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Biomedical subjects

M Dubuc

Publications and source records attributed to M Dubuc.

51 records · Page 3Linked to original sources
PubMed1992

Efficacy and electrophysiologic effects of oral sotalol in patients with sustained ventricular tachycardia caused by coronary artery disease.

The efficacy of oral sotalol in preventing sustained ventricular tachycardia induction by invasive electrophysiological testing was assessed in 22 patients (60 +/- 9 years) with prior myocardial infarction. Programmed stimulation consisted of two basic drives followed by up to three extrastimuli at two right ventricular sites. At baseline, sustained monomorphic ventricular tachycardia was inducible in all patients. With sotalol (360 +/- 172 mg/day), it was no longer inducible in 10 patients; in 12 others, it remained inducible and its cycle length was only minimally prolonged (322 +/- 42 to 345 +/- 44 msec, p less than 0.05). Sotalol markedly prolonged sinus cycle length, uncorrected QT interval, and right ventricular effective and functional refractory periods, but had little effect on ventricular conduction time either in sinus rhythm or with right ventricular pacing. There was no significant difference in drug dose or in electrophysiologic effect of drug that related to efficacy, nor was there any correlation between drug-induced prolongation of ventricular tachycardia cycle length and its effects. Six patients received oral sotalol over the long term without spontaneous recurrence of ventricular tachycardia (follow-up: 23 +/- 18 months). These results demonstrate that sotalol is effective (45%) against sustained ventricular tachycardia induction at moderate doses and is well tolerated over a long term in the setting of remote myocardial infarction. However, its electrophysiologic effects as measured at invasive testing are not predictive of efficacy against ventricular tachycardia induction.

Administration, Oral↗
PubMed1991

Evaluation of arrhythmic causes of syncope: correlation between Holter monitoring, electrophysiologic testing, and body surface potential mapping.

Holter monitoring, electrocardiographic (ECG) signal-averaging, body surface potential mapping (BSPM) for PQRST isoarea maps, and electrophysiologic study (EPS) were performed in 100 patients with syncope. Coronary artery disease (CAD) was found in 46 patients and other heart disease was found in 19. EPS was diagnostic in 44 patients, while Holter monitoring suggested a diagnosis in only 21 patients. Abnormal BSPM was frequently seen (56%), especially in CAD (70%), or with inducible ventricular tachycardia (VT) (87%). Late potentials were recorded in 13 patients with CAD; five had inducible VT. In seven other patients with VT, they were either absent or bundle branch block (BBB) was found. Thirteen deaths (three sudden) occurred in our series. EPS-guided therapy resulted in a low rate of total cardiac death. In conclusion, EPS had a higher diagnostic yield than Holter monitoring regardless of cardiac pathology. ECG signal-averaging was useful in predicting VT only in patients with CAD without BBB. BSPM was abnormal in most patients with cardiac disease, but poorly predicted VT.

Arrhythmias, Cardiac↗
PubMed1991

Epicardial and endocardial mapping of ventricular tachycardia in patients with myocardial infarction. Is the origin of the tachycardia always subendocardially localized?

BACKGROUND: Left ventricular endocardial reentry is the conventional concept underlying surgery for ventricular tachycardia (VT). We assessed the incidences of patterns showing complete reentry circuits at either the subendocardial or subepicardial level and of patterns in which left ventricular endocardial mapping could only in part account for a reentrant mechanism. METHODS AND RESULTS: We retrospectively analyzed epicardial and left ventricular endocardial isochronal maps of 47 VTs induced in 28 patients with chronic myocardial infarction (inferior, 14 patients; anteroseptal, 14 patients). Electrograms were recorded intraoperatively from 128 sites with epicardial sock and transatrial left ventricular endocardial balloon electrode arrays. Given the methodology used in this study, the mapping characteristics of the tachycardias suggested five types of activation patterns: 1) complete (90% or more of VT cycle length) subendocardial reentry circuits in seven VTs (15%) and seven patients (25%), 2) complete subepicardial reentry circuits in four VTs (9%) and four patients (14%), 3) incompletely mapped circuits with a left ventricular endocardial breakthrough preceding the epicardial breakthrough in 25 VTs (53%) and 21 patients (75%), 4) incompletely mapped circuits with a left ventricular epicardial breakthrough preceding the endocardial breakthrough in three VTs (6%) and three patients (11%), and 5) a right ventricular epicardial breakthrough preceding the left ventricular endocardial breakthrough in eight VTs (17%) and seven patients (25%). After surgery, one type 3 VT and three type 5 VTs were reinducible. Thus, left ventricular endocardial reentry substrates (types 1 and 3) accounted for 68% of VTs, but substrates involving subepicardial (types 2 and 4) and deep septal layers (type 5) accounted for 32% of VTs. CONCLUSIONS: In a substantial number of VTs, a substrate localization that is at variance with the conventional concept can be detected by simultaneous epicardial and endocardial mapping and may require modification of the surgical approach conventionally aimed at endocardial layers.

