Biomedical subjects
N G Dewhurst
Publications and source records attributed to N G Dewhurst.
Mechanical treatment for obesity.
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Severe pulmonary hypertension and multiple left coronary arterial fistulas in association with congenital hepatic fibrosis.
Multiple fistulous communications between the left anterior descending coronary artery and the left ventricle were found in a 55 year old woman with congenital hepatic fibrosis presenting with breathlessness. At cardiac catheterisation severe pulmonary hypertension was also found. In view of the persistent hypoprothrombinaemia, severe thrombocytopenia, and the multiple fistulas the risk of operation was thought to be unacceptable and she continues on medical treatment.
Diagnosis and prognosis of right ventricular infarction.
The values of several non-invasive methods for the diagnosis of right ventricular necrosis in inferior myocardial infarction were compared in 51 consecutive patients who underwent serial radionuclide ventriculography, pyrophosphate scintigraphy, and cross sectional echocardiography. In addition a unipolar electrocardiographic lead V4R was recorded on admission, daily, and during episodes of further pain. Profound right ventricular dysfunction was evident in 50% of patients studied by radionuclide methods after inferior myocardial infarction but recognition on clinical groups alone was poor. Functionally important right ventricular infarction was best detected and followed serially by radionuclide ventriculography. Echocardiographic methods for evaluating right ventricular ejection fraction correlated poorly with radionuclide methods. Increased uptake of radioactivity by the right ventricle on pyrophosphate scintigraphy usually indicated poor right ventricular function, but a scan that was negative in the right ventricular territory did not exclude dysfunction. ST segment elevation in V4R was not specific for right ventricular infarction and its routine use may lead to overdiagnosis of this condition. Serial measurements suggest that profound right ventricular dysfunction persists after acute inferior infarction and is associated with considerable morbidity and mortality. Of 25 patients with severe right ventricular dysfunction, six died in the late hospital period. In the remaining 19 patients mean right ventricular ejection fraction over a two month period did not improve; six patients had persistent right ventricular dyskinesia and features of chronic right ventricular failure developed in three survivors.
Clinical significance of "reciprocal" S-T segment depression in acute myocardial infarction. Relative contributions of infarct size and ischemia at a distance.
The early electrocardiographic results in 100 patients surviving their first myocardial infarction who thereafter underwent serial radionuclide ventriculography were reviewed. Site of infarction was anterior in 46 and inferior in 54, with lateral extension in two patients. Those with "reciprocal" S-T segment depression of more than 1 mm in the acute phase (n = 53) sustained larger infarcts on the basis of enzyme criteria (mean peak serum creatine kinase, +/- SD, 2,203 +/- 1,271 versus 1,544 +/- 1,197 IU/liter, p less than 0.02), with a higher incidence of ventricular akinesis and dyskinesis. Reciprocal change was more common during inferior infarction (n = 33) than anterior infarction (n = 20). Despite equivalent peak enzyme levels following anterior and inferior infarction with reciprocal S-T depression (mean peak creatine kinase 2,330 versus 2,128, NS), there was marked sparing of left ventricular function in the latter group (mean left ventricular ejection fraction 0.31 +/- 0.14 versus 0.42 +/- 0.09, p less than 0.01). Of 17 patients who died within two years of infarction, 14 had reciprocal changes. Patients who died after anterior infarction with reciprocal changes (n = 5) had poor left ventricular function compared with those who died after inferior infarction (n = 9; left ventricular ejection fraction, +/- SD, 0.21 +/- 0.05 versus 0.38 +/- 0.11, p less than 0.01). One third of those recovering from inferior infarction with reciprocal changes subsequently had positive results on exercise testing, and of the nine patients who died, five had good left ventricular function (left ventricular ejection fraction 0.44 to 0.50). Infarct size and ventricular wall motion abnormality proved to be of major importance in the production of inferior reciprocal S-T change during anterior infarction, and subsequent mortality was related to poor left ventricular function. The proximity of the precordial leads to left ventricular myocardium may increase the detection of concomitant anterior ischemia during inferior infarction, and those who exhibit reciprocal change are presumably at risk from left main stem or anterior descending lesions but with reasonably good ventricular function represent a more attractive population for invasive investigation.
Ventricular performance and prognosis after primary ventricular fibrillation complicating acute myocardial infarction.
To examine the relationship between early arrhythmias, infarct size and prognosis, we compared 22 consecutive patients surviving acute myocardial infarction (AMI) and primary ventricular fibrillation (VF) with a control population after AMI uncomplicated by primary VF. Left ventricular ejection fraction (EF) was measured by radionuclide ventriculography before discharge from hospital. Mean EF was significantly reduced below normal following AMI with or without primary VF (normal 0.57 +/- 0.05, mean +/- SD; P less than 0.01). Mean EF was lower among patients who survived primary VF than among those with infarction uncomplicated by primary arrhythmia (0.33 +/- 0.12 v. 0.46 +/- 0.07; P less than 0.01). There were striking differences in EF between those patients with anterior and those with inferior infarction. Mean EF for those surviving primary VF after transmural anterior infarction (0.23 +/- 0.06) was lower than those who had primary VF after transmural inferior infarction (0.43 +/- 0.06; P less than 0.01). Normal left ventricular function was seen in four individuals who developed no further complications. Recurrent primary ventricular arrhythmia was seen only in those individuals subsequently shown to have reduced EF. Low EF (less than 0.35) was seen in 12 patients with primary VF in the context of anterior infarction, five developed breakthrough ventricular arrhythmias despite therapy and in a limited follow-up period, three have died.
"Reciprocal" depression of the ST segment in acute myocardial infarction.
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Comparative prognostic value of radionuclide ventriculography at rest and during exercise in 100 patients after first myocardial infarction.
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An index of valvular regurgitation from a radionuclide bolus.
Mitral and aortic regurgitation was assessed from analysis of activity-time curves from right and left ventricles following the intravenous bolus injection of 99Tcm-labelled human serum albumin. The differences in the initial arrival times and the mean transit times for the ventricles were combined to provide an index of regurgitation. The mean index for 18 patients with good ventricular function and no regurgitation was -0.07 +/- 0.55 (SD) seconds. This was not significantly different from the mean value of 0.39 +/- 1.22 s obtained for 9 patients with left ventricular failure but no regurgitation. The indices for 16 patients with mitral or aortic regurgitation agreed well with the severity as assessed by contrast angiography. The mean indices for the mild, moderate and severe regurgitation groups were 2.62 +/- 1.13 s, 5.30 +/- 3.05 s and 10.15 +/- 3.62 s respectively.
The prevalence and prognosis of ventricular dyskinesis after myocardial infarction using radionuclide ventriculography.
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The influence of ectopic heart beats in gated ventricular blood-pool studies.
Direct data collection from ventricular blood-pool studies were stored in frame mode in a computer and by means of a modified tape recorder, the blood-pool image and ECG were recorded on tape. At the end of the study the tape data were replayed into the computer. The ECG signal was passed through a trigger circuit that detected the R wave which was sampled by the computer once every msec. Contractions outside of the desired range could be rejected along with the subsequent contraction. Of seven patients whose calculated ejection fractions were changed by more than 0.03, all had frequent (one in 20) ectopic contractions. The distorted ventricular volume curves were effectively restructured by the constraining procedure, changing the end-systolic volume and EF. Computer modeling showed a linear relationship between the percent of ectopic contractions and the underestimate of ejection fraction. One ectopic beat in ten led to a 5% underestimate of EF.