Orthodromic Atrioventricular Reentrant Tachycardia Research Articles

The Impact of Age on the Electrophysiological Characteristics and Different Arrhythmia Patterns in Patients with Wolff-Parkinson-White Syndrome

Information about the impact of age on the electrophysiological characteristics of accessory pathways (APs) in patients with Wolff-Parkinson-White (WPW) syndrome remains limited. A total of 1,885 consecutive patients (mean age 43 ± 17 years, male 61.5%) with WPW syndrome who were referred to the tertiary center for an electrophysiological study and radiofrequency catheter ablation were investigated. The patients were divided into 4 groups based on their age (Group 1: <20; Group 2: 20-39; Group 3: 40-59; Group 4: ≧60 years old). With age, more left-sided APs (53.2%, 67.7%, 71.7%, 75.7%, P < 0.001) and a longer duration of the arrhythmia (4.3 ± 2.8 years, 10.1 ± 7.0 years, 12.4 ± 10.9 years, 14.0 ± 12.4 years, P < 0.001) were noted. The incidence of concealed APs (53.5%, 53.0%, 57.8%, 60.9%, P = 0.01), and orthodromic atrioventricular (AV) reentrant tachycardia (92.4%, 94.2%, 96.5%, 96.3%, P = 0.023) increased with age. The tachycardia cycle length, antegrade (275.5 ± 42.2 ms, 286.7 ± 62.7 ms, 302.5 ± 66.5 ms, 315.2 ± 80.2 ms, P < 0.001) and retrograde AP effective refractory periods (APERPs) (254.0 ± 42.5 ms, 263.3 ± 51.8 ms, 274.5 ± 100.5 ms, 292.7 ± 57.0 ms, P < 0.001), atrial ERP, antegrade AV node effective refractory period (AVNERP), and ventricular effective refractory period (VERP) lengthened as the age increased. The incidence of decremental APs, multiple APs, and a catecholamine response were similar. The duration of the catheter ablation, total fluoroscopy time, acute success rate, complication rate, and incidence of a secondary procedure were similar between the different age groups. The electrophysiological characteristics and pattern of the arrhythmic attack associated with the AP changed with age.

Antidromic His Capture during Entrainment of Orthodromic AVRT

A narrow QRS tachycardia with eccentric atrial activation is presented with features favoring an orthodromic atrioventricular re-entrant tachycardia including an extranodal paraHisian response, and a short corrected post-pacing interval to tachycardia cycle length difference following right ventricular entrainment. However, during entrainment, the H-H interval was entrained by the pacing train several beats prior to the A-A interval which would suggest an atrioventricular nodal re-entry tachycardia. We discuss the diagnosis and its mechanism.

Atrioventricular Nodal Reentrant Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) represents the most common regular supraventricular arrhythmia in humans.1 The precise anatomic site and nature of the pathways involved have not yet been established, and several attempts to provide a reasonable hypothesis based on anatomic or anisotropic models have been made.2 There has been considerable evidence that the right and left inferior extensions of the human atrioventricular (AV) node and the atrionodal inputs they facilitate may provide the anatomic substrate of the slow pathway, and a comprehensive model of the tachycardia circuit for all forms of AVNRT based on the concept of atrionodal inputs has been proposed.2 Still, however, the circuit of AVNRT remains elusive. Recently, time-honored conventional schemes for the diagnosis and classification of the various forms of the arrhythmia have been refuted in part by evolving evidence. Recognition of the various types of AVNRT is important, however, to expedite diagnosis and allow implementation of appropriate ablation therapy without complications. We present an update on AVNRT with a particular emphasis on electrophysiological criteria used for the differential diagnosis of regular, supraventricular tachycardias. Typically, AVNRT is a narrow-complex tachycardia, ie, QRS duration <120 ms, unless aberrant conduction, which is usually of the right bundle-branch type, or a previous conduction defect exists. Tachycardia-related ST depression and RR-interval variation may be seen. RR alternans in AVNRT has been attributed to the proposed model of a figure of 8 reentry with continuous crossing over of antegrade activation through an inferior input to the contralateral superior input via the node.2 In the typical form of AVNRT (slow-fast), abnormal (retrograde) P′ waves are constantly related to the QRS and in the majority of cases are indiscernible or very close to the QRS complex (RP′/RR <0.5). Thus, P′ waves are either masked by the QRS complex or …

To the Editor—Response: Supraventricular tachycardia with delayed atrial depolarization after His-synchronous ventricular stimulation: What is the mechanism?

