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Biomedical subjects

A Natarajan

Publications and source records attributed to A Natarajan.

30 records · Page 2Linked to original sources
PubMed1994

Multiway sequential hypothesis testing for tachyarrhythmia discrimination.

A multiway sequential hypothesis testing (M-SHT) algorithm is proposed for simultaneous discrimination of cardiac tachyarrhythmias--supraventricular tachycardia (SVT) and ventricular tachycardia (VT)--from normal sinus rhythm (NSR). The M-SHT algorithm calculates a likelihood function from atrio-ventricular delay measurements, and compares this function with thresholds derived from specified error probabilities for the arrhythmias to be discriminated. Performance of this algorithm was evaluated on dual channel endocardial electrograms recorded in the cardiac electrophysiology laboratory. Two databases were developed, one for development of the algorithm and another for evaluation. The M-SHT algorithm accurately classified 26 out of 28 NSR (2 misclassified as SVT), 31 out of 31 cases of SVT, and 41 out of 43 VT (2 misclassified as NSR). The average length of time taken for classification of the three rhythms was: 3.6 s for NSR, 5.0 s for SVT, and 1.6 s for VT. Unique features of this algorithm are that acceptable error rates for each arrhythmia are independently specified and accuracy can be traded off for a faster detection time, and vice versa.

Adult↗
PubMed1993

Comparison of shortening with timing of wall motion in detecting regional abnormalities of the left ventricle in coronary disease.

Clinical observations suggest that ischemic myocardium may demonstrate delayed wall motion while absolute shortening remains normal. Wall motion timing and percent shortening were examined in 25 patients (7 normal, 18 coronary disease) with 35 mm biplane left ventriculograms and coronary arteriography. Mean age was 63 +/- 2.4 years. Of 17 males and 8 females, 13 had 3 vessel, 4 had 2 vessel, and 1 had 1 vessel disease. Left ventricular regions were analyzed using the Coronary Artery Surgery Study nomenclature and quantitative computer-based analysis as well as visual based qualitative analysis. Regional percent shortening and ejection fraction were calculated from end systolic and end diastolic frames. Regional shortening times were related to global ejection time from 30 frame/sec, frame by frame analysis. Feeder arteries were stenosed ( > 70%) in 135 of 225 left ventricular regions analyzed. Computer detection (shortening and timing) identified 97/225 as abnormal (p < 0.01 vs. feeder artery stenosis) while physicians identified 79/225 as abnormal (p < 0.01 vs. feeder artery stenosis). Of the 97 computer detected abnormal regions, shortening alone detected 47, timing alone detected 39, and 11 showed both abnormalities. Timing analysis increased detection of wall motion abnormalities from 58/225 (26%) to 97/225 (43%) (p < 0.001). Timing abnormalities were noted more (92%) in basal segments, while shortening abnormalities dominated (88%) in apical segments (p < 0.001). Use of temporal measurements in wall motion analysis significantly increases the likelihood of detecting abnormal left ventricular regional wall motion when compared to shortening measurements alone.

Coronary Angiography↗
PubMed1991

The automatic implantable cardioverter-defibrillator: technology for preventing sudden cardiac death.

Sudden cardiac death is caused by a malignant heart rhythm known as ventricular fibrillation. The automatic implantable cardioverter-defibrillator (AICD) is a device that recognizes this rhythm and converts it to a normal sinus rhythm by delivering an electrical shock directly to the heart. This article reviews the technology and clinical status of AICD technology, and the ongoing research into techniques for detecting malignant arrhythmias.

Arrhythmias, Cardiac↗
PubMed1991

Sensors for implantable pacemakers.

Cardiac pacemaker technology has progressed greatly since the first implantable pacemaker was invented in the 1950s. The most recent improvement incorporates sensors that measure the body's metabolic responses and then appropriately pace according to these measurements. This article reviews this technology and examines the various sensors used in rate-responsive pacemakers.

Biosensing Techniques↗
PubMed1988

Frequencies of chromosomal aberrations induced in human blood lymphocytes by low doses of X-rays.

The dose-response for radiation-induced chromosome aberrations in human lymphocytes is usually fitted to the quadratic model. This assumes that the slope is essentially linear at low doses. Empirical observations of linearity at less than 200 mGy are, however, sparse. Some data have been published indicating a non-linear (threshold) response and these are reviewed. In particular one study with X-rays showed a plateau in response up to 50 mGy and with a significant dip below the control level at 4 mGy. The mechanism proposed to explain non-linearity is that low doses stimulate the enzymic repair capability of lymphocytes. Preliminary data are presented from a large experiment by six laboratories in which the low dose-response for X-rays has been re-examined. The plateau in the dose-response relationship, if it exists, does not extend to doses above approximately 10 mGy. No irradiated cells yielded aberration levels significantly below the control. Over the range 0-300 mGy the response can be fitted to a linear regression. There are, however, variations in sensitivity between cells from different donors. An unexpected finding was that some lymphocytes contained greater than 1 exchange aberrations. This may indicate a small subset of cells that are especially susceptible to the induction of aberrations by low doses.

Adult↗
PubMedDate not supplied

Ruptured liver abscess with fulminant amoebic colitis: case report with review.

Amoebic liver abscess is the commonest extra intestinal manifestation of amoebiasis. Intraperitoneal rupture of liver abscess and fulminant necrotizing amoebic colitis are rare occurrences which complicate a severe form of invasive disease caused by Entamoeba histolytica. These complications are associated with a high morbidity and mortality. Synchronous pathological lesions in colon and liver are rare. Still rare is the occurrence of complicated colonic and hepatic invasive amoebiasis presenting as an acute abdomen. One such presentation of ruptured liver abscess and necrotizing amoebic colitis in a 70 year old male which was successfully managed is being reported.

Aged↗
PubMedDate not supplied

Cutaneous histiocytic lesions: a clinical dilemma.

The diagnosis of malignant histiocytosis requires a high index of clinical suspicion, awareness of its atypical features and availability of various tissue samples for morphological and special studies. The case reported here highlights the diagnostic difficulties encountered in a patient diagnosed as malignant histiocytosis who presented with cutaneous lesions in multiple foci, which included the face, groin and forearm. Only after repeated biopsies and special stains, a diagnosis of malignant histiocytosis was arrived at. Chemotherapy with CHOP regimen (cyclophosphamide, doxorubicin, vincristine and prednisone) was initiated. The response to chemotherapy was good and the patient is doing well eleven months after initial diagnosis.

Antineoplastic Combined Chemotherapy Protocols↗
PubMedDate not supplied

A rare case of dual obstruction of the colon.

The commonest cause of large bowel obstruction is colorectal malignancy. Volvulus of the colon is a rare cause and caecal volvulus accounts for less than 1% of all cases of intestinal obstruction. Reports of concurrent occurrence of obstructing lesions of the right and left colon are rare and anecdotal. We report a case of Caecal volvulus and carcinoma of the rectosigmoid in a 70-year-old lady.

Aged↗
PubMedDate not supplied

Emergency inferior mesenteric vein to left renal vein shunt in variceal bleeding: an alternative technique.

Shunt procedures being used in the emergency surgical management of variceal bleeding include total (portocaval shunt-PCS), partial (mesocaval H graft shunt-MCS) or selective shunts (distal splenorenal shunt-DSRS). We report the use of inferior mesenteric vein to left renal vein (IMV to LRV) shunt in an emergency situation in a 24 year old patient with noncirrhotic portal hypertension with variceal bleeding.

Adult↗