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Biomedical subjects

M F Shiu

Publications and source records attributed to M F Shiu.

At least 37 records · Page 2Linked to original sources
PubMed1990

An objective computer system for the quantification of artery stenoses.

We have developed a low cost, clinically usable system for the objective assessment of the severity of coronary artery stenoses from single view angiograms. The system is based on a desktop computer with incorporated frame grabber. Images are captured by means of a video camera. The user selects a region of interest which encompasses the stenosis. Facilities are provided for automatic or manual definition of the artery centre line and edges. The computer then calculates the artery diameter and cross-sectional area by videodensitometry along profile lines which are orthogonal to the long axis of the artery. These results can be expressed numerically as a percentage stenosis when compared to a normal region of the artery. The image is corrected for geometric distortion using a grid test object. The image grey scale is corrected by means of a ramp test object such that a pixel value is proportional to the attenuator thickness. The ramp is placed on the patient during the X-ray examination and an iterative technique has been developed for subtracting the underlying structures from the superimposed ramp image. The system has been assessed using test objects constructed in Perspex which simulate arteries of known cross-sectional area and stenoses of known severity.

Algorithms↗
PubMed1990

Sustained improvement in left ventricular function after successful coronary angioplasty.

The short and long term effects of successful percutaneous transluminal coronary angioplasty on left ventricular function, at rest and on exercise were investigated in 49 patients. Thirty-four had had no previous infarction (group 1) and 15 had (group 2). Technetium-99m gated blood pool images were obtained at rest and during exercise before, six weeks after, and a mean of fifteen months after successful angioplasty. Before angioplasty the mean (SD) ejection fraction fell significantly on exercise in both groups from 58 (10)% to 53 (13)% in group 1 and from 48 (10)% to 40 (16)% in group 2. This change was paralleled by a worsening wall motion score (from 0.6 (0.4) to 1.6 (1.2) in group 1 and from 2.3 (1.9) to 3.3 (2.4) in group 2). Six weeks after the procedure there was little change in resting ejection fraction but it increased significantly on exercise (to 62 (11)% in group 1 and to 53 (13)% in group 2). There was a concomitant significant improvement in the exercise wall motion score (to 0.4 (0.6) in group 1 and to 1.8 (1.1) in group 2). This improvement in exercise ejection fraction and wall motion was maintained at later follow up with no significant deterioration in either variable and a clearly sustained improvement in ejection fraction (60 (10)% in group 1 and 51 (10)% in group 2) and wall motion score (0.2 (0.2) in group 1 and 1.3 (0.8) in group 2) compared with values before angioplasty. The initial improvement in left ventricular function on exercise after successful angioplasty was maintained for at least 9-24 months both in patients with previous myocardial infarction and in those without.

Angioplasty, Balloon, Coronary↗
PubMed1989

Percutaneous transluminal coronary angioplasty in patients with reduced left ventricular ejection fraction: effects on myocardial perfusion and left ventricular response to exercise.

Many patients with coronary artery disease treated by percutaneous transluminal coronary angioplasty (PTCA) have a history of previous myocardial injury resulting in a reduced left ventricular ejection fraction (EF). The effects of successful PTCA on myocardial perfusion and left ventricular function in these patients were compared to treatment in patients with normal left ventricular EF. There were 21 patients with a normal EF (mean EF 59 +/- 2%) (Group I) and 15 patients with reduced EF (mean EF 43 +/- 1%) (Group II). Before PTCA a similar degree of reversible myocardial ischemia was present on thallium scintigraphy. At peak exercise left ventricular EF in the Group I patients decreased by 4 +/- 1% compared to 8 +/- 1% in Group II. At one month following successful PTCA there was resolution of reversible myocardial ischemia in both groups. No changes in EF at rest were observed. At the same level of exercise as before PTCA the mean EF was 5 +/- 1% higher than the pretreatment value in Group I and 10 +/- 1% higher in Group II. Thus in this study reversible myocardial ischemia was associated with severe compromise in the left ventricular response to exercise which was substantially improved by PTCA.

