Sirens to Scrubs: Acute Coronary Syndromes, Part Four – Spot the Lesion!

In Medical Concepts, Sirens to Scrubs by Paula SneathLeave a Comment

In Part One of this series, we reviewed the pathophysiology of Acute Coronary Syndromes (ACS), as well as some of the important features that should be elucidated on history-taking. In Part Two we discussed the current evidence-based practices for the management and transportation considerations in patients identified by paramedics to be suffering from a STEMI. In Part Three we described the series of events that occur when the care of a patient with suspected ACS is transferred to the ED. Now, in the final segment of this series, we’re going to learn to recognize coronary anatomy on common angiographic views and identify lesions that can lead to STEMI.

About Sirens to Scrubs

Sirens to Scrubs was created with the goal of helping to bridge the disconnect between pre-hospital and in-hospital care of emergency patients. The series offers in-hospital providers a glimpse into the challenges and scope of practice of out-of-hospital care while providing pre-hospital providers with an opportunity to learn about the diagnostic pathways and ED management of common (or not-so-common) clinical presentations. By opening this dialogue, we hope that these new perspectives will be translated into practice to create a smoother, more efficient, and overall positive transition for patients as they pass through the ED doors.


  1. To develop basic pattern recognition skills around coronary angiography1–5

Transporting STEMI patients directly to the PCI lab can be extremely rewarding for paramedics – it’s one of the few times we get to learn the outcomes for our patient. For most of us, though, angiographic images are just bunches of squiggly lines until the amazing PCI nurses explain where the lesion is. There are countless angiographic views, types of lesions, and anatomic variants of coronary vasculature, but here I will show you some of the frequently encountered images. Overall, the goal of angiography is to visualize the extent of each major artery in two perpendicular views (this is necessary anytime we try to evaluate 3D structures with a 2D imaging modality, such as x-ray).

Right Coronary Artery

This is the dominant artery in most people, which is to say that it gives rise to the Posterior Descending Artery. To summarize the most common branches:

Conus – circles away from the RCA toward the anterior surface of the RV near the pulmonic valve. This artery is of interest to cardiologists as it is commonly involved in the formation of collateral circulation.

Sinus nodal – arising from the RCA in 60% of the population (and the Left Circumflex in 40%), this branch feeds the SA node.

Marginal/Right Ventricular (RV branches) – supply the right atrium and ventricle.

AV nodal – arises from the RCA in 85 to 90% of the population to supply the AV node.

Posterior Descending/Ramus Descendens Posterior (RDP) – the first of two terminal branches of the RCA in right-dominant circulation, this branch feeds the posterior third of the interventricular septum, the diaphragmatic portion of the LV, and the posteromedial papillary muscle of the mitral valve.

Right Posterolateral (RPL)/Posterior Left Ventricular – the second terminal branch of the RCA in right-dominant circulation. Provides blood supply to the inferior portion of the heart (the posterior LV wall).







(The view of the RCA when looking at it from the left side of the heart)







(The view of the RCA with the camera on the right side of the heart)







(The view of the RCA looking down on it from the head and a bit to the left of the heart)

Left Main Coronary Artery (LM)

Left Anterior Descending (LAD) – perfuses the anterior two-thirds of the interventricular septum, the anterior, lateral and apical wall of the LV, most of the left and right bundle branches, and the anterior papillary muscle of the mitral valve. Further divided into:

  • Septal perforators
  • Diagonal branches (D1, D2, etc.)

Left Circumflex (LCx) – supplies most of the LA, the posterior and lateral free walls of the LV, and the anterior papillary muscle of the mitral valve. In 40% of the population, it also feeds the SA node. Further divided into:

  • Left atrial branches
  • Left ventricular/Obtuse marginal branches (OM1, OM2, etc.)

Ramus Intermedius (RI) – a variant in about 20% of the population in which a third major branch comes off of the LMCA.






(This isn’t a very intuitive view – it’s taken from the left side of the heart, looking up from the feet. It is also called the “spider view”.)







(The view of the left coronary arteries from the left side of the heart, looking down from the head)







(The view of the left coronary arteries from the right side of the heart, looking up from the feet)







(The view of the left coronary arteries from the right side of the heart, looking down from the head)

Spot the Lesion!

Got all that? Let’s try applying some pattern recognition to some actual lesions

Where is the lesion?

Proximal LAD.


Where is the lesion?

Left Circumflex.


Where is the lesion?



Where is the lesion? (black arrow only)

Left Circumflex.


Where is the lesion?



Where is the lesion?



Where is the lesion?

Posterior Descending Artery.

And that’s a wrap! Thank you for reading the final segment of our Acute Coronary Syndromes series. Find the first three segments and more Sirens to Scrubs articles here!

As always, if you have any questions, thoughts, alternative perspectives, or requests for future topics, feel free to comments below or send me an email at Please keep in mind that, although I will do my best to publish information that is accurate across Canada, there will inevitably be some regional differences in both pre-hospital and in-hospital management of emergency patients. As a paramedic and Emergency Medicine resident in Ontario, some posts may wind-up being somewhat Ontario-centric, hence, I encourage anyone whose experiences differ from mine to contribute to the conversation by commenting below.


Coronary Anatomy. PCIPedia. Published December 11, 2016. Accessed December 30, 2018.
Lee J-H. Interpretation of Coronary Angiogram. The Korean Society of Cardiology. Published 2007. Accessed December 30, 2018.
Narula J, J. Eapen Z, A. Harrington R, Fuster V. Hurst’s the Heart, 14th Edition: Two Volume Set. Vol 14. McGraw-Hill Education / Medical; 2017.
Gaillard F, Hacking C. Coronary Arteries. Radiopaedia. Published 2018. Accessed December 30, 2018.
Shavelle D. Basic Coronary Angiography. Keck School of Medicine of USC. Published 2017. Accessed December 30, 2018.
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Paula Sneath

Paula Sneath

Paula is an Emergency Medicine resident at McMaster University and an Advanced Care Paramedic in Ontario. She has a strong interest in improving access to education and resources for paramedics in Canada and fostering relationships between EM providers.
Paula Sneath
- 3 years ago