Biomedical subjects
Publications and source records attributed to M H Hamdan.
In a series of 14 patients undergoing transseptal catheterization for ablation of left-sided accessory pathways, hydrogen appearance time was used to detect left-to-right shunting after removal of the catheter. Six of the 12 patients who had no evidence of shunt before catheterization had evidence of shunting after the procedure.
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To review our experience with cases of narrow complex tachycardia with VA block, highlighting the difficulties in the differential diagnosis, and the therapeutic implications. Prior reports of patients with narrow complex tachycardia with VA block consist of isolated case reports. The differential diagnosis of this disorder includes: automatic junctional tachycardia, AV nodal reentry with final upper common pathway block, concealed nodofascicular (ventricular) pathway, and intra-Hissian reentry. Between June 1994 and January 1996, six patients with narrow complex tachycardia with episodes of ventriculoatrial block were referred for evaluation. All six patients underwent attempted radiofrequency ablation of the putative arrhythmic site. Three of six patients had evidence suggestive of a nodofascicular tract. Intermittent antegrade conduction over a left-sided nodofascicular tract was present in two patients and the diagnosis of a concealed nodofascicular was made in the third patient after ruling out other tachycardia mechanisms. Two patients had automatic junctional tachycardia, and one patient had atrioventricular nodal reentry with proximal common pathway block. Attempted ablation in the posterior and mid-septum was unsuccessful in patients with nodofascicular tachycardia. In contrast, those with atrioventricular nodal reentry and automatic junctional tachycardia readily responded to ablation. The presence of a nodofascicular tachycardia should be suspected if: (1) intermittent antegrade preexcitation is recorded, (2) the tachycardia can be initiated with a single atrial premature producing two ventricular complexes, and (3) a single ventricular extrastimulus initiates SVT without a retrograde His deflection. The presence of a nodofascicular pathway is common in patients with narrow complex tachycardia and VA block. Unlike AV nodal reentry and automatic junctional tachycardia, the response to ablation is poor.
Fourteen patients with typical atrial flutter underwent pacing from the low lateral right atrium and the proximal coronary sinus in normal sinus rhythm before and after catheter ablation. During low lateral right atrial pacing, a positive change in P-wave morphology in the inferior leads was noted in every patient (n = 12) in whom bidirectional block was achieved; no recurrence was noted in any of these patients.
We report our initial clinical experience with a new tined ventricular endocardial pacemaker lead, the Medtronic model 5034. This lead has a reduced electrode tip size, which provides a higher impedance. Based on early evidence of elevation of pacing lead threshold, we compared our clinical experience with the performance of this lead with that of other similar models with larger surface area (Medtronic models 4024 and 5024). Of 17 implant procedures performed at our institution with the model 5034 lead, two (11.2%) developed high thresholds, versus 0% in 121 implant procedures with models 4024 or 5024 leads (p = 0.014). We conclude that there is evidence of increased failure caused by elevation of pacing threshold in this lead. This increased failure rate needs to be confirmed in a multicenter observational study or randomized trial.
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.