A rare cause of acute ST-elevation myocardial infarction: a case of coronary embolism secondary to calcified bicuspid aortic valve

Contact address: Anda Bularga, MD, BHF Centre for Cardiovascular Science, Chancellors Building, Royal Infi rmary of Edinburgh, Edinburgh EH16 4SA, United Kingdom. E-mail: anda.bularga@ed.ac.uk 1 BHF Centre for Cardiovascular Science, University of Edinburgh, United Kingdom Abstract: Coronary embolism is an uncommon cause of acute myocardial infarction, which can have a similar clinical presentation to a plaque rupture event with acute onset of ischaemic symptoms, ST segment elevation on electrocardiogram (ECG) and signifi cant elevation in cardiac troponin, requiring immediate intervention. We report the case of a middle-aged female with a background history of previous non-ST elevation myocardial infarction, bicuspid aortic valve with severe stenosis and metastatic breast cancer. The patient underwent emergency coronary angiography following acute onset central chest pain and evidence of anterior ST segment elevation on ambulance 12-lead ECG. The procedure revealed complete occlusion of the mid left anterior descending coronary artery with immediate fl ow restoration following embolus aspiration and subsequent normal appearance of the left anterior descending coronary artery. Gross examination of the aspirated specimen resembled a calcifi ed hard lump, which was further confi rmed on microscopic examination revealing calcifi ed fi brous tissue most likely an embolus from the calcifi ed bicuspid aortic valve. The patient had evidence of near transmural myocardial infarction in the distribution of the left anterior descending coronary on cardiac magnetic resonance imaging (MRI). She made full recovery and was discharged on short-term dual antiplatelet therapy followed by lifelong aspirin and further assessment for aortic stenosis management.


INRODUCTION
Coronary embolism is a rare, but important non-atherosclerotic cause of acute myocardial infarction and can present as an acute ST segment elevation myocardial infarction (STEMI) requiring emergency percutaneous coronary intervention for individualised diag-nosis and management 1 . The 4 th universal defi nition of myocardial infarction classifi es coronary embolism as a mechanism for myocardial injury related to acute myocardial ischaemia due to reduced myocardial perfusion 2 . As such the pathophysiological mechanism of coronary embolism is classifi ed under the umbre- lla term of type 2 myocardial infarction secondary to oxygen supply-demand imbalance 2,3 .
The underlying causes of coronary embolism are multifactorial with atrial fi brillation as a common underlying predisposing clinical condition and a systemic hypercoagulable state as a potential risk factor 4 . Three types of coronary embolisms are described: direct embolisms originating from cardiac structures such as the left atrial appendage, aortic or mitral valves, cardiac neoplasms; paradoxical embolisms that arise from the venous circulation and pass through interatrial shunts and iatrogenic embolisms secondary to cardiac procedures 4 .
We present a rare case of a spontaneous calcifi c embolus from a native bicuspid aortic valve causing total occlusion of the left anterior descending coronary artery.