We thank Dr. Bhargava for his interest in our case.1 We agree that the findings in Figure 1 described by Dr. Bhargava, including S-A – VA interval >85 ms and postpacing interval – tachycardia cycle length (PPI – TCL) >115 ms are highly suggestive of atrioventricular nodal reentrant tachycardia and make orthodromic atrioventricular reentrant tachycardia (AVRT) using a septal accessory pathway unlikely.2 However, it also is true that delayed atrial activation induced by a His-synchronous ventricular extrastimulus is thought to rule in orthodromic reentrant tachycardia using a decremental accessory pathway.

210 Incidence and significance of antidromic tachycardia induction in the Wolff-Parkinson-White syndrome

Electrophysiological study (EPS) is recommended in Wolff-Parkinson-White syndrome (WPW). Induction of orthodromic AV reentrant tachycardia (AVRT) is the most frequent. Atrial fibrillation (AF) induction is associated with the prognosis of WPW. Less is known on the induction of antidromic tachycardia (ATD). The purpose of the study was to determine the clinical and electrophysiological data of patients (pts) with a WPW and inducible ATD. EPS was performed in 637 pts with a WPW either for tachycardias (n=335) or syncope (n=88); other pts were asymptomatic (n=213). In control state (CS), the higher rate conducted through accessory pathway (AP) was measured; programmed atrial stimulation with 1 and 2 extrastimuli was performed. The protocol was repeated after isoproterenol infusion. ATD was induced in 45 pts (7%) (group I). The group was compared to remaining pts without inducible ATD (group II). Group I differed from group II by the following data: female sex was less frequent in group I (29.5%) than in group II (47%)(p<0.01); AP was more frequently left lateral sided in group I (54%) than in group II (38%)(p<0.05). AVRT was induced less frequently in group I (34%) than in group II (57%) (p<0.01); maximal rate conducted through AP was higher in group I (214±51 b/min) than in group II (189±61.5) in CS and after isoproterenol (280±56.5 in group I vs 237±61 in group II) (p <0.001). Some data were similar: age was similar in group I (34±20 years) and II (34.5±17); EPS indications were similar: syncope, reentrant tachycardia, spontaneous AF or asymptomatic WPW were the reasons of evaluation respectively in 16%, 43%, 11%, 25% of group I pts and 14%, 46%, 5.5%, 35% of group II pts (NS); left and right posteroseptal AP, anteroseptal AP, right lateral AP and other locations were similar in both groups; AF was induced as frequently in group I (27%) as in group II (23%). ATD was induced more frequently in men than in women and in pts with a left lateral-sided AP, which conducted more rapidly than in pts without inducible ATD. Clinical presentation, age and AF induction were similar in pts with and without inducible ATD.

Successful Targeted Ablation of the Pathway Potential in the Noncoronary Cusp of the Aortic Valve in an Infant with Incessant Orthodromic Atrioventricular Reentrant Tachycardia

A 4-month-old infant presented with incessant SVT and severe failure to thrive. At EP study, orthodromic-reciprocating tachycardia using an anteroseptal accessory pathway was identified. Detailed mapping on the right atrial septum failed to disclose a distinctly early site of atrial activation or a near-field pathway potential. Mapping in the noncoronary cusp of the aortic valve identified a discrete pathway potential that was successfully targeted for ablation. At 12-month follow-up after the procedure, there had been no recurrence of tachycardia. Myocardial fibers above the aortic valve cusps may constitute the atrioventricular bypass connection and can be identified and targeted for successful ablation even in infants.

Is This Atrial Fibrillation?

