Mortality risk and patterns of practice in 2,070 patients with acute myocardial infarction, 1987-92. Relative importance of age, sex, and medical therapy.

OBJECTIVE: To define contemporary age- and sex-related mortality risks and patterns of medical practice in acute myocardial infarction (AMI). DESIGN: Retrospective comparison of demographic and clinical variables, including the use of proven effective AMI medical therapy, among AMI patients cohorts from 1987 to 1992. PATIENTS/SETTING: Of a total of 2,070 AMI patients, 629 were women and 1,441, men; 951 patients were managed in university hospitals, 641 in a regional hospital, and 478 in community hospitals. INTERVENTIONS: No direct study interventions; results of practice patterns and risk analyses of the earlier (1987-90) AMI cohorts, however, were published concurrently with the actual practices of the more recent (1991-92) cohorts and may have had some indirect effect on the recent practice patterns. RESULTS: Univariate analysis showed that mortality was higher (p < 0.0001) and use of thrombolysis, beta blockers, and acetylsalicylic acid was lower (p < 0.0001) in patients 70 years of age and older, compared with younger patients, and in women, compared with men. Multivariate analysis of the entire patient sample revealed age of 75 years or older (154 percent) and age 70 to 74 years (141 percent) to be associated with the highest relative risk of death in hospital. The increased relative risk associated with previous AMI was 45 percent. Acetylsalicylic acid use was associated with the greatest decrease in relative risk of death (-69 percent), followed by beta blockers (-36 percent) and thrombolysis (-31 percent). These patterns of relative risk were the same for men and women. CONCLUSIONS: Among contemporary AMI patients, advanced age and female sex are associated with relative under-utilization of proven effective medical therapy and increased risk of dying in the hospital. Although the contribution of age to AMI risk appears greater than that of gender, survival in any high risk group would likely be improved by increased use of proven medical therapy.

Changes in blood pressure and cardiac output during maximal isokinetic exercise.

This study was undertaken to determine the blood pressure (BP) and cardiac output (Qc) responses to maximal isokinetic exercise. The subjects (n = 5) performed unilateral knee extension/flexion exercise (knee exercise) and unilateral elbow extension/flexion exercise (elbow exercise) at 0.52, 1.57, and 2.62 rads.sec-1. The BP was monitored using a cannula placed in the radial artery. Heart rate (HR), stroke volume (SV), and Qc were measured by impedance cardiography. In response to isokinetic exercise, HR and Qc increased significantly (p less than .01), while the SV did not. The BP response was characterized by significant increases in systolic, diastolic, and mean arterial pressure (MAP) (p less than .01). The Qc and MAP, responses were not influenced by the exercise velocity. The adjustments in HR, MAP, and rate pressure product (RPP) to the elbow exercise were qualitatively similar to those seen during the knee exercise, but the absolute values achieved were smaller (p less than .05). Compared with maximal dynamic exercise, the HR and SV responses to the knee exercises were lower. The MAP response to isokinetic exercise equaled the highest value achieved during dynamic exercise. Findings from the present study suggest that the cardiovascular stress (the increase in HR, MAP, and RPP) associated with isokinetic exercise is independent of the velocity of movement and is proportional to the active muscle mass.

Cardiac output measured by impedance cardiography during maximal exercise tests.

The overall accuracy of cardiac output measurements made by impedance cardiography during maximum exercise was studied in man. Initially, the systematic error of the technique was assessed over the range 3.5 to 18 litre . min-1 by comparing with simultaneous measurements of cardiac output made using the direct Fick method. No systemic error was demonstrated in 40 estimations made in 20 subjects. The random error was assessed in 4 subjects in a steady state at rest and during exercise at 80 and 130 W and found to be less than 5% in each subject. The reproducibility of maximum exercise response was assessed in six healthy male subjects (age 26.2 +/- 4.4 years, +/- SEM) who underwent maximum exercise tests twice, 1 week apart, on a bicycle ergometer. Simultaneous recordings of cardiac output and oxygen uptake (VO2) at rest and during each 3 min stage of exercise were made. Highly significant correlations were obtained in the stroke volume (r = 0.84, p less than 0.001), cardiac output (r = 0.98, p less than 0.001) and VO2 (r = 0.98, p less than 0.001) between the two tests. Average maximum cardiac output was 27.0 +/- 1.2 litre . min-1 (+/- SEM) and maximum VO2 was 4.4 +/- 0.2 litre . min-1 (+/- SEM). These results show that measurements of cardiac output were reproducible over one week. Impedance cardiography is non-invasive technique which is as accurate as invasive methods and can be used for maximal exercise testing.

