[Prognostic value after 1 year of post-infarction exercise test with measurement of oxygen consumption]. / Valeur pronostique à un an du test d'effort postinfarctus avec mesure de la consommation d'oxygène.

A symptoms-limited exercise stress test with measurement of myocardial oxygen consumption (VO2) was carried out in 56 patients on the 44th +/- 16 days after infarction and in 48 patients on the 119th +/- 31 days. Analysis of the expired gases was performed by mass spectrography, cycle by cycle. The second test was coupled with an exercise gamma-angiography in 40 cases. The parameters on exercise were analysed in two groups at one year: group 1 asymptomatic and group 2 symptomatic (subgroup 2a with angina but no dyspnoea, subgroup 2b with dyspnoea). At the second test, the peak VO2 was lower in group 2 (19.46 +/- 5.78 ml/mn/kg) than in group 1 (24.2 +/- 6.5 ml/mn/kg) (p less than 0.008) irrespective of the symptom (angina and/or dyspnoea). The oxygen pulse was lower in group 2a with angina at one year (42.4% +/- 14.3%) compared with asymptomatic group 1 patient (58.5 +/- 12.4%) (p = 0.03). The 3 parameters: VO2, blood pressure and ejection fraction on exercise were independent. The lack of physical fitness may partially explain the absence of variation of the peak VO2 at the first test. These preliminary results should be confirmed by a multivariate analysis in a larger patient group.

[Effects of magnesium on early post-depolarization and trigger activity induced by cesium on Purkinje fibers in ferrets]. / Effets du magnésium sur les post-dépolarisations précoces et l'activité déclenchée induites par le césium sur les fibres de Purkinje de furet.

The effects of magnesium (Mg) on afterdepolarisations and cesium-induced activity were studied in 15 preparations of ferret Purkinje fibres. When the perfusion medium was enriched with Mg to concentrations of 5 mM, the duration of the action potentials stopped increasing and the diastolic membrane potential was stabilised despite persistent exposure to cesium. A suppressor effect of Mg on the high and low voltage early afterdepolarisations was observed which was significant at 2.2 mM (p less than 0.03) and even more so at 5 mM (p = 3. 10-5) related to a lower probability of early afterdepolarisations. A suppressor effect of Mg on high and low voltage induced activities was also recorded, significant at 5 mM, due to a reduction in the probability of apparition of a first induced action potential (p = 2. 10-4) and a reduction in the number of induced action potentials (p = 8. 10-4). The rapid onset of action (a few minutes) of Mg suggests an extracellular mode of action. The suppressor effect of Mg is probably related to inhibition of an unmasked current by the cesium, a calcium antagonist effect and/or non-specific membrane stabilising effect. The suppressor effect of Mg on early afterdepolarisations and induced activity could, at least partially, explain its in vito antiarrhythmic action on torsades de pointe.

[Wolff-Parkinson-White syndrome. Value of transesophageal atrial stimulation coupled with exercise test for the study of anterograde conduction in the accessory pathway]. / Syndrome de Wolff-Parkinson-White. Intérêt de la stimulation auriculaire transoesophagienne couplée à l'épreuve d'effort pour l'étude de la conduction antérograde dans la voie accessoire.

In patients with Wolff-Parkinson-White syndrome the anterograde conduction properties of the accessory pathway determine the ventricular rate in case of atrial fibrillation (AF). Anterograde conduction in the accessory pathway was evaluated in 20 patients (mean age 31 years) by means of transoesophageal atrial pacing with increasing frequency (up to 460 per minute), first at rest, then during exercise on an ergometric bicycle and upon immediate recovery. The exploration was completed by a search for the disappearance of pre-excitation during exercise and after an intravenous injection of ajmaline 1 mg/kg. The shortest cycle (SC) of atrial pacing with 1:1 conduction by the accessory pathway regularly decreased by 80 +/- 26 ms (n = 18), i.e. 27 p. 100 of its value at rest. At immediate recovery SC increased by 40 +/- 53 ms (n = 9). Atrial fibrillation was induced at rest and/or during exercise in 12 patients. The shortest interval (SI) between two pre-excited ventricular complexes was 290 +/- 80 ms (n = 8) at rest and 244 +/- 53 ms (n = 8) during exercise. With a substantial group of values (n = 12) there was good correlation between SC and SI both at rest and during exercise. With a smaller group of values (n = 3) SI was clearly greater than SC, suggesting a concealed conduction in the accessory pathway during atrial fibrillation. Disappearance of pre-excitation during exercise was observed in 4 patients, 3 of whom had a short (less than 250 ms) SC and/or SI.(ABSTRACT TRUNCATED AT 250 WORDS)