Echocardiography in cardiovascular drug assessment.

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Abstract
The validity of using echocardiography to measure the effects of cardiovascular drugs on the heart was studied. A standardized method of measuring left ventricular diameters is described and used to measure variability and reproducibility in 20 subjects. Immediate variability was measured in 10 normal subjects. In 5 of the subjects variability was measured every few minutes, hourly and weekly during control periods of drug studies and after an interval of 1 yr. Estimates were made of the minimum significant change in heart size which could be defined under these circumstances. Reproducibility decreased with increasing time interval between studies but overall was very good (coefficient of variation in diameters from 1-8%). Even with a time interval of 1 yr the individual absolute difference in the mean of diameters was never greater than 0.3 cm. Reproducibility was similar in small groups of patients with hypertension or ischemic heart disease (without dyskinesia). Estimated sensitivity could be increased for any time interval equally as much by increasing the number of measurements on each occasion and modifying statistical analysis accordingly as by doubling the number of subjects. There was a 4-fold difference between minimum and maximum sensitivity. After 0.5 mg sublingual glyceryl trinitrate, diastolic and systolic diameters decreased significantly in all subjects. Estimated ventricular and stroke volumes were reduced. Cardiac output was unchanged as heart rate increased from 67 to 80 beats/min while blood pressure fell. The estimated ejection phase indices (ejection fraction, fractional shortening, and fiber shortening rate) all increased significantly. With rigid standardization echocardiography could be a potentially useful non-invasive method of measuring the effects of cardiovascular drugs on the heart.