Atrial Cycle Length Research Articles

Prediction of sinus node dysfunction in patients with long-standing persistent atrial fibrillation using the atrial fibrillatory cycle length

BackgroundSinus node dysfunction (SND) occasionally coexists with long-standing atrial fibrillation (AF) but is unidentifiable during AF. We aimed to identify the predictors of underlying SND when deciding the indications for long-standing persistent AF ablation. MethodsWe included 105 patients undergoing ablation of long-standing persistent AF to assess the frequency of a permanent pacemaker implantation (PMI) for SND that manifested after sinus conversion and to determine the relationship between the corrected sinus node recovery time (CSNRT) and other clinical parameters obtained before the ablation including the atrial fibrillatory cycle length (AFCL). ResultsWe identified 7 patients (7%) requiring a PMI for SND after AF termination. The patients with a PMI were nearly all females (6/7) and had a significantly longer CSNRT (1197 ± 647 vs 612 ± 349 milliseconds; P = .0046) and more prolonged AFCL (179 ± 19 vs 153 ± 22 milliseconds; P = .0028) than those without. The age (r = 0.26; P = .011), female sex (r = 0.25; P = .012), hypertension (r = 0.22; P = .038), and AFCL (r = 0.4; P < .0001) were significantly correlated with the CSNRT. A stepwise multivariate linear regression analysis including these parameters revealed that the AFCL was the only independent determinant of the CSNRT (β = 0.38; P = .0012). A receiver operating characteristic curve identified an AFCL of more than 162 milliseconds as the optimal cutoff value for predicting SND requiring a PMI (area under the curve, 0.84; sensitivity, 86%; specificity, 74%; P = .0066). ConclusionsA prolonged AFCL was significantly associated with SND. Thus, assessing the AFCL in the patients with long-standing persistent AF may be helpful for the risk stratification of underlying SND.

New frontiers of supraventricular tachycardia and atrial flutter evaluation and catheter ablation

Radiofrequency catheter ablation (RFCA) has revolutionized treatment for tachyarrhythmias and has become first-line therapy for some tachycardias. Although developed in the 1980s and widely applied in the 1990s, the technique is still in development. Transesophageal atrial pacing (TAP) can used for initiation and termination of supraventricular tachycardia (SVT). Methods: The paroxysmal SVT include a wide spectrum of disorders including, in descending order of frequency, atrial flutter, atrioventricular (AV) nodal reentry, Wolff-Parkinson-White syndrome, and atrial tachycardia. While not lifethreatening in most cases, they may cause important symptoms, such as palpitations, chest discomfort, breathlessness, anxiety, and syncope, which significantly impair quality of life. Medical therapy has variable efficacy, and most patients are not rendered free of symptoms. Research over the past several decades has revealed fundamental mechanisms involved in the initiation and maintenance of all of these arrhythmias. Knowledge of mechanisms has in turn led to highly effective surgical and catheter-based treatments. The supraventricular arrhythmias and their treatment are de-scribed in this report. SVT initiation was analysed with programmed TAP in 49 patients with palpitations (age 47 ± 17 years, 24 females, 25 males). Results: In comparison to antiarrhythmic drug therapy the radiofrequency catheter ablation in patients suffering from atrial flutter, atrioventricular nodal reentry, atrioventricular reentry and atrial tachycardia is the better choice in most cases. TAP SVT initiation was possible in 23 patients before RFCA. Atrial cycle length of SVT was 320 ± 59 ms. We initiated AV nodal reentrant tachycardia (AVNRT, n=15), atrial tachycardia (AT, n=6) and AV reentrant tachycardia with Kent pathway conduction (AVRT, n=2) before RFCA. Conclusions: Radiofrequency catheter ablation is a successful and safe method to cure most patients with paroxysmal supraventricular tachycardias. TAP allowed initiation and termination of SVT especially in outpatients.

