1/26. Paroxysmal supraventricular tachycardia caused by 1:2 atrioventricular conduction in the presence of dual atrioventricular nodal pathways.One-to-two atrioventricular conduction, ie, the double response to a single sinus or atrial impulse, resulting in two QRS complexes for one P wave, is a rare manifestation of dual atrioventricular (AV) nodal pathways. This report describes the case of a 61-year-old woman with continuous episodes of supraventricular tachycardia caused by independent conduction to the ventricles of sinus impulses over both the fast and the slow AV nodal pathway, giving rise to a ventricular rate that was twice the sinus rate. A wide spectrum of electrocardiographic manifestations of 1:2 AV conduction was observed on the surface electrocardiogram. The diagnosis was suggested by several elements including evidence of dual AV nodal pathways during sinus rhythm and cycle length alternans during tachycardia. The patient underwent successful slow pathway ablation with complete disappearance of symptoms and electrocardiographic manifestations of 1:2 AV conduction.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
2/26. Shortening of conduction time over arborized atrioventricular accessory pathway with Mahaim fibers physiology just before interruption during radiofrequency ablation.A 21-year-old woman had paroxysmal wide QRS tachycardia with a left bundle branch block configuration and a retrograde conducted P wave just behind the QRS complex. An electrophysiological study revealed antidromic atrioventricular tachycardia involving an atrioventricular connection with decremental conduction as the anterograde limb and normal atrioventricular node as the retrograde limb. During constant pacing from the high right atrium (HRA) at the cycle length (CL) of 600 ms, the QRS configurations were not identical to those during the wide QRS tachycardia or constant pacing at the CL of less than 500 ms. The process by which this arborized atrioventricular accessory pathway with the Mahaim fibers physiology was interrupted by radiofrequency catheter ablation is described. Radiofrequency energy was delivered to the site recording a Mahaim potential at the tricuspid annulus during constant pacing from the HRA at the CL of 429 ms. The stimulus-QRS interval gradually shortened as it reached the power plateau without changing the preexcited QRS configuration. Shortening of the conduction time over the Mahiam pathway might have resulted in changing of the propagation from a slow to fast conduction zone or acceleration in response to thermal effect in a node-like structure on the atrial insertion site.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
3/26. Exit block of focal repetitive activity in the superior vena cava masquerading as a high right atrial tachycardia.An unusual case of atrial tachycardia (AT) originating from the superior vena cava (SVC) is reported. A 34-year-old man without structural heart disease underwent catheter ablation for drug-resistant AT. During the tachycardia, low-amplitude spiky electrograms with a cycle length of 120 to 175 msec were recorded in the SVC and exhibited 2:1 exit block to the atria, masquerading as the atrial activation observed with high right AT. These spiky electrograms also were observed during sinus rhythm, but they appeared immediately after the local atrial electrograms. The spikes were traced to a point 3 cm above the junction of the right atrium. Radiofrequency ablation at the site of the earliest appearance of the spike in the SVC successfully eliminated the tachycardia. During the following 15 months, no clinically significant atrial arrhythmias, including atrial fibrillation, occurred. This report indicates that careful mapping, including inside the SVC, will be a requisite in patients with high right atrial tachyarrhythmias.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
4/26. Effects of the pacing site on A-H conduction and refractoriness in patients with short P-R intervals.His bundle recordings were studied in four patients with short P-R and A-H intervals, and narrow QRS complexes, who had experienced several episodes of supraventricular tachyarrhythmias. The heart was paced from the high right atrium (HRA) and the coronary sinus (CS). In three patients the A-H Wenckebach phenomenon occurred at higher rates (greater than 200 pacing beats/min) when the CS was paced than when pacing was performed from the HRA. Moreover, CS stimulation produced smaller increments in the A-H interval than did pacing from HRA. The extrastimulus method of testing was done. In cases 1 and 2 the functional refractory period of the A-H tissues was 15 to 25 msec shorter during CS pacing than when pacing from the HRA. In case 3, the low right atrium (LRA) as well as the other two sites were paced. A type 1 gap was seen from HRA, a type 2 gap from CS, and both types appeared when the LRA was paced. Case 4, in which the mid-right atrium (MRA) was also stimulated, had a double pathway from HRA and CS with conduction through the accessory pathway late in the cycle and through the A-V node earlier in the cycle. However, the A-V node could not be penetrated during MRA stimulation. It appeared that the pacing site influenced the A-H conduction pattern and refractoriness, possibly by changing the site and/or mode of entry of the stimulus into the pathways that are responsible for this syndrome.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
5/26. Spontaneous atrial premature depolarizations during paroxysmal reentrant tachycardia.The spontaneous onset and termination of many episodes of paroxysmal tachycardia, each initiated by an atrial premature depolarization, were studied in one patient. Surface electrocardiograms alone were inadequate to define the mechanisms underlying the frequent irregularity of atrial and ventricular cycle lengths during the tachycardia and the nature of spontaneous termination of the tachycardia. Unipolar atrial electrograms demonstrated that the irregularity during the tachycardia was due to premature atrial depolarizations that reset the reentrant cycle sustaining the tachycardia, and each spontaneous termination was due to an even more premature atrial depolarization interrupting the reentrant pathway. The genesis of the atrial premature depolarizations resetting and terminating the tachycardia, and their relationship to those initiating the tachycardia, are discussed.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
