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Biomedical subjects

P Tchou

Publications and source records attributed to P Tchou.

47 records · Page 3Linked to original sources
PubMed1988

Efficacy of cryosurgery alone for refractory monomorphic sustained ventricular tachycardia due to inferior wall infarction.

The efficacy of cryosurgery alone was evaluated in 15 patients with refractory monomorphic sustained ventricular tachycardias related to inferior wall infarction. Patients were 64 +/- 9 (SD) years old and had a mean left ventricular ejection fraction of 39.2 +/- 11.2%. Thirty different tachycardias were mapped with the origin localized to the septum or inferior wall in 20 (67%), near the mitral valve anulus in 6 (20%) and at the base of the posterior papillary muscle in 4 (13%) tachycardias. Endocardial cryoablation of these sites was performed with 6 to 13 (mean 9.2 +/- 1.8) cryolesions per heart. No mitral valve replacement was performed. There was one postoperative death as a result of sepsis. Cryoablation abolished inducible ventricular tachycardia in 11 patients. Of the other three patients, the tachycardia in two was controlled with a single antiarrhythmic agent that had previously failed to suppress inducible ventricular tachycardia. Thus, clinical success was obtained in 13 (93%) of 14 patients. The remaining patient received an automatic implantable cardioverter defibrillator. Ejection fraction remained unchanged or improved after surgery in 14 patients (93%). There have been no late deaths, recurrence of sustained ventricular tachycardia or significant mitral regurgitation during a mean follow-up period of 19 +/- 7 months. These results compare quite favorably with those previously reported for subendocardial resection alone, and indicate that cryosurgery is highly effective, does not result in deterioration of left ventricular function and preserves mitral valve competence when cryoablation of the posterior papillary muscle is necessary.

Aged↗
PubMed1988

Atriofascicular connection or a nodoventricular Mahaim fiber? Electrophysiologic elucidation of the pathway and associated reentrant circuit.

Accessory pathways showing decremental properties and inserting into the right ventricle have been frequently described as "nodoventricular" or Mahaim pathways. However, conclusive evidence for a nodal origination of such pathways is lacking. The patient in this study had characteristics typical of such a pathway. Antegradely, the pathway showed decremental, nodelike conduction properties. With the aid of right bundle branch recordings, the pathway was demonstrated to insert directly into the right bundle branch. Atrioventricular reciprocating tachycardia could be readily initiated by atrial or ventricular pacing. The QRS morphology was normal during sinus rhythm and demonstrated a left bundle branch block pattern with normal axis during tachycardia. The reentrant circuit involved antegrade conduction over the accessory pathway and retrograde conduction via the bundle branches, His bundle, and the atrioventricular node. More significantly, late atrial stimuli delivered during tachycardia could preexcite the ventricle via the accessory pathway despite their inability to enter the atrioventricular node. Thus, the upper "turn around" of the reentrant circuit involved atrial tissue and the accessory pathway originated directly from the right atrium independent of the atrioventricular node. In view of these new findings and other recent observations during surgical resection of similar pathways, a reassessment of previous descriptions of "nodoventricular" fibers may be necessary. Many of these pathways may actually represent atriofascicular or atrioventricular connections with decremental properties.

Adolescent↗
PubMed1988

Transcatheter electrical ablation of right bundle branch. A method of treating macroreentrant ventricular tachycardia attributed to bundle branch reentry.

The present study describes the clinical and electrophysiological characteristics of sustained bundle branch reentrant ventricular tachycardia treated with electrical ablation of the right bundle branch. Seven patients presented with syncopal episodes, and six of the seven had documented episodes of ventricular tachycardia. All patients had depressed left ventricular ejection fraction with cardiomegaly. Six of the seven had dilated cardiomyopathy in the absence of significant coronary disease. Twelve-lead electrocardiograms in all seven patients during sinus rhythm were remarkably similar; six demonstrated intraventricular conduction defect resembling left bundle branch block, and one showed left anterior fascicular block. All patients showed prolonged His-to-ventricle intervals during sinus rhythm. Sustained ventricular tachycardia (with atrioventricular dissociation) because of bundle branch reentry was induced in all patients during baseline electrophysiological study. The His-to-ventricle intervals during tachycardia were similar to those seen during sinus rhythm. Electrical ablation of the right bundle branch was accomplished in each patient with delivery of two electrical shocks (170-310 J) through electrode catheters. Right bundle branch block developed on their surface electrocardiogram immediately after the ablation. Follow-up electrophysiological studies showed no inducible ventricular tachycardia. Clinical follow-up showed no recurrence of syncope or ventricular tachycardia. From the data presented, the following can be concluded. First, right bundle branch ablation is a safe and promising means of treating ventricular tachycardia because of bundle branch reentry and can obviate the need for antiarrhythmic drug therapy and its frequent undesirable side effects. Second, there are common clinical and electrophysiological characteristics that are frequently seen in patients with this tachycardia, and the recognition of these common characteristics should alert the physician to a bundle branch reentrant mechanism of ventricular tachycardia.

Aged↗
PubMed1988

Behavior of postextrasystolic His-Purkinje system refractoriness after multiple premature beats.

Although the steady-state refractoriness of the human His-Purkinje system has been shown to be directly related to the cycle length of pacing, the effect that a varying number of premature beats would have on His-Purkinje system refractoriness of the first postextrasystolic beat has not been described. These effects were systematically investigated in 10 patients with normal intraventricular conduction. The His-Purkinje system relative refractory period (HPS-RRP) of the postextrasystolic beat and that of a comparable constant cycle length ventricular drive were measured by the ventricular extrastimulus technique. Results were as follows: the HPS-RRP of the postextrasystolic beat after one premature beat was longer than the HPS-RRP during a comparable constant ventricular drive. However, with the addition of each successive premature beat, the HPS-RRP of the postextrasystolic beat alternated between lower and higher values, in a manner dependent on whether there was an odd or even number of premature beats. In contrast, ventricular refractoriness of the postextrasystolic beats behaved in a cumulative manner, decreasing progressively with the addition of each premature beat.