Angioplasty, Balloon↗
PubMed1989

Total coronary arterial occlusion: real or apparent?

We describe a case in which the angiographic appearance of total occlusion of the left anterior descending coronary artery was not due to a complete anatomical obstruction, but due to competitive and retrograde flow in the distal segment of the artery from collaterals via the contralateral vessel. This case has implications on our current practice and results of coronary angioplasty in total coronary arterial occlusion.

Angina Pectoris↗
PubMed1989

Balloon occlusion during coronary angioplasty as a model of myocardial ischaemia: reproducibility of sequential inflations.

In order to evaluate the potential of balloon occlusion during coronary angioplasty as a model of myocardial ischaemia in man we have measured coronary sinus blood flow (CSBF), myocardial oxygen consumption (MVO2), lactate extraction (LER) and electrocardiographic changes in 11 patients undergoing left anterior descending artery (LAD) angioplasty. Baseline measurements were made before balloon crossing and between inflations. Four consecutive inflations each of 60 s duration were made; 5 min return to baseline was allowed between inflations. There was a significant reduction in CSBF and MVO2 (ml min-1) during inflations 2, 3 and 4 (CSBF: 121 +/- 66----94 +/- 53, 113 +/- 49----99 +/- 42, 124 +/- 66----102 +/- 41, P less than 0.02; MVO2: 11.3 +/- 6.6-9.1 +/- 3.9, 10.4 +/- 3.7-8.7 +/- 2.4, 12.2 +/- 4.4----9.4 +/- 2.8, P less than 0.05). However during the first period of balloon occlusion there were inconsistent changes in coronary flow with an overall rise in mean flow (97 +/- 35----128 +/- 80 ml min-1, P = NS) and an overall rise in mean myocardial oxygen consumption (9.6 +/- 3.8----12.5 +/- 7.5 ml min-1, P = NS). There was lactate production during all four inflations but the changes during the first one did not achieve statistical significance. These inconsistent changes during the first inflation were thought to be due to partial obstruction of the stenosis by the deflated balloon before primary dilatation. The changes due to crossing and during the first two inflations were further investigated in another group of 12 patients undergoing LAD angioplasty. Great cardiac vein flow (GCVF), CSBF, MVO2 and LER were recorded at baseline, during crossing and during the first two inflations. With the deflated balloon across the stenosis there were no changes in CSBF or MVO2 but there was a fall in GCVF (103 +/- 28----77 +/- 50, P = NS) and a significant fall in LER (77 +/- 57----16 +/- 37, P less than 0.01). Although there was a fall during the first inflation in CSBF, GCVF, MVO2 and lactate extraction none of these changes were significant. During the second inflation these changes were of greater magnitude and achieved statistical significance. While balloon occlusion during coronary angioplasty has the potential of providing a model of ischaemia in man we have found the first inflation period unreliable, due to the variable degree of occlusion by the deflated balloon. We suggest that only subsequent inflations after the primary dilatation are used for observations.(ABSTRACT TRUNCATED AT 400 WORDS)

Angioplasty, Balloon, Coronary↗
PubMed1988

Percutaneous coronary angioplasty in a cardiac transplant recipient.

Two years after an orthotopic cardiac transplant a 28 year old man was found to have clinically significant stenosis of the right coronary artery at routine coronary angiography. This lesion was accompanied by a perfusion defect on exercise thallium scintigraphy. Percutaneous transluminal coronary angioplasty of the lesion improved the angiographic appearance of the stenosis and reduced the exercise thallium perfusion defect.

Adult↗
PubMed1988

Coronary angioplasty in unstable angina and stable angina: a comparison of success and complications.

