Prosthetic aortic valve dehiscence following infective endocarditis by a rare bacterium – Pandoraea pnomenusa

Abstract

Late prosthetic valve endocarditis (PVE) is a life-threatening condition, commonly caused by bacterial organisms such as staphylococci, streptococci, or enterococci. Infrequently, it can be caused by rare organisms. We hereby report a case of late PVE of the aortic valve, due to a rare gram-negative bacterium Pandoraea pnomenusa. It is the first reported case of PVE caused by this particular organism. The patient had infective endocarditis-induced prosthetic valve dehiscence, severe aortic regurgitation, and shock, which was managed with appropriate antibiotics and supportive medical treatment.

<Learning objective: Late prosthetic valve infective endocarditis should always be an important differential diagnosis in patients with artificial valve presenting with congestive cardiac failure. This case report is about aortic valve dehiscence and acute aortic regurgitation because of prosthetic valve infective endocarditis due to a rare bacterium Pandoraea pnomenusa.>

Introduction

Prosthetic heart valves are prone to infective endocarditis (IE). Any bacteremia can potentially lead to prosthetic valve infective endocarditis (PVE). It is commonly caused by bacterial organisms such as staphylococci, streptococci, or enterococci. An infective perivalvular invasion is common and leads to complications such as abscess, valve dehiscence, conduction disturbance, and prosthesis failure; each of which is associated with significant morbidity and mortality. We hereby report a case of late PVE caused by a rare bacterium - Pandoraea pnomenusa. The mechanical complications and management issues are discussed in the article.

Case report

A 42-year-old male, who had surgical prosthetic aortic valve replacement with a bi-leaflet mechanical valve (St. Jude Medical, St Paul, MN, USA) 20 years previously for chronic rheumatic valve disease, reported to the emergency room with worsening shortness of breath and fever of 3-weeks’ duration. On clinical examination, he had hypotension, tachycardia, and tachypnea, and arterial saturation of 88% on supplemental oxygen. Cardiac examination revealed auscultable left ventricle (LV) third heart sound (S₃), an early diastolic murmur of aortic regurgitation, and prosthetic aortic valve sound. There was basal crepitation of bilateral lung fields. Electrocardiogram showed normal sinus rhythm, prolonged PR interval (240 ms), and absence of LV hypertrophy. The chest radiograph showed pulmonary edema with bilateral basal pleural effusion. Echocardiography revealed severe prosthetic aortic paravalvular regurgitation (>30% of the circumference with sewing ring motion) (Fig. 1A and C), severe mitral regurgitation (MR), including diastolic MR, with LV ejection fraction of 65%. There was grade 2 dehiscence of the prosthetic aortic valve with the defect spanning from 9 to 3 o'clock position (180° dehiscence) in aortic short-axis view (Fig. 1A and B). The non-dilated LV had internal diastolic and systolic dimensions of 61 mm and 40 mm, respectively, and the dilated left atrium had an area of 25 cm². Fluoroscopy showed the rocking movement of prosthetic aortic valve suggestive of its dehiscence (Online Video 1). The presence of diastolic MR, non-dilated LV, and absence of peripheral signs of exaggerated diastolic run-off were suggestive of acute aortic regurgitation (AR). A computed tomography scan showed prosthetic valve dehiscence at 12–2 o'clock position (Fig. 1D).

Fig. 1.

Transthoracic 2D echocardiography in short-axis view (A) showed prosthetic aortic valve dehiscence from 9 to 3 o'clock position and eccentric para-valvular regurgitation. An apical 5-chamber view (C) showed severe aortic regurgitation with the para-valvular leak. Transthoracic 3D echocardiography, cropped view of the prosthetic aortic valve (B) showed peri-prosthetic defect suggestive of dehiscence. A computed tomography scan of the bi-leaflet mechanical prosthetic aortic valve (D) showed dehiscence at 12- 2 o'clock position.

