 mg) was administered. Adenosine sensitivity, defined by transient ventriculoatrial block, was observed in six patients, while in seven patients ventriculoatrial conduction was unaffected. An adenosine bolus administered during sinus rhythm or atrial pacing resulted in antegrade atrioventricular block in all the adenosine resistant patients in whom this was performed (n = 6). Comparisons of AVN electrophysiological characteristics between the adenosine sensitive and adenosine resistant patients were performed. There was no difference with respect to ventriculoatrial effective refractory period, ventriculoatrial Wenckebach, AVNRT cycle length, and His to atrial echo interval in AVNRT. However, there was a trend toward a longer antegrade fast pathway ERP in the adenosine sensitive group (P = 0.07). Electrophysiological properties do not predict retrograde AVN adenosine sensitivity. Adenosine does not cause retrograde AVN block in all patients with AVNRT, and therefore cannot reliably distinguish between retrograde conduction via the AVN or an accessory pathway.     

Electrophysiology of inducible atrial flutter in patients with atrioventricular nodal reentrant tachycardia

An association between atrial flutter and atrioventricular nodal reentrant tachycardia (AVNRT) has been observed, but the underlying mechanisms are poorly defined. This issue was therefore investigated by comparing the electrophysiological properties of AVNRT patients with and without inducible atrial flutter and those of patients with a history of flutter. Twenty-nine patients with clinically documented atrial flutter and 104 with AVNRT were studied. Atrial flutter was induced in 38 (37%) AVNRT patients during standardized electrophysiological testing before radiofrequency ablation. The atrial relative refractory periods in AVNRT patients with inducible flutter (260 +/- 30 ms) were significantly shorter than those of either patients with a history of flutter (282 +/- 30 ms; P = 0.02) or AVNRT patients without inducible flutter (284 +/- 38 ms; P = 0.006). The atrial effective refractory periods in AVNRT patients with inducible flutter (205 +/- 31 ms) were shorter than in AVNRT patients without inducible flutter (227 +/- 40 ms; P = 0.01). The maximum AH interval during premature atrial stimulation in patients with clinical flutter (239 +/- 94 ms) was shorter than in AVNRT patients either with (290 +/- 91 ms; P = 0.04) or without inducible flutter (313 +/- 101 ms; P = 0.002). However, no significant differences were found in the maximum AH interval achieved during incremental atrial pacing among different groups. Our data show that a non-clinical flutter could more often be induced in those who had short atrial refractoriness. Despite their anatomical proximity, the slow pathway conduction of AVNRT and the isthmus slow conduction of flutter may be related to different mechanisms.