Duration of phases of left ventricular systole using indirect methods. II. Acute myocardial infarction

Normal values of aortic dimensions assessed by multidetector computed tomography in the Copenhagen General Population Study

Aims

Accurate assessment of aortic dimensions can be achieved using contrast-enhanced computed tomography. The aim of this study was to define normal values and determinants of aortic dimensions throughout multiple key anatomical landmarks of the aorta in healthy individuals from the Copenhagen General Population Study.

Methods and results

The study group consisted of 902 healthy subjects selected from 3000 adults undergoing cardiovascular thoracic and abdominal computed tomography-angiography (CTA), where systematic measurements of aortic dimensions were performed retrospectively. Individuals included were without any of the following predefined cardiovascular risk factors: (i) self-reported angina pectoris; (ii) hypertension; (iii) hypercholesterolaemia; (iv) taking cardiovascular prescribed medication including diuretics, statins, or aspirin; (v) overweight (defined as body mass index ≥30 kg/m2); (vi) diabetes mellitus (self-reported or blood glucose >8 mmol/L); and (vii) chronic obstructive pulmonary disease. Maximal aortic diameters were measured at seven aortic regions: sinuses of Valsalva, sinotubular junction, ascending aorta, mid-descending aorta, abdominal aorta at the diaphragm, abdominal aorta at the coeliac trunk, and infrarenal abdominal aorta. Median age was 52 years, and 396 (40%) were men. Men had significantly larger aortic diameters at all levels compared with women (P < 0.001). Multivariable analysis revealed that sex, age, and body surface area were associated with increasing aortic dimensions.

Conclusion

Normal values of maximal aortic dimensions at key aortic anatomical locations by contrast-enhanced CTA have been defined. Age, sex, and body surface area were significantly associated with these measures at all levels of aorta. Aortic dimensions follow an almost identical pattern throughout the vessel regardless of sex.

Effect of cardioselective beta-blockade on heart function and chest pain in acute myocardial infarction

Systolic time intervals and the a/H ratio were recorded in 20 patients with uncomplicated acute myocardial infarction over a period of five days. The initial high heart rate and systolic blood pressure and the short PEP and ICT indicating a sympathetic overactivity were spontaneously normalized during the first week of infarction. LVET was reduced indicating a fall in stroke volume and the a/H ratio was unchanged at the high levels suggestive of elevated preload or LVEDP. In 10 patients with acute myocardial infarction and recurrent chest pain recordings on noninvasive parameters were made before and 30 min after intravenous injection of practolol. In addition, 7 patients with chest pain, classified as acute myocardial infarction, were given practolol. The average dose of practolol was 17.9 mg ranging from 5 to 30 mg. An almost immediate and pronounced relief of pain was observed in all patients and no signs of impaired left ventricular function appeared. The product of systolic blood pressure and heart rate was decreased by practolol and the PEP and the ICT were prolonged to normal values while no changes were seen in LVET and a/H ratio. On 126 occasions practolol was given in dosages ranging from 5 to 30 mg (mean 8 mg) to 75 patients with acute myocardial infarction and recurrent chest pain. A satisfactory pain relief was seen on 108 occasions. It is suggested that an inappropriate sympathetic overactivity is an important factor in provoking recurrent chest pain in acute myocardial infarction. Administration of the beta-adrenergic blocking agent practolol resulted in pain relief due to reduction of heart work and in severity of myocardial ischemia. The beta-blocking agent was well tolerated in the present study. Continuous beta-blockade during the whole hospital stay to patients with acute myocardial infarction seems to be a very attractive therapy in order to preserve the ischemic myocardium and limit the size of infarction.

