"V-H-A Pattern" as a criterion for the differential diagnosis of atypical AV nodal reentrant tachycardia from AV reciprocating tachycardia

BACKGROUND: During ventricular extrastimulation, His bundle potential (H) following ventricular (V) and followed by atrial potentials (A), i.e., V-H-A, is observed in the His bundle electrogram when ventriculo-atrial (VA) conduction occurs via the normal conduction system. We examined the diagnostic value of V-H-A for atypical form of atrioventricular nodal reentrant tachycardia (AVNRT), which showed the earliest atrial activation site at the posterior paraseptal region during the tachycardia. METHODS: We prospectively examined the response of VA conduction to ventricular extrastimulation during basic drive pacing performed during sinus rhythm in 16 patients with atypical AVNRT masquerading atrioventricular reciprocating tachycardia (AVRT) utilizing a posterior paraseptal accessory pathway and 21 with AVRT utilizing a posterior paraseptal accessory pathway. Long RP' tachycardia with RP'/RR > 0.5 was excluded. The incidences of V-H-A and dual AV nodal physiology (DP) were compared between atypical AVNRT and AVRT. RESULTS: V-H-A was demonstrated in all the 16 patients (100%) in atypical AVNRT and in only 1 of the 21 (5%) in AVRT (P < 0.001). DP was demonstrated in 10 patients (63%) in atypical AVNRT and in 4 (19%) in AVRT (P < 0.05). The sensitivity of V-H-A for atypical AVNRT was higher than that of DP (P < 0.05). Positive and negative predictive values were 94% and 100%, respectively, for V-H-A and 71% and 74%, respectively, for DP. CONCLUSIONS: The appearance of V-H-A during ventricular extrastimulation is a simple criterion for differentiating atypical AVNRT masquerading AVRT from AVRT utilizing a posterior paraseptal accessory pathway.     

Radiofrequency Catheter Ablation of Accessory Pathways During Entrainment of AV Reentrant Tachycardia

Radiofrequency ablation of accessory pathways must sometimes be done during orthodromic atrioventricular reentrant tachycardia when manifest anterograde accessory pathway conduction is absent or retrograde fusion obscures accessory pathway location during ventricular pacing. Unfortunately, abrupt heart rate slowing upon radiofrequency induced termination of atrioventricular reentrant tachycardia often causes catheter dislodgment. We report our experience in circumventing this problem during radiofrequency ablation by using entrainment of atrioventricular reentrant tachycardia. The latter maintains retrograde activation pattern over the accessory pathway while preventing abrupt ventricular rate change. Eight patients (4 men and 4 women, mean age 37.3 ± 17.9) with eleven left-sided accessory pathways were included. Ablation during entrainment was used as the first approach in three patients with concealed accessory pathways and one patient with a bidirectional accessory pathway. In another four patients, ablation during entrainment was used after technical difficulties in ablating during tachycardia. Only 1–3 radiofrequency applications were required to eliminate the accessory pathway using the entrainment technique. The catheter remained stable when accessory pathway conduction was interrupted by radiofrequency current. In conclusion, entrainment of atrioventricular reentrant tachycardia during radiofrequency application is useful for maintaining catheter position for accessory pathway ablation during atrioventricular reentrant tachycardia.     

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。     

One-to-Two Atrioventricular Conduction Causing Nonreentrant Tachycardia: Successful Treatment with Radiofrequency Ablation

The anatomical substrate for AV nodal reentrant tachycardia (AVNRT) is well known and is due to anterograde conduction through a siow conducting pathway and retrograde conduction using a fast conducting path way. In this report, we describe a patient with AVNRT who also presented with frequent episodes of paroxysmal nonreentrant tachycardia due to the occurrence of two conducted ventricular beats for each sinus depolarization. Palpitations and arrhythmias were abolished after radiofrequency ablation of the slow pathway.     

Significance of Ventricular Pacing Site in Manifest Entrainment During Orthodromic Atrioventricular Reentrant Tachycardia with Left-Sided Accessory Pathway

We examined entrainment by ventricular pacing in six patients during orthodromic atrioventricular reentrant tachycardia (AVRT) utilizing a left-sided lateral accessory pathway. Constant fusion and progressive fusion were demonstrated in all patients by left ventricular pacing during tachycardia, but in none of the patients by right ventricular pacing. When left ventricular pacing was performed during AVRT, the antidromic wave front from the pacing impulse (n) collided with the orthodromic wave front of the previous pacing beat (n - 1) within the ventricle, therefore, constant fusion and progressive fusion were demonstrated in the surface electrocardiographic QRS complexes. On the other hand, when right ventricular pacing was performed during orthodromic AVRT, the antidromic wave front from the pacing impulse (n) collided with the orthodromic wave front of the previous paced beat (n - 1) within the normal atrioventricular pathway, and constant fusion and progressive fusion were therefore not demonstrated. These phenomena were explained by the relationship of the ventricular pacing site and the reentrant circuit. This study demonstrates the importance of the pacing site in manifest entrainment of orthodromic AVRT during ventricular pacing.     