Bundle of His↗
PubMed1987

Electrophysiologic mechanisms of orthodromic tachycardia initiation during ventricular pacing in the Wolff-Parkinson-White syndrome.

Orthodromic tachycardia is the most common arrhythmia in patients with Wolff-Parkinson-White syndrome. It is often initiated during incremental ventricular pacing that requires the onset of retrograde block along the normal pathway (that is, atrioventricular [AV] node-His-Purkinje system) with concomitant retrograde atrial activation by way of the accessory pathway. However, the site of retrograde block, that is, the AV node versus the His-Purkinje system, during incremental ventricular pacing and, hence, the mechanism of orthodromic tachycardia initiation have not been systematically elucidated. The mechanisms of orthodromic tachycardia induction were studied in 17 patients with Wolff-Parkinson-White syndrome using a specially designed pacing protocol. A beat by beat analysis indicated that the retrograde His-Purkinje system block was the most common initiating mechanism of orthodromic tachycardia in 14 of the 17 cases. In two cases, AV node block preceded the onset of orthodromic tachycardia, whereas the data in the remaining case suggested that both mechanisms were operative but at different pacing cycle lengths. The orthodromic tachycardia induction with His-Purkinje system block occurred within the first two cycles in most cases. When orthodromic tachycardia initiation was delayed beyond the first two cycles of the ventricular train it represented either a 2:1 block in the His-Purkinje system; a linking phenomenon in the His-Purkinje system; or a block in the AV node. These data have methodologic, mechanistic and therapeutic implications for patients with the Wolff-Parkinson-White syndrome.

Cardiac Pacing, Artificial↗
PubMed1986

Incidence and clinical significance of ventricular fibrillation induced with single and double ventricular extrastimuli.

Of 718 patients evaluated for suspected or documented ventricular tachyarrhythmias, ventricular fibrillation (VF) was induced in 28 (incidence 3.9%) by single and double extrastimuli. Nine of the 28 patients had suspected but no clinically documented ventricular tachycardia (VT) or VF (group 1), 11 had documented VT (group 2) and 8 had out of hospital VF (group 3). In group 1, electropharmacologic control was achieved in 8 patients with the initial agent tested; however, symptoms recurred in 6 patients. In 4 patients the drug was discontinued. After a follow-up of 26 +/- 11 months in group 1, no patient had died. In only 2 of 19 patients in groups 2 and 3 were arrhythmias controlled with the initial agent; 15 patients had VT and 2 VF. Control with class I agents was achieved in 9 of 19 patients and none died until the drug regimen was changed empirically in 3 of these 9. Ten patients, all from groups 2 and 3, were treated empirically with amiodarone; 3 died. All patients died either suddenly or in VT. The mortality rate in groups 2 and 3 after a mean follow-up of 24 +/- 9 months was 32% (p less than 0.05). Continued symptoms and no deaths in group 1 suggests a nonclinical nature of induced VF. Control of induced VF on serial drug testing in group 2 and 3 also indicates a false-negative drug efficacy response, as pharmacologic control of emergent VT on subsequent studies appeared essential to their survival despite control of induced VF. Thus, even with single or double premature stimuli, induction of VF can be a nonclinical response, especially in patients without clinical VF.

Adult↗
PubMed1986

Normal electrophysiologic responses of the human heart.

A thorough understanding of physiologic behavior of the human conduction system is essential to define the abnormalities. This article deals with normal responses of the cardiac conduction system to both antegrade and retrograde direction. Responses to electrical as well as mechanical stimulation are discussed.

Electrophysiology↗
PubMed1985

Electrophysiologic mechanisms of functional bundle branch block at onset of induced orthodromic tachycardia in the Wolff-Parkinson-White syndrome. Role of stimulation method.

The mechanisms of aberrant conduction at the onset of induced orthodromic tachycardia in the Wolff-Parkinson-White syndrome were analyzed in 20 consecutive patients in whom this tachycardia was initiated by the atrial (A2) and/or right ventricular (V2) extrastimulus techniques. Of 13 patients in whom orthodromic tachycardia was induced by the A2 method, functional right bundle branch block occurred at tachycardia onset in four (31%) and left bundle aberrancy in two (15%), one of whom also manifested right bundle aberrancy. The occurrence of bundle branch block at the onset of tachycardia was linked to aberrant conduction of the initiating A2 impulse which, in turn, was associated with attainment of relatively short His1His2 intervals within the tachycardia initiation zone. Aberrant conduction of A2 was also more common in patients without manifest preexcitation. In contrast, of 14 patients in whom orthodromic tachycardia was induced by the V2 method, left bundle aberrancy occurred at the onset of tachycardia in 11 (79%), one of whom manifested right bundle branch block as well. Left bundle aberrancy was more likely to occur when the interval from the initiating V2 (or macro-reentrant V3) impulse to the first anterograde His deflection was less than 300 ms. This suggests that left bundle aberrancy at the onset of orthodromic tachycardia induced by the V2 method results from concealed retrograde penetration of the His-Purkinje system, with the left bundle being last to recover. Our findings provide the conceptual basis for a physiologic approach to the deliberate induction of specific types of aberrant conduction at onset of orthodromic tachycardia in patients with Wolff-Parkinson-White syndrome.

Adolescent↗