Search PubMed⌕ Search

Biomedical subjects

M K Heng

Publications and source records attributed to M K Heng.

At least 37 records · Page 2Linked to original sources
PubMed1987

Significance of T wave normalization in the electrocardiogram during exercise stress test.

Although normalization of previously inverted T waves in the ECG is not uncommon during exercise treadmill testing, the clinical significance of this finding is still unclear. This was investigated in 45 patients during thallium-201 exercise testing. Patients with secondary T wave abnormalities on the resting ECG and ischemic exercise ST segment depression were excluded. On the thallium-201 scans, the left ventricle was divided into anterior-septal and inferior-posterior segments; these were considered equivalent to T wave changes in leads V1 and V5, and aVF, respectively. A positive thallium-201 scan was found in 43 of 45 (95%) patients and in 49 of 52 (94%) cardiac segments that showed T wave normalization. When thallium scans and T wave changes were matched to sites of involvement, 76% of T wave normalization in lead aV, was associated with positive thallium scans in the inferior-posterior segments, and 77% of T wave normalization in V1 and V5 was associated with positive thallium scans in the anterior-septal segments. These site correlations were similar for reversible and fixed thallium defects, and for patients not on digoxin therapy. Similar correlations were noted for the sites of T wave changes and coronary artery lesions in 12 patients who had angiography. In patients with a high prevalence for coronary artery disease, exercise T wave normalization is highly specific for the presence of the disease. In addition, it represents predominantly either previous injury or exercise-induced ischemic changes over the site of ECG involvement, rather than reciprocal changes of the opposite ventricular wall.

Adult↗
PubMed1986

Blood pressure and electrocardiographic response to dental treatment with use of local anesthesia.

The incidence of ST segment depression during tooth extraction was significantly higher in patients with cardiac disease than it was in patients without cardiac disease, indicating that the cardiac patients experienced myocardial ischemia. The almost equivalent incidence of ST segment depression during anesthetic administration and surgery suggests that the administration of local anesthetic is as stressful as tooth extraction for cardiac patients. Medical consultation before dental treatment and use of stress-reduction techniques may be indicated for patients with or suspected to have cardiac disease.

Adult↗
PubMed1986

Antiguanosine antibodies: a new marker for procainamide-induced systemic lupus erythematosus.

Antinuclear antibodies are present in most patients receiving procainamide. To ascertain whether IgG antiguanosine antibodies are associated with the development of the symptoms of systemic lupus erythematosus, we compared the levels of these antibodies in the sera of 65 patients receiving procainamide: 18 with procainamide-induced symptoms and 47 asymptomatic patients. Antinuclear antibodies measured by immunofluorescence were present in the 18 patients with drug-induced symptoms but also in 24 asymptomatic patients. Similarly, elevated serum levels of antibodies to single-stranded DNA were found in 15 patients with symptoms and in 20 asymptomatic patients. In contrast, levels of IgG antiguanosine antibodies were elevated in 15 patients with drug-induced symptoms, but in only 3 asymptomatic patients. Antiguanosine antibodies binding to single-stranded DNA were found primarily in patients with arthritis, pleuritis, and pericarditis. These results suggest a strong association between IgG antiguanosine antibodies and major manifestations of procainamide-induced systemic lupus erythematosus.

Adult↗
PubMed1985

Clinical evaluation of left ventricular function using the cardiac helical fiber model: an echocardiographic study.

The cardiac helical fiber concept was introduced in 1969 and was shown mathematically to provide better approximations of normal ejection fractions compared with the conventional circumferential fiber model. The clinical applicability of this concept was evaluated noninvasively by M-mode and two-dimensional echocardiography in 55 subjects: 10 with aortic insufficiency, 10 with congestive cardiomyopathy, eight with hypertension, eight who were long-distance runners, 12 who were active and seven who were sedentary normals. Comparison of myocardial shortening by the circumferential and helical fiber models showed that the former discriminated only two groups of subjects, while endocardial and epicardial helical shortening discriminated three and four groups, respectively. Regression analyses suggest that more than 90% (r2 = 0.92) of variation in ejection fraction may be accounted for by variation in endocardial shortening, and that more than 75% (r2 = 0.77) of variation in observed endocardial shortening may be accounted for by variation in epicardial contraction. The study demonstrates that the helical fiber length concept may be useful for the noninvasive evaluation of left ventricular function in man.

Adult↗
PubMed1985

Mexiletine: double-blind comparison with procainamide in PVC suppression and open-label sequential comparison with amiodarone in life-threatening ventricular arrhythmias.

