Metallic embolus to the brain in a patient with mechanical heart valves: an extremely rare complication

Abstract

A 46-year-old man with a medical history of rheumatic valve disease underwent mitral and aortic valve replacements with On-X and CarboMedics Top Hat supra-annular mechanical valves, respectively. Seven months after the valve replacement surgery, the patient presented with dizziness. A CT scan of the brain was done as part of a thorough workup of dizziness. The CT scan revealed a small metallic density in the M2 branch of the right middle cerebral artery. The metallic density was believed to be a metallic embolus that originated from the mechanical valves or the suturing material, that is, Cor-Knot fastener. Although in our case, the dizziness was believed to be the result of benign paroxysmal positional vertigo, through this case, we aim to highlight this extremely rare structural complication of mechanical valves. This complication can have serious and potentially fatal consequences such as embolic component-related stroke or another organ infarction.

Background

Valvular heart disease is fairly common frequently needing intervention. Mechanical valves are the treatment of choice in a select group of patients with valvular heart disease, depending on various factors such as patient’s age, anatomy and comorbid conditions. Mechanical valves, however, can cause serious complications such as thromboembolism, bleeding, prosthetic valve endocarditis, non-structural dysfunction and very rarely structural dysfunction. The overall rate of mechanical valve complications is reported to be 0.7%–3.5% per patient years.¹ Embolisation from a structural component of a mechanical valve is an extremely rare occurrence. To the best of our knowledge, there are only four reported cases of such embolisation to the brain. Our case highlights the importance of being cognizant of this very rare complication in patients with mechanical heart valves who present with neurological symptoms.

Case presentation

A 46-year-old man, with a relevant medical history of rheumatic valve disease, underwent mitral valve repair at age 17 outside the USA and then redo mitral surgery with replacement of dysfunctional mitral valve with a bioprosthetic valve at age 30. The patient presented to our hospital with progressively worsening dyspnoea, orthopnoea and limitation of physical activity. The patient was admitted to the hospital with fluid overload. A transthoracic echocardiogram showed severe mitral and aortic valve regurgitation with severe pulmonary hypertension. This symptomatic valve dysfunction warranted a redo sternotomy and a dual-mechanical valve replacement. His aortic valve was thus replaced by a CarboMedics Top Hat supra-annular valve, while the mitral valve was substituted for an On-X mechanical valve.

Patient’s postoperative course was complicated by cardiogenic shock, supraventricular arrhythmias, acute kidney injury and pneumonia. The patient also developed empyema, which eventually required video-assisted thoracoscopic surgery. On his 45th postoperative day, he was discharged to cardiac rehabilitation.

After 7 months of benign course, the patient presented to the emergency department with complaints of positional dizziness associated with vomiting. Review of systems otherwise was unremarkable. Patient’s family history and social history was non-contributory. Neurological examination was significant for positional vertigo on the Dix-Hallpike test. The remaining physical examination including a detailed cardiovascular examination was unremarkable. A transthoracic echocardiogram showed normally functioning and structurally intact mitral and aortic mechanical valves. A CT scan of the head and neck with angiography was negative for cerebrovascular accident. It, however, revealed a small ovoid metallic density in the M2 branch of the right middle cerebral artery (MCA) (figure 1A). A non-contrasted CT head axial image was also obtained, which showed the metallic density in right Sylvian fissure with a streak artefact (figure 1B). Furthermore, a non-contrasted CT lateral topogram of the head revealed metallic embolus as focal hyperdensity (figure 2). A trans-oesophageal echocardiogram was subsequently done which was normal. A CT of the chest with contrast indicated that the mechanical valve density—as measured on Hounsfield units (HU)—was similar to the density in the M2 territory (figure 3).

Figure 1.

(A) Contrasted CT arteriogram head axial thick-slab image showing metallic density embolus within the right middle cerebral artery M2 branch (arrow). (B) Non-contrasted CT head axial soft tissue image showing metallic density foreign body (arrow) in the right Sylvian fissure—the foreign body is denser that cortical bone (higher Hounsfield units compared with bone) and gives rise to streak artefact, supportive of metal.

Figure 2.

Non-contrasted CT lateral topogram head image showing metallic embolus as focal hyperdensity (arrow).

Figure 3.