Specificity of Retrograde Conduction in Screening for Atrioventricular Nodal Reentrant Tachycardia

Baseline AV conduction properties (antegrade and retrograde) are often used to assess the presence of dual AV nodal physiology or concealed AV accessory pathways. Although retrograde conduction (RET) is assumed to be a prerequisite for AV nodal reentrant tachycardia (AVNRT), its prevalence during baseline measurements has not been evaluated. We reviewed all cases of AVNRT referred for radiofrequency ablation to determine the prevalence of RET at baseline evaluation and after isoproterenol infusion. Results: Seventy-three patients with AVNRT underwent full electrophysiological evaluation. Sixty-six patients had manifest RET and inducible AVNRT during baseline atrial and ventricular stimulation. Seven patients initially demonstrated complete RET block despite antegrade evidence of dual AV nodal physiology. In 3 of these 7 patients AVNRT was inducible at baseline despite the absence of RET. In the other four patients isoproterenol infusion was required for induction of AVNRT, however only 3 of these 4 patients developed RET. One of these remaining patients had persistent VA block after isoproterenol. Conclusions: The induction of AVNRT in the absence of RET suggests that this is not an obligatory feature of this arrhythmia. Therefore, baseline AV conduction properties are unreliable in assessing the presence of AVNRT and isoproterenol infusions should be used routinely to expose RET and reentrant tachycardia.     

The different ablation effects on atrioventricular nodal reentrant tachycardia in children with and without dual nodal pathways

BACKGROUND: Previous studies in adults have shown a significant shortening of the fast pathway effective refractory period (ERP) after successful slow pathway ablation. However, information on atrioventricular nodal reentrant tachycardia (AVNRT) in children is limited. The purpose of this retrospective study was to investigate the different effects of radiofrequency (RF) catheter ablation in pediatric AVNRT patients between those with and without dual atrioventricular (AV) nodal pathways. METHODS: From January 1992 to August 2004, a total 67 pediatric patients with AVNRT underwent an electrophysiologic study and RF catheter ablation at our institution. We compared the electrophysiologic characteristics between those obtained before and after ablation in the children with AVNRT with and without dual AV nodal pathways. RESULTS: Dual AV nodal pathways were found in 37 (55%) of 67 children, including 36 (54%) with antegrade and 10 (15%) with retrograde dual AV nodal pathways. The antegrade and retrograde fast pathway ERPs in children with dual AV nodal pathways were both longer than the antegrade and retrograde ERPs in children without dual AV nodal pathways (300 +/- 68 vs 264 +/- 58 ms, P = 0.004; 415 +/- 70 vs 250 +/- 45 ms, P < 0.001) before ablation. In children with antegrade dual AV nodal pathways, the antegrade fast pathway ERP decreased from 300 +/- 68 ms to 258 +/- 62 ms (P = 0.008). The retrograde fast pathway ERP also decreased after successful ablation in the children with retrograde dual AV nodal pathways (415 +/- 70 vs. 358 +/- 72 ms, P = 0.026). CONCLUSION: The dual AV nodal physiology could not be commonly demonstrated in pediatric patients with inducible AVNRT. After a successful slow pathway ablation, the fast pathway ERP shortened significantly in the children with dual AV nodal pathways.     

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.     

Orthodromic and Antidromic Pacemaker Circus Movement Tachycardia

Pacemaker circus movement tachycardia (PCMT) during DDD pacing is usually sustained by retrograde natural and antegrade electronic atrioventricular (AV) conduction. As PCMT is often initiated by a ventricular premature beat (VPB) one method of its prevention is the programming of an atrial stimulus synchronously following a ventricular extrasystole. A patient is described with preserved antegrade, but without retrograde, i.e., VA, conduction. The optional pacemaker mode of synchronous atrial stimulation following a VPB caused an unusual PCMT sustained by retrograde electronic and antegrade natural AV conduction. This PCMT is similar to a natural reentry tachycardia, the most common variety of which (based on retrograde conduction) is termed antidromic and that which we describe is orthodromic.     