6/26. Radiofrequency ablation of a slow pathway in AV-nodal tachycardia.A 35-year-old woman with frequent attacks of paroxysmal supraventricular tachycardia and psychiatric background was submitted to ablation of AV-nodal tachycardia. Before ablation, tachycardia with a cycle length of 455 ms was easily induced with regular atrial stimulation or with one extrastimulus. Radiofrequency current (35 Watts) was applied on a site, localized between the His bundle and the ostium of the coronary sinus. The local electrogram showed an atrial activation 20 ms before the atrial activation at the His bundle site during tachycardia. Application terminated AV-nodal tachycardia within 2.5 seconds. Two back-up applications were given during sinus rhythm. At the control study, conduction over the slow pathway was abolished, and the fast conduction remained intact with a Wenckebach 2:1 block point at 180 beats/min. She remained free of recurrences with a follow-up of more than 3 months. The possibility of selective ablation of the slow pathway in AV-nodal tachycardia is discussed.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
7/26. Participation of a concealed nodoventricular fiber in the genesis of paroxysmal tachycardias.An unusual form of tachycardia circuit is described. The circuit incorporates a concealed nodoventricular fiber that conducts in a retrograde path, connects the atrioventricular node and the right ventricle, and also includes the distal portion of the atrioventricular node, the His-Purkinje system, and the ventricle. The study patient was first seen with paroxysmal tachycardias of normal QRS duration, complete right bundle branch block, and complete left bundle branch block. Electrophysiologic studies disclosed poor anterograde atrioventricular nodal conduction with a block proximal to His deflection that occurred at an atrial paced cycle length of 600 msec with no ventriculoatrial conduction. The tachycardias were inducible with two ventricular extrastimuli, had a His deflection that preceded each QRS complex and an HV interval identical to that during sinus rhythm, and revealed ventriculoatrial dissociation. tachycardia with QRS patterns of right bundle branch block had a cycle 30 to 35 msec longer than tachycardias with either normal QRS duration or complete left bundle branch block. Tachycardias could be entrained by appropriate right ventricular pacing at rates slightly faster than the rate of tachycardia. Tachycardias could be terminated abruptly by an intravenous bolus of either adenosine triphosphate or verapamil.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
8/26. Spontaneous termination of paroxysmal supraventricular tachycardia following disappearance of bundle branch block ipsilateral to a concealed atrioventricular accessory pathway: the role of autonomic tone in tachycardia diagnosis.We present a case of an 18-year-old man with a history of palpitations in whom episodes of paroxysmal supraventricular tachycardia were easily initiated by administered atrial premature beats. In all 15 control episodes of tachycardia, functional left bundle branch block (LBBB) seen at the onset, resolved within 10-20 cycles (mean, 13.1 /- 0.95). The tachycardia ended with the normalized QRS complex in each episode. Eleven episodes ended because of block within the antegrade pathway (ended with a P-wave), and four episodes stopped because of block within the retrograde pathway (ended without a P-wave). During the administration of isoproterenol (1 mg/min IV) all six episodes of tachycardia had LBBB but these did not end when LBBB disappeared spontaneously. When LBBB subsided, the mean tachycardia cycle interval shortened from 328.5 /- 1.4 to 264.2 /- 2.1 ms (p less than 0.001). Each episode of tachycardia was then terminated by carotid sinus massage. The disappearance of LBBB in control conditions presented the retrograde and antegrade limbs of the reentrant circuit with an early impulse that stopped the tachycardia. After isoproterenol administration, the tachycardia did not end following disappearance of LBBB, thus enabling the tachycardia cycle interval to shorten by a mean of 64.3 /- 1.9 ms. This extent of tachycardia acceleration is diagnostic of the participation of a concealed, left free-wall bypass tract.- - - - - - - - - - ranking = 3keywords = cycle (Clic here for more details about this article) |
9/26. tachycardia- and bradycardia-dependent atrioventricular block: observations regarding the mechanism of block.A case of paroxysmal bradycardia- and tachycardia-dependent atrioventricular (AV) block is described in a patient with right bundle branch block. The His bundle recordings demonstrated the site of the AV block to be distal to the His bundle recording site (probably in the left bundle branch). Whereas AV block distal to the His bundle occurred at an atrial paced cycle length of 700 ms, intact ventriculoatrial (VA) conduction was present up to a ventricular paced cycle length of 400 ms. Resumption of AV conduction was dependent on a critical HH or RH (in case of escapes) interval. These findings suggest that the bradycardia-dependent block is related to a time-dependent decrease in the amplitude of the current intensity of the proximal segment during late diastole. Spontaneous diastolic depolarization during late diastole resulted in impaired anterograde (AV) conduction but facilitated retrograde (VA) conduction. These findings are consistent with experimental "in vitro" observation in the sucrose gap model of AV block.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
10/26. Anterograde conduction of a concealed accessory pathway after transvenous electric catheter ablation.An 18-year-old woman with a concealed right midseptal accessory pathway and refractory supraventricular tachycardia with a cycle length of 280-400 ms and a wide echo zone of 280-520 ms is reported. The transvenous electric catheter ablation with two shocks of 200 and 300 J, each on a separate occasion, was followed by anterograde and retrograde atrioventricular block. The patient received an implantable pacemaker (VVI). Four weeks later we observed a stable anterograde conduction of the pathway in spite of a persisting retrograde block. It is concluded that the site of unidirectional block in this patient is at the origin of the concealed accessory pathway in the ventricular septal muscle. The necrosis after ablation changed conduction conditions at the site of unidirectional block. Presently, the patient has been free of tachycardia for 19 months. This observation is of importance for the patient because another mechanism of tachycardia might be possible after ablation.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
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