Does Hypercalcemia Cause Right Bundle Branch Block?
No, hypercalcemia does not cause right bundle branch block (RBBB). Hypercalcemia primarily affects atrioventricular (AV) conduction and can cause complete heart block, but it does not produce the characteristic RBBB pattern on ECG.
Hypercalcemia's Actual Cardiac Conduction Effects
Hypercalcemia causes AV nodal block, not bundle branch block. The documented cardiac conduction abnormalities from hypercalcemia include:
- Complete heart block with narrow QRS escape rhythm has been reported as a reversible complication of severe hypercalcemia 1
- Complete AV nodal block can occur in malignancy-related hypercalcemia 2
- The mechanism involves effects at the AV node level, not the bundle branches 1
Key Clinical Distinction
The critical finding is that hypercalcemia-induced heart block presents with a narrow QRS escape rhythm, not the wide QRS pattern characteristic of RBBB 1. This narrow QRS indicates the block is occurring above the bundle branches (at the AV node), allowing the His-Purkinje system to generate a normal-width ventricular complex.
What Hypercalcemia Actually Does to the ECG
The classic ECG finding in hypercalcemia is QT interval shortening, not bundle branch block. Specific findings include:
- Shortened QT interval is the hallmark ECG change in hypercalcemia 3
- Moderate hypercalcemia (mean 2.85 mmol/L) causes significant QT shortening but has no clinically significant effect on cardiac conduction in most cases 3
- After surgical correction of hypercalcemia, QT intervals increase from 0.36 to 0.39 seconds and QTc intervals increase from 0.38 to 0.42 seconds 3
Important Clinical Caveat
While moderate hypercalcemia typically does not cause significant conduction disturbances 3, severe hypercalcemia can produce life-threatening complete heart block that resolves with calcium correction 1, 2. However, this manifests as AV block, not RBBB.
Actual Causes of RBBB
RBBB results from structural or functional interruption of the right bundle branch itself, not from metabolic derangements like hypercalcemia. The American College of Cardiology identifies these true causes 4:
- Ischemic heart disease, particularly anterior myocardial infarction 4
- Cardiomyopathies of various types 4
- Infiltrative diseases including sarcoidosis and amyloidosis (which require prophylactic pacing consideration) 4
- Congenital heart disease, especially after tetralogy of Fallot repair 4
- Degenerative lesions of the specialized conducting tissue, particularly in older individuals 4
- Hypertensive heart disease 4
Critical Pitfall to Avoid
Do not confuse calcium channel blocker toxicity with hypercalcemia. Calcium channel blocker overdose can cause ECG changes including RBBB, but this is a pharmacologic effect, not a metabolic consequence of elevated serum calcium 5. The American Heart Association notes that calcium channel blocker toxicity manifests with:
- Prolongation of QT interval, widening of QRS, and right bundle branch block 5
- Bradycardia, hypotension, and various arrhythmias 5
- Treatment includes calcium administration (ironically, to counteract the channel blockade), though effectiveness is variable 5
When to Monitor Calcium in Williams Syndrome
In Williams syndrome specifically, hypercalcemia monitoring is recommended because affected individuals have abnormal calcium metabolism 5:
- Serum calcium should be checked every 4-6 months until age 2 years, then every 2 years thereafter 5
- Symptomatic hypercalcemia is most common in the first 2 years and usually resolves during childhood 5
- However, the cardiac manifestations of Williams syndrome (supravalvular aortic stenosis, peripheral pulmonic stenosis) are structural, not metabolic consequences of hypercalcemia 5