Analysis of Atrioventricular Nodal Reentrant Tachycardia with Variable Ventriculoatrial Block: Characteristics of the Upper Common Pathway

Background: The precise nature of the upper turnaround part of atrioventricular nodal reentrant tachycardia (AVNRT) is not entirely understood.
Methods: In nine patients with AVNRT accompanied by variable ventriculoatrial (VA) conduction block, we examined the electrophysiologic characteristics of its upper common pathway.
Results: Tachycardia was induced by atrial burst and/or extrastimulus followed by atrial-His jump, and the earliest atrial electrogram was observed at the His bundle site in all patients. Twelve incidents of VA block: Wenckebach VA block (n = 7), 2:1 VA block (n = 4), and intermittent (n = 1) were observed. In two of seven Wenckebach VA block, the retrograde earliest atrial activation site shifted from the His bundle site to coronary sinus ostium just before VA block. Prolongation of His-His interval occurred during VA block in 11 of 12 incidents. After isoproterenol administration, 1:1 VA conduction resumed in all patients. Catheter ablation at the right inferoparaseptum eliminated antegrade slow pathway conduction and rendered AVNRT noninducible in all patients.
Conclusion: Selective elimination of the slow pathway conduction at the inferoparaseptal right atrium may suggest that the subatrial tissue linking the retrograde fast and antegrade slow pathways forms the upper common pathway in AVNRT with VA block.     

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.     

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.     

Double Response of the Ventricle During Transient Entrainment in a Common Atrioventricular Nodal Reentrant Tachycardia

We report a patient with slow-fast atrioventricuiar (AV)nodal reentrant tachycardia, in which double ventricuJar response was demonstrated during rapid pacing at cycle length of 300 msec or less from the high right atrium. The determinants of double ventricular response during transient entrainment in the present case were: (1)a crucial conduction delay in the slow pathway; (2)the collision between the activation via the antegrade fast pathway (antidromically)of the last paced beat and the activation via the antegrade slow pathway (orthodromically)of the previous paced beat, instead of the unidirectional block in the slow pathway; and (3)the enhanced AV nodal conduction over the antegrade fast pathway.     

Shortcut Link Between the Fast and Slow Pathways and the Mechanism of Cure in Atrioventricular Nodal Reentrant Tachycardia by Catheter Ablation

The mechanism of cure in AV nodal reentrant tachycardia (AVNRT) by catheter ablation has not been fully clarified. We hypothesized that disruption of a shortcut link between the fast and slow pathways is responsible for the elimination of tachycardia. Results: AVNRT was eliminated in 20 patients by catheter ablation. In five patients (25%; group 1) slow pathway conduction disappeared 1 week after ablation. In six patients (30%; group II), the effective refractory period of the slow pathway was prolonged by more than 50 ms (212 ± 81 ms vs 340 ± 81 ms; P < 0.05). In the remaining nine patients (45%; group III), there was no change in the refractory period (270 ± 65 ms vs 273 ± 74 ms), although tachycardia was not inducible. A shortcut link between the fast and slow pathways was examined by comparing the A-H intervals over the slow pathway during the tachycardia and during atrial pacing at the tachycardia cycle length. Prior to ablation, a shortcut link was assumed in 1 of group I patients, 2 of group II patients, and 8 of group III patients. Of the 9 patients in whom the slow pathway was not impaired after ablation (group III), 8 patients were found to have a shortcut link, while 8 of 11 patients with impairment of the slow pathway after ablation (groups I and II) had no shortcut link between the fast and slow pathways (P < 0.05). Conclusion: In patients with a shortcut link between the fast and slow pathways, slow pathway conduction itself does not need to be impaired to eliminate the AVNRT, whereas in patients without this shortcut link, slow pathway conduction must be impaired.     

Double Ventricular Responses to a Single Atrial Depolarization in a Patient with Dual AV Nodal Pathways

Electrophysiological study was performed in a patient with atrioventricular nodal reentrant tachycardia (AVNRT). Double ventricular responses through dual AV nodal pathways were observed by atrial extrastimulus technique followed by initiation of AVNRT. The difference in conduction time between the slow and fast AV nodal pathways was longer than 320 msec. A ventricular extrastimulus delivered during sinus rhythm, which was not followed by ventriculoatrial conduction, also induced AVNRT. These findings indicated the presence of an antegrade critical delay and retrograde block in the slow AV nodal pathway, criteria necessary for the occurrence of a double ventricular response.     

Latent atriofascicular pathway participating in a wide complex tachycardia: differentiation from ventricular tachycardia

Accessory pathways with anterograde decremental conduction properties usually are characterized by presence of antegrade preexcitation during atrial pacing. We report a 38-year-old man with frequent episodes of palpitation. No evidence of ventricular preexcitation was seen during sinus rhythm or atrial pacing. All electrophysiologic maneuvers were compatible with an antidromic tachycardia using atriofascicular pathway as the antegrade limb and the atrioventricular nodal pathway as retrograde limb. Radiofrequency ablation at recording site of accessory pathway potential resulted in cure of tachycardia with no recurrence during 3-month follow-up. This report indicated that atriofascicular pathway-mediated tachycardia should be considered in differential diagnosis of all cases of wide complex tachycardia with left bundle branch morphology and left axis.     