A 19-year-old girl was referred to our cardiology department for catheter ablation (isolation of the pulmonary veins) of paroxysmal atrial fibrillation (AF). The diagnosis was made upon a 12-lead ECG of the arrhythmia documented in the emergency room. The ECG showed an irregular tachycardia without wide QRS complexes. Careful assessment revealed the irregularity of the rhythm was a sweep artifact due to a mechanic failure of the ECG-machine to advance the article smoothly. During EP study a concealed anteroseptal accessory pathway causing an orthodromic AV reentrant tachycardia was eliminated by radio-frequency ablation. This example emphasizes the need for careful assessment of an ECG tracing, including printed legends and technical data.

Reversal of the Activation Sequence along the Coronary Sinus during RF Application with a Single Left Lateral Pathway:

A 16-year-old girl with a 4-year history of recurrent supraventricular tachycardia was referred for catheter ablation. A standard 12-lead electrocardiogram (ECG) during sinus rhythm revealed no abnormalities. Invasive electrophysiologic study was performed. Two quadripolar catheters were inserted via femoral venous access and placed in the high right atrium and right ventricle. A decapolar catheter was inserted via the right internal jugular vein into the coronary sinus with the proximal bipole at the os. Programmed atrial stimulation revealed a continuous atrioventricular (AV) node function curve. Right ventricular pacing at different cycle lengths (CLs) showed nondecremental ventriculoatrial (VA) conduction and the earliest atrial activation at the distal coronary sinus (CS). Rapid ventricular stimulation easily and repeatedly induced a regular narrow QRS complex tachycardia with a CL of 300 ms. The activation sequence on the CS leads during tachycardia is distal to proximal (Fig. 1). A diagnosis of orthodromic AV reentrant tachycardia (AVRT) using a left-sided free-wall accessory pathway (AP) was made. The retrograde transaortal approach was used. Due to difficulty in reaching a left anterolateral position beneath the mitral valve, the ablation catheter was positioned supra the mitral valve in a left anterolateral location. Radiofrequency (RF) energy was delivered to the earliest atrial activation site 4 mm above the distal CS catheter electrode at the mitral annulus. After 3 times RF energy application (10 second × 3) during sinus rhythm, another type of tachycardia was induced (Fig. 2). The catheter in CS were placed 1.5-cm distal to the original site. During tachycardia, CS3–4 electrodes showed double atrial potentials with an interval of 40 ms (Fig. 3). What has happened in Figures 2 and 3 and what is the mechanism of the changed tachycardia? Before ablation, tachycardia with a CL of 300 ms and the activation sequence on the CS leads was distal to proximal. After RF energy application, the earliest atrial activation was at the proximal CS electrogram with a reversal of activation sequence along the coronary sinus during tachycardia. The catheter in CS was placed 1.5-cm distal to the original site. CS3–4 electrodes showed double atrial potentials (↑↑) with the earliest atrial activation at the distal CS electrogram (↑) during tachycardia. During left lateral AP ablation, AVRT remained inducible with a change in the retrograde atrial activation sequence after application of radiofrequency energy can suggest a second AP. In our case, a reversal of activation sequence along the coronary sinus with the earliest atrial activation at the proximal CS electrogram was noted after three RF energy deliveries that did not eliminate AVRT. This phenomenon could be explained by the existence of a second septal or right side AP. The arguments against this mechanism are that the tachycardia CL and the VA interval at the ablation catheter remained unchanged during AVRT. This indicated the targeted AP has not been interrupted and there may be conduction block made by RF energy between the lateral AP insertion site and the distal CS electrode. Additionally, the CS3–4 electrodes presented double atrial potentials with the earliest atrial activation at the distal CS electrogram when more lateral positioning of the CS catheter. The double atrial potentials with an interval of 40 ms during AVRT provided direct evidence of intra-atrial conduction block along the mitral valve annulus. Luria et al. reported the phenomenon of intra-atrial conduction block in 11 patients during left AP ablation. They postulated that the area between the left inferior pulmonary vein and the inferolateral mitral annulus might serve as an mitral isthmus.1 Cheng et al. suggested a circumferential bundle of myocardial fibers with the minimum width of 0.8 cm in the inferoposterior left atrium may serve as the underlying anatomic substrate.2 Since the width was in the same order of magnitude as the typical RF lesion size, it is not surprising that a complete mitral isthmus block was made by a limited number of RF energy application, resulting a reversal of activation sequence along the coronary sinus as in this case. The ablation catheter was repositioned lateral to the site of the former attempts with atrial activation 25 ms earlier than the distal CS electrogram. A single application of radio frequency energy interrupted the tachycardia. Ventricular pacing at different CLs showed no VA conduction. Tachycardia could not be induced by programmed electrical stimulation both from the right atrium and ventricle.