Body Surface Two-Dimensional Spectral Map of Atrial Fibrillation Using Vector-Projected 187 Channel Electrocardiography

Atrial cycle length during atrial fibrillation and flutter waves may be correlated with atrial refractoriness and organization. The nature of the frequency by spectral analysis may reflect a profile of atrial cycle length. In this study, we developed a novel body surface 2-dimensional spectral map during fibrillation using vector-projected 187 channel ECG (187ch VP-ECG).The study consisted of 28 patients (24 with atrial fibrillation (AFIB) and 4 atrial flutter (AFL) with valvular heart disease). We performed spectral analysis by maximum entropy modeling (MEM) in 4 second nonaveraged 187ch electrical current waves by 187ch VP-ECG. Body surface spectral features were displayed according to the frequency and power magnitude components. We verified the accuracy of the spectral features by a 64ch magnetocardiography (MCG). The average dominant frequency in AFL by 187ch VP-ECG was lower than those in AFIB (4.6 ± 0.9 Hz in AFL, 7.2 ± 0.9 Hz in AFIB, P < 0.01). Comparison of average dominant frequency between 187ch VP-ECG and 64 ch MCG demonstrated good agreement (y = 0.86x+0.84, r(2) = 0.89, P < 0.0001). Body surface 2-dimensional spectral features demonstrated homogenous spectrum patterns in AFL, and in-homogenous spectrum patterns in AFIB.In conclusion, novel body surface spectral mapping using 187ch VP-ECG may represent a 2-dimensional spectral feature that may be related to atrial refractoriness and organization.

Characterisation of Activation Patterns at Sites of Short Atrial Fibrillation Cycle Length (AFCL) During Human Persistent AF: Do They Identify Drivers?

Characterisation of Activation Patterns at Sites of Short Atrial Fibrillation Cycle Length (AFCL) During Human Persistent AF: Do They Identify Drivers?

The Ventriculophasic Response Revisited: Analysis of Clinical Correlations Using a New Proposed Definition Derived in Pacemaker Patients

The ventriculophasic response (VR) refers to shortening of atrial cycle length during heart block when a QRS complex is interposed between P waves. No formal quantitative definition has heretofore been proposed, nor have its potential clinical correlations been studied. We hypothesized that VR is present in selected patients who are distinguished by clinical features from those who lack VR. Pacing devices were temporarily programmed to VVI mode at 30 ppm as electrocardiogram and intracardiac electrograms were recorded at 50 mm/sec paper speed. We measured the percentage decrease in a P-P interval (A-A interval on the atrial electrogram) containing a QRS, compared to the preceding P-P interval. Left ventricular ejection fraction (LVEF) was measured by echocardiogram. Shortening of P-P interval was observed chiefly when the interposed QRS occurred early in the anticipated P-P interval (as judged by the preceding P-P interval). P-P shortening of 0% to 3% occurred randomly. Defining VR as being a >3% P-P interval shortening when an interposed QRS occurred in the first 60% of the anticipated P-P interval, we found that VR was present in 28 (55%) of our patients. It was quite reproducible, was more common in women (81% vs 37% of men; P = 0.004), and positively correlated with LVEF (r = 0.41, P = 0.004). It did not correlate with age, diabetes, or β-blocker use. Using our newly derived definition of VR, we found the phenomenon was present in 55% of our patients. It was reproducible and more commonly seen in women and patients with LVEF ≥40%.

The Ventriculophasic Response May Be Related to Ventricular Synchrony

PURPOSE: The ventriculophasic response (VR) refers to shortening of the atrial cycle length (PP-interval) during heart block that occurs when a QRS complex is interposed between P-waves. The purpose of this study was to determine if VR varied in relation to the width of the interposed QRS complexes

Rate‐Dependent AV Nodal Function: Closely Bound Conduction and Refractory Properties

The atrioventricular node (AV) node conducts slowly and filters atrial impulses. Puzzlingly, the recovery (conduction time vs atrial cycle length) and refractory curve (His bundle cycle length vs atrial cycle length) characterizing AV nodal function undergo disparate rate-dependent changes. We sought the functional origin and significance of these disparate changes. Differences between the recovery and refractory curve were assessed in 30 steady state AV nodal responses (all potential paired combinations between 5 basic and 6 pretest cycle lengths imposed with S(1)S(2)S(3) protocols) in rabbit heart preparations. Five of these responses corresponded to standard premature protocols. Both basic and pretest cycle length shortenings increased pretest conduction time that in turn equally shortened the ensuing His-atrial interval at all test cycle lengths. This effect was mathematically predictable and tended to shift the refractory curve downward whereas not affecting the recovery curve. Moreover, increases in pretest conduction time also shifted the recovery and refractory curve equally rightward on their x-axis, thereby biasing curve comparison between steady states. This problem could be overcome with equivalent results either by accordingly correcting the atrial cycle length or by using the His-atrial interval as the recovery index. Recovery and refractory curves from AV nodal steady state responses including standard premature protocols only differ by the His-atrial interval that decreases with the pretest conduction time. The latter also biases curve comparison between steady states. Rate-dependent AV nodal function is best assessed with recovery curves freed from changes in pretest conduction time.

