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1/84. Radiofrequency ablation of a concealed nodoventricular Mahaim fiber guided by a discrete potential.

    INTRODUCTION: We present the case of a 17-year-old woman who underwent an electrophysiological study and radiofrequency (RF) ablation of supraventricular tachycardia refractory to medical treatment. Two right-sided, concealed, nondecremental atrioventricular accessory pathways (AV-APs) involved in orthodromic circus movement tachycardias were identified. After RF ablation of both AV-APs, evidence of bidirectional dual AV nodal conduction was demonstrated and regular narrow complex tachycardia was induced. methods AND RESULTS: During the tachycardia, retrograde slow and fast AV nodal pathway conduction with second-degree ventriculoatrial (VA) block and VA dissociation were observed. During the tachycardia with second-degree VA block, ventricular extrastimuli elicited during His-bundle refractoriness advanced the next His potential or terminated the tachycardia. Mapping the right atrial mid-septal region, a distinct high-frequency activation P potential was recorded in a discrete area, two thirds of the way from the His bundle toward the os of the coronary sinus. Detailed electrophysiologic testing with the recordable P potential demonstrated that the tachycardia utilized a concealed nodoventricular AP arising from the proximal slow AV nodal pathway. CONCLUSION: The tachycardia with slow 1:1 VA conduction could be reset by ventricular extrastimuli elicited during His-bundle refractoriness advancing the subsequent activation P potential and atrial activation. RF ablation guided by recording of the activation P potential resulted in elimination of both the slow AV nodal pathway and the nodoventricular connection with preservation of the normal AV conduction system.
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2/84. Unusual induction of slow-fast atrioventricular nodal reentrant tachycardia. Report of two cases.

    INTRODUCTION: Generally, the induction of typical atrioventricular nodal reentrant tachycardia (AVNRT) occurs with a premature atrial stimulus that blocks in the fast pathway and proceeds down the slow pathway slowly enough to allow the refractory fast pathway time to recover. We describe two cases in which a typical AVNRT was induced in an unusual fashion. RESULTS: The first case is a 41-year-old man with paroxysmal supraventricular tachycardia. During the electrophysiology study, the atrial extrastimulus inducing the typical AVNRT was conducted simultaneously over the fast (AH) and the slow pathway (AH'). A successful ablation of the slow pathway was performed. During the follow-up no recurrence was noted. The second case is a 52-year-old woman with a wolff-parkinson-white syndrome due to a left posterior accessory pathway. After 5 minutes of atrioventricular reentrant tachycardia (AVRT) induced by a ventricular extrastimulus, a variability of the antegrade conduction was noted in presence of the same VA conduction. In fact, a short AH interval (fast pathway) alternated with a more prolonged AH intervals (slow pathway) that progressively lengthened until a typical AVNRT was induced. The ablation of the accessory pathway eliminated both tachycardias. DISCUSSION: A rare manifestation of dual atrioventricular nodal pathways is a double ventricular response to an atrial impulse that may cause a tachycardia with an atrioventricular conduction of 1:2. In our first case, an atrial extrastimulus was simultaneously conducted over the fast and the slow pathway inducing an AVNRT. This nodal reentry implies two different mechanisms: 1) a retrograde block on the slow pathway impeding the activation of the slow pathway from the impulse coming down the fast pathway, and 2) a critical slowing of conduction in the slow pathway to allow the recovery of excitability of the fast pathway. Interestingly, in the second case, during an AVRT the atrial impulse suddenly proceeded alternately over the fast and the slow pathway. The progressive slowing of conduction over the slow pathway until a certain point which allows the recovery of excitability of the fast pathway determines the AVNRT. This is a case of "tachycardia-induced tachycardia" as confirmed by the fact that the ablation of the accessory pathway eliminated both tachycardias.
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3/84. Chronic intoxication by doxycycline use for more than 12 years.

    We report the clinical case of a 12-years' intoxication by doxycycline. A patient with a depersonalization and derealization syndrome took 1 g doxycycline per day. In addition to hepatocellular necrosis with cholestasis, nephrotoxicity, leukopenia, anaemia and skin hyperpigmentation he suffered from hitherto unreported adverse cardiac events as intermittent supraventricular tachycardia and sporadic Wenckebach heart block. Despite a long period of self-medication these side-effects were reversible.
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4/84. Orthodromic tachycardia with atrioventricular dissociation: evidence for a nodoventricular (Mahaim) fiber.

    We describe a patient in whom two tachycardias with AV dissociation were inducible by ventricular extrastimulation. The first tachycardia was characterized by a narrow QRS preceded by a His deflection with an HV interval identical to that recorded in sinus rhythm (40 ms). Premature ventricular depolarization delivered when the His bundle was refractory advanced the next His deflection. These findings suggest the presence of a nodoventricular bypass tract involved in an orthodromic tachycardia. The second tachycardia was induced after propafenone infusion and exhibited a wide QRS complex with left bundle branch block morphology; each ventricular complex was consistently associated with a His deflection with a HV interval of -15 ms. The second tachycardia may be considered to represent an antidromic tachycardia through the nodoventricular tract. However, a ventricular tachycardia cannot be excluded.
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5/84. Electrophysiologic characteristics and radiofrequency ablation of concealed nodofascicular and left anterograde atriofascicular pathways.

