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Biomedical subjects

N G Pandian

Publications and source records attributed to N G Pandian.

At least 145 records · Page 8Linked to original sources
PubMed1984

Laser myoplasty for hypertrophic cardiomyopathy. In vitro experience in human postmortem hearts and in vivo experience in a canine model (transarterial) and human patient (intraoperative).

The feasibility of performing a myotomy/myectomy for hypertrophic cardiomyopathy (HC) by means of laser phototherapy was evaluated experimentally in vitro and in vivo, and the procedure then applied to a patient intraoperatively. In vitro experience revealed that the beam of an argon laser, delivered directly or via an optical fiber, could both cut and vaporize myocardium, producing a myotomy/myectomy morphologically similar to that produced by the conventional blade technique. In vivo experiments, in which the beam of an argon laser was delivered via an optical fiber to the ventricular septum of a canine heart, confirmed that a laser myoplasty could be achieved in 4 of 5 dogs by a transarterial approach. Finally, laser myoplasty was performed intraoperatively in a patient with HC, using a 200-mu fiber interfaced with an argon laser. Measured laser power was 1.5 W; cumulative exposure was less than 4 minutes; the myoplasty was 4 X 1 X 0.5 cm. These investigations establish the feasibility of using laser therapy to create a myoplasty trough that is similar in appearance to that typically achieved by the conventional blade technique. Illumination of the intraventricular operative field and precise modeling of the myoplasty trough constitute the principal advantages of laser myoplasty for HC.

Adult↗
PubMed1984

In vitro analysis of boundary identification techniques used in quantification of two-dimensional echocardiograms.

Echocardiographic cross-sectional areas of 10 formalin-fixed animal left ventricles were determined by 5 independent observers using black-white (B-W) and mid-spot (M-S) endocardial boundary identification techniques. The echocardiographic cross-sectional areas were compared with the true anatomic cross-sectional areas of the same 10 hearts to determine the accuracy, variability and reliability of each technique. The results of these comparisons revealed that the M-S technique was more accurate than the B-W technique (3.3 +/- 7.2 vs 34.9 +/- 8.6% error). However, the B-W technique was more reliable in that it had a smaller interobserver and estimated intraobserver variability. The M-S technique had a 6% greater intraobserver variability.

Animals↗
PubMed1984

Computer-assisted edge detection in two-dimensional echocardiography: comparison with anatomic data.

Four methods of computer-based edge detection were evaluated for identification of endocardial and epicardial borders on 2-dimensional echocardiograms of excised hearts. A method was also evaluated for observer identification of cardiac borders in the same hearts. The accuracy of computer-derived borders and of observer-derived borders were determined by comparison to anatomic borders measured from photographs of slices of the excised hearts. Echocardiographic borders were compared with anatomic borders by calculation of segmental cavity areas and wall thickness. Each of the methods tested (computer and observer) identified endocardial borders accurately, resulting in cavity segment areas that correlated well with the corresponding anatomic data (r = 0.90 to 0.92). Regional wall thicknesses correlated less well with anatomic data (r = 0.74 to 0.80), suggesting that endocardial borders were identified more accurately than were epicardial borders. Thus, the methods of computer-assisted echocardiographic border detection tested identified the endocardium and epicardium as accurately as a trained observer evaluating unprocessed echocardiograms. Computer-based methods of border detection may be useful in the automated analysis of clinical echocardiograms.

Animals↗
PubMed1984

Diagnosis of constrictive pericarditis by two-dimensional echocardiography: studies in a new experimental model and in patients.

The purpose of this study was to determine the value of two-dimensional echocardiography in detecting constrictive pericarditis. Serial two-dimensional echocardiography was performed in eight closed chest conscious dogs with experimental constrictive pericarditis, using a new model that creates constrictive pericarditis by the introduction of a pericardial irritant mixture. Constrictive pericarditis was confirmed in these dogs by cardiac catheterization and pathologic examination. Four patients with constrictive pericarditis and three patients with restrictive cardiomyopathy (amyloidosis) were also studied. Analysis of short-axis two-dimensional echocardiograms was performed to determine the frame by frame change in left ventricular cavity areas throughout diastole. Curves of diastolic left ventricular cavity area change versus percent duration of diastole were constructed for each animal and human subject. Pericardial thickness was measured at various gain settings on two-dimensional and M-mode echocardiograms and at post-mortem examination. In dogs with constrictive pericarditis, the echocardiograms seriously overestimated and correlated poorly with pathologic measurements of pericardial thickness. In dogs after constrictive pericarditis developed, 69 +/- 11% (mean +/- SD) (range 50 to 84) of cavity area change occurred in the initial 30% of diastole compared with 35 +/- 7% (range 20 to 45) in control two-dimensional echocardiograms (p less than 0.001). Four patients with constrictive pericarditis showed similar accelerated cavity expansion in early diastole, but three patients with cardiac amyloidosis showed more variable left ventricular diastolic expansion rates. It is concluded that two-dimensional echocardiograms can demonstrate characteristic diastolic filling abnormalities in constrictive pericarditis, but cannot accurately measure pericardial thickness.

