Emergency medical services transport a 61-year-old male to the resuscitation bay following… — USMLE Step 2 CK

Emergency medical services transport a 61-year-old male to the resuscitation bay following the acute onset of heavy, retrosternal chest pressure, diaphoresis, and severe shortness of breath. The symptoms began approximately 90 minutes ago. His medical history includes type 2 diabetes mellitus and a 45-pack-year smoking history.

On arrival, his temperature is $37.4^{\circ}\text{C}$ ( $99.3^{\circ}\text{F}$ ), blood pressure is $82/50$ mmHg, heart rate is $108$ /min, and respiratory rate is $26$ /min. Pulse oximetry is $91\%$ on room air.

Physical examination reveals prominent jugular venous distention with a positive Kussmaul sign. Chest auscultation yields faint, bilateral expiratory wheezes, but no crackles. Cardiac auscultation reveals a regular tachycardia, a right-sided $S_4$ gallop, and no murmurs.

A 12-lead electrocardiogram displays $3$ -mm ST-segment elevations in leads II, III, and aVF, with reciprocal ST-segment depressions in leads I and aVL. Right-sided ECG leads show a $2$ -mm ST-segment elevation in lead $V_4R$ .

An arterial blood gas analysis on room air reveals:

Parameter	Value
$pH$	$7.32$
$pCO_2$	$52$ mmHg
$pO_2$	$60$ mmHg
$HCO_3^-$	$26$ mEq/L

The patient is immediately administered chewable aspirin and intravenous heparin.

Which of the following is the most appropriate initial step to address this patient's hemodynamic status prior to definitive reperfusion therapy?

A
Intravenous administration of furosemide
B
Administration of nebulized albuterol and ipratropium
Intravenous bolus of $0.9\%$ normal salineAnswer
D
Intravenous administration of ceftriaxone and azithromycin
E
Intravenous infusion of sodium bicarbonate

Answer

The correct answer is to administer an intravenous bolus of

0.9\%

normal saline.

The patient's electrocardiogram confirms an acute inferior ST-segment elevation myocardial infarction (STEMI) with right ventricular (RV) involvement (ST elevation in

V_4R

). The classic triad of RV infarction includes hypotension, elevated jugular venous pressure, and clear lung fields. The ischemic right ventricle loses contractility and dilates, requiring higher filling pressures (preload) to maintain forward blood flow into the left ventricle. Therefore, the immediate treatment for hypotension in RV infarction is volume expansion with isotonic intravenous fluids.

Step-by-Step Solution

Interpret the clinical presentation and 12-lead electrocardiogram findings.

The ECG shows ST-segment elevations in inferior leads (II, III, aVF) and the right-sided lead (

V_4R

), confirming an acute right ventricular myocardial infarction (RVMI).

Identifying the specific territory of the infarction is critical because RVMI has unique hemodynamic consequences compared to left ventricular infarction.

Analyze the patient's hemodynamic status and physical examination findings.

The patient is in cardiogenic shock (

82/50

mmHg) with signs of isolated right heart failure (elevated jugular venous pressure, Kussmaul sign, right-sided

S_4

) and notably clear lungs, despite chronic wheezing from his smoking history.

Recognizing preload-dependent hypotension is necessary to select the appropriate intervention and avoid contraindicated medications that lower preload.

Determine the most appropriate initial management to correct the hypotension.

The correct intervention is fluid resuscitation with an intravenous bolus of

0.9\%

normal saline.

The ischemic right ventricle loses its contractility and becomes highly dependent on elevated preload to maintain forward flow into the left ventricle. Volume expansion maximizes this preload.

Key Concept

Patients with right ventricular myocardial infarction are highly preload-dependent; hypotension must be initially managed with intravenous isotonic fluids, and preload-reducing agents (e.g., diuretics, nitrates) are strictly contraindicated.

Estimated Time:1m 30s

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