Electrophysiological characteristics of orthodromic reentrant tachycardia in patients with Wolf–Parkinson–White syndrome and atrial fibrillation

The aim of this study was to evaluate differences in the electrophysiological features of atrioventricular reentrant tachycardia (AVRT) in patients with Wolf–Parkinson–White syndrome (WPW) associated with or without atrial fibrillation (AF). We included 119 patients with WPW and orthodromic AVRT during electrophysiological study. The patients were divided into two groups; group I with documented episodes of AF ( n = 39, mean age 33.3 ± 11.5 years), and group II without AF ( n = 80, mean age 35.3 ± 13.8). We compared parameters of accessory pathway (AP), atrium and ventricle between two groups and found no significant difference. We next assessed the electrophysiological parameters of AVRT in both groups in terms of conduction times and atrioventricular (AV) activation relations. A significant negative correlation was found in group II between anterograde and retrograde conduction times measured as AV and VA intervals at the site of the earliest atrial activation ( r = − 0.43, P < 0.0001), whereas no significant correlation was seen in group I ( r = − 0.29, P = 0.1). Comparative analysis between two groups revealed significant difference in A–V/V–V index ( P = 0.05). These data suggest the presence of different electrophysiological properties of AP during AVRT in only few respects in patients with AF compared to those without it.

Left Ventricular Pseudoaneurysm Following a “POP” Phenomenon

A 56-year-old man was referred to our hospital for a catheter ablation of paroxysmal supraventricular tachycardia. An echocardiogram on admission revealed no abnormalities. During an electrophysiological study, the clinical tachycardia was induced by programmed atrial stimuli, and we diagnosed it as an orthodromic atrioventricular reentrant tachycardia (AVRT) that utilized a posteroseptal concealed accessory pathway as the retrograde conduction limb. Via a retrograde aortic approach, a 4 mm tip ablation catheter was inserted from the femoral artery, and an RF application was then delivered using the temperature control mode, limited to 60◦C. Immediately after delivering the RF application, the retrograde conduction via the accessory pathway was eliminated. However, soon after that, the patient’s blood pressure fell rapidly, following an audible “POP.” We promptly diagnosed it as an acute cardiac tamponade, and thus reversed

Entrainment from the para-Hisian region for differentiating atrioventricular node reentrant tachycardia from orthodromic atrioventricular reentrant tachycardia

The difference between the stimulus-atrial and ventriculo-atrial intervals (SA-VA) and between the post-pacing interval and the tachycardia cycle length (PPI-TCL) during entrainment from the right ventricular apex distinguishes atrioventricular node reentrant (AVNRT) from orthodromic atrioventricular reentrant tachycardia (AVRT). We hypothesized that these features still apply when entrainment is performed from the para-Hisian region. Forty-seven supraventricular tachycardias (34 AVNRT/13 AVRT) were included. The SA-VA and PPI-TCL were obtained in all patients by using two right-sided diagnostic catheters. In 24 of them, these measurements were also performed upon His-bundle capture during entrainment. A paced QRS widening of >or=40 ms during entrainment, when compared with the tachycardia QRS width, identified absence of His-bundle capture, P < 0.001. A SA-VA >75 ms distinguished AVNRT from AVRT, P < 0.001 (sensitivity/specificity 97%/100%). A PPI-TCL >100 ms was diagnostic of AVNRT, P < 0.001 (sensitivity/specificity 97%/92%). Upon His-bundle capture, the SA-VA and PPI-TCL shortened in AVNRT (121 +/- 23 to 66 +/- 24 ms; 139 +/- 30 to 85 +/- 31 ms, respectively, P < 0.001) and no longer differentiated AVNRT from AVRT. Para-Hisian entrainment without His-bundle capture distinguishes AVNRT from AVRT with the advantage of using only two diagnostic catheters.