Cardiac Pacing, Artificial↗
PubMed1990

Prolongation of ventricular refractoriness by class Ia antiarrhythmic drugs in the prevention of ventricular tachycardia induction.

The effects of class la antiarrhythmic drugs (procainamide, quinidine) on the right ventricular effective refractory period (VERP) and intraventricular conduction time were assessed during serial invasive electrophysiologic studies for sustained monomorphic ventricular tachycardia (VT). In 47 patients with remote myocardial infarction, sustained VT was inducible by up to two extrastimuli after the basic drive at one of two basic cycle lengths at the right ventricular apex. With oral drug administration, sustained VT was no longer inducible (group I) in 27 patients but remained inducible (group II) in 20 with the same protocol. Class la drugs prolonged the VERP in both groups, but there was greater lengthening when drugs were effective (e.g., +32 +/- 14 msec in group I vs +12 +/- 19 msec in group II; p less than 0.005, basic cycle length 600 to 700 msec). Prolongation of the VERP by greater than 30 msec had an 88% positive predictive value for prevention of sustained VT induction. In all except one patient in group I, drugs prolonged the VERP such that the coupling intervals that had resulted in sustained VT induction under control conditions were no longer attainable. In contrast, conduction time through the ventricle (surface QRS duration) in sinus rhythm and during right ventricular pacing was prolonged similarly regardless of efficacy (e.g., +33 +/- 21 msec vs +27 +/- 27 msec at a cycle length of 400 msec). The presence of similar plasma levels of drug did not imply equivalent prolongation of the VERP in the two groups. These results suggest that greater prolongation of the VERP by oral procainamide or quinidine correlates with drug efficacy against VT induction and is a better predictor of drug effect than achievement of a "therapeutic plasma level."

Adult↗
PubMed1990

Efficacy of propafenone in preventing ventricular tachycardia: inverse correlation with rate-related prolongation of conduction time.

The efficacy of propafenone in preventing induction of ventricular tachycardia was evaluated in 25 consecutive patients (mean age 62 +/- 8 years) with remote myocardial infarction who underwent programmed electrical stimulation for ventricular arrhythmia using up to three extra-stimuli after basic drive at the right ventricular apex. In nine patients (Group A), propafenone prevented induction of sustained ventricular tachycardia (noninducible in four, nonsustained [less than 30 s] in five). In the other 16 patients (Group B), sustained ventricular tachycardia was still inducible; in 11 of the 16, the tachycardia configuration was unchanged but the cycle length was significantly longer (431 +/- 99 versus 284 +/- 44 ms, p less than 0.001). Propafenone did not significantly affect either sinus cycle length or AH and HV intervals. However, it prolonged QRS duration during sinus rhythm equally in both groups of patients. With ventricular pacing, propafenone also prolonged right ventricular effective and functional refractory periods and surface QRS duration. There was greater lengthening of the paced surface QRS duration when drug therapy was ineffective (for example, +35 +/- 12 ms in Group A versus +69 +/- 23 ms in Group B at a basic drive of 400 ms, p less than 0.01). Drug-induced prolongation of a paced QRS complex greater than 40 ms had a 94% positive predictive value for drug failure to prevent induction of ventricular tachycardia. Drug-induced percent prolongation of ventricular tachycardia cycle length in Group B did not correlate well with percent QRS prolongation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1989

Electrophysiologic effects of intravenous propafenone in Wolff-Parkinson-White syndrome.