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.     

Differential diagnosis of slow/slow atrioventricular nodal reentrant tachycardia from atrioventricular reentrant tachycardia using concealed posteroseptal accessory pathway by 12-lead electrocardiography

Slow pathways are used as both antegrade and retrograde conduction pathway in slow/slow atrioventricular nodal reentrant tachycardia (SS-AVNRT), and patients with SS-AVNRT have tachycardia ECGs mimicking atrioventricular reentrant tachycardia using concealed posteroseptal accessory pathway (PS-AVRT). Therefore, SS-AVNRT can be misdiagnosed as PS-AVRT, and the differential diagnosis is clinically important. Standard 12-lead ECGs during tachycardia were analyzed in patients with SS-AVNRT (n = 10) and PS-AVRT (n = 10). All these patients were diagnosed by electrophysiological study and underwent successful catheter ablation. Differences of the RP' intervals (dRP') between V1 and the inferior leads were evaluated. SS-AVNRT had significantly longer RP' intervals measured in V1 (167 +/- 25.2 vs 137 +/- 26.8 ms, SS-AVNRT vs PS-AVRT, respectively, P = 0.02), longer dRP' between V1 and II (dRP'[V1-II], 37 +/- 14 vs 17 +/- 6.7 ms, P = 0.0007), longer dRP'[V1-III] (39 +/- 14 vs 17 +/- 9.9 ms, P = 0.0011), and longer dRP'[V1-aVF] (39 +/- 13 vs 20 +/- 9.5 ms, P = 0.0008). The following criteria were suggested for differential diagnosis of SS-AVNRT from PS-AVRT: dRP'[V1-II] >25 ms (sensitivity and specificity: 80% and 100%, respectively), dRP'[V1-III] >23 ms (90% and 90%), dRP'[V1-aVF] >30 ms (90% and 90%). Differences of the RP' intervals between V1 and the inferior leads in the tachycardia ECGs were useful for differential diagnosis of SS-AVNRT from PS-AVRT.     

Diagnostic Value of Comparison of Ventriculoatrial Interval During Junctional Tachycardia and Right Ventricular Apical Pacing

We postulated that comparison of ventriculoatrial intervals during junctional tachycardia and during right ventricular apical pacing may provide similar diagnostic information to that obtained from the insertion of ventricular extrasystoles during tachycardia. We studied 39 patients with either atrioventricular reentrant tachycardia (AVRT) (23 patients) using a single atrioventricular accessory pathway or atrioventricular nodal reentrant tachycardia (AVNRT) (16 patients). Ventriculoatrial [VA] intervals were measured during tachycardia, during right ventricular apical pacing at the same rate as that of the tachycardia and following a ventricular extrasystole delivered at the minimum reset interval (minimum prematurity of a ventricular extrasystole required to advance the subsequent atrial complex by more than 10 msec). The difference between the minimum VA interval during tachycardia and during ventricular pacing was closely related to both the minimum reset interval (r = 0.92, P less than 0.001) and the difference between the minimum VA interval during tachycardia and following a ventricular extrasystole delivered at the minimum reset interval (r = 0.97, P less than 0.001) in the 23 patients in whom the minimum reset interval could be determined. The ratio between the minimum ventriculoatrial interval during tachycardia and ventricular pacing could be determined in all cases and was between 1.53 and 1.68 in AVRT with right free wall (two patients), 0.94 and 1.29 with anteroseptal (three patients), 0.91 and 1.08 with posteroseptal (five patients) and 0.48 and 0.71 with left free wall (13 patients) pathways, while it was between 0.32 and 0.27 in AVNRT (16 patients). The ratio was more discriminative when corrected for ventricular latency and was also useful when calculated from the high right atrial electrogram. We concluded that comparison of ventriculoatrial intervals during junctional tachycardia and during right ventricular apical pacing can discriminate between the mechanisms of tachycardia and the site of pathway. It provides similar information to that obtained from ventricular extrasystoles during tachycardia with the advantage that it can be determined in all cases.(ABSTRACT TRUNCATED AT 400 WORDS)     

Diagnostic Approach to Narrow Complex Tachycardia with VA Block

Narrow complex tachycardia with VA block is rare. The differential diagnosis usually consists of (1) junctional tachycardia (JT) with retrograde block: (2) AV nodal reentrant tachycardia (AVNRT) with proximal common pathway block; and finally (3) nodofascicular tachycardia using the His-Purkinje system for antegrade conduction and a nodofascicular pathway for retrograde conduction. Analysis of tachycardia onset and termination, the effect of bundle branch block on tachycardia cycle length, and the response to atrial and ventricular premature depolarization must be carefully done. Making the correct diagnosis is crucial as the success rate in eliminating the tachycardia will depend on tachycardia mechanism.