ECG Signs of Hypocalcemia
The primary ECG sign of hypocalcemia is QT interval prolongation due to ST segment lengthening, not T wave changes. 1
Primary ECG Findings
- Prolonged QT interval (corrected for heart rate) is the most distinctive ECG sign of hypocalcemia 1, 2
- The QT prolongation in hypocalcemia occurs primarily due to ST segment lengthening, with minimal changes to the T wave morphology 1, 3
- In severe cases, hypocalcemia can occasionally manifest with ST segment elevation that may mimic acute myocardial infarction 3
- The QT interval prolongation can be extreme in cases of severe hypocalcemia, with reports of QTc intervals reaching 730ms without ventricular arrhythmias 4
Mechanism of QT Prolongation
- Hypocalcemia produces QT interval prolongation primarily through a calcium-dependent inactivation mechanism on the L-type calcium channel 2
- Lower extracellular calcium leads to decreased ICaL, causing intracellular calcium to take longer to reach the critical threshold to induce inactivation of the L-type calcium channel 2
- The resulting prolonged repolarization of ventricular myocytes can lead to early after-depolarizations and potentially life-threatening ventricular arrhythmias 2
Clinical Significance and Risk Assessment
- QT prolongation may be more pronounced in elderly patients and those with pre-existing cardiac disease 1
- Hypocalcemia-induced QT prolongation can be exacerbated by concomitant electrolyte abnormalities, particularly hypomagnesemia 1, 5
- QT-prolonging medications should be avoided in patients with known or suspected hypocalcemia 1
- The risk of cardiac arrhythmias increases with the severity of hypocalcemia 1, 2
- A weak association (r = -0.12; P = 0.09) has been noted between serum calcium level and QT interval 5
Special Considerations
- Hypocalcemia is extremely common in hospitalized patients (up to 88%) and correlates with severity of illness 5
- Hypocalcemia can be precipitated by biological stress such as surgery, childbirth, or infection 6
- Conditions like hypoparathyroidism (including post-surgical) and 22q11.2 deletion syndrome have a high prevalence of hypocalcemia 1, 4
- Hypocalcemia can mimic long QT syndrome, leading to syncope and other symptoms that resolve with calcium supplementation 7
Management Considerations
- Obtain an immediate ECG in patients with suspected hypocalcemia 1
- Administer intravenous calcium gluconate promptly for symptomatic or severe hypocalcemia with ECG changes 1
- Correct any concomitant electrolyte abnormalities, especially hypomagnesemia, which can perpetuate hypocalcemia despite calcium supplementation 1, 5
- Daily calcium and vitamin D supplementation is recommended for patients with chronic hypocalcemia 6
- Monitor calcium levels during vulnerable periods such as peri-operatively, perinatally, or during severe illness 6
Common Pitfalls to Avoid
- Failing to consider hypocalcemia as a cause of QT prolongation 1, 7
- Overlooking the need to correct hypomagnesemia in patients with hypocalcemia 1, 5
- Administering QT-prolonging medications to patients with known or suspected hypocalcemia 1
- Confusing hypocalcemia-induced ST segment changes with acute myocardial infarction 3
- Assuming that mild QT prolongation is always benign, especially in patients with multiple risk factors 1