A 58-year-old man has a sudden fall to the ground. 911 is called and paramedics arrive 4 minutes later while his business associates attempt CPR. The paramedics confirm that he is in cardiac arrest. A cardiac rhythm is established, but his blood pressure is 70/40 mm Hg with pulse 109/min and irregular.

Questions:

5.1 What do you suspect? What tests would you perform?

He may have an acute coronary syndrome.

His serum CK-MB fraction is 6%. His serum troponin I is 5 ng/mL.

An EKG shows ST segment and T wave changes.

5.2 How should he be treated at this point?

Electrical cardioversion may be needed when atrial or ventricular fibrillation, or significant bradycardia or tachycardia, occur.

Atropine may be used for bradycardia early in the course of an acute MI.

For ventricular ectopy, fibrillation, or tachycardia, cases refractory to electrical cardioversion may be treated with a bolus of amiodarone. Lidocaine (though useful for the acute suppression of ventricular arrhythmias) is not recommended for routine use during acute myocardial infarction but may be used when ventricular fibrillation does not respond to cardioversion or other drugs.

Antithrombotic therapies include anti-platelet agents. Intravenous anti-platelet inhibitors include glycoprotein IIb/IIIa inhibitors and heparin. Aspirin and thienopyridine (Clopidogrel or ticlopidine) in combination are often used following coronary angioplasty with stent placement.

The direct antithrombins include hirudin (from medicinal leeches) and its synthetic analogue bivalirudin given parenterally. The oral agent ximelagatran is converted to active melagatran once absorbed.

In cases of cardiogenic shock, urgent myocardial revascularization may be considered. Use of pressor agents such as dopamine and dobutamine may be considered.

Additional history:

He is in unstable condition. His blood pressure varies from 90/60 to 70/palpable. Two days later his urine output drops. Laboratory studies show sodium 141 mmol/L, potassium 3.9 mmol/L, chloride 96 mmol/L, CO2 15 mmol/L, glucose 75 mg/dL, creatinine 2.4 mg/dL, and urea nitrogen 52 mg/dL. His fractional excretion of sodium is <1% while his urine osmolality is 550 mosm/mL.

5.3 What do these findings suggest?

He has a prerenal azotemia (BUN/Cr ratio >20). The GFR decreases markedly once the mean arterial pressure drops below 80 mm Hg. The loss of blood pressure and diminished renal perfusion triggers the renin-angiotensin mechanism and ADH release in order to increase blood volume and increase blood pressure.