Systolic time intervals: a review of the method in the non-invasive investigation of cardiac function in health, disease and clinical pharmacology

The comparative cardiovascular effects of digoxin and food alone and in combination in normal males

The effects of the ingestion of food and digoxin on the cardiovascular system alone and in combination have been observed in eight healthy subjects. A positive inotropic response was seen following food (2.5 MJ) and intravenous digoxin (0.01 mg/kg) with significant decreases in QS2Index (QS2I) pre-ejection period (PEP) and PEP/LVET (LVET - left ventricular ejection time). These responses were potentiated when food and digoxin were combined. Opposing effects of food and digoxin on % diastole (%D) and diastolic time were observed, food decreasing %D and DT while digoxin increased these variables. Both food and digoxin decreased T-wave amplitude, and digoxin alone or in combination with food decreased QTc. The positive inotropic effect of a 2.5 MJ mixed meal and a loading dose of digoxin in healthy subjects are of similar degree, different mechanism, and are potentiated in combination.

A comparison of the haemodynamic effects of nifedipine, nisoldipine and nitrendipine in man

Nifedipine (10 mg), nisoldipine (10 mg) and nitrendipine (20 mg) were given orally to 8 normal volunteers in a placebo controlled, double blind, crossover study. Blood pressure (BP), pulse (P) and systolic time intervals (STI) were recorded at time 0, 30, 60, 90, 120 min after drug administration. Adverse effects were also recorded. There was a fall in BP, pre-ejection time (PEP), PEP/LVET (left ventricular ejection time) and electro-mechanical systole index (QS2 index), and a rise in LVET index in response to the three active drugs compared with placebo. All active drugs, but not placebo, were associated with adverse effects.

Cardiovascular action of calcitonin gene-related peptide in humans

Calcitonin gene-related peptide (CGRP) has been localized in cardiac nerve fibers and blood vessels from which it may be released as neurotransmitter or neuromodulator. Acute cardiovascular effects of i.v. administered CGRP have been studied in human subjects. CGRP (25.3 nmol) caused a mean maximal increase of the heart rate of 41 beats per min (P less than 0.01) and lowered arterial systolic and diastolic pressures by 26 mm Hg and 20 mm Hg, respectively (P less than 0.01) (n = 6 subjects). These effects were associated with facial flushing, and a rise of plasma levels of norepinephrine and epinephrine of 257 pg/ml and 9 pg/ml, respectively (P less than 0.01). Administration of equimolar amounts of human calcitonin caused no cardiovascular effects except for minor facial flushing. Serum calcium was marginally lowered with both CGRP (0.2 mg/100 ml) and calcitonin (0.4 mg/100 ml) (P less than 0.05). Furthermore, CGRP (12.7 nmol) reduced the preejection period and duration of the electromechanical systole by 26 msec and 66 msec, respectively (P less than 0.001 and P less than 0.01), presumably acting as positive inotropic agent. Labetalol, blocking adrenergic receptors, obliterated these inotropic effects, whereas the positive chronotropic and hypotensive actions of CGRP remained unchanged.

Systolic time intervals in adolescents with insulin-dependent diabetes mellitus

Systolic time intervals were used to evaluate left ventricular performance in 20 diabetic adolescents with a mean age of 15.2 +/- 2.2 years (range 9-17 years) and were compared with an age- and sex-matched control group. Pre-ejection period index (PEPI), left ventricular ejection time index (LVETI), total electromechanical systole index (QS2I) and the PEP to LVET ratio were calculated at rest and following sustained isometric handgrip (SIHG). None of the diabetics had demonstrable microangiopathy or autonomic neuropathy. There was no significant difference in resting or post-exercise heart rate, PEPI, LVETI or PEP/LVET ratio between the two groups. QS2I was significantly prolonged (p less than 0.05) at rest in the diabetics, but was not significantly different following SIHG. These results indicate that cardiac contractility is not detectably abnormal in young diabetics, compared to their adult counterparts who may develop impaired myocardial performance.

Electromechanical delay in the intact dog heart

A computer method was developed for the determination of electromechanical delay defined as the time between the onset of Q-wave and the onset of the left ventricular systolic pressure rise. It was validated for heart catheterization studies on 56 intact anaesthetized beagle dogs in 86 sessions. The mean basal value of the electromechanical delay was 22 +/- 4 msec. Heart rate, contractility, preload and afterload were changed by atrial pacing and by infusions of calcium chloride, isoproterenol, propranolol, dextran and phenylephrine. Increase of heart rate by pacing from the spontaneous rate of 90 per min to 240 per min prolonged the electromechanical delay from 21 +/- 5 to 33 +/- 14 msec (P less than 0.001). Otherwise the duration of electromechanical delay changed independently of the heart rate. If it changed, the direction of the change followed that of the pre-ejection period. Its proportion of the pre-ejection period varied from 26 to 52%. The electromechanical delay shortened when a positive inotropic effect was noticed or the presystolic fibre length increased.

The therapeutic implications of diastolic time changes in systemic hypertension

Twenty-five patients with chronic systemic hypertension were studied. Systolic time intervals and diastolic time were determined at baseline and after 12 weeks of therapy with nadolol, with or without bendroflumethiazide (treatment phase I), then after 12 weeks of therapy with hydralazine, bendroflumethiazide, or both (treatment phase II). Systolic, diastolic, and mean blood pressures were equally controlled after either treatment regimen. Heart rate was significantly slower after treatment phase I compared to baseline or after treatment phase II (p less than 0.001). Systolic time per minute was significantly shorter and diastolic time per beat and per minute were significantly longer after treatment phase I compared to baseline or after treatment phase II (p less than 0.001). Double and triple products decreased after either mode of therapy; however, these parameters were significantly lower after treatment phase I compared to treatment phase II (p less than 0.01). These changes in systolic and diastolic time and double and triple products may be of clinical significance during therapy of chronic systemic hypertension and may help explain the regression of left ventricular hypertrophy in patients with hypertension treated with sympathetic blocking agents.

Methodological variation in systolic time intervals

Systolic time intervals (STI) were recorded six times in 12 male students. All 72 recordings were measured twice by a physician and once by two nurses. By comparing these measurements an intra- and interobserver (= methodological) variation was obtained. For measured parameters (QS2- interval and LVET) variation was less than 2%. For calculated parameters the variation was larger, but did not reach the level of statistical significance. Methodological variation was smaller than physiologic variation. The internal consistency was almost perfect for measured parameters and only slightly worse for calculated parameters.