Contrasted CT thorax coronal bone image at the level of the aortic valve. When regions of interest placed over the valve and right clavicle (arrows), metallic valve show Hounsfield units similar to intracranial embolus and higher than cortical bone.

Differential diagnosis

The main differential diagnoses included stroke, vertebrobasilar insufficiency, a brain structural lesion and thromboembolism from mechanical valves. Neurology, neurosurgery, cardiothoracic surgery and cardiology were consulted after the CT of the head showed metallic density in the MCA branch. Imaging was also reviewed with the neuroradiologist. After a thorough review, the metallic density was believed to be an embolus from either a structural component of one of the mechanical cardiac valves or from the suturing material, that is, Cor-Knot fastener. Patient’s symptoms were deemed to be due to benign paroxysmal positional vertigo. Since patient’s symptoms were not related to the metallic embolus, its extraction was not pursued.

Treatment

The patient was treated with Epley’s manoeuvre and meclizine with improvement in his symptoms.

Outcome and follow-up

The patient had complete resolution of symptoms with the above treatment, although with intermittent symptoms needing maintenance treatment with meclizine. Patient’s heart failure has resolved since valve replacement with normal cardiac function without any symptoms of valve dysfunction.

Discussion

Mechanical valves have been implanted for more than half a century. Earlier first-generation valves such as Björk-Shiley had been associated with a relatively higher rate of complications especially thrombosis and structural complications such as the disc or strut fracture. The rate of outlet strut fracture was estimated to be 0.14%–0.72% per year.¹

With the newer devices such as the devices in our patient, the rate of complications has dropped significantly with virtually no structural complication reported so far in the literature. On extensive literature search, we did not find any reports of structural complication for Top Hat and On-X mechanical valves. We, however, found four cases in which a brain embolisation was suspected to originate from mechanical heart valves.

In the first case, a patient with a history of explanted Björk-Shiley mechanical aortic valve with subsequent replacement with Medtronic-Hall aortic valve was found to have multifocal brain MRI metallic artefacts, which were thought to result from the mechanical valve.²

In the second case, brain MRI done as a workup of tonic–clonic seizures showed multifocal hypointensities, which were suspected to embolise from explanted Starr-Edwards aortic valve or subsequently replaced St. Jude’s prosthesis. It remained unclear whether seizures were due to the metallic embolus. Pertinent to mention that in both of the aforementioned cases, the first explanted valves were grossly intact.³

In the third case, a metallic embolus from an unknown type of mechanical aortic valve was the cause of the right posterior cerebral artery stroke. The embolus was seen as a central signal void surrounded by the high-intensity rim on the brain MRI.⁴

In the fourth case, the patient underwent robotic mitral valve repair with 32 mm Edwards-Physio II annuloplasty ring. Five years later, the patient presented with stroke and was found to have metallic embolus within the right MCA associated with adjacent thrombus. The source of metallic density was thought to be Cor-Knot titanium fastener used in mitral valve repair surgery.⁵

There are a number of reasons to believe that the ovoid density in our case was a piece of metal. First, the metallic density in the M2 branch of MCA is denser than cortical bone not only on visual inspection but also on the measurement of HU with a difference of at least 1000 units (figure 1A). Second, the metallic density was associated with a streak artefact, which is typical of metal (figure 1B). Third, on CT of thorax, the HU of the mechanical valves correlate with the metallic density in the brain and are greater than the bone cortex (figure 3). Lastly, there was no other good explanation to justify the finding. Classifying the metallic density as a calcified lesion was excluded for reasons mentioned above.

Considering our patient’s history that lacked metal inoculating events such as previous vascular manipulations, or trauma, we strongly believe that the metallic embolism found in our patient was attributed to either Cor-Knot fastener (like the fourth case mentioned above) or a broken off component of one of the valves. Since both valves and the Cor-Knot fastener are radiopaque, it is almost impossible to differentiate the source based on the imaging.

Learning points.

• Even newer generation mechanical valves can be associated with structural complications.

• In a patient with mechanical heart valve—who presents with neurological symptoms—an embolisation from mechanical valve should be on the differential diagnosis after ruling out common aetiologies including valve-related thromboembolism.

• Non-contrast CT of the head is sensitive and specific to identify intracranial metal embolus and should be considered as the initial imaging modality.