Charge Circuit Timeout

Since the advent of the implantable cardioverter-defibrillator (ICD) for primary prevention of sudden cardiac death, much attention has been given to the possibility of ICD or lead hardware failures resulting in inappropriate ICD function. Less attention has been given to the potential for software programming errors resulting in inappropriate device behavior. We report a case of a software programming error that led to a premature “end of service” alert that triggered a “lock-up” of the device antitachycardia therapies. Typically, the capacitor charge time for the Medtronic Secura ICD in anticipation of a full energy shock is about 7.7 to 9.2 seconds, depending on how close the device is to the elective replacement time and other factors.1 A charge circuit timeout indicates that at least 1 charging period exceeded 30 seconds. When 3 consecutive charging periods each exceed 30 seconds, the ICD charge circuit becomes inactive, and all automatic therapy functions and manual system tests become disabled except for emergency VVI pacing, all for the purpose of conserving battery voltage for pacemaker dependent patients when the generator reaches end of service.1 An alert is displayed to indicate that the time allotted to reach the programmed output energy (30 seconds) has been exceeded. A charge circuit timeout usually occurs when the battery voltage is depleted below the “elective replacement indicator.” In this specific instance, the charge circuit timeout occurred because of a glitch in the software. Three events occurred almost simultaneously, exposing the software programming error.2 These events occurred during an episode of tachycardia in the brief time span between the end of charging the capacitors and redetection/confirmation before delivery of a shock. The 3 events are:

Typical Atrial Flutter in an Atypical Patient

Arrhythmias in adult congenital heart disease (ACHD) pose unique procedural challenges, especially with intravascular access. We report a unique case of ablation via a left-sided hepatic vein approach in a patient with situs inversus totalis. A 28-year-old woman with situs inversus totalis, ventriculoseptal defect, and dextro-transposition of the great arteries underwent ablation for documented narrow-complex tachycardia. Because of bilateral iliac venous occlusions, the coronary sinus (CS) was accessed through the left internal jugular vein. Rapid atrial pacing resulted in a tachycardia with an atrial cycle length of 225 msec and 2:1 atrioventricular association. Entrainment from the proximal and distal CS was consistent with typical atrial flutter around the left-sided tricuspid valve. Because of the iliac vein occlusions, access for ablation was obtained via a left-sided hepatic vein (Figure 1). Resetting from the cavotricuspid isthmus and three-dimensional electroanatomic mapping (Figure 2) confirmed typical atrial flutter, which, given the dextrocardia, occurred in a clockwise fashion around the tricuspid valve. Ablation was performed at the cavotricuspid isthmus resulting in arrhythmia termination and isthmus block. This case highlights the many unusual challenges that patients with ACHD can pose to the proceduralist, including atypical cardiac anatomy and difficult intravascular access. Unusual and creative approaches are often necessary to treat these patients successfully.

Stimulation of the Intrinsic Cardiac Autonomic Nervous System Results in a Gradient of Fibrillatory Cycle Length Shortening Across the Atria During Atrial Fibrillation in Humans

The intrinsic cardiac autonomic nervous system (ANS) is implicated in atrial fibrillation (AF) but little is known about its role in maintenance of the electrophysiological substrate during AF in humans. We hypothesized that ANS activation by high-frequency stimulation (HFS) of ganglionated plexi (GP) increases dispersion of atrial AF cycle lengths (AFCLs) via a parasympathetic effect. During AF in 25 patients, HFS was delivered to presumed GP sites to provoke a bradycardic vagal response and AFCL was continuously monitored from catheters placed in the pulmonary vein (PV), coronary sinus (CS), and high right atrium (HRA). A total of 163 vagal responses were identified from 271 HFS episodes. With a vagal response, the greatest reduction in AFCL was seen in the PV adjacent to the site of HFS (16% reduction, 166 ± 28 to 139 ± 26 ms, P < 0.0001) followed by the PV-atrial junction (9% reduction, 173 ± 21 to 158 ± 20 ms, P < 0.0001), followed by the rest of the atrium (3-7% reduction recorded in HRA and CS). Without a vagal response, AFCL changes were not observed. In 10 patients, atropine was administered in between HFS episodes. Before atropine administration, HFS led to a vagal response and a reduction in PV AFCL (164 ± 28 to 147 ± 26 ms, P < 0.0001). Following atropine, HFS at the same GP sites no longer provoked a vagal response, and the PV AFCL remained unchanged (164 ± 30 to 166 ± 33 ms, P = 0.34). Activation of the parasympathetic component of the cardiac ANS may cause heterogenous changes in atrial AFCL that might promote PV drivers.

