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Biomedical subjects

M M Laks

Publications and source records attributed to M M Laks.

At least 19 recordsLinked to original sources
PubMed1992

Functional significance of post-myocardial infarction left ventricular hypertrophy: a beneficial response.

Hypertrophy of noninfarcted myocardium occurs as a chronic response to myocardial infarction, but no previous study has related the changes in wall thickness to serial changes in left ventricular function. Thus the functional significance of postinfarction hypertrophy is unknown. The purpose of this study was to determine the relationship between the development of postinfarction hypertrophy and the resting left ventricular ejection fraction measured by two-dimensional echocardiography. After occlusion of the proximal left anterior descending coronary artery in 11 dogs, the ejection fraction fell acutely (0.63 +/- 0.08 to 0.33 +/- 0.10, p less than 0.001) and rose at 3.5 months to 0.62 +/- 0.12. End-diastolic thickness of the noninfarcted left ventricle increased (11 +/- 1.0 mm to 13 +/- 1.4 mm, p less than 0.01) as did left ventricular mass (101 +/- 18 gm to 134 +/- 21 gm, p less than 0.0001). Restoration of the ejection fraction toward the baseline value correlated with the increases in left ventricular mass (r = 0.79, p = 0.007) and wall thickness (r = 0.71, p = 0.025). Hypertrophy of the noninfarcted myocardium correlated with the magnitude and approximately paralleled the time course of the improvement in the ejection fraction and therefore may have had a beneficial effect on resting left ventricular function as a chronic adaptation to myocardial infarction.

Animals↗
PubMed1991

Current role of catheter ablative procedures in patients with cardiac arrhythmias. A report for health professionals from the Subcommittee on Electrocardiography and Electrophysiology, American Heart Association.

Catheter ablative techniques have assumed an increasingly important role in the treatment of patients with drug-refractory cardiac arrhythmias. Catheter ablation of the AV junction is considered the procedure of choice for management of patients without bypass tracts with drug-resistant supraventricular arrhythmias. Catheter techniques have been used with increasing frequency in attempts to ablate accessory AV tracts. These techniques currently appear to be less effective than surgical techniques but involve less morbidity and expense. In some centers, accessory pathway ablation using catheter techniques is the procedure of first choice in selected patients with drug-refractory tachycardia mediated by an accessory pathway. Catheter ablation of ventricular tachycardia should be reserved for patients with mappable ventricular tachycardia who are not candidates for cardiac electrosurgery or insertion of an automatic defibrillator. The development of more flexible catheters and more manageable energy delivery systems holds promise for more effective catheter techniques.

Arrhythmias, Cardiac↗
PubMed1989

Usefulness of esophageal pill electrode atrial pacing with quantitative two-dimensional echocardiography for diagnosing coronary artery disease.

Noninvasive diagnosis of coronary artery disease (CAD) is difficult in patients who are unable to exercise. In this study esophageal pill electrode atrial pacing was used as a myocardial stress not requiring exercise, and changes in ejection fraction and pressure volume ratio during pacing with 2-dimensional echocardiography were quantitatively analyzed. All patients had completed a Bruce protocol treadmill exercise test and had undergone coronary arteriography. Of 26 patients, 22 were successfully paced (85%). Comparable rate-pressure products were obtained for treadmill exercise (23,500 +/- 5,900 mm Hg/min) and pacing (24,100 +/- 4,400 mm Hg/min; difference not significant). Of the 22 patients completing the study 8 had normal coronary arteries (group I) and 14 had CAD (group II). The change in ejection fraction with pacing in group I patients was not significant (3 +/- 8%). In group II ejection fraction decreased with pacing (-8 +/- 13%; p = 0.025). The pressure/volume ratio increased in group I with pacing (3.8 +/- 1.8 mm Hg/min/m2; p = 0.05) and was unchanged in group II (0.3 +/- 1.8 mm Hg/min/m2; difference not significant). Using an ejection fraction decrease with pacing or a failure to increase pressure/volume ratio with pacing as criterion for the presence of CAD, similar predictive accuracies were obtained when compared to treadmill exercise testing. Esophageal pill electrode atrial pacing with quantitative 2-dimensional echocardiography may be a useful noninvasive, nonexercise method to detect CAD.

Adult↗
PubMed1989

Effects of chronic infusion of norepinephrine on cardiac structure, function, and biochemistry: physiologic versus pathologic hypertrophy.