Amyloidosis↗
PubMed1984

Contrast echocardiography in acute myocardial ischemia: I. In vivo determination of total left ventricular "area at risk".

Myocardial contrast echocardiography has been shown recently to accurately assess the "area at risk" for necrosis after acute coronary occlusion in the experimental model. Risk area quantitation, however, has been studied primarily from single tomographic planes. Because the three-dimensional extent of myocardial necrosis depends on the total volume of myocardium at risk, the total left ventricular "area at risk" was determined in 11 dogs (Group A) with either left anterior descending or left circumflex artery occlusion using contrast echocardiography and compared with risk area determined by technetium autoradiography. An excellent correlation was found between the two methods (r = 0.96%, y = 0.91x + 1.5, p less than 0.001, SEE = 3.17). A comparison of risk area for individual levels of the left ventricle using both methods, however, showed some variation in the degree of correlation, with the poorest fit being apparent at the apex. To identify the source of the variation, errors caused by data registration were minimized in six additional dogs (Group B) by implanting epicardial markers at a single level and measuring "area at risk" at this level using both methods. When no registration error was present, the correlation between the two methods was excellent (r = 0.99, y = 0.92x + 2.6, p less than 0.001, SEE = 0.55). In conclusion, the "area at risk" for infarction after acute coronary occlusion can be determined accurately for the entire left ventricle as well as for a single tomographic slice using myocardial contrast echocardiography. This was validated using technetium autoradiography, which is an established method of determining "area at risk" in the experimental setting.

Animals↗
PubMed1984

Tricuspid valve myxoma infected with dysgonic fermenter-2.

We have described a patient with an infected myxoma attached to the tricuspid valve. Unlike those previously reported, our patient had a significant underlying disease, chronic lymphocytic leukemia, and presented the problem of multiple pulmonary infiltrates in an immunosuppressed host, with persistently negative blood cultures. The infecting bacterium, isolated only at operation, was a recently described fastidious gram-negative rod belonging to the CDC group dysgonic fermenter-2.

Bacterial Infections↗
PubMed1983

Relations between 2-dimensional echocardiographic wall thickening abnormalities, myocardial infarct size and coronary risk area in normal and hypertrophied myocardium in dogs.

Systolic wall thickening abnormalities are sensitive indicators of ischemia and infarction. One purpose of this investigation was to assess the relation between coronary risk area, infarct size and wall thickening abnormalities (dyskinesia) using 2-dimensional echocardiography (2-D echo) in a closed-chest conscious dog model of acute myocardial infarction. The second purpose was to study the effects of systemic hypertension (SH) and left ventricular (LV) hypertrophy on these relations. Our hypothesis was that the infarct size and the extent of 2D echocardiographic dyskinesia would be quantitatively different in SH-LV hypertrophy, a condition in which coronary vascular reserve is diminished. Permanent circumflex coronary occlusion was performed in 15 conscious normal dogs and in 14 dogs with LV hypertrophy secondary to renal hypertension. Two-dimensional echocardiograms were obtained before, 20 minutes after and 2 days after coronary occlusion. The systolic wall thickening along 12 equidistant radii was analyzed in short-axis images. Percent dyskinesia on 2-D echo was defined as the percentage of radii showing systolic thinning. Infarct size was determined pathologically and risk area was determined angiographically. For a given risk area, coronary occlusion resulted in a larger infarction in dogs with SH-LV hypertrophy than in normal dogs (p less than 0.05). Two-dimensional echocardiographic dyskinesia correlated well with infarct size both at 20 minutes (r = 0.92) and 2 days (r = 0.94); dyskinesia modestly overestimated the infarct size and underestimated the risk area. The relations were similar in both normal and SH-LV hypertrophy groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Effect of ischemia, hypertrophy, hypoxia, acidosis, and alkalosis on canine defibrillation.

Our purpose was to assess the effect of myocardial ischemia, left ventricular hypertrophy, and systemic hypoxia and acid-base abnormalities on the energy requirements for defibrillation. We determined the defibrillation threshold (DFT), the minimum energy required to defibrillate. DFT was not significantly elevated after left anterior descending coronary occlusion, nor was there a relationship between the size of the occluded coronary distribution area (coronary risk area) and the change in DFT in individual animals. Renal hypertension and left ventricular hypertrophy were induced by unilateral nephrectomy and contralateral renal artery stenosis. DFT in left ventricular hypertrophy dogs was not significantly higher than in dogs without hypertrophy. Finally, we induced systemic hypoxia and acid-base abnormalities. Neither respiratory nor metabolic acid-base disturbances affected DFT, but during systemic hypoxia (O2 tension 45 +/- 2) DFT fell from 83 +/- 49 to 58 +/- 28 J (P less than 0.01). Thus in dogs, myocardial ischemia, left ventricular hypertrophy, and acid-base abnormalities do not elevate defibrillation energy requirements, whereas hypoxia reduces the energy needed to defibrillate.