The antiarrhythmic effects of mexiletine (n = 14) were compared to procainamide (n = 16) by a double-blind parallel protocol in 30 patients (group I) with frequent premature ventricular contractions (PVCs) (greater than 20/hr), and to amiodarone by an open-label sequential approach in 25 patients (mean left ventricular ejection fraction of 32.6 +/- 13.4%) with life-threatening ventricular arrhythmias (group II) resistant to two or more conventional agents. The predetermined end point of therapy in group I patients was met in 6 of 14 (43%) given mexiletine, with 7 (50%) requiring drug discontinuation for severe gastrointestinal or central nervous system side effects and only 3 of 16 patients (19%) given procainamide, with 5 (31%) developing limiting side effects. Increases in dose led to a higher efficacy rate for PVC suppression with a corresponding increase in side effects with mexiletine; with procainamide, the higher dose was not associated with greater PVC suppression. In group II patients, mexiletine was effective in 4 (16%), with one patient discontinuing the drug during long-term therapy; mexiletine was ineffective in 16 (64%) and early side effects developed in 5 (20%). Patients not responding to or not tolerating mexiletine were given amiodarone; 20 of 21 (95%) responded with arrhythmia control after the loading dose. During a mean follow-up period of 2 years, sudden death occurred in two patients, death from heart failure in two, and death from subarachnoid hemorrhage in one patient; 15 (75%) patients are alive and free of arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Reduction of ventricular arrhythmias by atenolol.

The effects of atenolol on ventricular arrhythmias were evaluated in 25 men with significant ventricular ectopy. The patients received 2 weeks each of placebo, 50, 100, and 200 mg of oral atenolol. Efficacy was determined by weekly 24-hour Holter monitors. In 20 patients who completed the protocol, the frequency of total ventricular ectopic beats, ectopic couplets, and ventricular tachycardia was significantly decreased after treatment. The complexity of ventricular ectopy was also decreased as measured by the Lown grade and the proportion of hours in which multiform ectopic beats were present. A therapeutic response, defined as the minimum percentage reduction in ventricular arrhythmias to demonstrate an effect due to atenolol rather than spontaneous variation, was achieved in up to 70% of patients for total number of ectopic beats, 75% for ectopic couplets, and 73% for ventricular tachycardia beats. The results show that oral atenolol is an effective agent for the treatment for ventricular arrhythmias.

Adult↗
PubMed1985

Estimation of regional stress in the left ventricular septum and free wall: an echocardiographic study suggesting a mechanism for asymmetric septal hypertrophy.

Although asymmetric septal hypertrophy is noted in a wide variety of cardiac disorders, its cause remains unclear. One possible mechanism is that the septum is subjected to greater systolic stress because of its flatter (more eccentric) contour. This was investigated noninvasively in nine subjects by estimation of regional myocardial stress from measurements of blood pressure by cuff sphygmomanometry and by echocardiographic examinations of left ventricular shape and dimensions. Analysis of left ventricular cavity shape showed that both the free and septal walls were elliptical, but the septum was more eccentric than the free wall. Using a conceptual model to determine changes in regional systolic stress, the theoretical rate of increase in regional stress relative to pressure (delta S/delta P) was significantly greater in the septum compared to the free wall. Increased hypertrophy of the septum to normalize this increased delta S/delta P may be the cause of asymmetric septal hypertrophy in many disorders associated with elevated left ventricular pressure.

Adolescent↗
PubMed1984

Exercise two-dimensional echocardiography for diagnosis of coronary artery disease.

To improve ultrasound images during exercise 2-dimensional echocardiography (2-D echo), a device was developed to hold the transducer and maintain its orientation relative to the heart. The value of this technique in detecting wall motion abnormalities and changes in ejection fraction was evaluated in 54 men undergoing stress test for angina. Thallium-201 scanning, electrocardiography and exercise 2-D echo were recorded concurrently. Technically satisfactory echo studies were obtained in 47 patients (87%). The sensitivity and specificity of exercise echo in the detection of myocardial ischemia as judged by wall motion abnormalities were 100% and 93%, respectively. Sixteen patients with normal thallium scans increased their ejection fraction (EF) estimated by echo (from 52 +/- 1% at rest to 67 +/- 1% at maximal exercise, p less than 0.001); all showed an increase of 5% or more. In contrast, 11 patients who had reversible thallium scan defects showed a consistent decrease in EF (from 53 +/- 2% at rest to 43 +/- 2% during exercise, p less than 0.001); 20 patients with irreversible thallium scan defects showed no specific trend in the EF (48 +/- 2% at rest and 50 +/- 2% during exercise, difference not significant). Changes in heart rate and blood pressure did not distinguish the 3 groups of patients. Our technique of exercise 2-D echo may be useful for detecting wall motion abnormalities and EF changes during exercise and possibly enhance the sensitivity of thallium scanning in the noninvasive diagnosis of coronary artery disease.

