Role of Invasive Evaluation with Cineradiography and Intracardiac Echocardiography (Full title below)

From the Departments of *Cardiovascular Medicine and §Cardiothoracic Surgery, Cleveland Clinic, Cleveland, Ohio. The authors report no conflicts of interest regarding the content herein. Manuscript submitted December 3, 2008, provisional acceptance given January 15, 2009, final version accepted January 19, 2009. Address for correspondence: Adnan K. Chhatriwalla, MD, Cleveland Clinic, Desk J2-3, 9500 Euclid Avenue, Cleveland, OH 44195. E-mail: chhatra@ccf.org __________________________________

Role of Invasive Evaluation with Cineradiography and Intracardiac Echocardiography to Detect Mechanical Prosthetic Valve Dysfunction

ABSTRACT: Prosthetic valve obstruction by pannus or thrombus represents a rare but potentially serious cause of prosthetic valve dysfunction. We report a case in which the diagnosis of prosthetic valve obstruction was made in the catheterization laboratory utilizing cineradiography, left ventriculography and intracardiac echocardiography. The findings in this case suggest that in patients with a prosthetic aortic valve and increased left ventricular outflow tract gradient, evaluation in the catheterization laboratory may provide useful diagnostic information in addition to that obtained by noninvasive studies. J INVASIVE CARDIOL 2009;21:190–192 Case Report. A 50-year-old male presented to our institution in 2005 with progressive shortness of breath and fatigue. He had a history of bicuspid aortic valve and had undergone aortic valve replacement with a #25 St. Jude mechanical valve in 1986 (St. Jude Medical, St. Paul, Minnesota). He had since been diagnosed with hypertrophic cardiomyopathy in 1998. The patient denied orthopnea, paroxysmal nocturnal dyspnea and syncope. A physical examination was remarkable for a regular cardiac rhythm, normal cardiac size and presence of a grade II/VI systolic ejection murmur. No peripheral edema was noted. Laboratory testing including a complete blood count, haptoglobin, sedimentation rate, metabolic panel and liver function panel, was unremarkable, with the exception of a mildly elevated lactate dehydrogenase level (309 U/L; normal = 100–220 U/L). The patient underwent stress echocardiography and exercised to 11.6 METS and 68% of his maximum predicted heart rate with a Bruce treadmill test protocol. Transthoracic echocardiography (TTE) revealed mild upper-septal hypertrophy, normal left and right ventricular systolic function and stage II diastolic dysfunction at rest. At rest, peak and mean gradients across the left ventricular outflow tract (LVOT) were measured at 60 mmHg and 29 mmHg, respectively. These gradients increased to 86 mmHg and 45 mmHg, respectively, with administration of amyl nitrite, and to 140 mmHg and 76 mmHg, respectively, at peak exercise stress. The patient proceeded to computed tomography of the chest, which suggested a relative delay in opening of the right aortic valve leaflet, however, this finding could not be confirmed by transesophageal echocardiography (TEE), and the gradient across the LVOT was somewhat lower than that observed on TTE (peak and mean gradients 43 mmHg and 23 mmHg, respectively). The patient then proceeded to left- and right-heart catheterization. Angiography revealed normal coronary arteries. A Swan-Ganz catheter was placed in the pulmonary artery to measure cardiac output. Simultaneous measurements of aortic and left ventricular pressure were obtained using a pigtail catheter seated in the aortic root and a second pigtail catheter passed through the atrial septum and mitral valve, and seated in the left ventricle. Pressure measurements were obtained at rest and with 10, 20 and 30 µg/kg/minute infusions of dobutamine. At rest, peak and mean gradients across the aortic valve were 18 mmHg and 9 mmHg, respectively, however, at peak dobutamine stress, these increased to 111 mmHg and 85 mmHg, respectively (Figure 1). The cardiac output increased from 5.0 L/minute to 8.5 L/minute at peak dobutamine stress. Intracardiac echocardiography (ICE) revealed subvalvular pannus formation, however, a clear membrane was not visualized. Furthermore, despite the increased gradient across the prosthetic valve, the aortic leaflets appeared to be moving freely on cineradiography and ICE (Figure 2). These findings suggested that the subaortic pannus was causing dynamic LVOT obstruction and therefore the patient was referred for repeat aortic valve replacement to alleviate this problem. Intraoperative TEE again revealed no convincing pathology. At the time of open-heart surgery, a simultaneous measurement of aortic and left ventricular pressures was again obtained and an increased gradient of 80 mmHg across the aortic valve was immediately provoked with dobutamine administration. On