Systolic time intervals in acute myocardial infarction

Systolic time intervals (STI) have been measured in 50 individuals without heart disease. Electromechanical systole (QS2), left ventricular ejection time (LVET) and preejection period (PEP), but not PEP/LVET, were correlated to heart rate (HR). Regression equations were made and used when correcting STI for HR in two groups of patients: a) 51 patients with acute myocardial infarction (AMI) b) 22 patients with chest pains, but no AMI. STI was measured on the first 4 days, on the 7th day, on the day of discharge and at a control about 60 days later. In the AMI group there was a reduction in left ventricular performance from the 1st to the 4th day, and the difference in shortening of LVET was significant (p less than 0.001), while PEP and PEP/LVET increased from the 1st to the 3rd day (p less than 0.001). Between the AMI and the control groups there were significant differences (p less than 0.001) in LVET and PEP/LVET on the 3rd, 4th and 7th day, and in PEP on the 3rd and 4th day. STI was not found to separate clinical groups with heart failure of different severity. The survivors had a lower (p less than 0.05) PEP/LVET on the 1st day than those who died. The various localization of the infarction made no difference in STI. LVET was found to be strongly correlated (p less than 0.001) to the hydroxybutyric dehydrogenase values.

Hemodynamic effects of the cardioselective beta-blocking agent metoprolol in acute myocardial infarction. A 24-hour catheterization study

Hemodynamic changes were studied in ten patients with uncomplicated transmural myocardial infection during 24 hours on beta-blockade. The cardioselective beta-adrenergic blocking drug metoprolol was injected (15 mg i.v.) within the first 24 hours after onset of chest pain and was followed by oral therapy (25-50 mg at 6-hour intervals). There was a decrease in heart rate, systolic BP, and cardiac output, which was most marked after the injection. The stroke volume and diastolic BP for the whole group of patients remained unchanged. The pulmonary artery end diastolic pressure did not change significantly after the injection but a continuous fall was obtained in three out of four patients with initially elevated values. The preejection period, measured from the ECG and carotid pressure curve, as initially short and was prolonged in all patients after administration of the beta-blocking drug. It is concluded that the cardioselective beta-blocking drug metoprolol may be used in selected patients in the acute phase of myocardial infarction without danger of hemodynamic deterioration during the first 24 hours of therapy. The selection of patients can be based on clinical criteria. In this study signs of left heart failure, hypotension, poor peripheral circulation, bradycardia, and AV block were regarded as contraindications.

Evaluation of systolic time intervals in patients with angina pectoris

We have explored the systolic time intervals of 52 patients with angina pectoris at the time of their hospitalization in our wards. Our results are in close agreement with published data, essentially indicating prolongation of the preejection time and shortening of the ejection time. These alterations of systolic times can be interpreted pathophysiologically as as expressing reduced myocardial contractility. The long PEP-short LVET polygraph picture, occurring in the course of chronic ischemic heart disease, reveals the deficit of myocardial contractility at a stage of the disease at which clinical evidence of left ventricular failure is usually not yet detectable.

Left ventricular systolic time intervals in patients with acute myocardial infarction

Left ventricular systolic time intervals were measured daily during 601 episodes of acute myocardial infarction. The ratio of pre-ejection period to ejection period during the first 24 hours permitted patients to be arranged in six prognostic groups with mortalities while in hospital ranging from 4 to 60 per cent. The only factors completely independent of the systolic time intervals which were shown statistically to be associated with high mortality while in hospital were defects in atrioventricular and intraventricular conduction.

A critical review of the systolic time intervals

The theoretical basis for the use of the systolic time intervals has been largely established. The method has been validated by direct measures from within the circulatory system. Standards for equipment and technique have been defined. Numerous clinical studies have demonstrated the value of this quantitative noninvasive technique for assessing left ventricular performance. At present there is need for further studies of the clinical usefulness of the systolic time intervals to improve both diagnosis and therapy of various cardiovascular disorders.

A study of systolic time intervals during uninterrupted exercise

A method has been developed for obtaining measurements of the systolic time intervals during uninterrupted graded exercise in the upright position on a bicycle ergometer. The method has been applied to 112 subjects divided into 4 groups: two of normal subjects below and above the age of 40, respectively (mean ages 30 and 48 years), and two of patients (mean ages for each about 50 years), both with coronary insufficiency, but one without and the other with abnormality of left ventricular function as shown by ventriculography. The measurements obtained yield linear relations between total electromechanical systole (QS2) and heart rate, between pre-ejection period (PEP) and RR interval for each subject. The average standard deviation about the regression is less than 6 ms for all three regression lines; the average correlation coefficient is greater than 0-93. The younger group of normal subjects have a significantly shorter PEP compared to the older group. Indices have been derived which separate the patient groups from each other and from the normal subjects. Using these indices 86 per cent of all the subjects were correctly classified according to the group to which they belonged. It is concluded that measurements of STI during uninterrupted exercise offer valuable information in the assessment of cardiac patients.