Adult↗
PubMed1984

Hemodynamic effects of high-dose sustained-action oral isosorbide dinitrate in stable angina.

Hemodynamic effects of sustained-action oral isosorbide dinitrate (40 or 80 mg) were studied in 10 patients with stable angina for a period of 16 hours. Control hemodynamic parameters monitored for eight hours prior to the administration of isosorbide dinitrate showed no significant change. However significant reduction in mean arterial pressure, cardiac index, pulmonary artery wedge pressure, mean pulmonary artery pressure, double product (systolic pressure multiplied by heart rate), stroke volume index, and stroke work index occurred in the first two hours and persisted for 12 hours following the administration of isosorbide dinitrate. Heart rate did not change significantly for 12 hours. It can be concluded that the hemodynamic effects of sustained-action oral isosorbide dinitrate occur in the first two hours and last up to 12 hours. The predominant hemodynamic effect appears to be on the myocardial preload. The antianginal effect of the drug could be attributed to the reduction of myocardial oxygen demand reflected by a decrease in the double product and stroke work. The duration of the hemodynamic changes observed in this study indicates that high-dose oral isosorbide dinitrate could be administered conveniently two or three times daily.

Administration, Oral↗
PubMed1983

Exercise two-dimensional echocardiography: a technique for improving ultrasound images during exercise stress.

A system of exercise stress echocardiography was developed in which, during exercise on a bicycle ergometer in a semirecumbent position, the echocardiographic transducer is held by a special device which maintains a relatively constant position between the transducer and the heart. The system was evaluated in 21 healthy subjects and technically satisfactory studies were obtained in 20. In these, the resolution and relative position of the cardiac image remained stable throughout exercise. Blood pressure and heart rate increased appropriately with our protocol with supine exercise; 95% of the subjects reached 90% of their predicted maximum heart rate for age. Ejection fraction measured by echocardiography increased from 54 +/- 1% to 70 +/- 1%. It is concluded that the use of our transducer-holding device in subjects performing exercise in the supine position significantly improves ultrasonic image quality and should enhance the clinical usefulness of exercise stress echocardiography.

Adult↗
PubMed1981

Experimental evaluation of the extent of myocardial dyssynergy and infarct size by two-dimensional echocardiography.

The extent of left ventricular (LV) dyssynergy was assessed noninvasively in 19 dogs with two-dimensional echocardiographic short-axis sections during myocardial ischemia and infarction. After coronary occlusion, two-dimensional echocardiography uniformly indicated an increase in LV end-diastolic volume and a decrease in LV ejection fraction. Two-dimensional echocardiographic measurements of dyssynergy were evaluated and compared in three subgroups against (1) the extent of LV dyssynergy determined by force-gauge mapping during 10 coronary occlusions of 30-60 minutes' duration in eight open-chest dogs, (2) infarct size delineated by nitroblue tetrazolium (NBT) staining of left ventricular slabs after 48 hours of left anterior descending coronary artery (LAD) occlusion in five closed-chest dogs, and (3) NBT infarct size after 3-hour LAD occlusion followed by 45 hours of reperfusion in six closed-chest dogs. Linear regression analysis of results from these three comparisons gave good correlations (r = 0.89) for groups 1 and 2; in group 2, the extent of dyssynergy by two-dimensional echocardiography was consistently greater than infarct size by NBT. In group 3, the correlation was poor (r = 0.39). These results suggest that an adequate estimate for the extent of LV dyssynergy or infarct size may be obtained with two-dimensional echocardiography during myocardial ischemia or infarction, but not in the presence of coronary reflow, which causes an acute discrepancy between myocardial viability and function.

Animals↗
PubMed1980

Cross-sectional echocardiography. III. Analysis of mathematic models for quantifying volume of symmetric and asymmetric left ventricles.

Cross-sectional echocardiography was utilized for quantification of volume in 19 formalin-fixed left ventricles in the presence or absence of ventricular symmetry, defined by the ratio of septal-lateral to anterior-posterior diameter. In 10 symmetric ventricles this ratio was 1.23 +/- 0.06 (mean +/- SEM), whereas in nine asymmetric ventricles the ratio was 1.80 +/- 0.07. Area, diameter, and length measurements were obtained from short- and long-axis cross-sectional images of the left ventricle and volume was calculated by five mathematical models previously described. To evaluate the reliability of each model, echocardiographic left ventricular volume was compared by linear regression and percent error analyses to directly measured fluid volume. In symmetric ventricles, excellent correlations (r = 0.996 to 0.967) and reasonable mean percent errors (6% to 31%) were observed for all models. In asymmetric ventricles, models utilizing short-axis area or two short-axis diameters retained high correlation coefficients (r = 0.985 to 0.956) and similar mean percent errors, but standard formulas previously used with M-mode echo and angiography showed lower correlations (r = 0.886 to 0.873) and higher mean percent errors (52% to 54%). Thus, in the presence of ventricular asymmetry, analysis of short-axis areas or diameters with cross-sectional echocardiography is well suited for quantification of left ventricular volumes.