Acidosis↗
PubMed1983

Quantitative texture analysis in two-dimensional echocardiography: application to the diagnosis of experimental myocardial contusion.

We postulated that the analysis of regional image texture in two-dimensional (2D) echocardiograms would be an accurate method to differentiate normal from abnormal myocardial structure. We tested this hypothesis with quantitative texture measures to study the regional, spatial distribution of echo amplitudes in 2D echocardiograms performed before and immediately after blunt left chest trauma was induced in six anesthetized dogs. After trauma the contused region of myocardium appeared brighter and exhibited an altered myocardial texture. By use of a set quantitative texture measures, we found no significant differences in pretrauma images when normal regions were compared with regions to be contused. Also, we found no difference when we compared the normal regions in each animal in pretrauma vs posttrauma images. Twelve measures, however, differentiated normal from contused regions within the posttrauma images (p values ranged from .0057 to .0001 by multivariate analysis of variance). These texture measures were capable of differentiating normal from abnormal tissue only when texture along the azimuthal (lateral) direction was calculated. We conclude that regions of myocardial contusion exhibit visibly altered local echo-amplitude patterns (altered image texture) and that these image texture alterations may be quantified with digital image analysis techniques. These findings suggest that quantitative texture calculations may be a useful approach to ultrasound tissue characterization.

Animals↗
PubMed1983

Detection of acute myocardial infarction in closed-chest dogs by analysis of regional two-dimensional echocardiographic gray-level distributions.

We hypothesized that acute myocardial infarction could be detected in standard two-dimensional echocardiograms of closed-chest dogs by evaluating regional echo amplitude distributions using computerized image analysis. We tested this hypothesis by performing standard, 2.4 MHz two-dimensional echoes before and 2 days after circumflex coronary occlusion in seven closed-chest dogs. Control and infarcted regions of interest were studied in digitized stop-frame images. Average gray level was calculated for each region of interest, and the shape of the gray-level distribution was analyzed by calculation of skewness and kurtosis and by qualitative features of shape. Average gray level increased significantly from the pre- to postocclusion images in the infarcted regions (16.7 +/- 4.2 vs. 32.4 +/- 4.4 units, P less than 0.01), but not in the control regions (17.4 +/- 4 vs. 22.3 +/- 5.5., P = NS). Average gray level could not distinguish between infarcted and normal regions within the postocclusion images (36 +/- 5.2 vs. 33.6 +/- 5.8, P = NS). Three independent observers qualitatively evaluated histogram shape and correctly identified 7/7 MI regions (100% sensitivity) and 14/20 normal regions (70% specificity). Quantitatively, infarct regions exhibited a significant decrease in kurtosis from pre- to postocclusion images (7.1 +/- 4.0 vs. 5.2 +/- 2.9, P = NS). Within postocclusion images, infarcted regions displayed a significantly lower kurtosis than did normal regions (0.27 +/- .47 vs. 2.5 +/- 1.0, P less than .01). We conclude that acute myocardial infarction may be detected in closed-chest dogs by analyzing regional echo amplitude data from standard two-dimensional echocardiograms.

Animals↗
PubMed1982

Two-dimensional echocardiography in experimental coronary stenosis. I. Sensitivity and specificity in detecting transient myocardial dyskinesis: comparison with sonomicrometers.

The purpose of this study was to assess the sensitivity and specificity of two-dimensional echocardiography in detecting ischemia-induced transient myocardial dyskinesis. We prepared an open-chest dog model of severe coronary stenosis (90% reduction of circumflex coronary artery diameter) and induced ischemia by acutely raising myocardial oxygen requirements with i.v. isoproterenol and acute aortic constriction. The changes observed with echocardiography were compared with those obtained by intramyocardial sonomicrometers placed side by side or in an endocardial-epicardial orientation. Ischemia was defined as systolic wall expansion or thinning on sonomicrometers and two-dimensional echocardiography. We found complete agreement between sonomicrometers and two-dimensional echocardiography in all control tracings and after ischemia was induced; whenever dyskinesis occurred it was seen by both techniques. Although there was qualitative agreement between echocardiographic and sonomicrometric techniques, there were quantitative differences in the assessment of wall thickening. Such differences may be related to malalignment of the sonomicrometers, echocardiographic resolution limitations or other technical factors. We conclude that two-dimensional echocardiography is a sensitive and specific technique for detecting transient myocardial ischemia, and therefore should be useful for demonstrating exercise-induced ischemia in patients with coronary artery disease.

