THE WEEKLY USMLE TIMES
Issue #66
Welcome to this week’s issue of The USMLE Times.
In today’s email, you’ll get:
A High-Yield Cardio/IM Question
Video & Audio Training Recommendations
My Tweet of the Week
Question Breakdown + Related Step 1 Facts
Let’s dive in!
A 65-year-old male with a history of hypertension, type 2 diabetes mellitus, and a 20-pack-year smoking history presents to the emergency department with a 3-hour history of severe, crushing chest pain that began at rest and radiates to his left arm. He is diaphoretic, anxious, and nauseous. His vital signs are: temperature 98.6℉ (37°C), blood pressure 145/85 mmHg, pulse 110/minute, respiratory rate 20/minute, and oxygen saturation 95% on room air. An ECG reveals 1.5 mm ST-segment elevations in leads II, III, and aVF with reciprocal ST-segment depressions in leads I, aVL, and V2-V4. His cardiac troponin T level is 0.5 ng/mL (normal: <0.01 ng/mL). He is administered aspirin, sublingual nitroglycerin, and supplemental oxygen. Given his clinical presentation, which of the following is the most appropriate next step in management?
A. Administer a beta-blocker, nitroglycerin, and IV heparin
B. Administer an ACE inhibitor and a statin
C. Immediate percutaneous coronary intervention
D. Administer a CCB and an ARB
E. Thrombolytic therapy with IV tPA
The answer & question breakdown is at the bottom of the post.
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💎 ANSWER + QUESTION BREAKDOWN
This patient presents with severe, crushing chest pain, diaphoresis, nausea, and ECG changes indicative of ST-segment elevations in leads II, III, and aVF. Based on this presentation, the most likely diagnosis is an ST-elevation myocardial infarction (STEMI).
The answer can be found at the bottom of this post. If you’d prefer to do a deep-dive into the answer choices first, let’s proceed.
ANSWER CHOICE A: Administer a beta-blocker, nitroglycerin, and IV heparin.
While beta-blockers, nitroglycerin, and heparin are part of the management for acute coronary syndromes, reperfusion therapy is the priority in a patient with ST-elevation myocardial infarction, as suggested by the ECG findings and symptoms. Beta-blockers should be used cautiously in the acute setting of STEMI and are not the immediate next step.
Integrating Step 1 into this answer choice:
Beta-blockers decrease heart rate, myocardial contractility, and myocardial oxygen demand, making them helpful in managing ischemic heart disease. They block the effects of catecholamines (epinephrine and norepinephrine) at the β-adrenergic receptors.
Nitroglycerin causes vasodilation, primarily of venous vessels, which decreases preload and myocardial oxygen demand. It is a nitrate that converts to nitric oxide, leading to smooth muscle relaxation.
Heparin enhances the activity of antithrombin III, leading to the inactivation of thrombin and factor Xa, preventing the conversion of fibrinogen to fibrin. It is essential in the management of acute coronary syndromes to prevent further thrombus formation.
ANSWER CHOICE B: Administer an ACE inhibitor and a statin.
ACE inhibitors and statins are important in the long-term management of patients with coronary artery disease and post-STEMI for secondary prevention. However, they are not the immediate next step in the acute phase where reperfusion is the priority.
Integrating Step 1 into this answer choice:
ACE inhibitors prevent the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. Thus, they lower blood pressure and reduce the workload on the heart. They also reduce the progression of ventricular remodeling after myocardial infarction.
Statins inhibit HMG-CoA reductase, the rate-limiting enzyme in cholesterol synthesis, leading to reduced LDL levels. They also have pleiotropic effects, such as improving endothelial function and reducing inflammation and thrombus formation.
ANSWER CHOICE C: Immediate percutaneous coronary intervention.
For a patient with STEMI, immediate PCI is the preferred reperfusion strategy if it can be performed within the recommended time frame (ideally within 90 minutes from the first point of medical contact).
Integrating Step 1 into this answer choice:
PCI physically opens the blocked coronary artery, restoring blood flow to the ischemic myocardium. The success of PCI depends on the "door-to-balloon" time, emphasizing the importance of rapid triage and treatment in acute coronary syndromes.
ANSWER CHOICE D: Administer a CCB and an ARB.
Calcium channel blockers are not first-line for STEMI management and could potentially be harmful in certain types of heart attacks. ARBs are used similarly to ACE inhibitors but are not the priority in acute management.
Integrating Step 1 into this answer choice:
Calcium channel blockers inhibit the entry of calcium ions into vascular smooth muscle and cardiac cells, leading to vasodilation and decreased heart rate and contractility. They are especially useful in treating hypertension and angina.
ARBs block the action of angiotensin II at its receptor, preventing vasoconstriction and aldosterone-mediated volume expansion. They provide similar benefits to ACE inhibitors but without the side effects of coughing.
ANSWER CHOICE E: Thrombolytic therapy with IV tPA.
Thrombolytic therapy is an alternative to PCI when PCI is unavailable within the recommended time frame. However, if PCI is available, it is preferred due to better outcomes and lower risk of complications like bleeding, especially in a tertiary care setting or when the time frame for effective thrombolysis (typically within 12 hours of symptom onset) may be closing.
Integrating Step 1 into this answer choice:
tPA and other thrombolytics convert plasminogen to plasmin, which breaks down fibrin clots and restores perfusion in occluded vessels. This is an alternative to PCI in STEMI when PCI is unavailable within the recommended timeframe.
The concerning risk associated with thrombolytic therapy is bleeding.
THE VERDICT: Given the clinical scenario of STEMI, the most appropriate and immediate next step is immediate percutaneous coronary intervention (PCI).
FINAL ANSWER: C. Immediate percutaneous coronary intervention
That’s all for this week’s issue of The USMLE Times!
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