Cardiac Volume↗
PubMed1980

Cross-sectional echocardiography. II. Analysis of mathematic models for quantifying volume of the formalin-fixed left ventricle.

Cross-sectional echocardiography was used to quantify volume in 21 canine left ventricles that were fixed in formalin and immersed in mineral oil. Area, length and diameter measurements were obtained from short- and long-axis cross-sectional images of the left ventricle and volume was calculated by seven mathematic models. Calculated volume was then compared, by linear regression and percent error analyses, with fluid volume of the left ventricle, obtained by filling the chamber with a known amount of fluid. Volumes ranged from 13-146 ml. Mathematic models using short-axis area and long-axis length gave higher correlation coefficients (r = 0.982 and r = 0.969) and lower mean errors (10-20%) than standard formulas previously used for M-mode echo and angiography. Thus, short-axis area analysis with cross-sectional echocardiography is well-suited for quantifying left ventricular volumes in dogs.

Animals↗
PubMed1979

Regional 99m technetium diphosphonate uptake in experimental dog heart infarct: relation to duration and severity of ischaemia.

Regional uptake of 99mTechnetium diphosphonate was compared with regional myocardial blood flow 6, 12 and 24 h after the onset of myocardial infarction in dogs, and with regional creatine kinase depletion 24 h after the onset. Uptake of the imaging agent increased from 6 to 24 h, but no consistent relationship could be demonstrated between regional myocardial blood flow and regional uptake of the diphosphonate nor between uptake and regional creatine kinase depletion at the centre or border of the infarct. In addition, inappropriately high levels of 99m Technetium uptake could be demonstrated in the epicardial layer of the normal tissue surrounding the infarct. We conclude that diphosphonate uptake is not quantitatively related to the severity of ischaemia, and that use of this substance for imaging may over-estimate myocardial infarct size.

Animals↗
PubMed1979

Cross-sectional echocardiography. I. Analysis of mathematic models for quantifying mass of the left ventricle in dogs.

Cross-sectional echocardiography was used to quantify left ventricular mass noninvasively in 21 dogs. Short- and long-axis cross-sectional images of the left ventricle were reproducibly traced at endocardial and epicardial borders during stop-motion video-tape replay. We used area, length and diameter measurements to calculate left ventricular mass by seven mathematic models, including the standard formulas used with M-mode echocardiography and cineangiography. Calculated mass was compared with excised weight of the left ventricle by regression and percent error analyses. Formulas using short-axis areas and long-axis length resulted in higher correlation coefficients (0.94--0.95) and lower mean errors (6--7%) than for standard formulas. Since short-axis areas account for regional left ventricular irregularities, noninvasive quantification of left ventricular mass by cross-sectional echocardiography in dogs is most accurate with formulas using short-axis areas.

Animals↗
PubMed1978

The effect of glucose-insulin-potassium on experimental myocardial infarction in the dog.

The effect of glucose-insulin-potassium (GIK) infusions was studied in 45 dogs after left anterior descending coronary artery ligation. GIK caused a modest increase in lactate concentration in small veins draining the infarct but did not affect glucose uptake. No effect on creatine kinase activity in the infarct was seen from GIK, although there was a slight increase in blood flow to the centre of the infarct. We concluded that GIK did not reduce infarct size in this experimental model.

Animals↗
PubMed1978

Failure of high doses of propranolol to reduce experimental myocardial ischemic damage.

Myocardial creatine phosphokinase (CPK) activity and myocardial blood flow (MFB, 15 +/- mu microspheres) were measured at 24 hours after ligation of the left anterior descending coronary artery in nine untreated anesthetized dogs, in eight dogs pretreated with intravenous propranolol 5 mg/kg and in eight which had both pretreatment as well as infusion of propranolol (1.25 mg/kg/hour) after occlusion. Loss of CPK activity from the border and center zones of the myocardial infarct was similar in extent in dogs which had pretreatment but no infusion of propranolol as it was in the control group. Loss of CPK from the center zone was greater (P less than 0.005) in dogs receiving pretreatment followed by constant infusion of the drug. Propranolol had no significant effect on collateral blood flow to the border or center zone of the infarct. In separate experiments, there was no important difference in hemodynamic measurements, except a slower heart rate (P less than 0.01), when pretreated dogs were compared with control dogs up to 2 hours after coronary ligation. We conclude that propranolol given in this dose does not influence nyocardial damage, on the basis of regional myocardial blood flow or tissue CPK depletion values at 24 hr after coronary occlusion.

Animals↗