Abolition of digitalis tachyarrhythmias by caffeine

Digitalis-induced ventricular tachyarrhythmias (VTAs) are believed to be due to oscillatory afterpotentials (OAPs) generated by an oscillatory release of calcium from the sarcoplasmic reticulum (SR). Caffeine blocks the calcium uptake into the SR and then may influence VTAs by depleting the SR stores of calcium. We studied the action of digitalis and caffeine, singly and in combination, in the isolated guinea pig heart perfused by means of a modified Langendorff apparatus. Digitalis (beta-methyldigoxin 1.27 X 10(-6) M) caused VTAs and ventricular fibrillation (VF) in all the hearts. Caffeine alone decreased heart rate but never caused VTAs. With the administration of digitalis and caffeine (1 mM), VTAs rarely developed and VF never occurs. With digitalis and higher concentration of caffeine (10 mM), neither VTAs nor VF were observed. In hearts with complete atrioventricular block, digitalis increased the ventricular rate from 143 +/- 10 to 270 +/- 13 beats/min (n = 8) in 12 +/- 1.9 min and provoked the appearance of multiple ventricular pacemakers. The addition of 10 mM caffeine to the digitalis-containing solution reduced the ventricular rate to 171 +/- 12 beats/min (P less than 0.001 vs. digitalis alone, not significant vs. control, n = 8) and abolished the digitalis-induced multiple pacemakers. Ventricular asystole was occasionally observed during the perfusion with digitalis + 10 mM caffeine. Caffeine alone did not modify the diastolic pressure, whereas caffeine and digitalis rapidly increase it. These results represent indirect evidence to support that SR plays an important role in the origin of the digitalis-induced VTAs.

Antepartum pneumonia in pregnancy

Thirty-nine patients satisfying criteria for antepartum pneumonia in pregnancy were retrospectively reviewed. Twenty-one patients had culture-proved bacterial pneumonias. Streptococcus pneumoniae was the most common organism isolated (13/39). Significant anemia (hemoglobin less than or equal to 10 gm) was present in 49% of patients (19/37) on admission. In the patients presenting in the second and third trimesters (25 to 36 weeks) of pregnancy, 85% (11/13) were delivered at term. The perinatal mortality rate for the entire group was 40/1,000. There were no maternal deaths.

Inhibitory effect of anoxia on reperfusion- and digitalis-induced ventricular tachyarrhythmias

In the isolated rat heart, anoxia or ischemia do not induce important ventricular tachyarrhythmias (VTAs). During the 1st min of reperfusion, VTAs are frequent. The frequency and severity of VTAs during reperfusion depend on the duration and the extent of the myocardial damage. Anoxia abolishes reperfusion-induced VTAs as did verapamil (2.5 X 10(-6) M). In isolated guinea pig hearts, beta-methyldigoxin (1.27 X 10(-6) M) provokes VTAs that are progressively increasing in severity. After 26 min of perfusion with an oxygenated beta-methyldigoxin-containing medium, all isolated guinea pig hearts develop ventricular fibrillation. By changing the abnormal rapid ventricular rhythms into progressively slower irregular idioventricular rhythm, anoxia counteracts all types of VTAs exhibited by the intoxicated guinea pig hearts. In conclusion, two conditions seem to be necessary for the development of VTAs during the reperfusion: 1) a sufficient degree of myocardial damage provoked by the preceding ischemic perfusion, and 2) the presence of oxygen during the reperfusion.

Use of glycopyrrolate in the parturient: effect on the maternal and fetal heart and uterine activity

The effects of intravenous glycopyrrolate on maternal and fetal heart rate, heart rate variability, and maternal electromechanical intervals and blood pressure were evaluated in 20 term parturients in labor. Direct continuous fetal heart rate and intrauterine pressure were monitored via an intrauterine catheter. Maternal heart rate and R-pulse-wave intervals were measured and maternal blood pressure was recorded at 5-minute intervals. There were no significant changes in fetal heart rate or fetal heart rate variability. The maternal heart rate increased in all cases and the electromechanical interval decreased with the onset of maternal tachycardia. There were no significant changes in maternal blood pressure. Uterine activity increased in all cases; however, this increase does not appear to be greater than that expected in uterine activity as labor progresses.

Intracellular calcium and electrogram in ischemic isolated rat heart

The electrogram (EG) of the isolated rat heart during ischemic or anoxic perfusion has been studied. Reduction of the coronary flow rate (CFR) induced an increase of voltage (V) both in unipolar epicardial EG and in transmural bipolar EG. The V increase did not occur during anoxic perfusin. The ischemic increase cannot be due to a disturbance in the His-Purkinje or intraventricular conduction because it was observed also in the circumscribed myocardial area, which was explored by means of the transmural bipolar EG. Likewise it cannot be due to an intramural block because it occurs before one observes an augmentation of epicardial activation time or a decrease of dV/dtmax. Therefore, the ischemic V increase should be due to a modification of transmembrane potential. The variation rate of V, of dP/dt, and of myocardial ATP behaved in a similar way during underperfusion. Varying intracellular Ca2+ by means of a Ca2+-free medium or verapamil reduces the ischemic V increase. The dynamics of the ischemic V increase may be represented in order of succession by: inhibition of oxidative metabolism, augmentation of intracellular Ca2+, increase of K+ conductance, and hyperpolarization of cardiac cells.

Induced resistance in Staphylococcus aureus for assay of antibiotic mixtures in pharmaceutical preparations

A new microbiological method was developed for the assay of neomycin and spiramycin. These antibiotics usually cannot be quantitated individually when they are combined in a pharmaceutical preparation since both act on the same test organism. By inducing resistance to each antibiotic in Staphylococcus aureus, two new strains were obtained. Quantitation can be accomplished easily with these strains.