Electrophysiological Observations During QRS Alternans in a Patient with Incessant Tachycardia

Electrophysiological observations during preoperative and intraoperative study of a 46-year-old patient with incessant ventricular tachycardia and QRS alternans demonstrated a potential mechanism for this electrocardiographic finding. During QRS alternans, conduction delay (or block) was recorded from the site of origin of the tachycardia, high on the anterior septum to the His bundle: After procainamide infusion, the tachycardias slowed and, concurrent with the disappearance of QRS alternans, conduction from the site of tachycardia origin to the His bundle could no longer be demonstrated.     

Changes of the RR Interval and the QRS Morphology in AV Nodal Tachycardia: Further Evidence for Extranodal Involvement

A young patient wilh AV nodal tachycardia was referred for ablation. During electrophysiological testing, a stable succession of up to four different RR intervals with comcomitantly changing QRS morphologies were recorded. This observation might reflect the conduction of the reentry circuit through different extranodal "pathways" in the low right atrium. Radiofrequency current was applied near the ostium of the coronary sinus; this abolished conduction through the slow pathway, as dual AV conduction was no longer present. She remains free of recurrences for a follow-up period of 8 months.     

Atrioventricular Nodal Supraventricular Tachycardia with 2:1 Block above the Bundle of His

A patient with narrow complex supraventricular tachycardia underwent electrophysiological study at which time a tachycardia was initiated which had 2:1 AV conduction, with block occurring above the His bundle. The modes of tachycardia initiation, as well as the responses to atrial and ventricular premature depolarizations during tachycardia, made a diagnosis of atrioventricular nodal reentry as the tachycardia mechanism. The unusual finding of 2:1 supra-His block suggests the presence of tissue situated between the tachycardia circuit and His bundle, and effectively excludes the possibility of a His-atrial bypass tract as the retrograde limb of the tachycardia circuit.     

Narrow QRS Complex Tachycardia with Atrioventricular Dissociation

We describe the case of a 22-year-old man who had frequent episodes of narrow QRS complex tachycardia with atrioventricular dissociation. The ECG during sinus rhythm showed normal PR and QRS intervals, but it showed a left bundle branch block configuration during atrial pacing or after injection of verapamil. An electrophysiological study demonstrated that the patient had nodoventricular Mahaim fibers. The narrow QRS complex tachycardia was explained by a circuit involving antegrade conduction via the atrioventricular nodo-His axis and retrograde conduction via the nodoventricular bypass tract.     

AV Node Reentry Tachycardia in Infants

The purpose of this study was to determine the frequency of atrioventricular (AV) node reentry tachycardia in infants undergoing transesophageal electrophysiological study for paroxysmal tachycardia. The records of all 52 infants < 1-year-old with structurally normal hearts who underwent transesophageal study for paroxysmal tachycardia over a 3-year period were reviewed. Those with a diagnosis of AV node reentry tachycardia underwent complete data review, and follow-up of > 12 months was obtained. Six of 52 infants had a diagnosis of the common type of AV node reentry tachycardia. Tachycardia was diagnosed at a mean age of 2.1 months (range 1 day to 10 months), and 3 of 6 underwent transesophageal study within the first month. Although no patient had structural heart disease, three patients had significant noncardiac disease. Follow-up of 15–38 months (mean 24 ± 7.8) revealed recurrences in 2 of 6 patients. The mean tachycardia cycle length was 240 ms (range 200–310 ms), and the transesophageal ventriculoatrial intervals ranged from < 30 to 55 ms. All patients had an inducible reentrant tachycardia with a ventriculoatrial interval that remained constant even when tachycardia cycle length increased following verapamil or adenosine administration, or decreased following isoproterenol infusion. Five of 6 had evidence for discontinuous AV node conduction curves. In our patients the substrate for AV node reentry tachycardia was present early in life, and AV node reentry tachycardia can be a clinical problem even in the newborn period.     

Wide QRS Tachycardia Due to AV Nodal Reentry and a "Bystander" Bypass Tract with Slow Conduction Properties

An unusual mechanism for recurrent, wide QRS complex supraventricular tachycardia is described in this report. A 25-year-old man with normal PR and QRS intervals during sinus rhythm was shown to have preexcitation with a left bundle branch block pattern during tachycardia and during atrial pacing. Electrophysiologic studies demonstrated slow and decremental conduction properties in an accessory "bystander" AV pathway utilized for antegrade conduction during AV nodal reciprocating tachycardia. The differential diagnosis of this tachycardia is discussed in detail.     