Animals↗
PubMed1982

Two-dimensional echocardiography in experimental coronary stenosis. II. Relationship between systolic wall thinning and regional myocardial perfusion in severe coronary stenosis.

To determine if there is a quantitative relationship between systolic contraction abnormalities (demonstrated by two-dimensional echocardiography) and reduced myocardial perfusion in a setting of moderate and severe coronary stenosis, we created 70% or 90% reduction in circumflex coronary artery diameter in open-chest dogs. Transient ischemia was induced by superimposing increased myocardial oxygen requirements (i.v. isoproterenol, aortic constriction) in the presence of the stenosis or by decreased coronary perfusion (lowering arterial pressure with i.v. nitroprusside, nitroglycerin, or hemorrhage). Acute systolic wall thinning show by two-dimensional echocardiography or by implanted myocardial sonomicrometers was taken as functional evidence of myocardial ischemia. Myocardial perfusion was determined by radiolabeled microspheres when wall thinning was apparent. Systolic wall thinning could not be induced by these interventions when the degree of coronary stenosis was only 70%. Systolic wall thinning occurred only when increased myocardial oxygen requirements or decreased aortic pressure were superimposed on 90% coronary stenosis. Under these conditions, myocardial perfusion was reduced to 28 +/- 27 ml/100 g/min (mean +/- SD), 15--25% of control. Aortic diastolic pressure was a major determinant of ischemia in that contraction abnormalities produced by a 90% stenosis and vasodilators or hemorrhage could be acutely reversed by superimposing acute aortic constriction, which elevated arterial pressure; myocardial perfusion increased correspondingly. Thus, the demonstration of transient systolic wall thinning by two-dimensional echocardiography during a stressful intervention indicated that severe coronary stenosis was present, and that the perfusion of the acutely dyskinetic myocardial area was 25% of control or less.

Animals↗
PubMed1980

Transfemoral temporary pacing and deep vein thrombosis.

The incidence of deep vein thrombosis following transfemoral temporary pacing was prospectively assessed in 20 consecutive patients using serial 125I-fibrinogen scanning, impedance plethysmography, and measurements of fibrin degradation products. Four patients underwent venography. Of the twenty patients, five (25%) had definite evidence of deep vein thrombosis, six demonstrated equivocal abnormalities, and nine had no evidence of thrombosis. Thrombosis was found only in the legs used for pacing. Of the five with deep vein thrombosis, one had positive findings in all the noninvasive tests. Venography confirmed the diagnosis in the other four; one had thrombosis of the femoral vein, one had thrombosis of several calf veins, and one had thrombosis of both the thigh and calf veins; the fourth patient had thrombosis of the entire deep venous system of the leg. This latter patient was the only one who had clinical evidence of venous thrombosis. The patients with deep vein thrombosis did not differ in clinical characteristics from those without thrombosis. There was no relationship between the occurrence of deep vein thrombosis and the number of venepunctures, the state of the electrode, the presence of the introducer sheath in the femoral vein, or the duration of pacing. In conclusion, deep vein thrombosis is a common complication of transfemoral temporary pacing and the high incidence of its occurrence should be considered before deciding upon the site of entry for a temporary pacemaker.

Adult↗
PubMedDate not supplied

Echocardiographic assessment of the right ventricular response to exercise.

Although exercise echocardiography has been widely used among adult patients, its application in the pediatric population has not been well explored. A few studies have examined the response of the pediatric left ventricle (LV) to exercise. However, although many congenital heart defects result in abnormalities of right ventricle (RV) anatomy and function, little is known about the RV's response to exercise. The purpose of this study was to assess the effect of exercise on RV dimensions and function and to compare the RV's response to that of the LV. Twenty-nine consecutive pediatric subjects (age 12.1 +/- 3.2 years) with structurally normal hearts, who were referred for exercise stress testing, were studied echocardiographically prior to and within 2 minutes following peak exercise. Adequate studies were obtained in 28 of the 29 patients. RV dimensions and area during the first 2 minutes following the termination of exercise were slightly smaller than those observed prior to exercise. However, the decline in RV area at end systole was proportionally greater than the decline in RV area at end diastole. Consequently, the RV fractional area change following exercise exceeded the preexercise value. The response of the LV to exercise was qualitatively similar to that observed for the RV. This study demonstrates that echocardiographic measurement of RV size and function immediately after exercise is feasible. Data from this study can be used as normal reference standards against which data from patients with congenital heart defects may be compared.

Adolescent↗