Aortic valve replacement. Doppler echocardiographic studies of prognosis, effects of valve replacement and assessment of prosthetic valve function

Abstract

Background. Aortic valve replacement (AVR) due to aortic valve stenosis (AS) is the most common surgical procedure on cardiac valves in the adult population. The patients early mortality, occurrence of residual heart disease and prosthetic valve-related morbidity and mortality are important determinants of the outcome of AVR. The aims of the present thesis were to identify factors of importance for early mortality, describe the effects of AVR at two years of follow-up, determine the occurrence of residual heart disease and to study prosthetic valve function. Patients and Methods. The study comprised 303 patients who received either a mechanical valve of bileaflet (St. Jude Medical, SJM) or monoleaflet (Omnicarbon) design or a stented biological porcine valve (Biocor). They were investigated with Doppler echocardiography preoperatively, within the first week postoperatively (baseline) and after approximately two years. The prosthetic valves used in the clinical studies were also investigated in a steady-flow in vitro model with catheter pressure measurements and Doppler echocardiography. Results. Patients with severe AS who died within 30 days of the operation had a smaller left ventricular outflow tract (LVOT) than survivors, as well as a higher incidence of abnormal intraventricular flow velocity and increased relative wall thickness (RWT). An LVOT of = 22 mm identified 10 of 13 patients receiving a small prosthesis (size 19 or 21). At the two-year follow-up, patients displayed improved functional status, systolic and diastolic LV function and a regression in LV mass, but 14% still had severe symptomatology (NYHA class III/IV); 46% had an abnormally increased LV mass, 12% had systolic dysfunction with a reduced ejection fraction and 33% had signs of disturbed diastolic function. Reference Doppler echocardiographic findings at baseline and at the two-year follow-up were defined. The SJM and Omnicarbon valves displayed similar Doppler gradients both in vivo and in vitro, whereas the Biocor valve had significantly higher Doppler gradients. However, the pressure recovery (as a percentage of maximum catheter pressure) was most pronounced in the SJM central orifice (53±8.6%) compared with Omnicarbon (23±7.4%) and Biocor (18±9.3%). Valve size significantly influenced pressure recovery. Conclusions. The echocardiographic findings of a narrow LVOT, an abnormal increase in intraventricular velocity and an increase in RWT identified patients running an increased risk of early postoperative mortality. Patients undergoing AVR improved their functional status and systolic and diastolic LV function and displayed a reduction in LVM, but a fairly large proportion of the patients had severe symptomatology, LV hypertrophy and signs of disturbed systolic and diastolic function at the two-year follow-up. This indicates suboptimal timing of surgical intervention for many patients. When valve dysfunction is suspected, a previous investigation for comparison may be helpful and our data describes the changes that may normally be seen between an early baseline and a late investigation. Prosthetic valve design and size influence the degree of pressure recovery, making Doppler gradients potentially misleading in the assessment of hemodynamic performance and when comparing one design with another.