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Coronary Stenting: Flow Restoration

Source: John Hopkins Medicine

This blog will allow us to take a peek beyond the curtain to see what happens after you transfer care of the STEMI patient. In many systems the best practice is to completely bypass the ED and go straight to the cardiac catheterization lab for definitive care. STEMI and its many equivalents are time sensitive emergencies, and it is important to reinforce that minutes matter when you're trying desperately to save myocardial tissue and keep overall morbidity/mortality low. Reductions in Door to balloon (D2B) and first medical contact (EMS) to balloon times are known to correlate nicely with improved patient outcomes.

Your coronary vessels have a pretty important job. They are in direct physical contact with the epicardium and their main focus is to supply the myocardium with oxygen during the diastolic period. Their origins come from the aorta directly. Of note, if you have an occlusion near this opening they are referred to ostial lesions and they can be difficult, but not impossible to fix.

It may also be important to have a working knowledge of coronary dominance as well. Coronary arterial dominance is defined by the vessel which gives rise to the posterior descending artery (PDA), which supplies the myocardium of the inferior third of the interventricular septum. Most hearts (80-85%) are right dominant where the PDA is supplied by the right coronary artery (RCA). The remaining 15-20% of hearts are roughly equally divided between left dominant (~10%) and codominant (~20%).

So - your pre-hospital tracing has confirmed the presence of an acute infarction pattern (STEMI). The proceed emergently to the cath lab. In the lab with imaging and dye they confirm that a vessel is 100% occluded. The occlusion could be from plaque rupture and/or coronary thrombus. As with our line of work the situation and circumstances around a particular case dictates what actions are taken. In some cases, cardiology will perform a thrombectomy only (via suction) and not provide any drug-eluting stents. In other cases, coronary artery disease (CAD) is present and with NSTEMI medical management where are vessel may only be 50-60% blocked (anti platelets and aggressive statin therapy) only may be the best route.

When it comes to stent placement - the physician inserts a guidewire in either a femoral or radial vessel. The wrist in more commonly accessed today as it comes with fewer risk and occult hemorrhages can't hide as well here. As you can imagine the groin has been known to hold considerable amounts of blood before clinicians or the patient may be aware. A ballon is passed over catheter and inflated with air. This pushes the plaque to the periphery of the vessel. From there a drug-eluting stent is placed and essentially acts a scaffolding. The drug can prevent scar tissues formation which could lead to restenosis at a later time. Thats why patients should follow their pharmacological regimens and maintain compliance. I have cardiology tell me medication non-compliance can just about assure "in-stent" restenosis within 6 months - 1 year.

Source: New York Times

After the stent gets placed, the team with be on the lookout for reperfusion arrythmias which are common immediately after implantation. Some of the rhythm disturbances may require defibrillation while still on the procedure table. The myocardium gets flooded with fresh oxygen and essentially doesn't know how to act. The images above help illustrate the size of the stent (both length and diameter can vary) some coronaries are so large that renal stents have to get placed. The last image shows a nice pre and post angioplasty of the RCA.

Though these invasive procedures are very commonplace today, they do come with risks. To minimize the risks and ensure procedures are clinically necessary; lots of focus is shifting towards prevention of cardiac disease and also more novel, non-invasive approaches like stress tests, coronary CTA imaging, AI powered algorithms, and more personalized 3D models to identify and quantify coronary narrowing.

EMS is absolutely part of the equation moving forward - I urge you to continue educating your communities, as we bring together human ingenuity and technological advances to combat America's perennial #1 killer -- HEART DISEASE.

December 25, 2023

Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP

Pass with PASS, LLC.

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