Hypercalcaemia
Definition
Hypercalcaemia is defined as a serum calcium concentration higher than 2.6 mM.
ECG changes
Shortening of the QT interval is the most common ECG change in hypercalcaemia. Severe hypercalcaemia can lead to atrioventricular block, complete heart block and cardiac arrest.
Short QT interval in hypercalcaemia
Pathophysiology
The mechanisms are not completely understood. Current theories suggest that the L-type calcium channel, which is responsible for the plateau phase, employs a calcium-dependent inactivation mechanism. Other theories include a reduction in the activity of the inward Na+-Ca2+-exchanger.
Hypercalcaemia allows calcium to enter cells quicker than normal for a given channel opening. Consequently, they can act on and inactivate the L-type calcium channel more rapidly. This leads to shortening of the plateau phase, which is reflected in the ST and QT intervals.
Management
Acutely, administer IV fluids to reduce serum calcium concentration and offer bisphosphonates. Any underlying causes of hypercalcaemia should be treated.
Hypocalcaemia
Definition
Hypocalcaemia is defined as a serum calcium concentration lower than 2.1 mM.
ECG changes
Prolongation of ST and QT intervals. Severe hypocalcaemia can lead to ventricular tachycardia, including torsades de pointes.
Long QT interval in hypocalcaemia
Pathophysiology
The mechanisms are not completely understood. Current theories suggest that the L-type calcium channel, which is responsible for the plateau phase, employs a calcium-dependent inactivation mechanism.
Hypocalcaemia produces a slower calcium entry into cells during the plateau phase of the action potential. Consequently, the inactivation of L-type calcium channels requires a longer length of time. This leads to a prolongation of the plateau phase, which is reflected in the ST and QT intervals.
Management
Acutely, calcium levels should be replaced, which can be achieved with orally or intravenously. Any underlying causes of hypocalcaemia should be treated.
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