Ventricular hypertrophy should be divided into at least physiologic and patholgic states in order to clarify structural and functional clinical alterations. The elucidation of the structural, functional, and biochemical mechanisms of ventricular hypertrophy is vital to designing effective preventive and therapeutic measures for the hypertensive patient. Tissue markers may help differentiate pathologic from physiologic hypertrophy. Studies have established the concept that norepinephrine may be a myocardial cellular hypertrophying hormone. The studies ranged from the direct application of norepinephrine to isolated myocardial cells to the chronic subhypertensive infusion of norepinephrine into the conscious, free-roaming dog. Norepinephrine infusion can produce physiologic ventricular hypertrophy or a pathologic state of hypertrophic cardiomyopathy, the former by a three- to four-month infusion and the latter by an infusion of more than six months. The biochemical effect of subhypertensive infusion of norepinephrine was studied prior to the production of ventricular hypertrophy, thereby permitting the elucidation of the mechanism of the hypertrophic process. The biochemical stimulus for the production of myocardial cellular hypertrophy is postulated to be a diminution of cyclic AMP and a stimulation of alpha-1 receptors. Because the ventricular septum has the highest content of adenylate cyclase, which does not increase with cyclic AMP, these changes are postulated to be the biochemical basis for septal hypertrophy in the disease entity hypertrophic cardiomyopathy. A unique conscious-canine model for the production of a myocardial infarction capable of creating a controlled localized occlusion of the coronary artery is presented.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effect of long-term high intensity aerobic training on left ventricular volume during maximal upright exercise.

The purpose of this study was to determine whether high intensity, long-term aerobic training causes the left ventricle to develop different mechanisms for increasing cardiac output during submaximal and maximal upright bicycle exercise. Fifteen competitive collegiate long distance runners and 14 healthy sedentary adults were studied with use of subcostal view four chamber two-dimensional echocardiography at rest and during and at peak maximal upright bicycle exercise. At rest, the athletes had a larger end-diastolic volume index (85 +/- 14 ml/m2) (mean +/- 1 SD) than that of the sedentary adults (62 +/- 14 ml/m2) and a larger end-systolic volume index (37 +/- 11 versus 21 +/- 6 ml/m2). During low and moderate intensity exercise, end-diastolic and stroke volume indexes increased in both groups, but at high intensity exercise and at peak exercise the end-diastolic volume index of both groups decreased significantly below rest value (athletes, 61 +/- 14; sedentary subjects, 46 +/- 10 ml/m2, both p less than 0.001 compared with rest). Reflecting the decreased end-diastolic volume index, at peak exercise, the stroke volume index had decreased from intermediate exercise values in both groups and was not different from rest values. Therefore, although long distance runners have a dilated left ventricle at rest, they utilize the same mechanisms as sedentary adults for increasing cardiac output during upright dynamic exercise. At low and moderate level exercise, the Frank-Starling mechanism is a dominant mechanism for increasing cardiac output, but at peak exercise, probably because of reduced diastolic left ventricular filling, enhanced contractility is the major mechanism for maintaining stroke volume.

Adult↗
PubMed1989

Regional stress in a noncircular cylinder.

Several mathematical formulas are presented for estimating regional average circumferential stress and shear stress in a thick-wall, noncircular cylinder with a plane of symmetry. The formulas require images of exterior and interior chamber silhouettes plus surface pressures. The formulas are primarily intended for application to the left ventricle in the short axis plane near the base (where the meridional radius of curvature is normally much larger than the circumferential radius of curvature) and to blood vessels. The formulas predict stresses in a variety of chambers to within 3% of finite element values determined from a large-scale structural analysis computer program called ANSYS.

Animals↗
PubMed1989

Verapamil induced ventricular hypertrophy in conscious dogs.

Verapamil is used clinically in the treatment of various cardiac diseases including hypertrophic cardiomyopathy. Its long term effects on ventricular mass are not well known. In 11 conscious dogs heart rate, aortic and left ventricular pressures, cardiac output, a methoxamine induced stress ventricular function test and left ventriculography were performed. These variables were measured prior to and following a mean 7.2 month infusion of verapamil at 0.005 or 0.01 mg.kg-1.min-1 using a subcutaneously implanted pump. Resting haemodynamic variables and left ventricular ejection fraction [60(SD 6) v 55(6)%] were unchanged between baseline and chronic verapamil studies, but the slope of the methoxamine induced stress ventricular function test decreased from 3.9(0.8) to 2.1 (1.3). After verapamil was discontinued the mean slope of the stress ventricular function test returned to the baseline 4.0(1.7). Total ventricular weight increased 22% from 176.1(17.5) g.m-2 in controls to 215.6(29.5) g.m-2 (p less than 0.01) in the verapamil animals. The right ventricular weight increased 25% from 46(5.9) to 57.6(9.1) g.m-2 (p less than 0.01); the septum weight increased 26% from 42.5(4.1) to 53.7(7.2) g.m-2 (p less than 0.001); and the left ventricular free wall weight increased 19% from 87.4(9.8) to 103.9(15.7) g.m-2 (p less than 0.01). The increase in ventricular weights was not due to fibrosis or oedema since hydroxyproline contents and wet/dry ratios were not increased. In conclusion, a chronic infusion of verapamil in conscious dogs caused no change in resting haemodynamic variables but produced reversible depression of stress ventricular function and biventricular and septal hypertrophy.

