ECG Findings in Pheochromocytoma
The most characteristic ECG finding in pheochromocytoma is QT interval prolongation, which can be accompanied by ventricular arrhythmias, ST-T segment changes mimicking acute myocardial infarction, and prominent U waves. 1
Primary ECG Abnormalities
QT Prolongation and Ventricular Arrhythmias
- Long QT interval is the hallmark ECG finding in patients with ventricular tachycardia associated with pheochromocytoma 1
- Ventricular tachycardia and sudden cardiac death can occur, though the incidence is likely low and may be exacerbated by reversible catecholamine-induced hypertrophic or dilated cardiomyopathy 1
- The dispersion of ventricular repolarization from QT prolongation creates the substrate for life-threatening arrhythmias including torsades de pointes, ventricular tachycardia, and ventricular fibrillation 2
U Wave Abnormalities
- Prominent U waves appear in approximately 83% of untreated pheochromocytoma patients 2
- The presence and magnitude of U waves correlate directly with urinary metanephrine levels (r²=0.333, p=0.015) and tumor size (r²=0.429, p=0.003) 2
- After surgical removal, U wave prevalence drops dramatically from 91% to 9% 2
- The number of leads showing U waves correlates with 3-methoxytyramine levels (r²=0.458, p=0.006) 2
ST-T Segment Changes
- ST-segment depression or elevation and T-wave inversions frequently mimic acute myocardial infarction 3, 4, 5, 6
- These ischemic-appearing changes occur despite normal coronary arteries on angiography 4, 5, 6
- Right-sided pheochromocytomas may produce more striking electrocardiographic abnormalities 6
- Alpha-adrenergic receptor blockade (phentolamine 10 mg) can normalize T-wave inversions, suggesting alpha-receptor involvement in these ECG changes 4
Additional ECG Manifestations
Rhythm Disturbances
- Tachycardia and frequent ventricular ectopic beats are common 4, 6
- Atrial flutter can occur 4
- Supraventricular and ventricular arrhythmias requiring beta-blockade (after adequate alpha-blockade) 7
QRS Complex Changes
- QRS prolongation may accompany electrolyte disturbances from catecholamine excess 1
Mechanism and Reversibility
The ECG abnormalities result from catecholamine-induced hyperactivation of the sympathetic nervous system with cardiac sympathetic nerve terminal disruption and norepinephrine spillover 3. These changes are characteristically reversible with appropriate alpha-adrenergic blockade and surgical tumor resection 1, 3, 2.
Clinical Pitfalls
- Do not dismiss chest pain with ischemic ECG changes as acute coronary syndrome without considering pheochromocytoma, especially when troponin elevations are mild-to-moderate and coronary angiography shows normal arteries 5, 6
- Fluctuating blood pressure combined with chest pain and ischemic ECG changes should raise suspicion for pheochromocytoma even without typical enzyme changes 6
- Beta-blockade administered without prior alpha-blockade can paradoxically worsen ECG changes by unopposed alpha-receptor stimulation 4
Management Implications
- Preoperative alpha-adrenergic blockade (phenoxybenzamine or doxazosin) helps prevent recurrence of ventricular arrhythmias 1
- Beta-blockade should only be added after adequate alpha-blockade for persistent tachycardia, extrasystoles, or arrhythmias 7
- Early definitive surgical treatment is a priority in cases with documented life-threatening arrhythmias 1
- Intraoperative ventricular arrhythmias are treated with lidocaine 7