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Biomedical subjects

R M Donaldson

Publications and source records attributed to R M Donaldson.

At least 73 records · Page 4Linked to original sources
PubMed1982

Evaluation of drug-induced changes in myocardial repolarisation using the paced evoked response.

The use of the pace evoked response system in the assessment of drug-induced changes in myocardial repolarisation is reported. Using a conventional pacing electrode lead for both pacing and sensing, this system records the dominantly local repolarisation which follows a controlled (paced) depolarisation from the same site. Measurements of the latency of the ventricular evoked response at matched heart rates before and after drug administration permit the accurate direct comparison of the effects of drugs with class 3 mode of action on cardiac muscle repolarisation. Using this method we have evaluated the effect on the timing of the evoked T wave of two drugs which are known to prolong phase 2 of the action potential. Intravenous amiodarone (5 mg/kg) prolonged the stimulus-peak evoked T wave interval by an average of 39-4 ms (15% of control values); three hours after oral bethanidine (2 mg/kg) this interval increased by an average of 25.8 ms (10% of control values). The effect of therapeutic interventions on the latency of the local paced evoked response provides a simple, accurate assessment of their effect on the cellular action potential duration and constitutes a new tool in electrophysiological investigations.

Amiodarone↗
PubMed1982

Irreversible morphological changes contributing to depressed cardiac function after surgery for chronic aortic regurgitation.

The timing of surgery in chronic aortic regurgitation remains a difficult problem. To identify variables predictive of postoperative haemodynamic improvement, changes in left ventricular mass, volume, morphology, and histochemistry were analysed in 67 patients undergoing surgery for chronic aortic regurgitation. Patients were divided into two groups: those in whom the left ventricular echo diameters returned to normal after operation (51 patients, group A), and those with postoperative dilatation (16 patients, group B). A preoperative biopsy was obtained in all patients; postoperative tissue samples were available in 13 patients (five from group A, eight from group B). Data were correlated with the postoperative clinical, haemodynamic state over a follow-up period of three years. Regression of hypertrophy was usually incomplete. Echocardiographic and angiographic data could not define the type and degree of dysfunction which was irreversible. Massive fibre hypertrophy (mean 34.1 micrometers), moderately or severely increased interstitial fibrous tissue, reduced levels of the myofibrillar and mitochondrial enzymes adenosine triphosphates and succinate dehydrogenase in pre- and post-operative tissue samples correlated with persistent dilation, cardiac failure, and early death (group B). Irreversible morphological and functional changes contributed to a depressed cardiac function after operation. Preoperative ventricular biopsies are thus of prognostic importance in volume overload.

Adolescent↗
PubMed1982

Diagnosis of atrial thrombi by ultrasound.

Left atrial thrombi were shown by two-dimensional echocardiography in three patients with mitral valve disease and neurological symptoms. In two patients the atrial thrombi had probably been the source of a previous cerebrovascular embolus. In the third, two-dimensional echocardiography detected the development of a recent ball-valve thrombus in the left atrial cavity, which caused intermittent obstruction and syncope. Echocardiographic findings were correlated with anatomical and histological data in all three patients. The spatial orientation provided by the multiple imaging planes of two-dimensional echocardiography permitted correct estimates of the size and position of the thrombus, and this mode was superior to the standard M-mode technique for non-invasive imaging of thrombus. Despite limitations of technique and resolution, the information provided by ultrasound can be extremely helpful in the management of patients. Ultrasonic screening (particularly the two-dimensional mode) is to be recommended in patients with neurological symptoms and clinical evidence of cardiac disease or arrhythmia.

Adult↗
PubMed1982

Emission tomography in embolic lung disease.

Ventilation-perfusion lung scans and emission tomography studies were performed in 84 patients with suspected embolic lung disease. Concordant data were obtained in 72 patients (57 positive, 15 negative); results were discordant in ten patients and indeterminate in two. Although the diagnosis of pulmonary embolism with the conventional two-dimensional planar projections of standard ventilation-perfusion lung scans is still the mainstay, a greater sensitivity in lesion detection can be expected with multiplane detection imaging.

Journal Article↗
PubMed1982

Composite graft replacement for the treatment of aneurysms of the ascending aorta associated with aortic valvular disease.

Composite graft replacement of the ascending aorta and aortic valve was performed in 78 patients over an 8 1/2-year period. Degenerative lesions of the aortic root in Marfan's syndrome (annuloaortic ectasia) was the indication for operation in 56 cases; the other 22 patients had other causes of aortic root dilatation and aortic valve disease. Overall hospital mortality was 8%. Follow-up ranged from 1-9 years (average 5 years). Reoperation was required in six of the 72 hospital survivors. Overall 5-year actuarial survival was 77%, and 85% of the survivors have shown significant clinical and radiologic improvement. Composite graft replacement reduces the risk of aneurysm formation of the sinuses of Valsalva and eliminates paraprosthetic leakage; postoperative hemorrhage is also reduced. It appears to be the method of choice for patients with degenerative lesions in the ascending aorta and valve, particularly annuloaortic ectasia.

Adolescent↗
PubMed1981

Replacement of the ascending aorta and aortic valve with a composite graft. Results and follow-up in 71 patients.

