Which of the following is the most common ECG finding in moderate hyperkalemia (K+ 6.5–8 mEq/L)?

Explanation

## ECG Changes in Hyperkalemia: A Progression **Key Point:** ECG changes in hyperkalemia follow a predictable sequence based on serum K+ concentration and reflect progressive cardiac membrane depolarization. ### Stages of ECG Changes | Serum K+ (mEq/L) | ECG Finding | Mechanism | |---|---|---| | 5.5–6.5 | Peaked (tented) T waves | Shortened repolarization; tall, narrow T waves in precordial leads | | 6.5–8.0 | Peaked T waves + prolonged PR interval | Slowed AV nodal conduction | | 8.0–10.0 | Widened QRS, loss of P waves, ST depression | Severe slowing of all conduction | | >10.0 | Sine wave pattern, ventricular fibrillation | Imminent cardiac collapse | **High-Yield:** The **peaked T wave** is the earliest and most sensitive ECG sign of hyperkalemia. It appears when K+ exceeds 5.5–6.0 mEq/L and is best seen in precordial leads (V2–V4). **Clinical Pearl:** Peaked T waves are narrow, symmetrical, and tall (often >50% of QRS height). They differ from the broad, asymmetrical T wave inversion seen in ischemia or hypertrophy. **Mnemonic: "PEAKED T WAVES COME FIRST"** — Remember the sequence: **P**eaked T waves → **R**aised PR interval → **O**utstanding QRS widening → **N**o P waves visible → **E**ventual sine wave and arrest. ### Why Moderate Hyperkalemia Shows Peaked T + Prolonged PR At K+ 6.5–8 mEq/L: - Peaked T waves reflect enhanced ventricular repolarization (earliest sign). - Prolonged PR interval reflects slowed atrial and AV nodal conduction. - QRS is still normal width (not yet severely widened). - P waves are still visible (not yet lost). This combination is pathognomonic for moderate hyperkalemia and warrants urgent treatment. [cite:Harrison 21e Ch 280]