Fig. 7.1
Prolonged Q-T interval
7.2 Hyperkalemia
[ECG Recognition]
1.
Mild hyperkalemia: when the serum potassium level is approximately between 5.7 and 6.5 mmol/L, P wave widens; tall, peaked, narrow-based, and tented T waves occur in many leads; P-R interval prolongs, and first-degree AVB can happen.
2.
Severe hyperkalemia: when serum potassium level is over 6.5 mmol/L, the latter portion of the QRS complex is significantly widened, which shows marked notching or slurring. As a result, the widened QRS will merge with tall and tented T wave, and ST segment will be elevated.
3.
High-degree AVB: P wave disappears.
4.
Ventricular tachycardia, ventricular fibrillation, or autonomous ventricular rhythm.
[ECG Tracing] (Fig. 7.2)
Fig. 7.2
Different levels of hyperkalemia. Day 1, the serum potassium level is 8.6 mmol/L: P wave disappeared, and QRS complex broadened obviously. Day 2, the serum potassium level is 5.8 mmol/L: P wave is present; P-R interval lengthened; QRS complex is normal and T wave is tented
1.
Serum potassium >6.0 mmol/L: the earliest change is that T wave tends to be tall, narrow-based, and tented, and P-R interval may be prolonged.
2.
Serum potassium >7.0 mmol/L: P wave flattens or disappears; QRS complex widens; and prominent S wave can be seen.
3.
Serum potassium >8.0 mmol/L: S wave widens and deepens progressively, and the ST segment is steeper; no ST segment is isoelectric.
7.3 Hypokalemia
[ECG Recognition]
1.
Mild hypokalemia: when the serum potassium level is approximately between 3.0 and 3.5 mmol/L, the amplitude of T wave decreases progressively, and the amplitude of U wave is as small as T wave.
2.
Severe hypokalemia: when the serum potassium level is less than 3.0 mmol/L, there is an apparent increase in the amplitude of U wave, and U wave grows taller than T wave. When the serum potassium level is less than 1.5 mmol/L, T wave and U wave can merge, which is most obvious in leads V2 to V5.
3.
ST segment depresses progressively.
4.
QRS complex duration is prolonged.
5.
P-R interval is slightly prolonged.
[ECG Tracing] (Fig. 7.3)
Fig. 7.3
Different levels of hypokalemia. Day 1, serum potassium level is 1.5 mmol/L: T wave and U wave are fused; U wave is obvious and QU interval prolongs. Day 2, serum potassium level is 3.7 mmol/L: the ECG returned to be normal
7.4 Digitalis Effect
Digitalis is an effective medication used in treating heart failure and some arrhythmias. Digitalis effect refers to the shortening of Q-T interval and ST-T changes in ECG after taking therapeutic dosage (Fig. 7.4).
[ECG Recognition]
1.
ST segment depresses, which is concave upward, hook-like change.
2.
T wave can be biphasic with its amplitude decrease.
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