One hundred and five patients with unstable angina and 175 with chronic stable angina were treated by primary percutaneous transluminal coronary angioplasty. Patients with unstable angina had had symptoms for a shorter time and were more likely to have angiographically complex lesions and lesions less than 10 mm in length than patients with chronic stable angina. Other baseline variables were not significantly different in the two groups. The overall primary success rate was similar in both groups (87% v 86%). Nine of the 14 unsuccessful procedures in those with unstable angina and nine of the 24 unsuccessful procedures in those with stable angina were the result of acute occlusion. These results led to a 9% frequency of procedure related myocardial infarction in patients with unstable angina and a 5% rate in those with stable angina (NS). The procedure related infarct rate tended to be higher in patients with unstable angina who had coronary angioplasty soon after an episode of unstable angina (mean 10 days) than in those in whom it was delayed (mean 35 days) (12% v 3%) (NS). In patients with unstable angina who had had a previous myocardial infarction procedure related infarction was significantly more common (18%) than in patients with no previous myocardial infarction (3%). The difference between those with and without previous infarction was also significant in patients with stable angina (10% v 3%).

Angina Pectoris↗
PubMed1988

Management of unstable angina soon after myocardial infarction.

The recurrence of angina soon after myocardial infarction is not uncommon and represents areas of viable myocardium at risk from infarct extension and thus a worse prognosis. A better understanding of the pathogenesis of acute ischaemic syndromes and developments in interventional cardiology in the past decade have helped us rationalize our approach to this high-risk subset and achieve maximal myocardial salvage with its short- and long-term benefits.

Adrenergic beta-Antagonists↗
PubMed1988

Success and complication rates of coronary angioplasty in patients with and without previous myocardial infarction.

The primary success rate and incidence of major complications have been retrospectively assessed in a consecutive series of 224 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) in one centre. The patients have been divided into three groups; those with angina and no previous myocardial infarction (Group 1; N = 130), those with angina and a previous transmural myocardial infarction (TMI) (Group 2; N = 59), and those with angina and a previous non-transmural myocardial infarction (NTMI) (Group 3; N = 26). The three groups were well matched for age, gender and angiographic severity of stenosis. The primary success rate in Group 1 was 90% compared to 64% in Group 2. The success rate in Group 3 lay in between at 77%. The lower success rates in Groups 2 and 3 were mainly due to an increase in the frequency of major complications. Acute coronary occlusion occurred in seven patients in Group 1, nine patients in Group 2 and four patients in Group 3. In all these patients in Groups 2 and 3 the outcome of acute occlusion was a procedure-related clinical myocardial infarction despite immediate re-angioplasty and/or emergency coronary artery bypass grafting whereas only four patients in Group 1 sustained an acute infarct. In this series of patients undergoing coronary angioplasty for symptom limiting angina, previous myocardial infarction appears to be a risk factor for a lower success rate mainly due to an increase in the frequency and severity of major complications.

Adult↗
PubMed1987

Entanglement of embolised thrombus with an endocardial lead causing pacemaker malfunction and subsequent pulmonary embolism.

A 67 year old woman with a permanent pacemaker was admitted with pulmonary oedema and mitral valve incompetence two months after a myocardial infarction. Echocardiograms showed good left ventricular function and a large coil of apparent thrombus in the right atrium prolapsing into the right ventricle. Intermittent loss of pacemaker sensing and capture was noticed on admission and probably caused the supraventricular tachycardia and ventricular fibrillation that occurred before an exploratory bypass operation. At operation rupture of the papillary muscle was found and the mitral valve was replaced. A large piece of thrombus was retrieved from the right pulmonary artery. The right heart contained no clot and the pacemaker wire was not displaced. It is envisaged that the strand of venous thrombus was caught in the permanent pacing wire at the tricuspid valve level resulting in an unusual case of pacemaker malfunction. The eventual poor outcome was almost certainly influenced by the arrhythmias and pulmonary embolism caused by the clot and might have been avoided by early operation.

Aged↗
PubMed1987

Myocardial salvage following elective angioplasty for total coronary occlusion.

A 65-year-old man with unstable angina had a critical left anterior descending coronary artery stenosis which progressed to total occlusion, without evidence of acute myocardial infarction. Thallium imaging revealed defects in the distribution of the left anterior descending coronary artery on exercise and redistribution, 4 h later. 99mTc radionuclide angiography showed a fall in left ventricular ejection fraction on exercise, and contrast cineangiography showed an extensive area of akinesia. Percutaneous transluminal coronary angioplasty was successful without any complications. Repeat radionuclide studies demonstrated improvement of both myocardial perfusion and function. Angiography at 1 year showed normal left ventricular contraction and no evidence of recurrent stenosis. The patient is free of angina, on no medication 2 years after angioplasty. This case illustrates the feasibility of myocardial salvage by elective coronary angioplasty in patients with unstable angina total coronary occlusion.