Effect of stimulation of left atrial receptors on the concentration of adrenocorticotropic hormone (ACTH).

The effect of stimulating atrial receptors on the concentration of ACTH in jugular venous blood was examined in dogs anaesthetized with chloralose. The atrial receptors were stimulated by stretching the pulmonary vein-atrial junctions and the atrial appendage. In 13 experimental runs in 9 dogs, it was found that the concentration of ACTH fell in 11 and remained unchanged in 2. The average concentration during control periods was 76.5 +/- 13.6 (pg/ml) and that during stimulation was 60.0 +/- 11.8 (pg/ml). This difference was statistically significant (p less than 0.05; 2 tailed t test). Cutting (2 dogs) or cooling the cervical vagi (3 dogs) abolished this response. It is concluded that stimulation of left atrial receptors reduces the concentration of ACTH in plasma.

Pericarditis resulting from infection and fistula between the left ventricle and transverse colon.

A patient is described who presented with acute pericarditis and acute ulcerative colitis. Previous resection of a left ventricular apical aneurysm had been performed four years earlier, and no problems had arisen until pericarditis developed. After hospital admission and investigation, the patient's condition suddenly deteriorated, and he died. Autopsy showed the causes of death to be a fistula between the left ventricle and transverse colon and septicemia.

Physical training with minimal hospital supervision of patients after coronary artery bypass surgery.

The effect of a program of rehabilitative training involving minimal hospital supervision was investigated in a group of 30 patients who had undergone coronary artery bypass surgery (CABPS). Fifteen of these undertook the training program while the remainder, who undertook a self-regulated program of activity, served as controls. It was found that the surgery per se had significantly improved both the effort tolerance and the highest rate pressure products generated. In the 15 surgical patients who trained we observed a further improvement in work capacity and in the highest rate pressure products achieved. These findings suggest that the effects of training and coronary revascularization are additive and that an effective training program can be instituted with minimal hospital supervision in selected patients who have undergone CABPS.

Reflex inotropic responses of the heart from lung inflation in anaesthetized dogs.

In anaesthetized dogs a tracheal divider was inserted to allow inflation of one lung with various pressures. Left ventricular inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) using a preparation in which aortic pressure, carotid sinus pressure and heart rate were held constant. Heart responses to lung inflation were variable. In five dogs there was a consistent tachycardia, in three bradycardia and in six there was no change. In the dogs in which heart rate increased, inflation of one lung with pressures between 0.5 and 2.0kkPa (5 and 20 cm H2O) resulted in no significant change in dP/dt max. In the remaining dogs there was a decrease in dP/dt max which was more pronounced at the higher inflation pressures. The negative inotropic response was shown to be a reflex with afferent nerve endings in the lung and with the efferent pathway in the sympathetic nerves.

Acid-base changes after cardiorespiratory arrest in the dog.

1. To assess the non-respiratory acid-base disturbance which results from cardiorespiratory arrest experiments were performed on anaesthetized dogs, and circulatory arrest was established either by inducing ventricular fibrillation or by complete occlusion of the great veins. 2. In the first series of experiments (group A) the period of cardiorespiratory arrest was limited to 2.0-3.5 min. It was shown that the nonrespiratory component of the ensuing acid-base disturbance as expressed by the non-respiratory pH was small: in the nine episodes of circulatory arrest after occlusion of the great veins there was a mean reduction in the non-respiratory pH or 0.04 pH unit (range 0.025-0.055), and in seven episodes of ventricular fibrillation the mean reduction was 0.024 pH unit (range 0-0.055). 3. In the second series of experiments (group B) the period of cardiorespiratory arrest was varied from 3.0 to 11.0 min. It was found that the degree of non-respiratory acidaemia was correlated with the duration of arrest but the magnitude of these changes was not large.