CASE REPORT
We report the case of a 53 years old female who presented with sudden onset central chest pain at rest described as "chest tightness" with no preceding symptoms of exertional angina. She had a background history of a previous non-ST elevation myocardial infarction, six years ago in the context of minor coronary plaque disease, which was managed medically with secondary prevention therapy; severe bicuspid aortic stenosis with preserved left ventricular systolic function for which she was receiving regular follow up and metastatic breast cancer on palliative treatment. The patient was a smoker, with no signifi cant family history, her most recent cholesterol profi le showed a total cholesterol of 3.5mmol/L with LDL choleste-rol of 2.0mmol/L on regular statin therapy. An echocardiogram performed one month prior to this acute admission revealed progressive severe bicuspid aortic valve stenosis with a mean gradient of 72mmHg and peak gradient of 114mmHg across the valve and preserved left ventricular systolic function ( Figure 1). The patient reported mild breathlessness on exertion and was referred for further investigations, multidisciplinary team discussion and consideration of valve intervention one month prior to this admission.
On initial assessment the patient was haemodynamically stable. Cardiovascular examination revealed fi rst heart sound followed by an ejection systolic murmur radiating to the carotids with absent second heart sound. An ambulance trace showed evidence of ST segment elevation in the anteroseptal leads (V1-V4) with reciprocal ST segment depression in the lateral leads ( Figure 2). Initial high-sensitivity cardiac troponin I was elevated at 1.319ng/L with a peak troponin of >50.000ng/L at 12 hours following symptom onset. She received emergency medical therapy with antiplatelet therapy and was taken directly to the cardiac catheterization laboratory for a primary percutaneous coronary intervention. The procedure was performed two hours after the initial symptom onset. The angiogram procedure showed an abrupt complete occlusion of the mid left anterior descending artery with thrombolysis in myocardial infarction (TIMI) grade zero fl ow in the distal segment, with no evidence of plaque disease proximal to the lesion or in the other coronary arteries (Figure 3).
The lesion was aspirated using an Export Advance catheter on fi rst pass with immediate fl ow restoratinot reveal evidence of organized thrombus, and, therefore, this was presumed to be embolic debris from the native calcifi ed aortic valve.
Following the emergency percutaneous coronary intervention procedure, the patient was monitored on the coronary care unit for the next 48 hours and she made full recovery. She was managed with dual antiplatelet therapy for three months followed by aspirin monotherapy lifelong. The patient underwent cardiac magnetic resonance imaging (MRI) as part of a research study evaluating the mechanisms of myo-on in the distal vessel and normal appearances of the left anterior descending coronary artery (TIMI grade three fl ow) (Figure 3), therefore angioplasty with stent deployment was not required. On further inspection the aspirated tissue appeared as hard, ivory-white fibrous tissue resembling calcifi ed deposits. The sample was sent for histopathological examination. Microscopic evaluation revealed granular proteinaceous material, which was focally calcifi ed and surrounded by fi brin with occasional infl ammatory cells and no other atypical features identifi ed. The histopathology report did  of a coronary vessel and can happen in the presence of absence of underlying coronary disease. It can have clinical presentations of varying severity including ST segment elevation myocardial infarction requiring emergency management and intervention similar to acute coronary syndrome due to atherosclerotic plaque rupture 6 . In clinical practice it is diffi cult to distinguish coronary embolism from atherothrombotic acute coronary syndrome, prior to diagnostic coronary angiography, hence the initial management and assessment of these patients is similar 5,6 . Intracoronary imaging by means of optical coherence tomography (OCT) or intravascular ultrasound may be considered in selected cases to help evaluate for potential evidence of plaque rupture or erosion versus an embolic event 4,5 .
The current universal defi nition of myocardial infarction classifi es coronary embolism as a mechanism of reduced myocardial perfusion due to coronary fl ow disruption in the absence of plaque rupture or erosion (type 1 myocardial infarction) 2 . As such coronary embolism is defi ned as a distinct mechanism of decreased oxygen supply under the umbrella term of type 2 myocardial infarction 2 . Type 2 myocardial infarction is a heterogeneous condition with poor clinical outcomes encompassing a range of cardiac and systemic pathophysiological processes 8 . Arguably, coronary embolism has many similarities to a type 1 myocardial infarction, both from the clinical presentation, diagnostic approach and management perspectives. This case illustrates some of these similarities -the cardial injury and role of coronary artery disease in patients with type 2 myocardial infarction (DEMAND-MI, NCT 03338504). The cardiac MRI scan, which was performed four days following the acute event, showed evidence of severe hypokinesis of the antero-septal wall extending towards the apex with near transmural late gadolinium enhancement in the same territory, consistent with myocardial infarction (Figure 4). There was evidence of mild to moderate left ventricular systolic dysfunction with ejection fraction of 47% and severe fl ow acceleration through a thickened aortic valve innkeeping with the background history of severe aortic stenosis.
The patient was discharge from hospital with plans for timely follow up and discussion of aortic valve stenosis management following multidisciplinary team consensus in view of her underlying comorbidities and metastatic cancer disease. Following thorough assessment and discussion with the Oncology team and in view of her progressive shortness of breath on follow up the patient underwent prosthetic aortic valve replacement six months following this acute admission.

