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Biomedical subjects

J L Mercer

Publications and source records attributed to J L Mercer.

At least 19 recordsLinked to original sources
PubMed1992

A comparison between the inlet and outlet diameters of the normal aortic valve.

Two studies are described comparing the inlet and outlet diameters of the normal aortic valve. Both studies show the valve inlet to be smaller than the valve outlet. The first study is of measurements made on 12 casts of physiologically pressurised human aortic valves. The mean ratio between the diameter of the aortic ring and of the aorta just distal to the sinus ridge was 1.1, and the mean ratio between the diameter of the aortic ring and the maximum diameter of the valve leaflets was 1.18. The second study presents echocardiographic data from normal volunteers. The mean ratio between the diameter of the aortic ring and of the aorta just distal to the sinus ridge was 1.17. It is suggested that stents made to support the leaflets of prosthetic valves are made in conical or hyperbolic form, with the outlet being approximately 20% larger than the inlet.

Adolescent↗
PubMed1992

Mitral valve replacement in patients with severe mitral regurgitation and impaired left ventricular function.

We have studied short- and mid-term effects of preservation and excision of the mitral subvalvar support during mitral valve replacement in 40 patients, who had developed moderate to severe degree of left ventricular function impairment, secondary to pure severe mitral regurgitation. These patients had valve replacement, because valve anatomy was unsuitable for reconstructive procedures. Mitral subvalvar support was excised and valve replaced with a Björk-Shiley prosthesis, in 10 patients with moderately impaired left ventricular ejection fraction (mean 32% +/- 1.2%) and in 18 patients with severely impaired left ventricular function (left ventricular ejection fraction: 22% +/- 0.8%). In 12 patients with severely impaired left ventricular function (left ventricular ejection fraction: 20% +/- 1%) posterior subvalvar apparatus was preserved and valve replaced with a bioprosthesis. Prognosis of patients with moderately impaired left ventricular function was not influenced by the loss of chordopapillary support. Actuarial survival at 8 and 10 years was 46% +/- 7.8% for patients with severely impaired left ventricular function with chordopapillary support excised and 70% +/- 10% for patients with severely impaired left ventricular function with chordopapillary support preserved (p less than 0.01). Preservation of mitral subvalvar support is important in patients with severely impaired left ventricular function (left ventricular ejection fraction less than 25%).

Aged↗
PubMed1991

Functional tricuspid regurgitation following replacement of the mitral valve.

In this series, the effect of replacement of the mitral valve was examined in 86/900 (9.6%) patients who had developed moderate functional tricuspid regurgitation, secondary to rheumatic mitral valvar disease. These patients were subdivided according to the severity of pulmonary hypertension and impairment of right ventricular function. Forty-six patients presented with severe pulmonary hypertension and 40 patients had moderate pulmonary hypertension (mean main pulmonary arterial pressure: 78 +/- 14 mmHg vs 41 +/- 6 mmHg; P less than 0.05). The latter had more advanced disease, greater impairment of right ventricular function and dilatation of the right heart chambers. Functional tricuspid regurgitation regressed in 38/42 survivors with severe pulmonary hypertension and persisted or progressed significantly in 22/34 survivors with impaired right ventricular function despite successful replacement of the mitral valve. The latter underwent replacement of the tricuspid valve (n = 16) or tricuspid annuloplasty (n = 6), at a mean interval of 44 +/- 4.4 months after replacement of the mitral valve, which resulted in 8/22 (23.5%) early deaths. Functional tricuspid regurgitation is more likely to persist in patients with advanced right ventricular failure. Tricuspid valvar competence should be restored in these patients at initial replacement of the mitral valve.

Adult↗
PubMed1990

Tricuspid valve replacement: factors influencing early and late mortality.