Animals↗
PubMed1989

Functional significance of hypertrophy of the noninfarcted myocardium after myocardial infarction in humans.

Hypertrophy of the noninfarcted left ventricle as a chronic response to myocardial infarction has been demonstrated in animals and at autopsy in humans. However, the functional significance of postmyocardial infarction hypertrophy is a subject of dispute. The purpose of this study was to determine the time course of development of postmyocardial infarction hypertrophy of the noninfarcted myocardium in humans and to assess its functional significance. Subcostal view, two-dimensional echocardiograms were recorded at rest and during peak exercise, 6 and 40 weeks postmyocardial infarction in 45 patients (16 anterior, 20 inferior, nine non-Q wave infarcts), for measurement of left ventricular mass and ejection fraction. The left ventricular mass index increased from 94 +/- 30 to 118 +/- 27 g/m2 (p less than 0.01) during the time of the two studies. There was a significant correlation between the change in left ventricular mass index and improved resting ejection fraction (r = 0.48, p less than 0.001) and exercise ejection fraction (r = 0.48, p less than 0.001) at the follow-up study. Of the 32 patients who increased their left ventricular mass index greater than 7%, 18 improved their rest ejection fraction greater than 0.05 units and 17 improved their exercise ejection fraction greater than 0.05 units. Conversely, of the 13 patients who failed to increase their left ventricular mass index, only three improved their rest ejection fraction and one improved the exercise ejection fraction (Fisher's exact test, p less than 0.05). We reached three conclusions. First, in humans, significant hypertrophy of the noninfarcted myocardium can be detected by two-dimensional echocardiography, 9 months postmyocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

A predictive instrument for acute ischemic heart disease to improve coronary care unit admission practices: a potential on-line tool in a computerized electrocardiograph.

Each year, 1.5 million patients are admitted to coronary care units (CCUs) for suspected acute ischemic heart disease, but for half of these, the diagnosis is ultimately ruled out. In this study, conducted in the emergency rooms (ERs) of six New England hospitals, the authors sought to develop a diagnostic aid to help ER physicians reduce the numbers of CCU admissions for patients without true acute cardiac ischemia. In phase 1, from data on 2,801 patients, they developed a predictive instrument for use in a handheld programmable calculator, which, based on a mathematical logistic regression formula, computes a patient's probability of having acute cardiac ischemia. In phase 2, a 1-year prospective trial including 2,320 ER patients at the six hospitals, physicians' diagnostic specificity for acute ischemia increased when the probability value determined by the instrument was made available to them (p = 0.002), without a drop in sensitivity. Among patients without acute ischemia, the number of CCU admissions decreased 30% (p = 0.003), without an increase in missed diagnoses of ischemia. The proportion of patients in the CCU without acute ischemia dropped from 44% to 33%. If similar findings were widespread, the use of this predictive instrument could reduce the number of CCU admissions in the United States by more than 250,000 per year. As originally envisioned, the physician could use a pocket-sized programmable calculator to allow quick access to the instrument's probability value, or an ER triage nurse might compute the probability value and write it on the clinical record for the physician's use.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Care Units↗
PubMed1988

Effects of pulmonary emphysema on QRS infarct size score.

Pulmonary emphysema can produce false-positive electrocardiographic (ECG) changes of anterior myocardial infarction (MI). This problem was not addressed in earlier studies of the Selvester 54 Criteria/32 Point QRS score for MI size. The purpose of this study was to examine an automated Hewlett Packard ECG Computer Language (HP-ECL) implementation of the QRS score in the following groups of subjects. Patients who had been studied for possible lung disease with pulmonary tests, including lung volumes, were divided into two groups: group 1 (n = 133), with abnormal tests (emphysema); and group 2 (n = 102), with normal tests (no emphysema). Two other groups were studied: group 3 (positive controls, n = 44), with greater than 3 QRS points for MI on ECG and documented coronary disease with wall motion abnormalities on angiography; and group 4 (negative controls, n = 146), 49 house staff and 97 clinically normal men. A frontal plane P axis greater than 65 separated 90% of patients with emphysema from those without. Of 133 patients with emphysema, 60 (45%) had greater than 3 QRS points for MI on ECG, mainly from Q criteria in aVL and V1-V3; decreased R criteria 1 in V2, V3, and V6; and abnormal R/S criteria in V4-V6. Using HP-ECL, the QRS score was readily modified so that when P axis was greater than 65 these MI size criteria were suppressed. This resulted in a more appropriate incidence of MI diagnoses: 2% (down from 45%) in emphysema patients, no change in specificity, and minor reduction in sensitivity to MI in infarct controls from 100% to 96%.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