Assessment of severity of mechanical prosthetic mitral regurgitation by transoesophageal echocardiography

Multimodality Imaging of Complications of Cardiac Valve Surgeries

Replacement with a prosthetic heart valve (PHV) remains the definitive surgical procedure for management of severe cardiac valve disease. PHV dysfunction is uncommon but can be a life-threatening condition. The broad hemodynamic and pathophysiologic manifestations of PHV dysfunction are stenosis, regurgitation, and a stuck leaflet. Specific structural abnormalities that cause PHV dysfunction include prosthetic valve-patient mismatch, structural failure, valve calcification, dehiscence, paravalvular leak, infective endocarditis, abscess, pseudoaneurysm, abnormal connections, thrombus, hypoattenuating leaflet thickening, and pannus. Multiple imaging modalities are available for evaluating a PHV and its dysfunction. Transthoracic echocardiography is often the first-line imaging modality, with additional modalities such as transesophageal echocardiography, CT, MRI, cine fluoroscopy, and nuclear medicine used for further characterization and establishing a specific cause. The authors review PHVs and the role of imaging modalities in evaluation of PHV dysfunction and illustrate the imaging appearances of different complications. Online supplemental material is available for this article. ^©RSNA, 2019.

Echocardiographic evaluation of prosthetic heart valves

The specific flow pattern and imaging features of prosthetic heart valves poses major challenges for the Doppler echocardiographic assessment of prosthetic valve structure and function. A comprehensive approach that integrates several semi-quantitative and quantitative parameters obtained from multiple views is key to appropriately detect and quantitate prosthetic valve dysfunction and complications. In patients with prosthetic valves, and particularly in those with mitral prostheses, transesophageal echocardiography is often required to confirm and/or complement information obtained by transthoracic echocardiography. Three-dimensional echocardiography may provide incremental information for the identification of the underlying etiology of prosthetic valve stenosis or regurgitation. Transcatheter aortic valve implantation has rapidly expanded in the past 10 years and paravalvular regurgitation is frequent following this procedure. Given that paravalvular regurgitant jets are often multiple, irregular, and eccentric, the grading of this type of regurgitation is particularly challenging and requires an integrative multiwindow, multiplane, multiparametric approach.

Echocardiographic Assessment of Heart Valve Prostheses

Patients submitted to valve replacement with mechanical or biological prosthesis, may present symptoms related either to valvular malfunction or ventricular dysfunction from other causes. Because a clinical examination is not sufficient to evaluate a prosthetic valve, several diagnostic methods have been proposed to assess the functional status of a prosthetic valve. This review provides an overview of echocardiographic and Doppler techniques useful in evaluation of prosthetic heart valves. Compared to native valves, echocardiographic evaluation of prosthetic valves is certainly more complex, both for the examination and the interpretation. Echocardiography also allows discriminating between intra- and/or peri-prosthetic regurgitation, present in the majority of mechanical valves. Transthoracic echocardiography (TTE) requires different angles of the probe with unconventional views. Transesophageal echocardiography (TEE) is the method of choice in presence of technical difficulties. Three-dimensional (3D)-TEE seems to be superior to 2D-TEE, especially in the assessment of paravalvular leak regurgitation (PVL) that it provides improved localization and analysis of the PVL size and shape.

The role of echocardiography during mitral valve percutaneous interventions

Transesophageal echocardiography is routinely used to guide percutaneous interventions involving the mitral valve. Mitral balloon valvuloplasty for rheumatic mitral valve stenosis (MS) was the first percutaneous intervention to gain wide acceptance. New techniques have been developed to treat degenerative and functional mitral regurgitation (MR) as well as paravalvular mitral leak (PVML). This review describes the use of echocardiography for transcatheter treatment of MS, MR, and PVML.

Identification and quantification of prosthetic mitral regurgitation by flow convergence method using transthoracic approach

The present case report illustrates the clinical applicability of the proximal isovelocity surface area (PISA) method in identifying, locating and assessing paravalvular prosthetic mitral regurgitation by transthoracic echocardiography.

A rabbit model with acute thrombo-embolic pulmonary hypertension created with echocardiography guidance

A rabbit model of acute thrombo-embolic pulmonary hypertension was developed by infusing self-thrombi into the right femoral vein and simultaneously measuring the pulmonary artery pressure via a right heart catheter and echocardiography. The model was used to explore the usefulness of an ultrasound-guided protocol. In the present study, acute thrombo-embolic pulmonary hypertension was produced in 25 of 30 healthy New Zealand rabbits; the success rate was 83%. A significant and positive correlation between the right ventricle-right atrial pressure gradient, an estimate of the pulmonary artery systolic pressure derived from tricuspid regurgitation and the pulmonary artery systolic pressure measured using the right heart catheter (r=0.765, P=0.002) was noted. During the process of establishing a rabbit model of acute thrombo-embolic pulmonary hypertension, it was demonstrated that echocardiography can be used to guide the right heart catheter to obtain pulmonary artery systolic pressure measurements, to quantify the tricuspid regurgitation jet to assess the pulmonary artery systolic pressure and to observe cardiac morphologic changes so as to evaluate cardiac function. Based on the present study, it is clear that echocardiography is valuable in improving the success rate of producing the animal model of acute thrombo-embolic pulmonary hypertension. This could ultimately facilitate preclinical research and clinical research in humans.

Assessing prosthetic mitral valve regurgitation by transoesophageal echo/Doppler

Transoesophageal echocardiography has greatly improved our ability to detect structural and regurgitant abnormalities associated with prosthetic mitral valves.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.