ECG Pointers: Post Myocardial Infarction Complications – Stent Thrombosis

Author: Lloyd Tannenbaum, MD (Emergency Medicine Resident, San Antonio, TX) // Edited by:  Jamie Santistevan, MD (@jamie_rae_EMdoc – EM Physician, Presbyterian Hospital, Albuquerque, NM); Manpreet Singh, MD (@MPrizzleER – Assistant Professor of Emergency Medicine / Department of Emergency Medicine – Harbor-UCLA Medical Center); and Brit Long, MD (@long_brit  – EM Attending Physician, San Antonio, TX)

Welcome to this edition of ECG Pointers, an emDOCs series designed to give you high yield tips about ECGs to keep your interpretation skills sharp. For a deeper dive on ECGs, we will include links to other great ECG FOAMed!


This week we begin a new series on post myocardial infarction complications.  Today we present a case of a patient who had stent thrombosis, discuss the diagnosis, and figure out how to treat the patient appropriately.

The Case:

A 63-year-old male presents to the ED via EMS with chest pressure that he rates 10/10.  He is sweating, extremely uncomfortable, and states that this pain feels exactly like the heart attack he had 8 months ago.  At that time, he was transferred to a percutaneous coronary intervention (PCI) center, had a drug eluting stent placed, and has been compliant with his dual antiplatelet therapy.  He tried some sublingual nitroglycerine at home, which did not help his pain.

As you move the patient over from the EMS stretcher to the ED bed, EMS hands you the ECG that they obtained en route.

Notice that this ECG is consistent with an inferior-posterior STEMI.  The inferior portion is suggested by the ST segment elevation in leads III and aVF and associated ST segment depressions in I and aVL, while the posterior portion is suggested by the ST depression in V2 with continued depressions in the anterior leads and upright R waves in V1-V3.

SIDE NOTE: From an academic point of view, it would have been interesting to see a posterior ECG.  From a patient care standpoint, obtaining a posterior ECG would likely not have added much to the diagnosis, as a diagnosis of STEMI had already been made based on the initial ECG.  Just as a quick refresher, a posterior ECG moves leads V4/5/6 to the back of the patient, as shown in the picture below. 0.5 mm of ST elevation in these leads is significant.

Picture reproduced from Life in the Fast Lane [1]

Remember, posterior STEMIs can accompany 15-20% of inferior and lateral STEMIs, signifying a larger area of myocardial involvement.  The more myocardium involved, the higher likelihood of ventricular arrhythmias and complications [1]. For more on ECG findings of Posterior STEMI, visit this prior EMdocs post: http://www.emdocs.net/ecg-pointers-posterior-mi/.

Back to our case: Astutely, you notice that the ECG that EMS handed you is consistent with a STEMI.  You have your techs repeat an ECG just to double check, and it is identical to the one EMS handed you.  You activate your hospital’s STEMI protocol and get ready to ship the patient off to a PCI center. After shift, you decided to learn a little more about stent thrombosis.

On September 16, 1977, Dr. Andreas Gruentzig performed the first PCI in Switzerland.  Interestingly, the tools for a PCI were not invented yet, and he had to invent his own tools for the procedure on his kitchen table.  Early PCIs were done with balloon angioplasty, as stents were not invented yet. Early balloon angioplasty had many complications, such as rapid restenosis as plaques would frequently prolapse or vessels would constrict shortly after the procedure.  In 1986, the first stents were used in conjunction with balloon angioplasty. These early stents helped to prevent early restenosis and keep the affected vessels patent, but they were also not perfect [2].

Early stents were done with bare metal stents, and approximately 25% of them would be completely occluded at 14 days post PCI.  These occlusions and thromboses were seen despite high doses of heparin and other antithrombotic medications. There were several strategies attempted to decrease thrombosis including using high pressure balloon expandable stents and heparin impregnated stents, which were able to decrease the rates of occlusion to around 3%, but with increasing doses of antithrombotic medications, rates of hemorrhagic complications increased from 3-4% to 7-13% [2,3].  In the early 1990s, several studies looked at combining aspirin and ticlopidine, and from those studies, dual antiplatelet therapy was born [3,4].

Current stents are drug eluting stents, which are stents that send out (or elute) drugs that prevent inflammation and scar tissue in the blood vessels.  This helps to prevent stent thrombosis and failure. Interestingly, current stents can even be bioresorbable, where over time, the body will completely reabsorb the stent [2].  Currently, using dual antiplatelet therapy and modern stents, the rate of stent thrombosis, 9-12 months after stent placement is 0.61% [2].

Case Conclusions:

As your shift is ending, you get a text from your local, friendly cardiologist, letting you know that the patient had a stent thrombosis.  She was able to restent the vessel and expects the patient to make a full recovery.

Key Points:

– Stent thrombosis is an uncommon complication that can happen at any point after the placement of a stent. Presentation resembles acute MI.

– Posterior STEMIs can accompany 15-20% of Inferior and Lateral STEMIs. Consider getting a posterior EKG in these patients.

– Dual antiplatelet therapy and modern, drug eluting stents have significantly reduced the rate of stent thrombosis.

References:

1. Burns, Ed. Life in the Fast Lane: Posterior Myocardial Infarction. 16 Mar 2019. https://litfl.com/posterior-myocardial-infarction-ecg-library/

2. Byrne RA, Joner M, Kastrati A. Stent thrombosis and restenosis: what have we learned and where are we going? The Andreas Gruentzig Lecture ESC 2014. Eur Heart J. 2015;36:3320–31.

3. Leon MB, Baim DS, Popma JJ, et al. A clinical trial comparing three antithrombotic-drug regimens after coronary-artery stenting. Stent Anticoagulation Restenosis Study Investigators. N Engl J Med 1998;339:1665–1671.

4. Schömig A, Neumann F-J, Kastrati A, et al. A randomized comparison of antiplatelet and anticoagulant therapy after the placement of coronary- artery stents. N Engl J Med 1996;334:1084-9

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