A new algorithm for concealed accessory pathway localization using T-wave-subtracted retrograde P-wave polarity during orthodromic atrioventricular reentrant tachycardia

AP localization can be predicted by analyzing the polarity of the delta wave, QRS polarity, and R/S ratio in patients with Wolff-Parkinson-White syndrome. However, the estimation of AP location is limited in patients with concealed pathways during atrioventricular reentrant tachycardias (AVRT). Thus, we analyzed retrograde P-wave polarity during orthodromic AVRT and developed an algorithm to predict the localization of concealed accessory pathways (AP). A total number of 131 patients with a single AP and inducible orthodromic AVRT were included. The initial 61 patients were analyzed retrospectively for algorithm development, whereas 70 patients were evaluated prospectively. The retrograde P-wave polarity was analyzed by subtracting the superimposing T-wave during orthodromic AVRT using custom-designed software. Four leads of the surface electrocardiogram (ECG) were identified to accurately distinguish AP locations assigned to four different regions around each AV annulus: I, aVR, aVL, and V(1). Lead V(1) was used to differentiate right (negative or isoelectric) from left (solely positive) APs. Retrograde P-wave in lead I was negative in left posterior APs exclusively and became more positive with an AP location shifting towards right anterior. P-wave polarity in lead aVR demonstrated a shift from a positive polarity from left APs to isoelectric in right APs. The opposite direction (shift from positive to isoelectric) was observed for lead aVL. The subsequently developed algorithm for concealed AP localization using these surface ECG leads demonstrated a high sensitivity, specificity, and positive predictive value particularly for common AP localizations (left posterior and inferior, and right septal) when applied in a prospective fashion. Concealed AP localization can be accurately predicted by the analysis of retrograde P-wave polarity during orthodromic AVRT using the algorithm derived from the presented study.

QRS alternans and cycle length oscillation during narrow QRS tachycardia

Pre-excitation with R waves greater in amplitude than S waves in V1 and a positive delta wave in inferior leads are consistent with antegrade conduction over a left antero-lateral accessory pathway. In the presence of an accessory pathway, the most likely mechanism of the narrow QRS tachycardia is an orthodromic atrio-ventricular (AV) re-entrant tachycardia. The timing of the discrete P-wave visible during tachycardia at the beginning of the T-wave, best seen in lead V1 …

Orthodromic Atrioventricular Reentrant Tachycardia Masquerading as Atrial Fibrillation

A 17-year-old boy with a heart rate of 210 beats per minute was referred to our department for catheter ablation to treat his paroxysmal supraventricular tachycardia. The 12-lead electrocardiogram (ECG) was normal at baseline. Cardiac electrophysiologic study was performed after the informed consent was obtained. There was retrograde conduction via the atrioventricular (AV) node and the bypass tract. Irregular narrow QRS tachycardia was induced by programmed electrical stimulation (Fig. 1). During the tachycardia, there was a stable 1:1 ventriculoatrial (VA) relation and the same retrograde atrial activation sequence was seen with a fixed VA interval of 100 ms at the distal coronary sinus. Variations in the AH interval preceded the respective changes in the subsequent ventricular cycle length [the relative risk (RR) interval]. Catheter ablation of the concealed left free wall bypass tract was successfully done. Because there were AH jump and two AV nodal echo beats with the patient under isoproterenol infusion, ablation of the slow pathway was also performed. He remained free of palpitations during a 6-months follow-up period after the procedure. The differential diagnosis of irregular narrow QRS tachycardia includes atrial fibrillation, atrial tachycardia or flutter with variable AV block and a sinus rhythm with a double ventricular response. The dual AV node physiology and changes in the AV node refractoriness in this patient were attributed to the cycle length alternation during the atrioventricular reentrant tachycardia. Orthodromic AV reentrant tachycardia with marked cycle length alternations can mimic atrial fibrillation and it should be included in the differential diagnosis of irregular narrow QRS tachycardia.