The electrophysiologic effects of intravenous propafenone were studied in 15 consecutive patients with accessory pathways. Thirteen patients had sustained orthodromic supraventricular tachycardia induced during baseline study, and two patients needed isoproterenol to render it sustained. In all except one patient, propafenone, 2 mg/kg given intravenously over a 10-minute period, was successful in converting the arrhythmia to sinus rhythm. Atrial fibrillation was inducible in 10 patients before propafenone, but was no longer inducible in seven of these patients after the drug. The HV interval (23 +/- 20 to 41 +/- 25 msec) and the anterograde (310 +/- 96 to 509 +/- 145 msec) and retrograde (256 +/- 30 to 334 +/- 105 msec) effective refractory periods of the bypass tract were all significantly prolonged after the drug. The pacing cycle length that produced conduction block over the bypass tract anterogradely (319 +/- 126 to 446 +/- 150 msec) and retrogradely (272 +/- 25 to 360 +/- 97 msec) was also increased. During orthodromic tachycardia, propafenone increased conduction time in both the anterograde and retrograde limbs of the tachycardia. Tachycardia terminated in the retrograde limb in 64% of the patients. We conclude that propafenone is very effective in terminating orthodromic tachycardia when given intravenously and that it should be considered in patients initially seen with atrial fibrillation and short refractory periods.

Adult↗
PubMed1988

Effect of intravenous and oral calcium antagonists (diltiazem and verapamil) on sustenance of atrial fibrillation.

Both verapamil and diltiazem are used to control ventricular response during atrial fibrillation (AF). Their effect on the maintenance of AF is not known. The effects of the intravenous and oral administration of verapamil and diltiazem were investigated in 35 patients, 18 with (group I) and 17 without (group II) documented paroxysmal AF. Programmed electrical stimulation, either extra-stimuli or burst atrial pacing, was used to induce AF. In group I, the mean values of the duration of AF before and after the intravenous and oral administration of the calcium antagonists were 31 +/- 12, 112 +/- 49 and 69 +/- 25 minutes, respectively. For group II, the values were 5 +/- 3.4, 39 +/- 13 and 14 +/- 7 minutes, respectively. The differences were statistically highly significant (p less than 0.001), after both oral and intravenous administration compared with the baseline value in both groups. The data suggest that both intravenously and orally administered calcium antagonists enhance sustenance of electrically induced AF, especially in patients with spontaneous arrhythmia. Thus, in patients with paroxysmal AF, verapamil or diltiazem should be administered cautiously, because these drugs may prolong the duration of arrhythmia. Further studies are warranted to investigate the role of calcium antagonists in spontaneously occurring paroxysmal AF.

Administration, Oral↗
PubMed1988

Effect of induced ventricular tachycardia on atrial natriuretic peptide in humans.

The effects of induced sustained ventricular tachycardia on the release of plasma-immunoreactive atrial natriuretic peptide were evaluated in 11 adult patients undergoing diagnostic electrophysiologic study. Plasma concentrations of atrial natriuretic peptide withdrawn from the right atrium before and during sustained ventricular tachycardia (mean tachycardia cycle length 320 +/- 68 ms, duration greater than 30 s) were determined by radioimmunoassay. Hemodynamic measurements included phasic femoral artery blood pressure and mean right atrial blood pressure before and during ventricular tachycardia. During ventricular tachycardia, atrial natriuretic peptide increased from 93 +/- 49 pg/ml to 234 +/- 195 pg/ml (p less than 0.05), systolic arterial blood pressure decreased from 120 +/- 16 to 70 +/- 23 mm Hg (p less than 0.001), diastolic arterial blood pressure decreased from 63 +/- 8 to 51 +/- 16 mm Hg (p = NS) and mean right atrial blood pressure increased from 3 +/- 1 to 8 +/- 5 mm Hg (p less than 0.02). In six patients, all hemodynamic variables and the atrial natriuretic peptide were measured during repeated stimulation protocols to investigate the effect of ventricular stimulation for ventricular tachycardia induction on atrial natriuretic factor release. Compared with the values obtained during sinus rhythm, there was no significant increase in atrial natriuretic factor during ventricular stimulation at a cycle length of 600 ms (45 +/- 20 versus 52 +/- 21 pg/ml) or at a cycle length of 400 ms (45 +/- 20 versus 57 +/- 18 pg/ml). No significant linear relation could be found among the changes in mean right atrial pressure, systolic arterial blood pressure and the increase in atrial natriuretic peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Congenital tracheoesophageal fistula without esophageal atresia.