Usefulness of systolic time intervals in coronary artery disease

This review summarizes current knowledge concerning the value of systolic time intervals in coronary artery disease. Although the usual pattern of prolongation of the preejection period (PEP) and shortening of the left ventricular ejection time (LVET) characteristic of left ventricular failure is seen in acute myocardial infarction, the systolic time intervals (as well as all other measures) are profoundly influenced by adrenergic hyperactivity characteristics of this disorder. Adrenergic stimulation normally shortens both the PEP and LVET indexes and decreases the PEP/LVET ratio. The degree of shortening of electromechanical systole (QS2) is directed related to the excessive adrenergic tone. Patients with the greatest systolic time interval abnormalities have a poorer prognosis, a greater incidence of congestive heart failure and more abnormalities of directly measured indexes of left ventricular performance. The systolic time intervals are useful for assessing left ventricular performance in chronic coronary artery disease as well. In chronic coronary artery disease the PEP/LVET ratio and angiographically determined left ventricular ejection fraction are closely correlated ( r = -0.76), but the level of this correlation is less than that in other forms of left ventricular disease. The left ventricular ejection time index is prolonged after exercise in patients with angina pectoris when compared with findings in normal subjects. Failure of the ischemic ventricle to respond to adrenergic stimulation is the most likely mechanism. Addition of the postexercise left ventricular ejection time to standard treadmill stress testing identifies a significant number of patients (23 percent) who would have had false negative results by electrocardiographic criteria alone. In addition, this index provides confirmatory evidence in those with apparently positive electrocardiographic test data. The systolic time intervals have been useful in assessing both medical and surgical therapy in coronary artery disease. The test can be performed repeatedly and provides a measure of both left ventricular performance and extent of adrenergic hyperactivity. Thus, evaluation of therapy represents the most useful future application of systolic time intervals.

Effect of chronic beta-adrenergic receptor blockade in congestive cardiomyopathy

Adrenergic beta-blocking agents were given to 7 patients with advanced congestive cardiomyopathy who had tachycardia at rest (98 plus or minus 13 beats/min). The patients were on beta-adrenergic receptor blockade for 2 to 12 months (average 5-4 months). One patient was given alprenolol 50 mg twice daily and the other patients were given practolol 50 to 400 mg twice daily. Virus infection had occurred in 6 of the patients before the onset of symptoms of cardiac disease. All patients were in a steady state or were progressively deteriorating at the start of beta-adrenergic receptor blockade. Conventional treatment with digitalis and diuretics was unaltered or reduced during treatment with beta-blocking agents. An improvement was seen in their clinical condition shortly after administration of the drugs. Continued treatment resulted in an increase in physical working capacity and a reduction of heart size. Noninvasive investigations including phonocardiogram, carotid pulse curve, apex cardiogram, and echocardiogram showed improved ventricular function in all cases. The present study indicates that adrenergic beta-blocking agents can improve heart function in at lease some patients with congestive cardiomyopathy. Furthermore, it is suggested that increased catecholamine activity may be an important factor for the development of this disease, as has been shown in animal experiments.

Evaluation of impedance cardiography as a non-invasive means of measuring systolic time intervals and cardiac output

Impedance cardiography was used for non-invasive determinations of systolic time intervals (STI) and cardiac output. The results were compared with simultaneously obtained invasive measurements of STI from central aortic pressure curves and of cardiac output using the dye-dilution technique. The study was performed on eight dogs during increasing halothane concentration. A close correlation was found between non-invasively and invasively measured left ventricular ejection time = LVET (r = 0.986) and pre-ejection period - PEP (r - 0.948). Measurements of cardiac output derived from changes in thoracic impedance were determined 1) using a fixed value of p (p - the resistivity of blood) and 2) using an individual value of p based on the actual hematocrits. When compared to cardiac outputs obtained by dye-dilution the correlation coefficients were r = 0.806 and r = 0.816, respectively. Impedance cardiography is a useful method of evaluating changes in cardiac output. The method permits simultaneous observations of changes in STI and cardiac output as an index of cardiac function.