Multiple Atrial Tachycardias After Atrial Fibrillation Ablation

A combination of pulmonary vein isolation (PV), electrogram-based ablation, and linear lesions have been demonstrated to result in medium-term freedom from atrial fibrillation (AF) in the majority of patients with persistent AF in several studies. Such an extensive ablation is associated with a high incidence of postablation atrial tachycardia (AT), which is often complex and multiple. Deductive mapping strategy,1,2 which consists of activation mapping and entrainment mapping, can identify the mechanism and/or source of the postablation AT rapidly and accurately. However, careful mapping and close observation to identify subtle changes between the ATs are necessary. Postpacing interval (PPI) mapping is a useful technique, with some limitation for focal AT.3–5 We present a case that demonstrated multiple postablation ATs requiring careful mapping for identifying each of them. It also demonstrated the utility of PPI mapping in the precise diagnosis of the sources of focal ATs. A 47-year-old man with an 8-year history of paroxysmal lone AF, not controlled with amiodarone, was admitted to our institution with persistent AT for his third catheter ablation procedure. At the first procedure, 7 years ago, PV isolation was performed. Six months ago, reisolation of PVs, electrogram-based ablation, and linear ablation of left atrial (LA) roof and left mitral isthmus for inducible AT were performed, which completely blocked both lines. The AT cycle length (ATCL) was 275 ms during the start of the third procedure. A steerable decapolar catheter was inserted into the coronary sinus (CS), and an externally irrigated ablation catheter (Thermocool, Biosense Webster) was advanced into the LA via a transseptal puncture. Oral anticoagulation therapy was discontinued 3 days before the procedure. After transseptal puncture, a bolus of 50 IU/kg of heparin was administered. No PV reconnection was observed. Mapping revealed the mechanism of clinical AT as a …

Ventricular tachycardia triggered by blanked flutter search-mediated cycle length alternation

Blanked flutter search (BFS) is an algorithm designed to unmask persistent 2:1 atrial flutters in which every other atrial event falls within atrial blanking period, concealing the arrhythmia. When the sensed atrial cycle length (CL) is less than: (i) twice the sum …

Robustness analysis of processing blocks in T-wave alternans detection

Background: Predictors of arrhythmia recurrence after catheter ablation of atrial fibrillation (AF) are still unclear. The aim of this study was to determine the relationship between dominant atrial cycle lengths (DACL) obtained from surface electrocardiogram (ECG) and clinical outcome after catheter ablation. Methods: In 21 patients (mean age, 52 ± 9 years), left atrial radiofrequency ablation was performed for paroxysmal (n = 9) or persistent (n = 12) AF. Dominant atrial cycle length was assessed before ablation from the V1 lead surface ECG using digital signal processing (filtering, subtraction of averaged QRST complexes, and power spectral analysis). All patients underwent pulmonary vein isolation (PVI). Linear ablation was performed in 12 patients. Results: Dominant atrial cycle length was significantly higher in paroxysmal (186 ± 31 milliseconds) than persistent AF (146 ± 17 milliseconds) and in PVI -only-treated patients (182 ± 33 milliseconds) than in patients who underwent additional linear ablation (149 ± 21 milliseconds). Follow-up was 11 ± 5 months. Dominant atrial cycle length was significantly greater in patients without recurrence AF (176 ± 28 vs 152 ± 31 milliseconds). Conclusions: Higher baseline fibrillatory rates are associated with recurrence AF, which suggests advanced electrical remodeling and reduced atrial refractoriness.