Differentiating atrioventricular nodal reentrant tachycardia from atrioventricular reentrant tachycardia by ΔHA values during entrainment from the ventricle

Differentiating atrioventricular nodal reentrant tachycardia (AVNRT) from orthodromic atrioventricular reentrant tachycardia (AVRT) can be difficult. The His bundle and atria are activated sequentially over the AV node during entrainment of AVNRT from the ventricle but simultaneously during supraventricular tachycardia (SVT). They are activated in parallel during entrainment of AVRT but sequentially during SVT. The purpose of this study was to test the hypothesis that a DeltaHA (HA((entrainment)) - HA((SVT))) cutoff value of 0 reliably differentiates AVNRT from AVRT. Of 61 patients undergoing electrophysiologic evaluation for paroxysmal SVT, retrograde His-bundle potentials were recorded in 57 (93%) and entrainment performed in 49 (34 AVNRT, 15 AVRT). DeltaHA values during entrainment from the ventricle were significantly longer during AVNRT than AVRT (31 +/- 24 ms vs -38 +/- 31 ms, P <.001). All DeltaHA values were positive (minimum: 3 ms) for AVNRT and negative (maximum: -2 ms) for AVRT. DeltaHA of 0 had sensitivity, specificity. and positive predictive value of 100% for correct diagnosis. The DeltaHA criterion during entrainment of tachycardia from the ventricle reliably differentiates AVNRT (positive values) from AVRT (negative values).

Limited Dose-Effect Relationship of Adenosine for Detection of Atrioventricular Nodal Duality in Patients with Supraventricular Tachycardias

Objective: The purpose of the study was to test the dose-effect relationship of adenosine for the diagnosis of dual atrioventricular (AV) nodal physiology in patients presenting with supraventricular tachycardia. Subjects and Methods: The study population consisted of 57 patients (mean age 50 ± 14 years; 36 females, 21 males) with palpitations related to supraventricular tachycardia. Adenosine was injected as bolus during sinus rhythm at rest in order to unmask dual AV nodal physiology by a PR jump on surface ECG (defined as a sudden increase by ≧50 ms measured from the onset of the P-wave to the R-wave between two consecutive sinus beats). According to a stepwise clinical approach, adenosine was administered as bolus in incremental dosages (6 mg followed by 12 mg, if necessary up to 18 mg). Once a PR jump ≧50 ms or a high-grade AV block was noted on surface ECG, the injection was stopped at that dose. Results: A significant PR jump was noted after injection of 6 mg (n = 21, 99 ± 30 ms) or 12 mg (n = 13, 94 ± 35 ms), but not after 18 mg (n = 4, 35 ± 10 ms) adenosine. Provocation of temporary first-grade AV block (n = 13) was associated with the longest increment of PR interval, whereas high-grade AV block (n = 36) produced a significantly shorter PR jump (105 ± 35 vs. 65 ± 40 ms, p = 0.0024). Electrophysiological study and ablation were performed in 37 highly symptomatic patients. AV nodal reentrant tachycardia was diagnosed in 33 patients and orthodromic AV reentrant tachycardia in 4 patients. Conclusion: The adenosine test was characterized by a reverse dose-effect relationship as far as identification of AV nodal duality was concerned.

Decremental Ramp Atrial Extrastimuli Pacing Protocol for the Induction of Atrioventricular Nodal Re‐entrant Tachycardia and Other Supraventricular Tachycardias