exploration, a fibromembranous ring was observed underneath the aortic valve in contact with the aortic valve leaflets and potentially restricting leaflet motion (Figure 3). Therefore, the aortic valve and the subvalvular membrane were excised and replaced with a CarboMedics #25 composite graft (CarboMedics, Inc., Arvada, Colorado). The patient’s immediate post-operative course and the remainder of his hospitalization were unremarkable. On post-operative TTE, resting peak and mean gradients across the aortic valve were 25 mmHg and 18 mmHg, respectively. Discussion Prosthetic valve dysfunction due to obstructive thrombus or pannus formation is a relatively rare but potentially serious complication following valve surgery, and the mechanism of thrombus or pannus formation remains unclear.1 Although prosthetic valve obstruction is associated with thrombus formation in the majority of cases, significant pannus formation may be observed in up to 20% of cases.2 Dyspnea at rest, low cardiac output and signs of systemic embolization are frequently seen, but symptoms vary depending on the degree of valve obstruction, and patients may be entirely asymptomatic in cases in which valve function is not impaired. However, in the extreme situation in which thrombus or pannus completely occludes the valve orifice, this complication can lead to rapid decompensation and death. Typically, prosthetic valve dysfunction may be diagnosed by a combination of cineradiography and echocardiography. Specifically, an opening angle ≥ 20° on cineradiography signifies restricted valve opening (Figure 4).3 Similarly, the presence of valvular insufficiency, increased peak transvalvular velocity and/or peak transvalvular gradients measured by Doppler echocardiography might signify prosthetic valve obstruction. Nevertheless, echocardiographic evaluation of prosthetic valve dysfunction is often difficult due to limited visibility secondary to the shielding effect of mechanical valves. Furthermore, the range of observed peak transvalvular velocities is wide, even in normally-functioning prosthetic valves, and there is significant overlap in the range of normal transvalvular velocities across different-sized prosthetic valves. In one series, abnormal valvular motion was evident by TEE in 14/14 (100%) cases of valve obstruction due to thrombus, but in only 6/10 (60%) cases of valve obstruction due to pannus formation.4 Treatment of prosthetic valvular obstruction can include fibrinolysis, surgical debridement or valve replacement. Fibrinolytic therapy for prosthetic valve obstruction has had up to 90% success in published reports, however, this therapy may increase the risk of thromboembolic events.5 Furthermore, in cases of obstruction due to pannus formation as opposed to thrombus, fibrinolytic therapy is likely to be ineffective. Nevertheless, fibrinolytic therapy may be the only therapeutic option for patients with thrombotic prosthetic valve dysfunction who are unable to undergo surgery. The optimal surgical technique for treatment of prosthetic valve obstruction has been debated. Debridement of thrombus or pannus can be performed with good results, however, the rate of rethrombosis may be somewhat higher than with valve replacement.6 In the present case, prosthetic valve dysfunction was suspected due to the patient’s symptoms of shortness of breath and fatigue, as well as the observation of greatly increased transvalvular gradients on several occasions with dobutamine administration. These elevated gradients were confirmed on invasive testing, however, no clear evidence of prosthetic leaflet restriction was observed on cineradiography, TTE or TEE. Pannus formation was observed on cineradiography and ICE imaging and confirmed on surgical exploration. It is therefore likely that in this case, the fibromembranous ring produced LVOT obstruction only during exercise or with dobutamine administration. The exact mechanism of this obstruction remains unclear but it is likely that the fibromembranous ring attached to the muscular septum produced valvular obstruction only in the setting of increased myocardial contractility. It is also possible that the membrane interfered with leaflet motion in the setting of increased myocardial contractility. The findings in this case suggest that in the setting of clinical symptoms and increased transvalvular gradients, evaluation of the aortic valve in the catheterization laboratory with invasive monitoring, left ventriculography and ICE may provide useful diagnostic information in addition to that obtained by noninvasive studies. Left ventriculography may provide superior visualization of the LVOT, while ICE allows for the visualization of the outflow tract from the right ventricle without shadowing from the aortic valve.

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