Thinking "outside" the heart -a rare case report of MI with extrinsic coronary compression.

External compression of the left main coronary artery (LMCA) by a pulmonary arterial aneurysm (PAA) usually presents as stable angina pectoris. However, acute myocardial infarction as an index presentation is very rare. Sharma et al have highlighted this rare association in the latest issue of Hindawi journal. the patient ultimately underwent coronary stenting to manage his chest pain.

Pulmonary arterial hypertension (PAH) is associated with aneurysm of the main pulmonary artery (PA). In normal anatomy, the PA lies adjacent to the left coronary sinus of the aorta. As the left main coronary artery (LMCA) arises from the left coronary sinus, it may be compressed by a PA aneurysm (PAA).

A 62-year-old man with a past history of severe fibrotic lung disease requiring long-term oxygen therapy was hospitalised with typical angina pain with no resolution despite sublingual glyceryl trinitrate use. ECG , 2D ECHO and cardiac enzymes, all suggested a diagnosis of anterolateral wall ST elevation myocardial infarction (STEMI). Estimated pulmonary artery systolic pressure from 2DECHO was very high (110 mmHg).

Most importantly, cardiac catheterisation assessment as part of a lung transplant work-up 7 years earlier had shown no significant coronary disease. The differential diagnosis included pulmonary thromboembolism and pulmonary/aortic dissection, although the clinical picture was most consistent with acute MI. The patient was commenced on pharmacological treatment for non-ST elevation myocardial infarction. In view of the significant lung disease, an initial conservative approach was taken, but after continual chest pain despite optimal medical therapy, invasive coronary angiography was necessitated.

The transradial coronary angiogram showed a tight narrowing of the LMCA ostium (Figure). The smooth tapering appearance raised the possibility of external compression. This was subsequently confirmed with the use of intravascular ultrasound (IVUS) which showed dynamic external compression of LMCA with a slit-like lumen and absence of atheroma—suggesting that the patient had developed a type 2 STEMI due to demand ischaemia. A gated CT scan confirmed normal origin and course of the LMCA; however, it was compressed by a grossly dilated PA measuring 58 mm (normal ~30 mm) at its maximal diameter (Figure), compared to 33 mm 7 years ago.

The patient was not felt to be a suitable candidate for surgery and underwent IVUS-guided percutaneous coronary intervention with a  5 x 20 mm everolimus drug-eluting stent deployed directly without any predilatation. Postdeployment, IVUS confirmed a well-apposed stent with resolution of extrinsic compression and restoration of the LMCA lumen. The patient was rendered pain free and discharged home after a short period of observation and remained angina free on subsequent follow-up.

MI due to external compression of the left main stem can occur by 2 main mechanisms. In normal coronary anatomy, severe PAA can develop following longstanding PAH, resulting in acute compression of the LMCA. In patients with anomalous coronary origin or course interruption of coronary flow, it occurs due to compression of the LMCA between the PA and the high-pressured aorta and can occur without PAA. Although stable angina is the classical presentation of this syndrome but this case highlights that compression can behave as a MI mimic.

It is worth noting that because of the slit-like nature of the narrowing, 45° left anterior oblique (LAO) or 30° LAO cranial angulation coronary angiographic planes cross-sectioning the narrow axis of the compressed LMCA best visualise this pathology, whereas other planes crossing the wide axis of the narrowing frequently miss the compression.

The case serves to remind clinicians to be mindful of acute coronary syndromes in patients with long-standing pulmonary hypertension presenting with chest pain.

Source: Hindawi case reports: H. Sharma, S. N. Doshi, M. A. Nadir, "Acute Myocardial Infarction due to External Compression of the Left Main Coronary Artery by a Large Pulmonary Artery Aneurysm", Case Reports in Cardiology, vol. 2021, Article ID 8850044, 4 pages, 2021. https://doi.org/10.1155/2021/8850044