Surface atrial frequency analysis as a useful tool in patients undergoing catheter ablation of atrial fibrillation

Background: Predictors of arrhythmia recurrence after catheter ablation of atrial fibrillation (AF) are still unclear. The aim of this study was to determine the relationship between dominant atrial cycle lengths (DACL) obtained from surface electrocardiogram (ECG) and clinical outcome after catheter ablation. Methods: In 21 patients (mean age, 52 ± 9 years), left atrial radiofrequency ablation was performed for paroxysmal (n = 9) or persistent (n = 12) AF. Dominant atrial cycle length was assessed before ablation from the V1 lead surface ECG using digital signal processing (filtering, subtraction of averaged QRST complexes, and power spectral analysis). All patients underwent pulmonary vein isolation (PVI). Linear ablation was performed in 12 patients. Results: Dominant atrial cycle length was significantly higher in paroxysmal (186 ± 31 milliseconds) than persistent AF (146 ± 17 milliseconds) and in PVI -only-treated patients (182 ± 33 milliseconds) than in patients who underwent additional linear ablation (149 ± 21 milliseconds). Follow-up was 11 ± 5 months. Dominant atrial cycle length was significantly greater in patients without recurrence AF (176 ± 28 vs 152 ± 31 milliseconds). Conclusions: Higher baseline fibrillatory rates are associated with recurrence AF, which suggests advanced electrical remodeling and reduced atrial refractoriness.

Differential Diagnosis of Supraventricular Tachycardia with Ventriculoatrial Dissociation during Ventricular Overdrive Pacing

Case Presentation A 72-year-old man with a history of multiple episodes of paroxysmal supraventricular tachycardia underwent electrophysiologic studies and a catheter ablation procedure. The 12-lead electrocardiogram during tachycardia showed long RP’ tachycardia with negative P waves in leads II, III, and aVF. Ventriculoatrial (VA) conduction with a shortest 1:1 pacing cycle length of 780 ms and earliest atrial activation at the ostium of coronary sinus was observed during ventricular overdrive pacing. A narrow QRS tachycardia documented previously was reproducibly induced by programmed atrial, though not ventricular, stimulation. During tachycardia, the His-atrial (HA) and atrial-His (AH) intervals were 381 and 156 ms, respectively. The atrial activation sequence during tachycardia seemed identical to that during ventricular pacing. A 2-mg bolus injection of adenosine triphosphate reproducibly terminated the tachycardia after a last ventricular event, following progressive prolongation of the atrial cycle length. Overdrive ventricular pacing for >30 seconds during tachycardia, at a cycle length 10‐30 ms shorter than the tachycardia cycle length, invariably caused VA dissociation without atrial capture or termination of the tachycardia (Fig. 1). What is the tachycardia mechanism? Comment

Long RP′ Tachycardia with an Initial A‐A‐V Activation Sequence: What Is the Mechanism?

A 79-year-old man with a history of multiple episodes of paroxysmal supraventricular tachycardia underwent electrophysiologic studies and a catheter ablation procedure. The 12-lead electrocardiogram during tachycardia showed a long RP′ tachycardia with negative P waves in leads II, III, and aVF. No dual anterograde atrioventricular (AV) nodal conduction was elicited by atrial extrastimulation. A narrow QRS tachycardia documented previously was reproducibly induced by atrial extrastimulation (Fig. 1A). During tachycardia, the HA and AH intervals measured 136 and 252 ms, respectively, and the earliest atrial activation was recorded at the ostium of the coronary sinus. Atrial extrastimuli delivered during the tachycardia did not reset the atrial cycle. Atrial overdrive pacing induced a second tachycardia with a similar atrial activation sequence and cycle length, and 2:1AV conduction (Fig. 1B). Ventricular overdrive pacing was delivered at a slightly shorter cycle length than the tachycardia (Fig. 2). Based upon these observations, what is the mechanism of tachycardia?

Atrioventricular Nodal Reentry with Retrograde Lower Common Pathway Block: A Case Report

Retrograde lower common pathway block during AV nodal reentrant tachycardia has rarely been reported. In this report, we demonstrate retrograde ventriculoatrial block during sinus rhythm and during AV nodal reentrant tachycardia in a woman with recurrent supraventricular tachycardia. In addition, evidence of antegrade decremental lower common pathway conduction is presented that produced variable HA intervals despite a constant atrial cycle length. These features may lead to the misdiagnosis of atrial tachycardia if not recognized.