Between Jan. 1, 1961 and Dec. 31, 1981, 16 infants (9 boys, 7 girls) with tracheoesophageal fistula without esophageal atresia (H-type fistula) were treated at the Hôpital Sainte-Justine and Centre Hospitalier de l'Université Laval. The mean birth weight was 2.8 kg. Five infants were premature. All presented at first feeding with coughing, choking and cyanosis. Seven had abdominal distension and six had hypersalivation. Mean age at the time of definitive diagnosis was 39.1 days. The diagnosis was confirmed radiologically in all infants, a mean of 1.69 roentgenographic procedures per patient being required. Cervicothoracic (C7 to T2) fistulas were present in 14 and thoracic fistulas in 2 infants. Twelve were operated upon through a cervical and 4 through a thoracic approach. A Fogarty catheter was placed in two fistulas preoperatively. Two patients required gastrostomy. Feeding was started again 3 days postoperatively. One infant died and one had a recurrent fistula. One survivor had 20 episodes of cardiorespiratory arrest. None had dysphagia. The authors consider it imperative that fistulas be visualized before any operative procedure is performed. Catheterization of the fistula with a Fogarty catheter should be attempted preoperatively. It is dangerous to dissect a cervical fistula through a thoracotomy.

Catheterization↗
PubMed1983

[Congenital tracheoesophageal fistulas without esophageal atresia].

Between 1961 and 1982 sixteen patients with tracheo-oesophageal fistulae without oesophageal atresia (H type fistula) were treated at Hôpital Ste-Justine and Centre Hospitalier de l'Université Laval. Nine patients were male and seven female, with a mean birth weight of 2.8 kg. Five were premature. All presented at first feeding with coughing, choking and cyanosis. Seven had abdominal distension and six had hypersalivation. Mean age at time of definitive diagnosis was 39.1 days. The diagnosis was confirmed radiologically in all patients, a mean of 1.69 cine-radiographic procedures per patient being required. Cervical region (C7 - T2) fistulas were present in 14 and thoracic in 2 patients. Twelve patients were operated via a cervical approach and four via a thoracic approach. A Fogarty catheter was in place in 2 fistulae pre-op. Two patients required gastrostomy. Refeeding was started 3 days post-operatively. One died and one had fistula recurrence. Fifteen patients survived. One survivor had multiple episodes of cardio-respiratory arrest. None had major swallowing difficulties. We consider it imperative that fistulae be visualized before surgical intervention. Catheterization of the fistula utilizing a Fogarty catheter should be attempted prior to surgery. It is dangerous to dissect a cervical fistula via a thoracotomy.

Catheterization↗
PubMed1977

Response recovery cycles in the visual cortex and superior colliculus following conditioning "ON" and "OFF" stimulation in the rabbit.

The responsiveness of visual cortex (VC) and superior colliculus (SC) was simultaneously compared following conditioning "ON" or "OFF" stimulation, in the rabbit. Average evoked responses were recorded simultaneously from the visual cortex ans superior colliculus. "ON" or "OFF" steps constituted the conditioning stimuli whereas the test stimulus consisted of optic nerve stimulation. All evoked responses exhibited a reversal of their polarity when the electrode was moved in the dorsoventral direction (Negative-Positive in the SC, Positive-Negative in the VC). This assured the somato-dentritic origin of the potentials. The results showed that responsiveness in both structures was significantly higher following an "OFF" simulus than after an "ON" step. Collicular responsiveness was higher than in the VC when the same conditioning stimulus was applied. The spatial distribution of the source of "OFF" responses was circumscribed to the ventral part of the superficial layer of the superior colliculus. These results suggest specific properties associated with the brightening and dimming systems.

Animals↗
PubMed1975

Simultaneous recordings of visual cortex and superior colliculus field potentials in the rabbit.

The field potentials recorded simultaneously at various depth of the rabbit's visual cortex and superior colliculus were analysed following light ON and light OFF. The collicular ON and OFF potentials exhibited three slow components superimposed by fast rhythmic oscillations. Only the first slow component reversed its polarity with penetration from surface negative to positive in depth. The cortical ON and OFF responses similarly contained three slow waves which all reversed their polarity with electrode penetration: from surface positive to negative in deeper layers. The most striking difference between ON and OFF cortical responses is the absence of fast rhythmic oscillations in the cortical ON response.

Animals↗