Microbubbles in the left ventricle associated with mechanical aortic valve regurgitation signifies valvular (not peri-valvular) regurgitation.

A 67-year-old female presented with progressive dyspnea. Physical examination was significant for a wide pulse pressure and a murmur of aortic regurgitation. Five years earlier, she received a bileaflet mechanical aortic valve prosthesis (St. Jude) for symptomatic aortic stenosis. Two-dimensional echocardiography revealed findings of severe prosthetic valve regurgitation (Fig. 1, movie clip S1). In addition, bright echoes, consistent with microbubbles (MBs), were noted within the left ventricle (LV) during diastole (Fig. 2, movie clips S2 and S3). The patient underwent aortic valve replacement, receiving a porcine prosthesis. At the time of surgery, it was evident that pannus ingrowth had partially obstructed 1 leaflet resulting in incomplete closure of that leaflet. The prosthetic annulus was normal with no evidence of a perivalvular leak. Postoperatively, the new porcine valve functioned normally, and the MBs seen preoperatively, were no longer present. Microbubbles noted in the LV have been attributed to mechanical heart valves, predominately in the mitral position. These MBs have not been reported to occur with tissue valves. Two different processes may produce so-called gas MBs. The first, which is termed cavitation, is vaporization of blood by a localized rapid pressure drop at the site of closure of the prosthetic ring and leaflet. This is a short-lived occurrence, and is not detected by echocardiography or Doppler. Degassing, a second process of MB formation, occurs by separation of gas from within a liquid. With a transient localized drop in pressure at the site of prosthetic valve closure, gas bubbles are formed, and then redissolve in normal pressures of the cardiac chambers. It is this process of degassing that is felt to be the etiology of MB formation detected by echocardiography. Several authors report that these MBs are relatively long-lived, and are detected by transcranial Doppler (TCD). It has been the experience in our laboratory, that when MBs are seen within the LV cavity, they are generally not detected by TCD, suggesting that MBs redissolve back into blood relatively quickly. It is reported that when MBs are found in association with a mechanical aortic valve prosthesis, they will be noted only within the upper left ventricular outflow tract (LVOT), in close proximity to the mechanical valve. This is thought to be a normal phenomenon and of no consequence. This patient’s MBs noted deep within the LV cavity are presumably related to mechanical valvular regurgitation. It is logical that the valvular regurgitation “washed” the MBs back into the body of the LV. As the process of Address for correspondence and reprint requests: Edmund Kenneth Kerut, M.D., Heart Clinic of Louisiana, 1111 Medical Center Blvd, Suite N613, Marrero, Louisiana 70072. Fax: 504-349-6621; E-mail: [email protected] Figure 1. Diastolic frame with color Doppler in the parasternal long-axis view demonstrates color turbulence of aortic regurgitation (arrows). Ao = aorta; LA = left atrium; LV = left ventricle.