Composite graft replacement of the ascending aorta and aortic valve was performed in 71 patients over an 8-year period. Degenerative lesions of the aortic root in Marfan's syndrome (annuloaortic ectasia) was the indication for operation in 51 cases. Other causes of aortic root dilatation and aortic valve disease were present in the remaining 20 patients. Overall hospital mortality was 8%. Reoperation was required in 6 of the 65 hospital survivors. Follow-up has ranged from 1 to 9 years (average 41/2 years). Four year actuarial survival was 77%. Composite graft replacement eliminates paraprosthetic leakage and the risk of aneurysm formation of the sinuses of Valsalva; postoperative hemorrhage is also reduced. It appears to be the method of choice for the aortic root complications of the Marfan's syndrome.

Adolescent↗
PubMed1981

The role of two-dimensional echocardiography in the detection of potentially embolic intracardiac masses in patients with cerebral ischaemia.

The M-mode and two dimensional echocardiographic data of 62 consecutive cardiac patients referred from neurology centres were analysed retrospectively to establish the use of these techniques in detecting underlying cardiac pathology. All patients had presented initially to a neurologist with transient or permanent focal cerebral or retinal ischaemia, and had been referred for cardiac assessment after neurological investigations failed to establish the underlying cause of the neurological event. Patients were divided into two groups. In 30 patients the referring neurologist had found no evidence of cardiac disease (Group I); in the other 32 patients either heart disease or an arrhythmia had been diagnosed prior to cardiac referral (Group II). One of the patients in Group I had echocardiographic evidence of mitral valve prolapse not detected by the neurologist prior to referral; no cardiac pathology was recognised in the other 29 patients in this group. In seven of the 32 (22%) patients from Group II, a cardiac mass presumed responsible for the neurological manifestations was demonstrated echocardiographically, and in six of these histological confirmation was obtained following surgery or at necropsy. Two dimensional echocardiography was the only investigation which visualised the intracardiac pathology in four patients. In the remaining three patients, valve vegetations (two cases) and an atrial tumour (one case) were demonstrated by both echocardiographic methods. In patients with either clinical evidence of cardiac disease or an arrhythmia who have experienced one or more episodes of cerebral or retinal ischaemia, the presence of an intracardiac mass is not uncommon. Two dimensional echocardiography was the method of choice for detecting cardiac thrombus but the use of both methods of ultrasound should be considered as complementary techniques in the investigation of these cases. Routine echocardiography is unlikely to be of value in screening patients who have had a cerebrovascular event and who do not have clinical evidence of heart disease or an arrhythmia.

Adolescent↗
PubMed1980

Management of cardiovascular complications in Marfan syndrome.

From 1965 to 1979, 59 patients with the Marfan syndrome and cardiovascular complications underwent aortic root and aortic valve surgery. The hospital mortality was 12% (6.5% over the past 5 years). At follow-up an average of 5.1 years later, 2 patients had postoperative heart block, and late complications required reoperation in 4. There was 8 late deaths (overall mortality 25%). Survival at 6 years was 77% and improvement was noted in the functional class of 32 (74%) of the 43 survivors. 3 patients with abnormal preoperative ventricular function have continued in cardiac failure; 3 have moderate mitral regurgitation and 2 have aortic regurgitation. Aneurysms of the abdominal aorta and pulmonary artery have developed in 2 patients. Initially patients underwent surgery when their condition deteriorated despite medical treatment. Echocardiographic assessment of the aortic root has improved diagnosis and management; a large, progressively dilating aorta and evidence of ventricular dilatation were indications for surgery in 11 symptom-free patients. Although patients with Marfan syndrome are prone to other cardiovascular manifestation which affect survival, elective prophylactic surgery to the ascending aorta can be done with a low mortality and expectation of improved lifespan.

Adolescent↗
PubMed1980

Paediatric nuclear cardiology in intensive care.

The role of non-invasive nuclear medicine procedures in the management of paediatric cardiac abnormalities is reviewed. The studies can be performed at the bedside of the very sick infant using a mobile gamma camera computer system, and provide functional structural information essential for management.

Adolescent↗
PubMed1979

Evidence for involvement of cyclic nucleotides in intrinsic factor secretion by isolated rabbit gastric mucosa.

Secretion of intrinsic factor (IF) has previously been demonstrated in isolated rabbit fundic mucosa maintained in organ culture. We have now investigated the possibility that cyclic nucleotides may play a role in IF secretion. A phosphodiesterase inhibitor, 3-isobutyl methylxanthine (IBMX), stimulated IF secretion nearly fourfold while increasing tissue levels of both cyclic AMP (cAMP) and cyclic GMP (cGMP). Peak IF secretion in response to IBMX was not reached until after tissue cAMP levels were maximal. Dibutyryl cAMP and 8-Br-cAMP increased secretion by the same order of magnitude as did IBMX, whereas corresponding analogues of cGMP had no such effect. Histamine increased secretion of IF. In the presence of 40 microM IBMX, histamine elevated tissue levels of cAMP, but not of cGMP, and the stimulating effect of 10 microM histamine on IF secretion was potentiated. An H2 receptor antagonist, cimetidine, blocked the increases in IF secretion and tissue cAMP levels due to histamine, and the increase in IF secretion due to IBMX. These observations are consistent with a role for cAMP in the secretion of IF by isolated gastric mucosa.

1-Methyl-3-isobutylxanthine↗