    INTRODUCTION: True nodoventricular or nodofascicular pathways and left-sided anterograde decremental accessory pathways (APs) are considered rare findings. methods AND RESULTS: Two unusual patients with paroxysmal supraventricular tachycardia were referred for radiofrequency (RF) ablation. Both patients had evidence of dual AV nodal conduction. In case 1, programmed atrial and ventricular stimulation induced regular tachycardia with a narrow QRS complex or episodes of right and left bundle branch block not altering the tachycardia cycle length and long concentric ventriculoatrial (VA) conduction. Ventricular extrastimuli elicited during His-bundle refractoriness resulted in tachycardia termination. During the tachycardia, both the ventricles and the distal right bundle were not part of the reentrant circuit. These findings were consistent with a concealed nodofascicular pathway. RF ablation in the right atrial mid-septal region with the earliest atrial activation preceded by a possible AP potential resulted in tachycardia termination and elimination of VA conduction. In case 2, antidromic reciprocating tachycardia of a right bundle branch block pattern was considered to involve an anterograde left posteroseptal atriofascicular pathway. For this pathway, decremental conduction properties as typically observed for right atriofascicular pathways could be demonstrated. During atrial stimulation and tachycardia, a discrete AP potential was recorded at the atrial and ventricular insertion sites and along the AP. Mechanical conduction block of the AP was reproducibly induced at the annular level and at the distal insertion site. Successful RF ablation was performed at the mitral annulus. CONCLUSION: This report describes two unusual cases consistent with concealed nodofascicular and left anterograde atriofascicular pathways, which were ablated successfully without impairing normal AV conduction system.
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6/84. The use of echocardiographic colour kinetic wall motion to differentiate broad complex tachycardia.

    Discrimination between supraventricular tachycardia (SVT) with aberrant conduction from ventricular tachycardia (VT) is vital for the safe and effective management of both conditions. Electrocardiographic algorithms for the differentiation of broad complex tachycardia are complex and difficult to implement in the acute setting, with misdiagnosis occurring in up to 40% of acute presentations. This case study shows the potential for echocardiographic colour kinesis (eck) to support electrocardiographic differentiation. A 74-year old man in sinus rhythm with left bundle branch block (lbbb), a history of myocardial infarction and recurrent sustained VT underwent eck analysis of wall motion propagation during a programmed electrical ventricular stimulation study. Sequential 40 ms time frames of echocardiographic colour coded endocardial wall motion velocity were recorded on video during both induced VT of lbbb configuration and near isochronic atrially paced tachycardia in lbbb. During VT there was initial eck propagation of ventricular septal wall motion from the apex to the atria secondary to electrical depolarisation. During atrially paced tachycardia initial eck motion developed in the interatrial septum and atrial wall followed by propagation in the ventricular endocardial septal wall motion from the atria toward the ventricular apex. This eck technique potentially could be used to support the electrocardiographic diagnosis of a broad complex tachycardia.
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7/84. Transvenous cryothermal catheter ablation of a right anteroseptal accessory pathway.

    In patients with wolff-parkinson-white syndrome, right anteroseptal accessory pathways are uncommon and run from the atrium to the ventricle in close anatomic proximity to the normal AV conduction system. Radiofrequency catheter ablation is the first-line therapy for elimination of these accessory pathways. Although the initial success rate is high, there is a potential risk of inadvertent development of complete heart block, and the recurrence rate is relatively high. The capability of cryothermal energy to create reversible lesions (ice mapping) at less severe temperatures provides a potential benefit in ablation of pathways located in a complex anatomic area, such as the mid-septum and anteroseptum.
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8/84. Mustard procedure in atrial situs inversus: three-dimensional ablation of intra-atrial reentry tachycardia on a surgically created inversus cavo-tricuspid isthmus.

    It has been demonstrated that the Biosense Carto system can improve the success rate of ablation in case of an intra-atrial reentry tachycardia in patients submitted to the Mustard repair. This system was used to map an intra-atrial reentry tachycardia in a young patient who had been submitted to the Mustard procedure for atrial situs inversus. A line of block was created connecting the right sided tricuspid valve to the left sided inferior vena cava. This terminated the arrhythmia and prevented its re-initiation. This case confirmed the notion that the cavo-tricuspid isthmus is often critical to the maintenance of an intra-atrial reentry tachycardia after the Mustard procedure even if its location is in the inversus side.
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9/84. Paroxysmal supraventricular tachycardia with persistent ventriculoatrial block.

    We report the case of a 64-year-old patient with paroxysmal supraventricular tachycardia and persistent VA block. Induction and maintenance of tachycardia occurred without apparent activation of the atria. Diagnostic characteristics were most compatible with AV nodal reentrant tachycardia (AVNRT). Automatic junctional tachycardia and orthodromic nodoventricular or nodofascicular reentry tachycardia were considered in the differential diagnosis. Upper common pathway block during AVNRT may be explained by either intra-atrial conduction block or purely intranodal confined AVNRT. The arrhythmia was cured by a typical posteroseptal ablation approach guided by slow pathway potentials.
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10/84. amiodarone-induced 2 to 1 atrioventricular block in association with prolongation of the QT interval.

    The potential for development of 2 to 1 atrioventricular conduction in children with prolongation of the QT interval has been previously reported secondary to electrolytic disturbances. We report here a child who developed 2 to 1 atrioventricular conduction with prolongation of the QT interval following treatment with amiodarone for refractory supraventricular tachycardia. We highlight the importance of electrocardiographic monitoring to assess for those at risk of amiodarone toxicity, which may be manifested by prolongation of the QT interval and the simultaneous loss of atrioventricular conduction, and of equal importance the need for prompt conversion to an alternative anti-arrhythmic agent.
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