Case Presentation

A 52-year-old man was admitted complaining of left-sided abdominal pain, fever, and weakness. He had a history of supra-annular aortic valve replacement 5 years prior with a 25-mm ATS Medical mechanical valve. At that time, the patient had his native valve replaced because of endocarditis. The patient’s body temperature was 38.9°C, his blood pressure was 120/80 mm Hg, his pulse was 88 beats/min, and he had normal oxygen saturation on room air. On examination, the patient was in no distress, and the lungs were clear without crackles. Cardiac examination revealed a regular rhythm with an audible mechanical aortic diastolic sound and a grade 2/6 systolic ejection murmur at the left upper sternal border. There was no diastolic murmur. There was left flank tenderness in the abdomen, with warmth and fullness. The extremities were without edema. Laboratory findings revealed a white blood cell count of 16,900, with 84% neutrophils.

Computed tomography of the abdomen showed a soft tissue density with surrounding fluid in the region of the left lateral wall of the abdomen suggestive of an abscess. Three sets of blood cultures and a urine culture were negative. Transesophageal echocardiography was performed ( Video 1 ) and revealed aortic valve dehiscence with prominent rocking of the valve on a hinge point. The motion mimicked that of a flap valve. The downward motion in diastole formed a seal against the walls of the aortic root. Thus, on color Doppler ( Video 2 ), there was only mild perivalvular regurgitation seen in diastole ( Figures 1 and 2 ).

Still image of the transesophageal long-axis view of the aortic valve demonstrating minimal diastolic perivalvular aortic regurgitation. The jet is clearly narrow at its origin. The diastolic entrainment of flow in the left ventricular outflow tract should not be mistaken to imply a more severe lesion. Ao , Aorta; Apro , aortic valve prosthesis; ARjet , aortic regurgitation jet; LV , left ventricle.

Transthoracic continuous-wave Doppler demonstrating a shallow slope, a prolonged pressure half-time, and a faint spectral profile. All of these findings suggest mild aortic regurgitation.

The patient was treated with broad-spectrum antibiotics and had surgical drainage of his abdominal wall abscess. Culture of the abscess revealed no bacterial growth; however, this was obtained after the patient had received many days of antibiotic therapy. The valve was subsequently replaced and at the time of surgery was found to be approximately 50% dehisced.

Discussion

Prosthetic valve endocarditis is increasing in frequency and may occur relatively early postoperatively or late. Late prosthetic valve endocarditis is generally considered to occur ≥1 year after surgery. The prosthesis is usually seeded during a transient bacteremia that originated at another site. Bacteria adhere to the prosthetic surface and produce a biofilm that protects from both host defenses and antibiotics. In prosthetic valve endocarditis, the infection commonly affects the prosthetic suture line of the annulus. Invasion of the suture line can cause weakening and necrosis, leading to complications of abscess, fistula, or valve dehiscence. A rare but catastrophic complication is complete valve dehiscence with embolization of the prosthesis. Death of cardiogenic shock is the usual outcome.

Transesophageal echocardiography is superior to transthoracic echocardiography in diagnosing prosthetic valve endocarditis and its complications because of the image artifacts caused by the prosthesis on transthoracic examination. Besides visualizing a vegetation or abscess, identifying a new dehiscence of a prosthetic valve fulfills a major diagnostic Duke criterion for the echocardiographic diagnosis of endocarditis. Treatment involves a prolonged course of appropriate antibiotics coupled with surgical debridement of any infected tissues and replacement of the infected prosthesis.

The dehiscence of a prosthetic aortic valve usually produces severe perivalvular regurgitation, which is an independent predictor of increased mortality. The regurgitation often causes congestive heart failure, an additional predictor of poor outcome. In our case, the flap valve motion of the dehisced valve with each cardiac cycle prevented significant perivalvular regurgitation in diastole. This permitted the patient to remain hemodynamically stable and prevented progression to congestive heart failure or pulmonary edema.

Recent studies have shown that implantation of supra-annular prosthetic valves leads to less patient-prosthesis size mismatch and better hemodynamic performance than intra-annular implantation, especially in elderly patients with small aortic annuluses. Hence, supra-annular prostheses are being implanted with greater frequency. Supra-annular valve types would predictably be more predisposed to display the “flap valve phenomenon” as seen in our case. In such patients, the lack of heart failure or severe aortic regurgitation should not deter prompt valve replacement, because catastrophic total dehiscence could unpredictably occur if surgical treatment is delayed.