Seventy four patients underwent tricuspid valve replacement (TVR), between 1968 and 1983. 93% were female, mean age was 44 +/- 4 years. Tricuspid valve was replaced with a mechanical prosthesis in 52 and a bioprosthesis in 22 patients. Fifty seven patients underwent primary TVR and 17 underwent a secondary TVR following a mean interval of 41 +/- 2 months (SEM) following a previous mitral or tricuspid valve operation. Preoperatively 86% patients were in NYHA class III-IV and congestive cardiac failure (CHF). Early mortality for primary TVR was 36.8% and 35.2% for secondary TVR. Early mortality has been significantly reduced since the introduction of cardioplegic protection for the associated valve lesions. Early mortality was significantly influenced by the reduced preoperative values of FVC and FEV1 in patients with long standing mitral valve disease and by raised preoperative levels of plasma bilirubin and alkaline phosphate in patients with CHF. Risk of thrombotic occlusion and late deaths remained high during the first year after TVR with a mechanical prosthesis.

Adult↗
PubMed1990

Combined mitral and aortic valve replacement with Bjørk-Shiley prostheses: long term survival and valve-related complications.

Between 1974 and 1985, combined aortic and mitral valve replacement (DVR) was performed in 209 patients using Bjørk-Shiley tilting-disc prostheses. Early and late mortality were 9.5% and 10.5% respectively for the entire series. Factors significantly influencing early mortality were: Emergency DVR, preoperative NYHA Class IV, double valve, critical stenosis, and small aortic replacement prostheses. The effect of the latter was augmented by the suboptimal orientation of the implanted prostheses. The overall survival was 74 +/- 4.4% at 12 years; but was only 40 +/- 6.1% at 8 years in patients who were in NYHA class IV preoperatively. Intermittent disc occlusion (DO) and thrombotic disc occlusion (TO), presented as early, anticoagulant related haemorrhage (AH) and prosthetic valve endocarditis (ENDO) as sporadic, and thromboembolism (TE) and paravalvular leak (PVL) as continuous risk factors. Freedom from all known valve-related complications was 77 +/- 4.5% at 12 years (DO, TO, AH, ENDO, TE, PVL: 98%, 97%, 96%, 96%, 88% and 89% respectively). Lethal DO and TO occurred in mitral prostheses. Freedom from reoperation was 95% at 5 and 12 years. Patient-related valve failure rate in this series is comparable with the other series which used mechanical prostheses and is lower than those which used bioprostheses.

Adult↗
PubMed1990

The results of surgery for atrial septal defect in patients aged fifty years and over.

We examined the cases of 31 patients over the age of 50 years undergoing operative closure of isolated ostium secundum atrial septal defect. The lesion had been diagnosed in all cases prior to cardiac catheterization. To assess the importance of pre-operative data on surgical outcome, the patients were first divided into three groups according to mean pulmonary artery pressure (PAP): less than 16 mmHg (Group A), 16-30 mmHg (Group B) and greater than 30 mmHg (Group C). Symptomatic improvement occurred in all groups but more patients in Group C, although symptomatically improved, remained short of breath and in atrial fibrillation than in Group A. Patients in Group A had a higher actual forced vital capacity expressed as a percentage of the predicted value (FVCa/FVCp) than patients in Group B or Group C (P less than 0.015). There was a good correlation between FVCa/FVCp and percentage oxygen saturation of the arterial blood (P less than 0.0009). This simple non-invasive investigation was therefore found to correlate with previously documented parameters, pulmonary artery pressure and percentage oxygen saturation of the arterial blood, affecting surgical outcome. Patients were also divided into groups according to FVCa/FVCp: less than 75% (Group 1), 50-75% (Group 2) and less than 50% (Group 3). Postoperative symptoms were more common in Group 3 than in Group 1. We conclude that respiratory function tests, as well as measurement of pulmonary artery pressures, are useful in predicting improvement following atrial septal repair.

