Myocardial infarction

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Myocardial infarction

Cardiovascular system

Cardiac tumors

Cardiac tumors




Myocardial infarction


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USMLE® Step 1 questions

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High Yield Notes

5 pages


Myocardial infarction

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USMLE® Step 1 style questions USMLE

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A 60-year-old man comes to the emergency department due to 20 minutes of crushing chest pain and diaphoresis that began suddenly while watching television. According to the patient’s partner, lately he has had occasional chest pain occurring during rest that resolved after a few minutes. Medical history is significant for hyperlipidemia, hypertension, and diabetes mellitus. The patient has not been compliant with the medications. The patient’s temperature is 37.0°C (98.6° F), pulse is 80/min, respirations are 20/min, and blood pressure is 135/85 mm Hg. The patient appears to be in acute distress and in pain. Cardiac examination shows an additional sound just prior to S1 on auscultation. ECG demonstrates ST segment elevation in leads V1-V5. While being prepared for percutaneous coronary intervention, the patient suddenly dies. Following this patient’s death, an autopsy is performed to better understand the underlying pathology. At the time of this patient's death, which of the following sets of findings is most likely to be seen in the anterior wall of the myocardium?  

External References

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Left anterior descending artery

myocardial infarction and p. 311

Myocardial infarction (MI) p. 310

antiarrhythmics after p. 328

β -blockers for p. 247

complications of p. 316

diabetes mellitus p. 352

diagnosis of p. 313

on ECG p. 312, 313

evolution of p. 311

heart failure caused by p. 318

heparin for p. 443

homocystinuria p. 81

hypertensive emergency and p. 306

shock caused by p. 321

thrombolytics for p. 445


According to the world health organization, cardiovascular disease is the leading cause of death worldwide, as well as in the US. Of those, a large proportion are caused by heart attacks, also known as acute myocardial infarctions, or just myocardial infarctions, sometimes just called MI.

The word infarction means that some area of tissue has died due to a lack of blood flow, and therefore a lack of oxygen. “Myo” refers to the muscle, and “cardial” refers to the heart tissue. So with a heart attack, or MI, you have death of heart muscle cells because of a lack in blood flow, a process called necrosis. Now the heart’s main job is to pump blood to your body’s tissues right? Well, the heart also needs blood, and so it also pumps blood to itself, using the coronary circulation. The coronary circulation is this system of small arteries and veins that help keep the heart cells supplied with fresh oxygen. Heart attacks happen when these small arteries become blocked and stop supplying blood to the heart tissue, and if this happens for long enough, heart tissue dies.

Almost all heart attacks are ultimately a result of endothelial cell dysfunction, which relates to anything that irritates or inflames the slippery inner lining of the artery—the tunica intima. One classic irritant are the toxins found in tobacco which float around in the blood and damage these cells. That damage then becomes a site for atherosclerosis, a type of coronary artery disease where deposits of fat, cholesterol, proteins, calcium, and white blood cells build up and start to block blood flow to the heart tissue. This mound of stuff has two parts to it, the soft cheesy-textured interior and the hard outer shell which is called the fibrous cap. Collectively this whole thing’s ominously called plaque. Usually, though, it takes years for plaque to build up, and this slow blockage only partially blocks the coronary arteries, and so even though less blood makes it to heart tissue, there’s still blood. Heart attacks happen when there’s a sudden complete blockage or occlusion of a coronary artery—so let’s see how that can happen. Since these plaques sit right in the lumen of the blood vessel, they’re constantly being stressed by mechanical forces from blood flow, and interestingly it’s often the smaller plaques with softer caps rather than the larger ones with harder caps that are especially prone to break or get ripped off. Once that happens the inner cheesy filling which remember is this mix of fat, cholesterol, proteins, calcium, and white blood cells, is thrombogenic, and this means that it tends to form clots very quickly. So platelets, or blood-clotting components in the blood, flow by and get excited; and they adhere to the exposed cheesy material. In addition to piling up, the platelets also release chemicals that enhance the clotting process. Now this happens super fast, think about how quickly a small cut stops bleeding, that’s a very similar process—it happens in a matter of minutes, right? And now that coronary artery is fully occluded.


Myocardial infarction (MI), also known as a heart attack, occurs when the blood supply to part of the heart muscle is blocked. This is usually caused by a buildup of fatty deposits in the lining of an artery that supplies blood to the heart, a process called atherosclerosis. Symptoms of MI include crushing chest pain or pressure that might radiate up to the left arm or jaw, sweating, nausea, and dyspnea. Treatment of MI includes re-establishing blood flow using medications, angioplasty, or percutaneous coronary intervention.


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  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Coronary Plaque Disruption" Circulation (1995)
  6. "The role of oxidants and free radicals in reperfusion injury" Cardiovascular Research (2006)

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