Insomnia as an Atypical Presentation of Acute Circumflex-Territory Transmural Myocardial Infarction with Persistent Sinus Tachycardia: a Case Report

Abstract

Background: Acute myocardial infarction (AMI) may be present without classical
chest pain, particularly in patients with multiple cardiovascular risk factors.
Atypical and nonspecific symptoms may obscure acute myocardial infarction, particularly
when classical ischemic symptoms are absent. In this case, persistent insomnia was the
atypical presenting symptom, while persistent sinus tachycardia was an important clinical
sign that prompted further cardiovascular assessment. Cardiac magnetic resonance (CMR)
provides comprehensive assessment of myocardial function, oedema, infarct
distribution, late gadolinium enhancement, and myocardial viability.

Case presentation: A 51-year-old man presented to his general practitioner with a several-week history of persistent insomnia. He denied chest pain, dyspnea, palpitations, syncope, and constitutional symptoms. His medical history was otherwise unremarkable. He was a current smoker and had a strong family history of premature coronary artery disease; his father had undergone coronary artery
bypass grafting at 50 years of age. Clinical examination identified persistent tachycardia, an objective clinical sign that prompted referral to the emergency department. Laboratory
evaluation demonstrated markedly elevated cardiac troponin, reported as 2,285,
and he was managed initially as acute coronary syndrome. Thyroid function testing was within normal limits. The persistent tachycardia was investigated diagnostically with adenosine; the rhythm
remained consistent with sinus tachycardia. Bisoprolol subsequently commenced, resulting in good rate control. Transthoracic echocardiography demonstrated mildly impaired left ventricular systolic function with an estimated ejection fraction of 40–45% and regional wall-motion abnormalities. CT coronary angiography demonstrated severe coronary artery disease involving the circumflex territory, with likely 70–90% stenosis of the mid circumflex/obtuse marginal segment. The coronary calcium score was 350.4, while the LAD and RCA showed non-obstructive disease. CMR demonstrated regional akinesia involving the basal-to-apical lateral segments,
extensive myocardial oedema, and a recent transmural myocardial infarction in
the conventional circumflex territory. Biochemical testing during admission
also established a new diagnosis of type 2 diabetes mellitus.

Conclusion: This case highlights that acute myocardial infarction may present with an atypical symptom such as persistent insomnia in the absence of classical ischemic symptoms. In this patient,
persistent sinus tachycardia was an important clinical sign that prompted escalation of
cardiovascular assessment. Multimodality cardiac imaging was instrumental in establishing
the extent and territory of myocardial injury. Normal thyroid function testing helped exclude
thyroid dysfunction as a potential reversible cause of persistent tachycardia.