DISCUSSION
Coronary embolism is an uncommon, but important and serious pathophysiological cause of acute myocardial infarction with potential adverse clinical consequences 5 . The reported prevalence varies according to angiographic or autopsy studies ranging between 4% and 13% 6,7 . This pathological phenomenon is a recognised distinct mechanism for acute total occlusion The risk of calcifi c embolisation from aortic stenosis is recognised and can affect cerebral, renal, coronary and retinal circulation 9 and thought to be more common with bicuspid valves and severe stenotic disease due to turbulent fl ow through the diseased valve and calcium debris rupture 10,11 . In this case the coronary embolus caused clinically signifi cant anteroseptal myocardial infarction as evidenced by extensive late gadolinium enhancement in the affected coronary territory. Although rare, calcifi ed embolus from valve disease should be a differential cause of coronary embolus and this case highlights the importance of thorough evaluation of the embolism source to guide medical management and further evaluation of the severity of valvular heart disease. Whilst septic emboli in the context of infective endocarditis is an indication for surgical valve replacement 12 , emboli from calcifi c, degenerative native valve disease are not a recognised indication for valve intervention, however careful assessment and consideration should be given in individual cases.

CONCLUSION
This case shows a rare cause of an anteroseptal STelevation myocardial infarction due to total occlusion of the left anterior coronary artery caused by calcifi ed material from severe calcifi c disease of a native bicuspid aortic valve. Whilst many pathophysiological causes of coronary embolisms can be identifi ed, thorough, individualised assessment of these patients is necessary to determine the underlying mechanism of the coronary embolism for appropriate immediate and long-term management.
Confl ict of interest: none declared. patient presented with an acute anteroseptal ST-elevation myocardial infarction. In view of her background history of a previous acute coronary syndrome in the context of mild plaque disease and cardiovascular risk factors there was a strong suspicion of an atherothrombotic event. She received antiplatelet therapy and underwent emergency percutaneous coronary intervention, which revealed total occlusion of the left anterior coronary artery with no signifi cant coronary disease in the proximal vessel or other coronary arteries. Thrombus aspiration restored normal fl ow and macroscopic evaluation of the specimen showed distinct features in keeping with a calcifi ed mass. The patient did not undergo further intracoronary imaging following clot aspiration; however, this may play a role when the suspicion of a plaque rupture event is high.
Determining the underlying cause of the coronary embolism is in itself an important step, which can have implications on long-term management particularly when considering regular antithrombotic therapy, follow up and prevention of recurrent events 4 . Whilst a range of embolisation sources and associated predisposing clinical conditions are recognised, some of these are more common than others. In a number of recently published cohort studies atrial fi brillation was reported as the most common cause of coronary embolism with a period of monitoring being potentially warranted in the absence of further aetiological evidence 5,6 . Clinical history and structural cardiac imaging are important when considering direct, paradoxical emboli or iatrogenic causes.
In this case the underlying aetiology was strongly suspected following coronary intervention which revealed abrupt occlusion of the left anterior descending coronary artery with normal appearance of the artery following embolus aspiration without signifi cant residual coronary disease and evidence of collateral circulation. Furthermore, gross examination of the aspirated embolus, which resembled calcifi ed material was in keeping with the known calcifi c bicuspid aortic valve disease with severe stenosis. In considering alternative embolic sources, patient's underlying history of metastatic breast cancer increases predisposition to a procoagulant state and indeed would be a plausible alternative cause. However, the histopathological evaluation of the aspirated embolus confi rmed the suspected aetiology showing evidence of calcifi ed fi brous material and absence of organised thrombus formation.