Polarcardiographic criteria for myocardial infarction in Chinese men

Polarcardiograms (PCG) derived from xyz leads of the Frank electrocardiogram (ECG) were recorded in the supine position in 1264 initially healthy middle-aged Chinese men who had been under continuing medical surveillance and were re-examined seven years later. Polarcardiographic criteria for myocardial infarction (MI) were demonstrated in 97 men (7.7%), but only 15 of them showed diagnostic Q waves in the electrocardiogram (ECG). Polarcardiographic criteria for MI were independent of age, but ranged from 4.3% in 464 apparently normal men to 38% in 21 men with manifestations of ischemic heart disease. The possible association of polarcardiographic criteria and a history of smoking was limited to those with clinical evidence of heart disease. The “false positive” rate of 4.3% in clinically normal men was similar to that reported in younger Canadians and in Cretan population samples.     

Comprehensive evaluation of electrocardiographic methods for detection of myocardial infarction

In two groups of patients the detection of myocardial infarction (MI) by analysis of four different electrocardiographic methods was evaluated. The various methods included the conventional 12 lead ECG (CV-ECG), the 12 lead ECG derived from Frank XYZ lead system signals (D-ECG), the polarcardiogram (PCG) and the vectorcardiogram (VCG). An invasive group consisted of 137 patients who had undergone cardiac catheterization. An MI was defined as a regional wall motion abnormality in the distribution of a coronary artery with at least 70% diameter reduction. The noninvasive group consisted of 116 patients in whom independent clinical information was limited to noninvasive assessments. In this group, Telemed Computer Systems' interpretation of the conventional (TC-ECG) and derived (TD-ECG) electrocardiogram was also available for comparison. An MI was defined in this group as either a compatible history with documented cardiac enzyme elevations, a resting defect on thallium scan, or a regional wall motion abnormality in a resting, radionuclide isotope ventriculogram. In this study the other methods of ECG evaluation demonstrated no advantage over the electrocardiographer's reading of the conventional ECG.     

Prognostic value of risk factors and exercise testing in men with atypical chest pain

Of 551 men with atypical chest pain enrolled in the Seattle Heart Watch Study, annual follow-up over a 5- to 10-year period identified 36 persons who experienced a primary coronary heart disease event. Only three events were fatal, and they were in men over the age of 50. Cox's regression model confirmed a significant association of the conventional risk factors of smoking (P = 0.03), elevated resting systolic blood pressure (P = 0.02) and hypercholesterolemia (P = 0.03) with primary coronary heart disease events. A count of these three variables was highly predictive (P = 0.002). A positive family history was not predictive. Functional aerobic impairment (P = 0.002) and ST depression (P = 0.0003) were the most useful exercise predictors. In men who had neither risk factors nor abnormal exercise predictors, the percentage free of coronary events at 9 years was 96% compared to 76% in men with one or more of the abnormal exercise findings (P < 0.0001). Of men with only risk factors, 86% remained free of events at 9 years.This study demonstrates that the evaluation of both risk factors and exercise responses enhances the prognostic evaluation of men with atypical chest pain. The classification of men into low-, medium- and high-risk groups can be easily accomplished in office practice.     

Maximal oxygen intake and nomographic assessment of functional aerobic impairment in cardiovascular disease

Maximal oxygen intake (V?o₂max) was measured, using an open circuit technique, during the last 2 to 4 minutes of a multistage treadmill test of maximal exercise in 151 men and 144 women of 29 to 73 years of age. V?o₂max was higher in men than in women (P < 0.0001), lower in sedentary than in physically active persons (P < 0.001 in men, < 0.01 in women), and diminished with age in cross-sectional comparisons. It was highly correlated with duration of exercise by this standardized protocol. Accordingly, by regression equations average normal values for healthy persons could be predicted from sex, activity status, and age; values expected on testing could be estimated from the duration of exercise.Over 800 measurements of V?o₂max were also made during submaximal exercise to define the aerobic requirements under these conditions of testing. This revealed different coefficients for slope and intercept of regression equation for relationship of V?o₂submax to duration of submaximal exercise.Functional aerobic impairment (FAI) is the per cent difference between observed (or estimated) V?o₂max and that predicted from age, sex, and activity status by regression equations. Nomograms for rapid derivation of FAI from age in years and duration of maximal exercise were constructed for healthy men, women, and cardiac men to facilitate clinical usage of these methods.Functional aerobic impairment was 23 per cent in a group of symptomatic hypertensive men; it was 24 per cent in men with healed myocardial infarction, free from angina on maximal exertion, but 41 per cent in men with angina of effort, with or without evidence of prior infarction. In men with either angina or only healed myocardial infarction, impairment was reduced during treatment with nitroglycerin.     