Alterations of Orthodromic Circus Movement Tachycardia by Dual Atrioventricular Nodal Pathways in a Patient with Wolff-Parkinson-White Syndrome

In a patient with a left sided accessory pathway (AP) three different types of orthodromic circus movement tachycardia were observed; (1) narrow QRS complex tachycardia with a stable cycle length (CL); (2) wide QRS complex tachycardia with a functional bundle branch block ipsilateral to the AP, which, paradoxically, had a shorter CL. The decrease in CL was due to a decrease of the AH interval; and (3) narrow QRS complex tachycardia with alternating CL, due to alternations of the AH interval. These phenomena were attributed to a concomitant dual airioventricular (AV) node, which was eventually proven after successful catheter ablation of the AP.     

Nonreentrant Supraventricular Tachycardia Misdiagnosed as Inappropriate Sinus Tachycardia

We report a case of a woman with incessant palpitations initially misdiagnosed as inappropriate sinus tachycardia that proved refractory to β‐blockers. At the time of electrophysiologic testing, a sustained narrow‐complex tachycardia with a 1:2 atrioventricular relationship was repeatedly initiated by a posterior fascicle depolarization induced by means of a timed ventricular extrastimulus. The tachycardia was repeatedly terminated with a timed atrial extrastimulus, which excluded junctional bigeminy and confirmed the diagnosis of nonreentrant supraventricular tachycardia. Catheter ablation of the slow pathway eliminated dual‐pathway conduction and tachycardia. (PACE 2011; 34:e70–e73)     

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.     

Alternans in QRS amplitude during ventricular tachycardia

Although the value of T wave alternans as an index of electrical instability has been extensively investigated, little is known about QRS alternans during VT. Intracardiac electrograms of 111 episodes of spontaneous monomorphic regular VT retrieved from implantable defibrillators in 25 patients were retrospectively selected. Three beat series, representing the total amplitudes and amplitudes from baseline to summit and from baseline to lower point of 16 or 32 successive QRS complexes before deliverance of electrical therapy were generated for each episode. Spectral analysis was then performed using the fast Fourier transform. VT was considered as alternans if the magnitude of the spectral power at the 0.5-cycle/beat frequency was greater than the mean +/- 3 SD of the noise in at least one of the three spectral curves. QRS alternans was present in 23 (20%) of 111 episodes and in 9 (36%) of 25 patients. Alternans was not related to the VT cycle length, QRS duration, QRS amplitude, signal amplification, nor to clinical variables. Alternans was more frequently detected in unipolar configuration and when a higher number of complexes was included in analysis. Failure of antitachycardia pacing was more frequent in case of alternans VT (50% vs 75% success in nonalternans VT, P = 0.05). Spontaneous termination before deliverance of therapy occurred in 16 non-alternans VT but never in alternans episodes (P = 0.02). Alternans in QRS amplitude is a relatively common finding during VT and could be associated with failure of antitachycardia pacing and lack of spontaneous termination. Lower efficacy of electrical therapies in case of QRS alternans must be confirmed in a way to improve the effectiveness of antitachycardia pacing.     

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.     

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)     

Inappropriate Sinus Tachycardia Following Radiofrequency Ablation of AV Nodal Tachycardia: Incidence and Clinical Significance

The incidence and consequences of inappropriate sinus tachycardia following modification of the AV nodal area with radiofrequency energy were prospectively studied in a consecutive series of 118 patients. Twelve (10%) patients developed this complication, which persisted less than 1 week in all but three patients. Inappropriate sinus tachycardia was only observed after fast pathway ablation. Only four patients required temporary treatment with a beta blocker.     

