A study of the factors influencing the appearance of the Ashman phenomenon.

The electrocardiograms of 29 patients with atrial fibrillation and aberrancy (Ashman phenomenon) were studied. The length of the cycles manifesting aberrancy (R-RA) varied from 270 to 520 msec (mean 372 +/- 55). It correlated negatively with the heart rate (r-0.899, p less than 0.001) and for equal heart rates in separate persons it varied with the length of the preceding R-R cycle (p less than 0.01). Above a critical R-RA length of 520 msec and outside an R-R/R-RA ratio range of 1.5-3.6 aberrancy is never observed: this finding is important for the differentiation of aberrancy from ventricular ectopy.

Comparison of the inotropic action of digitalis and isoproterenol in younger and older individuals.

The positive inotropic effects of digitalis (deslanoside C, 1.2 mg. intravenously) and isoproterenol (2 microgram/minute intravenously) were compared in two groups of younger and older individuals using the systolic time interval method. Both groups responded in a completely comparable way to deslanoside C. However, after isoproterenol administration, the LVET of the older group was significantly shortened. Consequently, the PEP/LVET ratio did not change significantly. This difference is attributed to a lesser increase of the stroke volume in the older group.

Effect of digitalis on diminished baroreceptor sensitivity in diabetics.

The baroreceptor sensitivity was estimated in 50 normal controls (Group A) and in 50 diabetics of comparable age (Group B). The technique used was infusion of angiotensin (0.5 microgram/min) and measurement of the bradycardic response resulting from the increase of blood pressure. The slope was used as an index of baroreceptor sensitivity. Diabetics had significantly lower baroreceptor sensitivity and a higher resting heart rate. Sensitivity decreased with age in both groups. The reproducibility of the method was excellent. Deslanoside-C (0.8 mg) significantly increased the baroreceptor sensitivity in 11 normal controls and 9 diabetics. Very low sensitivity was found in 26 diabetics who had no evidence of orthostatic hypotension, neuropathy, or retinopathy. However all 17 patients with the above findings had very low sensitivity.

Electrocardiographic criteria of left ventricular hypertrophy in left bundle-branch block.

In order to determine whether the electrocardiographic criteria of left ventricular hypertrophy apply in the presence of left bundle-branch block we studied 79 cases of intermittent left bundle-branch block and compared the QRS voltage and axis before and after its onset. Cases of incomplete left bundle-branch block were excluded. There was a statistically significant correlation between pre- and post-left bundle-branch block values of R or S wave voltage in leads I, V1, V2, V5, and V6, the Sokolow index (R V5 or V6 + S V1), and the QRS axis. There was a statistically significant reduction in R wave voltage in leads I, V5, and V6, an increase in S wave voltage in V1 and V2, and leftward shift of QRS axis, but the Sokolow index remained unchanged, after the onset of left bundle-branch block. The Sokolow criteria for left ventricular hypertrophy apply satisfactorily even in the presence of left bundle-branch block, though specificity is low, but QRS axis is unhelpful.

Influence of digitalis on cardiac function before and after autonomic blockade.

The influence of Deslanoside C (D), 1.2 mg intravenously on the systolic time intervals (STI) was assessed in 15 individuals with right ventricular pacemakers, who were studied on two occasions, ten days apart. In the first case D was given under basal conditions, and in the second after autonomic blockade (with practolol 20 mg intravenously and atropine 1.5 and 1.0 mg intravenously) at 1 hour's interval. There were similar changes of the STI with digitalis administration both before and after automic blockade. Autonomic blockade is not necessary for full expression of digitalis action on the human heart, as advocated by some authors to be the case in experimental animals.

Influence of heart rate increase on uncorrected pre-ejection period/left ventricular ejection time (PEP/LVET) ratio in normal individuals.

In 26 normal volunteers, increase in heart rate from mean 73-94 +/- 1-97 to 103-61 +/- 2-72/min, by either intravenous atropine administration or rapid right atrial pacing, produced definite changes in the uncorrected systolic time intervals. As expected, total electromechanical systole (QS2) and left ventricular ejection time (LVET) were shortened, while the pre-ejection period (PEP) was unaffected. There was a consistent and significant increase of the PEP/LVET ratio (P less than 0-001). It is postulated that when this ratio is taken to express left ventricular contractility, it should probably be corrected for heart rate. Appropriate regression equations for such a correction were calculated (PEP/LVET=0-249 + 0-0168 HR).