ECG: Electrolyte Abnormalities

Question 1

Hyperkalemia

Answer 1

Peaked T waves
P wave widening/flattening, PR prolongation
Bradyarrhythmias: sinus bradycardia, high-grade AV block with slow junctional and ventricular escape rhythms, slow AF
Conduction blocks (bundle branch block, fascicular blocks)
QRS widening with bizarre QRS morphology

Question 2

Hyperkalemia

Answer 2

With worsening hyperkalaemia… (> 9.0 mmol/L):

Development of sine wave appearance (pre-terminal rhythm)
Ventricular fibrillation
PEA with bizarre, wide complex rhythm
Asystole

Question 3

Potassium levels: 5.5-6.5 mmol/L

Answer 3

Repolarisation abnormalities

Peaked T waves

Question 4

Potassium levels: 6.5-7.0 mmol/L

Answer 4

Progressive atrial paralysis
P wave widening/flattening
PR prolongation
P waves eventually disappear

Question 5

Potassium levels: 7.0-9.0

Answer 5

Conduction abnormalities
Bradyarrhythmias: sinus bradycardia, high grade AV block, slow junctional and ventricular escape rhythms, slow AF
conduction blocks (BBB, fascicular blocks)
prolonged QRS interval with bizarre QRS morphology

Question 6

Potassium levels: >9.0 mmol/L

Answer 6

All of above
Development of sine wave appearance (pre-terminal rhythm)
asystole
VF
PEA with bizarre, wide complex rhythm

Question 7

Hypo vs Hyperkalemia

push-pull effect

Answer 7

Hypokalemia:
T wave inversion
ST depression
Prominent U wave

Hyperkalemia:
Peaked T waves, P wave flattening, PR prolongation, wide QRS

Question 8

Degree of hyperkalemia

Answer 8

Potassium level: mmol/L
Mild: 5.3-6.0
Moderate: 6.0-6.9
Severe: >7.0

Question 9

Suspect hyperkalemia in:

Answer 9

Suspect hyperkalaemia in any patient with a new bradyarrhythmia or AV block, especially patients with renal failure, on haemodialysis, or taking any combination of ACE inhibitors, potassium-sparing diuretics and potassium supplements.

Question 10

Hypokalemia

Answer 10

Hypokalaemia is defined as a serum potassium level of < 3.5 mmol/L. ECG changes generally do not manifest until there is a moderate degree of hypokalaemia (2.5-2.9 mmol/L). The earliest ECG manifestation of hypokalaemia is a decrease in T wave amplitude.

Question 11

Hyperkalemia

Answer 11

Hyperkalaemia is defined as a serum potassium level of > 5.2 mmol/L. ECG changes generally do not manifest until there is a moderate degree of hyperkalaemia (≥ 6.0 mmol/L). The earliest manifestation of hyperkalaemia is an increase in T wave amplitude.

Question 12

Hypokalemia

Answer 12

<2.7 mmol/L

Increased P wave amplitude
Prolongation of PR interval
Widespread ST depression and T wave flattening/inversion
Prominent U waves (best seen in the precordial leads V2-V3)
Apparent long QT interval due to fusion of T and U waves (= long QU interval)

Question 13

Hypokalemia (with worsening)

Answer 13

Frequent supraventricular and ventricular ectopics
Supraventricular tachyarrhythmias: AF, atrial flutter, atrial tachycardia
Potential to develop life-threatening ventricular arrhythmias, e.g. VT, VF and Torsades de Pointes

Question 14

Degree of hypokalemia

Answer 14

Potassium level: mmol/L
Mild: 3.0-3.4
Moderate: 2.5-2.9
Severe: <2.4

Question 15

Hypokalemia

Answer 15

Hypokalaemia is often associated with hypomagnesaemia, which increases the risk of malignant ventricular arrhythmias
Check both potassium and magnesium levels in any patient with an arrhythmia
Replace potassium to ≥ 4.0 mmol/L and magnesium to ≥ 1.0 mmol/L to stabilise the myocardium and protect against arrhythmias – this is standard practice in most CCUs and ICUs

Question 16

Hypercalcemia

Answer 16

The main ECG abnormality seen with hypercalcaemia is shortening of the QT interval
In severe hypercalcaemia, Osborn waves (J waves) may be seen
Ventricular irritability and VF arrest has been reported with extreme hypercalcaemia

Question 17

Degree of Hypercalcemia

Answer 17

Normal serum corrected calcium = 2.1 – 2.6 mmol/L
Mild hypercalcaemia = 2.7 – 2.9 mmol/L
Moderate hypercalcaemia = 3.0 – 3.4 mmol/L
Severe hypercalcaemia = greater than 3.4 mmol/L

Question 18

Causes of Hypercalcemia

Answer 18

Hyperparathyroidism (primary and tertiary)
Myeloma
Bony metastases
Paraneoplastic syndromes
Milk-alkali syndrome
Sarcoidosis
Excess vitamin D (e.g. iatrogenic)

Question 19

Hypocalcemia

Answer 19

Hypocalcaemia causes QTc prolongation primarily by prolonging the ST segment
The T wave is typically left unchanged
Dysrhythmias are uncommon, although atrial fibrillation has been reported
Torsades de pointes may occur, but is much less common than with hypokalaemia or hypomagnesaemia

Question 20

Degree of Hypocalcemia

Answer 20

Normal serum corrected calcium = 2.2 – 2.6 mmol/L.
Mild-moderate hypocalcaemia = 1.9 – 2.2 mmol/L.
Severe hypocalcaemia = < 1.9 mmol/L.

Question 21

Causes of Hypocalcemia

Answer 21

Hypoparathyroidism
Vitamin D deficiency
Acute pancreatitis
Hyperphosphataemia
Hypomagnesaemia
Diuretics (frusemide)
Pseudohypoparathyroidism
Congenital disorders (e.g. DiGeorge syndrome)
Critical illness (e.g. sepsis)
Factitious (e.g. EDTA blood tube contamination)

Question 22

Symptoms of Hypocalcemia

Answer 22

Neuromuscular excitability
Carpopedal spasm
Tetany
Chvostek sign
Trousseau sign
Seizures

Question 23

Hypomagnesemia

Answer 23

Normal serum magnesium levels are generally considered to be 0.8 – 1.0 mmol/L. Hypomagnesaemia, defined as a level < 0.8 mmol/L, is associated with QT interval prolongation and an increased risk of ventricular arrhythmias.

Question 24

Hypomagnesemia

Answer 24

Prolonged PR interval
Prolonged QT interval
Atrial and ventricular ectopy
Predisposition to ventricular tachycardia and torsades de pointes

Question 25

Hypomagnesemia

Answer 25

Correction of serum magnesium to > 1.0 mmol/L, with concurrent correction of serum potassium to > 4.0 mmol/L, is often effective in suppressing ectopy and supraventricular tachyarrhythmias
A rapid IV bolus of magnesium 2g is a standard emergency treatment for torsades de pointes