Value of maximal exercise tests in risk assessment of primary coronary heart disease events in healthy men: Five years' experience of the seattle heart watch study

Of 2,365 clinically healthy men who participated in the exercise testing unit of the Seattle Heart Watch, follow-up by annual mail questionnaires identified 47 persons (2 percent) who experienced primary coronary heart disease events. The mean follow-up period (± standard deviation) was 5.6 ±1.4 years. The rates of such events was higher in men 55 or more years of age than in the younger men. A count of the conventional risk factors identified at the time of initial examination was associated with increased 5 year probability of primary coronary heart disease events. However, univariate analysis of the individual risk factors (positive family history, hypertension, smoking, hypercholesterolemia) did not show a significant increase in 5 year probability.Four variables obtained from the response to symptom-limited maximal exercise testing were significantly associated with subsequent primary coronary heart disease events. These predictors were chest pain during maximal exertion, duration of exercise less than 6 minutes with the Bruce protocol, failure to attain at least 90 percent of the age-predicted maximal heart rate and ischémie S-T segment depression.When the conventional risk factors and the exercise predictors are both considered in asymptomatic men, maximal exercise testing identified a small group (1 percent of the total population) who had the highest 5 year probability of primary coronary heart disease (0.33). This group had one or more conventional risk factors and two or more exercise predictors identified. The probability in those with conventional risk factors but with less than two exercise predictors was 0.015. Forty-one percent of the population had no risk factors and the 5 year probability in this group was 0.01. Exercise testing was of no predictive value in the latter group.     

Enhanced risk assessment for primary coronary heart disease events by maximal exercise testing: 10 years'' experience of Seattle Heart Watch

A 10 year prospective community practice study in Seattle of risk of primary morbidity (defined by hospital admission) and mortality due to coronary heart disease in 3,611 men and 547 women initially free of clinical manifestations of this disease revealed a crude incidence of 202 coronary heart disease events, or 4.9% in 6.1 +/- 2.6 years of follow-up. The case fatality rate was 16.8%. Stratification by clinical classification of asymptomatic healthy persons versus patients with atypical chest pain syndrome (not angina pectoris) and hypertension (as classified by physicians) showed an incidence rate of primary events due to coronary heart disease of 2.9, 5.5 (not significant) and 10.0% (p less than 0.001), respectively. Identification of conventional risk factors is known to be important for risk assessment. However, the presence of any conventional risk factor, in conjunction with two or more selected maximal exercise predictors (which vary with the clinical classification) at enrollment, substantially increased the cumulative 6 year incidence rate to 24.3, 15.5 and 33.3% in asymptomatic healthy men, patients with atypical chest pain syndrome and hypertensive patients, respectively. Observation of the exercise predictors in the absence of conventional risk factors increased the risk much less, suggesting that the use of maximal exercise testing for risk assessment in those with no clinical manifestations of disease might be limited to persons with one or more conventional risk factors.     

Approximate normal standards of maximal cardiac output during upright exercise in women

The observed normal ranges of age- and weight-adjusted maximal oxygen uptake and age-adjusted maximal heart rate during upright exercise using the Bruce protocol are shown for 104 asymptomatic women. Cardiac output was measured during upright exercise in 11 normal women with the use of the direct Fick method. On the basis of the relation between oxygen uptake and cardiac output in these 11 women, the cardiac output and stroke volume were estimated by regression in the 104 women to provide normal ranges of age-adjusted values for cardiac output and stroke volume. The potential usefulness of these age-adjusted normal ranges is illustrated by analysis of 21 observations of maximal cardiac output in 16 women with heart disease.     