Arrhythmias, Cardiac↗
PubMed1989

Late results of aortic valve replacement with Bjork Shiley prostheses: a comparison of standard aortic valve prosthesis with reversed mitral valve prosthesis implanted in aortic position.

Between 1976 and 1983, 435 patients underwent aortic valve replacement (AVR) with Bjork Shiley prostheses. Standard aortic Bjork Shiley prostheses (ABP) were used in 150 patients (Group I) and a reversed mitral Bjork Shiley prostheses in 285 (MBP in 250 and MBC in 35) patients (Group II). There was no significant difference in the number of the patients with valve calcification or the size of aortic root in the 2 groups. There was no significant difference in the early mortality in these two groups. The total follow up period in Group I was 912 years and 2130 years in Group II. The incidence of major aseptic prosthetic dehiscence and valve occlusion with tissue ingrowth were higher in Group I than in Group II. Reversed Bjork Shiley mitral valve prosthesis was successfully used in aortic position with reduced incidence of valve related complications.

Aortic Valve↗
PubMed1989

Plasma albumin and calcium levels following cardiopulmonary bypass.

A significant fall in the levels of plasma albumin and a corresponding fall i in the levels of extracellular calcium occurred following cardiopulmonary bypass with the crystalloid prime. Postoperative hypoalbuminaemia was well tolerated, except in the patients with poor left ventricular function. Postoperative hypocalcaemia may increase digoxin sensitivity and may augment the negative inotropic effect of verapamil.

Calcium↗
PubMed1988

Late results of total correction of tetralogy of Fallot in adults.

Between 1966 and 1986, 30 patients underwent total correction of the tetralogy of Fallot. Preoperative presenting features were: dyspnoea on exertion, clubbing, cyanosis and polycythaemia. Twenty-six patients had one or more palliative procedures prior to definitive repair. Preoperatively, all patients had a significant gradient across the right ventricular outflow tract (mean gradient 70 +/- 46 mmHg). Peak right ventricle to left ventricle systolic pressure ratio (pRV/LV) was 0.9 +/- 0.2. A functioning Blalock Taussig shunt was ligated in 11 patients prior to the institution of cardiopulmonary bypass. All patients had a patch closure of the ventricular septal defect. An additional muscle bundle resection from the right ventricular outflow tract was performed in 15, pulmonary valvotomy in 6 and enlargement of the right ventricular outflow tract in 2 patients. There was a significant fall in pRV/LV ratio postoperatively (P less than 0.05). There were 3 early and 2 late deaths. Mild right ventricular outflow tract obstruction has persisted in all survivors. Four patients have remained on antiarrhythmic drugs. Long term results after definitive repair were satisfactory in this group of adult patients who have survived due to palliative procedures performed during childhood.

Adult↗
PubMed1985

Re-operation for aortic and mitral prosthetic dysfunctions.

The overall incidence of re-operation and prosthetic valve endocarditis was low in the present series as mechanical prostheses were used predominantly. The prosthetic dysfunctions were less frequent following the primary implantation with Bjork Shiley prostheses, but high operative risk was associated with the clotted Bjork Shiley prostheses. We also had unusual experience of strut fracture and sticking of Bjork Shiley discs in the closed position in both aortic and mitral positions. The early deaths were nil since the use of cardioplegic protection. Intra-operative bleeding due to adhesions can be minimised by using synthetic or heterologous pericardium during the primary operation.

Adult↗
PubMed1975

Acceptable size of the pulmonary valve ring in congenital cardiac defects.

Because congenital defects are being corrected at progressively younger ages, knowledge of the normal sizes of cardiac orifices and their acceptable limits is becoming increasingly important. A graphically corrected table of normal children's heights and pulmonary artery diameters is given. In addition, reasons are presented for the belief that a decrease in the cross-sectional area of up to 50% of normal may be considered acceptable during corrective procedures; in light of present knowledge any further decrease in cross-sectional area, in particular below 25% of normal, should probably not be left uncorrected.

Age Factors↗