He was continued on vancomycin and piperacillin-tazobactam, diuretics, and inotropes as initiated from a primary care center. His-initial three consecutive blood culture samples at the time of admission were sterile for bacterial infection. On day 3, he had worsening hypotension and renal shutdown, for which hemodialysis was started. From day 5 onwards, he had worsening septic shock, following which antibiotics were changed to meropenem and vancomycin. A repeat blood culture on day 5 grew a rare Gram-negative bacterium –P. pnomenusa, which was sensitive to levofloxacin, minocycline, and sulfamethoxazole-trimethoprim. Accordingly, levofloxacin was added to ongoing meropenem and vancomycin antibiotics. Consecutive blood cultures during hospital stay were sterile. He had partial improvement in septic shock. A heart team was approached for possible surgical aortic valve replacement. As it was a high-risk case with predicted surgical mortality of 16% by STS score and 37% by EuroSCORE II, the patient was continued on optimal medical treatment. Later he had a worsening septicemic shock, renal shutdown, ventilation-associated pneumonia, and multi-organ failure, and died on day 14 due to refractory shock and respiratory failure. An autopsy could not be performed as attendants did not give consent.

Discussion

PVE is a serious complication occurring in surgically replaced valves, with an incidence of 0.3–1.2% per patient-year [1]. Although PVE is common during the initial three months after surgery, late infection after years of surgery is also frequent. Late PVE after a year is usually caused by organisms similar to those of native valve endocarditis such as staphylococci, enterococci, and oral streptococci [1]. Gram-negative organisms are less common causes of infective endocarditis and mainly by HACEK group, followed by Escherichia coli and Pseudomonas species. Certain Gram-negative bacteria such as Salmonella enterica, Morganella morganii, Yersinia enterocolitica, Burkholderia cepacia, Achromobacter species, and Acinetobacter baumannii are rarely associated with PVE [2]. There is no published report about IE caused by Pandoraea species. P. pnomenusa is a Gram-negative, rod-shaped, aerobic bacterium belonging to the family Burkholderiaceae of class Betaproteobacteria. It is an emerging pathogen being increasingly reported in patients with cystic fibrosis and post-lung transplantation [3,4]. They are resistant to most of the antimicrobials agents such as aminoglycosides, beta-lactams, quinolones, and have variable sensitivity to piperacillin-tazobactam, tetracycline, and trimethoprim-sulfamethoxazole. They produce a biofilm layer which helps for bacterial persistence and antibiotic resistance [5]. The portal of entry for this pathogen was unknown in the index case. It seems to have high virulence, as blood culture is mostly positive with the isolated lung infection [6]. In the index case, P. pnomenusa was the causal agent for PVE, although initial blood culture reports were sterile. Low and variable bacterial load in blood is well known in IE, requiring multiple blood cultures for isolation of causal agent [7]. The patient had empirically received vancomycin, piperacillin-tazobactam, and meropenem, which were not effective against the isolate.

Acute kidney injury is observed in one-third of patients with IE and is related to immune complex-mediated glomerulonephritis, renal artery emboli, cortical necrosis, and drug-related or cardiorenal syndrome. It is associated with the worse outcomes in IE patients. The index case also had significant renal dysfunction requiring replacement therapy. Perivalvular invasion of the infection may lead to dehiscence of the prosthesis, paravalvular regurgitation, conduction abnormality, and myocardial abscess [8]. The index case had valve dehiscence with paravalvular regurgitation, and possible annular extension as PR interval was increased. On echocardiography, prosthetic valve dehiscence is defined as a rocking motion that exceeds 15° in at least one plane as was apparent in the index case [1]. Paravalvular regurgitation resulting from dehiscence carries serious hemodynamic consequences often resulting in heart failure and cardiogenic shock [9].

Repeat valve surgery is indicated when PVE is associated with intractable heart failure, valve dehiscence and dysfunction, heart block, annular abscess, non-HACEK Gram-negative bacteria, highly antibiotic-resistant organisms, and persistent bacteremia despite antibiotics for 7–10 days [1,10]. Those PVE patients with high STS score and EuroSCORE II are associated with poor outcome. The index case was a high-risk candidate for open surgery because of multi-organ dysfunction. Percutaneous device closure is an effective alternative for a significant paravalvular leak; however, it is contraindicated with an active infection. Multiple factors such as septicemic shock, valve dehiscence with acute AR, congestive cardiac failure, renal dysfunction, and hospital-acquired pneumonia led to the death in the index patient.

In conclusion, late PVE can be caused by rare emerging organisms such as P. pnomenusa. This is the first reported case of PVE caused by it. The patient had a worse outcome and died due to septicemia, mechanical complications, and multi-organ failure caused by the particular organism.

Video 1 Fluoroscopy showed the rocking movement of the bi-leaflet mechanical prosthetic aortic valve, suggestive of its dehiscence.