12-Lead ECG Interpretation Flashcards

Reciprocal ST depression in leads I and aVL, along with ST elevation in leads II, III, and aVF, suggests occlusion of which artery?

Answer: Right coronary artery

Inferior STEMI (II, III, aVF) is most commonly caused by right coronary artery occlusion, with reciprocal changes in lateral leads.

A 12-lead ECG shows a QTc of 520 ms. Which of the following is the most serious risk?

Answer: Torsades de pointes

A markedly prolonged QTc (>500 ms) greatly increases the risk of torsades de pointes, a potentially fatal polymorphic ventricular tachycardia.

On a 12-lead ECG, which leads are considered the lateral leads?

Answer: I, aVL, V5, V6

Leads I, aVL, V5, and V6 view the lateral wall of the left ventricle, supplied by the left circumflex artery.

Tall, peaked, narrow (tented) T waves on a 12-lead ECG are a classic early sign of:

Answer: Hyperkalemia

Early hyperkalemia causes tall, narrow, peaked (tent-shaped) T waves before progressing to wider QRS and sine wave pattern.

What ECG finding best differentiates left ventricular hypertrophy (LVH) from anterior STEMI?

Answer: LVH shows ST elevation in V1–V3 with deep S waves and large R waves elsewhere

LVH produces a strain pattern with ST-T changes in V1–V3 (repolarization abnormality) accompanied by voltage criteria—deep S in V1 and tall R in V5/V6—unlike STEMI's acute injury pattern.

A patient's 12-lead ECG shows no P waves, an irregular RR interval, and fibrillatory baseline. The diagnosis is:

Answer: Atrial fibrillation

Atrial fibrillation is characterized by the absence of distinct P waves, an irregularly irregular rhythm, and a chaotic fibrillatory baseline.

In a 12-lead ECG, lead aVR views the heart from which direction?

Answer: Right shoulder looking toward the heart

Lead aVR is oriented from the right shoulder toward the heart's base, making it uniquely positioned to show the right atrium and outflow tracts.