Aged↗
PubMed1985

Acute coronary occlusion during percutaneous transluminal coronary angioplasty.

Two hundred and forty percutaneous transluminal coronary angioplasty procedures were performed in three centres over a two year period. Acute occlusion of the vessel undergoing angioplasty was seen on 20 (8%) occasions. The cause of occlusion was determined angiographically and in some cases confirmed at the time of emergency open heart surgery. The mechanism of coronary occlusion was arterial dissection in six cases, persisting coronary arterial spasm in seven, and coronary thrombosis in four. In three patients the mechanism could not be determined. Immediate reintroduction of a balloon dilatation catheter was attempted in 10 patients and resulted in restoration of adequate coronary flow in six. The remaining 14 patients underwent open heart surgery as an emergency procedure.

Acute Disease↗
PubMed1985

Spontaneous recanalisation of side branches occluded during percutaneous transluminal coronary angioplasty.

Percutaneous transluminal coronary angioplasty was performed in a 56 year old man with postinfarction angina. During an otherwise uncomplicated dilatation of a left anterior descending artery with a 70% stenosis two diagonal branches, each measuring 1.5 mm in diameter, were occluded. The occlusions were not associated with any adverse clinical effects, though there was a small rise in plasma creatine kinase concentration. The patient became free of angina two weeks after angioplasty, and follow up angiography showed spontaneous reappearance of the occluded side branches. Redistribution of atheromatous material and its later reabsorption may have been the mechanism for the initial occlusion and later reappearance of the vessels.

Angioplasty, Balloon↗
PubMed1984

Mitral valve disease.

Mitral stenosis is a progressive lesion carrying a relatively high risk of sudden incapacitation from systemic embolus or the onset of atrial fibrillation. Since the condition is likely to be significant when diagnosed, it is not compatible with single-crew professional operations and requires careful supervision. The presence of mild mitral regurgitation where the aetiology has been shown not to be due to chordal rupture, papillary muscle dysfunction secondary to coronary artery disease, rheumatic mitral valve disease, or Marfan's disease, where left atrial and left ventricular dimensions are shown to be normal on the echocardiogram, and where follow-up over at least a year has shown no progression of disease, may be consistent with full certification. Regular cardiological review with echocardiography and exercise electrocardiography is required. Any departure from these guidelines may lead to restriction of flying status to multi-crew operations, or denial.

Adult↗
PubMed1983

Echocardiographic features of free floating thrombus mimicking right ventricular myxoma.

M-mode and cross-sectional echocardiography performed in a patient with acute pulmonary embolism showed a sausage shaped, mobile mass in the right ventricular cavity highly suggestive of a right ventricular myxoma. Emergency thoracotomy 24 hours later showed the right ventricle to be free of tumour but both pulmonary arteries contained embolised venous thrombi, one or more of which were thought to have given rise to the false echocardiographic diagnosis of a right ventricular tumour.

Diagnosis, Differential↗
PubMed1983

Diagnosis of right ventricular outflow obstruction in infants by cross sectional echocardiography.

Cross sectional echocardiographic studies were assessed prospectively in 58 infants in whom right ventricular outflow obstruction was subsequently shown angiographically. A subcostal cut was used to display simultaneously the short axis of the aortic root and the long axis of the right ventricular outflow tract. This facilitated the differentiation of the common right ventricular outflow tract obstructive lesions. Tetralogy of Fallot was diagnosed correctly in 22 of 26 infants; pulmonary atresia with intact septum in all of 14 neonates; isolated severe pulmonary valve stenosis in all of nine infants; and pulmonary atresia with ventricular septal defect in eight of nine infants. The subcostal approach is the technique of choice for evaluating right ventricular outflow tract obstruction as it is more reliable than the left parasternal approach.

Coronary Circulation↗