Maximal cardiac output during upright exercise: Approximate normal standards and variations with coronary heart disease

The observed normal ranges for age- and weight-adjusted maximal oxygen uptake and age-adjusted maximal heart rate measured during the Bruce protocol are shown for 99 normal sedentary men. On the basis of observations in 10 normal men, the relation between oxygen uptake and cardiac output (measured with the direct Fick principle) was used to estimate normal limits of maximal cardiac output and stroke volume for the 99 normal sedentary men. These normal standards were then used to evaluate the results of 77 studies in patients with coronary heart disease who had various clinical and angiographic findings and who performed symptom-limited upright exercise while cardiac output was measured using the direct Fick principle. Patients with angina and infarction showed the greatest impairment of age- and weight-adjusted maximal oxygen uptake and age-adjusted maximal cardiac output, maximal heart rate and maximal stroke volume when compared with patients with angina or healed infarction alone. Arterial-mixed venous oxygen difference at maximal exercise was comparable in the three groups. The surgical cohort (studled after aortocoronary vein bypass grafting) had significantly higher maximal heart rates. Patients with an ejection fraction of less than 50 percent had significantly impaired age-adjusted maximal cardiac output and stroke volume.     

Reduction of plasma triglyceride concentration by acute stress in man.

Three different forms of stress all resulted in acute reduction of plasma triglyceride concentrations. Pyrogen reactions in two hypertriglyceridemic men resulted in the lowering of very-low-density lipoprotein (VLDL) triglyceride levels by 93% and 73% due to decreased secretion of this lipoprotein into plasma. More modest reductions in plasma triglycerides were observed after 2-deoxyglucose-induced intracellular glucopenia and insulin-induced hypoglycemia. With hypoglycemia, the lowering of plasma triglyceride concentration correlated significantly with the stimulation of urinary epinephrine output (r = 0.86) but with neither the urinary norepinephrine response nor with the increase in plasma immunoreactive glucagon levels. To further test whether these changes in plasma triglyceride levels were mediated via the sympathetic nervous system, hypoglycemia was evoked by insulin in subjects with traumatic spinal cord transactions. Two such subjects, who demonstrated sympathetic stimulation in response to hypoglycemia, had evidence of reduced VLDL secretion into plasma, while in two who had no evidence of an adrenergic response. VLDL secretion was not inhibited. Thus, acute lowering of plasma triglyceride concentrations by certain forms of stress appears to be mediated via the sympathetic nervous system.     

Postprandial adipose tissue lipoprotein lipase activity in primary hypertriglyceridemia

The fasting activity of adipose tissue lipoprotein lipase has been previously reported to be either normal or reduced in subjects with a primary form of hypertriglyceridemia. The postprandial activity of adipose tissue lipoprotein lipase has not been previously reported in these subjects. In subjects with primary hypertriglyceridemia the fasting lipoprotein lipase activity eluted from pieces of adipose tissue by heparin and the enzyme activity present in extracts of acetone-ether tissue powders were similar to the level of enzyme activity found in normal subjects. There also was no difference in the postprandial adipose tissue heparin-elutable lipoprotein lipase activity between these two groups when measured after high carbohydrate feeding. When the subjects with primary hypertriglyceridemia were further subdivided by genetic diagnosis, there was no difference in the level of adipose tissue lipoprotein lipase of subjects with familial hypertriglyceridemia, familial combined hyperlipidemia, or in those in whom no specific genetic diagnosis could be made. The change in lipoprotein lipase activity after feeding was inversely related to the fasting enzyme level in both the normal subjects (r = ?0.58, p < 0.05, n = 12) and the hypertriglyceridemic subjects (r = ?0.92, p < 0.01, n = 11). In the normal subjects, the plasma triglyceride response to feeding correlated inversely with the postprandial change in lipoprotein lipase activity (r = ?0.76, p < 0.02, n = 12). Adipose tissue lipoprotein lipase activity in patients with primary lipoprotein lipase deficiency was markedly reduced in the fasting state and remained essentially zero after feeding. This suggests that a functional role exists for the enzyme activity as measured.     

Methods of exercise testing. Step test, bicycle, treadmill, isometrics

Methods of exercise testing are considered in relation to physiologic types, clinical applications and objectives, physiologic differences in end points and inferences, and comparison of oxygen requirements and circulatory responses. Hazards and safety precautions are cited.The multistage treadmill test of submaximal and maximal exercise is described in terms of oxygen requirements, measurement of maximal oxygen uptake, approach to maximal uptake, determination of functional aerobic impairment and assessment of circulatory and electrocardiographic responses. Initial findings are presented of a new, prospective community study (“Seattle Heart Watch”) designed to test the hypothesis that specific persons at risk for future angina pectoris, myocardial infarction or sudden death can be identified by this method.