Two-Dimensional Body Surface Dominant Frequency by Vector-Projected 187-Channel Electrocardiography May Evaluate a Characteristics of Atrial Fibrillation

The atrial cycle length during atrial fibrillation (AFIB) and flutter (AFL) waves has been shown to be correlated with atrial refractoriness and organization. In this study, a novel body surface 2-dimensional (2D) spectral mapping of AFIB and AFL was developed using vector-projected 187-channel ECG (187ch DREAM-ECG). The study consisted of 28 patients (24 AFIB and 4 AFL with valvular heart disease). Spectral analysis of a 4 seconds of non-averaged 187ch wave during AFIB and AFL was performed by maximum entropy modeling. The 2D body surface spectral feature was displayed according to the frequency and power magnitude components of the dominant frequency. The accuracy of this spectral feature was verified by 64ch magnetocardiography (MCG). The average dominant frequency in AFL by 187ch VP-ECG was lower than that in AFIB (4.6±0.9 Hz in AFL vs. 7.2±0.9 Hz in AFIB). The average dominant frequency by 187ch SACEG was agreed well with those by 64ch MCG (y=0.86x+0.84, r2=0.89). The body surface 2D spectral feature of the dominant frequency demonstrated a homogenous spectrum pattern in AFL and a non-homogenous pattern in AFIB. In conclusion, 2D novel body surface spectral mapping of the dominant frequency using 187ch DREAM-ECG may evaluate non-invasively the atrial cycle length during AFIB and AFL.

Left Atrial Appendage Flow Cycle Length Is an Important Predictor of Sinus Rhythm Maintenance after Catheter Ablation of Persistent or Long-Standing Persistent Atrial Fibrillation

Purpose: Rate of sinus rhythm (SR) maintenance after catheter ablation (CA) of persistent or long-standing persistent atrial fibrillation (perAF or ls-perAF) is inferior to paroxysmal AF. This is mainly associated with atrial remodeling, so we assumed we could select responder to CA of perAF or ls-perAF before procedure. We hypothesized left atrial appendage flow cycle length (LAAFCL) measured by trans-esophageal echocardiography (TEE) was related to the extent of atrial electrical remodeling. This time, we evaluated the relationship between the LAAFCL before procedure and the rate of SR maintenance after CA of perAF or ls-perAF. Methods: We selected 25 patients (age 60.6±9.2 years). TEE was performed during AF rhythm in all patients. All patients underwent extensive encircling pulmonary vein isolation. Substrate modifications were added as necessary. Results: 16 patients maintained SR, and 9 patients had recurrence of AF. SR maintenance group had significant longer LAAFCL (216.4±115.4 vs. 142.144±27.1 ms, p<0.05) than AF recurrence group. There were no significant differences between two groups in age (p=NS), left atrial diameter (p=NS), left ventricular ejection fraction (p=NS), left ventricular end-diastolic dimension (p=0.076), LAA peak flow velocity (p=0.105), CHADS2 score (p=0.141), follow up period (p=NS), and receiving AAD after procedure (p=NS). Conclusions: LAAFCL is useful to determine indication for CA of perAF or ls-perAF.

Intermittent Right and Left Bundle Branch Blocks and 2:1 Narrow QRS in a Patient with Uncommon Atrioventicular Nodal Reentrant Tachycardia

The development of bundle branch block, especially left bundle branch block and 2:1 narrow QRS morphology, during atrioventricular nodal reentrant tachycardia (AVNRT) is unusual. We report a case of AVNRT patient with a short tachycardia cycle length, in whom transient wide QRS tachycardia with right and left bundle branch blocks (RBBB and LBBB). The patient was a 28 year-old-male whose chief complaint was palpitation with short of breath and pre-syncope for past 18 years. There was no structural organic heart disease on the echocardiogram. An electrophysiological study was performed without any anti-arrhythmic drugs. Uncommon (fast/slow) AVNRT was induced by atrial burst pacing at 300 ms and atrial programmed extra-stimuli without jump up phenomenon. Spontaneous conversion of QRS morphology from narrow QRS to RBBB and LBBB was observed during tachycardia. There was no change in atrial cycle length by a single premature ventricular stimulus during tachycardia. The wide QRS tachycardia with LBBB was transformed to narrow QRS tachycardia by the introduction of a single premature ventricular stimulus without changing the tachycardia cycle length. Radiofrequency catheter ablation targeting anatomical slow-pathway area was performed and successfully eliminated tachycardia. We speculated that enhanced AV nodal conduction could be closely related with the bundle branch block during AVNRT in this patient.