The primary aim of this study was to evaluate the utility of decremental ramp atrial extrastimuli pacing protocol (PRTCL) for induction of atrioventricular nodal re-entrant tachycardia (AVNRT), and other supraventricular tachycardias (SVTs), compared to standard (STD) methods. The study cohort of 121 patients (age 57.51 +/- 14.02 years) who presented with documented SVTs and/or symptoms of palpitations and dizziness, and underwent invasive electrophysiological evaluation was divided into Group I (AVNRT, n = 42) and Group II (Control, n = 79). The PRTCL involved a train of six atrial extrastimuli, delivered in a decremental ramp fashion. The STD methods included continuous burst and rapid incremental pacing up to atrioventricular (AV) block cycle length, and single and occasionally double atrial extrastimuli. Prolongation in the Atrio-Hisian (Delta-AH) intervals achieved by both methods were compared, as were induction frequencies. In Group I, three categories of responses--(1) induction of AVNRT, (2) induction of echo beats only, and (3) none--were observed in 29 (69%), 11 (26%), and 2 (5%) patients with the PRTCL, when compared with 14 (33%), 16 (38%), and 12 (29%) patients with STD methods in the baseline state without the use of pharmacological agents. The Delta-AH intervals for each of these three categories were larger using PRTCL versus STD methods; 293.3 +/- 95.2 ms versus 192.9 +/- 61.4 ms (P < 0.005), 308.6 +/- 68.5 ms versus 189. 9 +/- 64.9 ms (P < 0.0005), and 203.0 +/- 86.3 ms versus 145.8 +/- 58.9 ms (P = NS), respectively. In Group II, in one patient with dual AV nodal physiology but no clinical tachycardia, the PRTCL induced nonsustained (12 beats) AVNRT. Additionally, in this group, both PRTCL and STD methods induced atrial tachycardia in two patients and orthodromic AV re-entrant tachycardia in one patient. Decremental ramp atrial extrastimuli pacing PRTCL demonstrates a superior response for induction of typical AVNRT as compared to STD techniques. Because of easy and reliable induction of AVNRT and echo beats by the PRTCL, we recommend it as a method to increase the likelihood of induction of AVNRT. For induction of other SVTs, the PRTCL and the STD methods are comparable.

Double potentials at successful catheter ablation site of left-sided retrograde accessory pathway: Mitral isthmus block or conduction through coronary sinus musculature

Introduction We studied three patients who had orthodromic atrioventricular reentrant tachycardia (AVRT) using left lateral accessory pathway (AP), with difficulty in identifying the earliest site of retrograde atrial activation. Methods and results Electrophysiological studies and radiofrequency ablation were performed in three patients with refractory AVRT (Case 1 was a 42-year-old woman, Cases 2 and 3 were a 52- and a 40-year-old man, respectively). During AVRT, a prolonged ventriculoatrial (VA) interval (100–180 ms) and nearly simultaneous excitation of both distal and proximal coronary sinus (CS) sites were observed. During both AVRT and ventricular pacing, double atrial potentials were recorded in all patients. Ablation of the mitral annular site showing double atrial potentials (with the first component being present just after the ventricular potential at the left lateral atrioventricular annulus) eliminated retrograde AP conduction. In Cases 1 and 2 the first component of the double potentials was atrial activation conducted through AP distal to mitral isthmus block and the second component was activation proximal to block that conducted turning around the left-sided pulmonary veins. In Case 3 the first component was CS musculature activation conducted through AP and the second component was left atrium activation via CS musculature. Conclusion In AVRT that has a long VA interval and difficulty in identifying the earliest site of retrograde atrial activation, two different mechanisms existed (mitral isthmus block and conduction through CS musculature). Careful mapping of double atrial potentials and continuous VA activation at the left lateral mitral annulus is essential for determination of a successful ablation site.

Evidence for an incomplete mitral isthmus block after failed ablation of a left postero-inferior concealed accessory pathway

We report the case of a young woman in whom previous ablation of a concealed left-sided accessory pathway (AP) created an iatrogenic mitral block. The mitral block was responsible for a split retrograde atrial activation pattern during orthodromic atrioventricular re-entrant tachycardia (AVRT). The differential diagnoses are discussed. The AP was ablated at the site with the shortest interval between the ventricular signal and the earliest component of the retrograde atrial activation. Meticulous mapping is paramount during AVRT with an unusual retrograde atrial activation pattern.

P6-60: Differentiation of atrio-ventricular nodal reentrant tachycardia from orthodromic atrio-ventricular reentrant tachycardia by ΔHA intervals during entrainment from the ventricle

Differentiating atrio-ventricular nodal reentrant tachycardia (AVNRT) from orthodromic atrio-ventricular reentrant tachycardia (AVRT) can be problematic. Differences in His bundle-atrial (HA) intervals during supraventricular tachycardia (SVT) and ventricular pacing in sinus rhythm facilitate diagnosis, but would be better analyzed during ongoing tachycardia when retrogradely conducting structures are operative. The ΔHA interval (HA Entrain - HA SVT) during entrainment of SVT from the ventricle has not been studied.