Discussion
Cardiovascular events have been reported as side effects of the COVID-19 vaccine; however, it is still unclear how vaccination can be associated with acute coronary syndrome (ACS) [2,3,4], coronary embolism due to severe inflammation induced by the vaccine, or coronary thrombosis mainly caused by plaque rupture.
Coronary embolism is a rare disease and is difficult to distinguish from coronary thrombosis. It has been reported to be caused occasionally in patients with arrhythmia and valvular disease [5]. Moreover, inflammatory hypercoagulation is known as a mechanism of coronary embolism [6]. It is often diagnosed by relating these conditions to embolism and by features such as fewer atherosclerosis lesions on specific angiographic images [6]. The typical thrombus is found to be platelet and fibrin rich on pathological examination [6].
This patient had an atypical clinical history, leading to myocardial infarction shortly after vaccination. Therefore, we considered that the onset was related to the vaccine. It was difficult to find the culprit lesion even using IVUS and OCT. However, we suspected myocardial infarction caused by plaque rupture, rather than by emboli, from the results of the pathological examination of the collected thrombus, which contained atheroma rich in cholesterin crystals and foam cells.
The vasa vasorum are small vessels that provide blood to the walls of arteries and veins. It is known that atherosclerosis facilitates the growth of vulnerable plaques and promotes neovascularisation of the vasa vasorum, which predisposes plaques to rupture [7]. Treatment with a low dose of statin has a little effect on the vasa vasorum, and a high dose is often needed [8]. Other medications for this condition are not known to date.
Through OCT, we discovered a rare large vasa vasorum in a thick plaque, indicating that it was unstable. These findings support the theory that plaque rupture led to the patient’s ACS. Therefore, angioplasty was performed, and high-dose statins were administered for these lesions.
Only three cases of acute myocardial infarction have been reported to occur within 2 hours after COVID-19 vaccination [2,3,4]. Patients in all three cases had RCA lesions; this finding was similar to that in the present case report. Kounis syndrome has been reported to occur after the vaccination [9]. Around 70% of patients with Kounis syndrome show ST elevation in inferior leads on electrocardiography [10]; the reason for high probability of RCA lesion still has been unknown. It might also support the fact that acute myocardial infarct immediately after vaccination is caused by allergic factors like Kounis syndrome. The patient in the present case was at a high risk of ACS. We suspected that stress or an allergic reaction caused by the vaccination might have led to elevated blood pressure and vasoconstriction, which affected the vulnerable plaque and caused plaque rupture.