The most interesting ECG interpretation isn’t matching the key—it’s understanding why the patient doesn’t .

One Tuesday, a student named Jamie handed in a practice tracing labeled “Case 14.” Lena glanced at the answer key: “Atrial flutter with variable block. Left ventricular hypertrophy.” But Jamie’s interpretation was different: “Wandering atrial pacemaker. Old inferior MI.”

Lena froze. She compared the tracing in Jamie’s packet to the master answer key’s description. The key said “sawtooth flutter waves in II, III, aVF”—but on Jamie’s strip, the baseline was flat. Then she noticed: the ECG machine had misprinted lead labels due to a loose cable. Jamie had interpreted the actual morphology , not the labels.