Mechanisms of Spontaneous Tachycardia Termination in a Patient with the Wolff-Parkinson-White Syndrome and Dual Atrioventricular Nodal Pathways

A patient with the Wolff-Parkinson-White syndrome and recurrent bouts of paroxysmal supraventricular tachycardia underwent electrophysiologic studies. These studies revealed evidence of dual atrioventricular nodal pathways and a septal accessory pathway. The tachycardia circuit involved anterograde conduction over a slow atrioventricular nodal pathway and retrograde conduction over the accessory pathway. Spontaneous tachycardia termination was frequently observed, was almost always abrupt, and was associated with a beat-to-beat decrease in the A-H interval, In this patient, the mechanism for spontaneous tachycardia termination appeared to be an abrupt shift in anterograde conduction from the slow to the fast pathway, advancing the tachycardia so that the block occurred in the accessory pathway (or atrium). To our knowledge, this mechanism of spontaneous tachycardia termination has not been described previously. Use of agents to facilitate fast atrioventricular nodal conduction (i.e., atro-pine) may be effective in tachycardia termination for these patients.     

Atypical AV nodal reentry with bystander accessory pathway: an unusual mechanism of preexcited tachycardia

We present an unusual mechanism of preexcited tachycardia--atypical AV nodal reentry with bystander AP. It can be differentiated from other preexcited tachycardias by its variable degree of preexcitation (either spontaneous or in response to atrial pacing), higher degree of preexcitation with pacing near the origin of the AP than during tachycardia, inability to preexcite the tachycardia by either late atrial or ventricular premature beats, the presence of nonpreexcited atypical AV nodal reentry tachycardia following successful AP ablation, and by exclusion of atrial tachycardia.     

Propranolol Induced Electrical and Mechanical Alternans in Orthodromic Reciprocating Tachycardia

During an electrophysiological study in a patient with a concealed accessory connection, there was no evidence of eiectrical or mechanical alfernans during tachycardia until propranolol was adminislered, but both forms of alternans developed with tachycardia of a slower rate following propranolol. Echocardiographic. arterial pressure, and electrocardiographic data obtained prior to and following propranolol administration are presented.     

Effect of Intraatrial Reentry on Initiation of Atrioventricular Reentrant Tachycardia

We studied the effect of intratrial reentry (IAE) on initiation of orthodromic reentrant tachycardia (ORT) in 150 patients with Wolff-Parkinson-White syndrome using His-bundle recording and the atrial extrastimulus technique. IAR was initiated by premature atrial stimulation in 44 patients (29%), and it was followed by ORT in 16 patients (11%). In 8 patients (5%), IAR promoted the initiation of ORT, whereas in 5 patients (3%), IAR inhibited the initiation of ORT. These findings suggest that ORT is frequently induced following IAR. IAR, which was frequently observed during electrophysiological studies, seems to play an important role in the initiation of ORT.     

Cycle Length Alternation During Supraventricular Tachycardia: Occurrence and Mechanism in a Canine Model of AV Reentrant Tachycardia

Cycle length alternation (CLA) is commonly observed during supraventricular tachycardia (SVT) onset and termination. The present study was designed to gain insights into the mechanism and potential clinical relevance of CLA by comparing computer simulations of tachycardia to directly observed behavior in a canine model of AV reentrant tachycardia (AVRT). The computer model was based on the hypothesis that CLA is secondary to feedback between AV nodal output during SVT and subsequent AV nodal input, and used the measured anterograde AV nodal recovery curve (AV vs A1A2) to predict sequential AV and RR intervals during SVT. Orthodromic AVRT was created experimentally in 11 open-chested, autonomically-blocked (atropine plus nadolol) dogs using a sensing and pacing circuit that mimicked a retrograde-conducting accessory pathway. Steady-state cycle length and AV interval during experimental AVRT closely paralleled predictions made by the computer model. CLA appeared consistently at the onset of experimental AVRT at programmed VA intervals less than or equal to 100 msec (corresponding to VA less than or equal to 150 msec as measured clinically) in all dogs. The amplitude and duration of CLA increased as the VA interval decreased, and closely paralleled predictions based on the computer model. Abrupt accelerations in atrial pacing to the same rate as AVRT did not result in alternation of cycle length. In conclusion, alternation of cycle length results from feedback between AV nodal output and subsequent AV nodal input at the onset of reentrant supraventricular tachycardia, and does not require changes in autonomic tone or dual AV nodal pathways. CLA occurrence, amplitude, and duration are predictable based on AV node recovery properties, and depend on retrograde conduction properties of the reentrant circuit. The presence of CLA suggests that the AV node is an integral component of the SVT reentry circuit, and may be useful clinically to identify the mechanism of supraventricular tachycardias.