What ECG changes are expected in a patient with Ebstein's anomaly, acute myocardial infarction (heart attack) and type 2 diabetes mellitus (T2DM)?

ECG Changes in Ebstein's Anomaly

The ECG in Ebstein's anomaly characteristically shows tall, peaked P waves ("Himalayan P waves"), a QR pattern in V1 extending to V4, prolonged QRS duration with right bundle-branch block pattern that appears "splintered," and inverted T waves, with preexcitation present in approximately 25% of patients via right-sided accessory pathways. 1

Primary ECG Abnormalities

P Wave Changes

• Tall, peaked P waves (termed "Himalayan P waves") are a hallmark finding, reflecting massive right atrial enlargement from severe tricuspid regurgitation 1
• Right atrial hypertrophy is present in approximately 42% of patients 2

QRS Complex Abnormalities

• QR pattern in lead V1 is characteristic and may extend through V4, distinguishing Ebstein's from other right heart pathology 1
• Right bundle-branch block pattern occurs in 84% of patients, with complete RBBB in 27% 2
• The QRS appears "splintered" or fragmented, which correlates with greater atrialized right ventricular volume (80 ± 31 vs. 45 ± 37 mL/m² without fractionation) 1, 3
• Prolonged QRS duration (≥120 ms in 30% of patients) serves as a marker of RV enlargement and dysfunction 1, 3, 2

Prognostic Significance of QRS Duration

• QRS duration correlates directly with anatomic RV diastolic volume (r = +0.56, P < 0.0001) and inversely with RV ejection fraction (r = -0.62, P < 0.0001) 3
• Normal QRS duration predicts better outcomes: smaller RV volumes (150 ± 57 vs. 256 ± 100 mL/m²), higher RV EF (48 ± 6% vs. 34 ± 14%), higher oxygen consumption (25.8 vs. 21.8 mL/kg/min), and lower incidence of exercise-induced desaturation (25% vs. 65%) 3

T Wave Changes

• Inverted T waves follow the splintered QRS complexes in right precordial leads 1

Conduction Abnormalities and Arrhythmias

Preexcitation Patterns

• Preexcitation occurs in approximately 25% of patients, typically via right-sided bypass tracts 1
• Multiple accessory pathways may be present in nearly 50% of those with preexcitation 1
• When present, accessory pathways are right postero-septal in location 2
• Preexcitation was documented in 23% of one cohort, all with right postero-septal pathways 2

Rhythm Disturbances

• Supraventricular arrhythmias occur in 34% of patients, including junctional tachycardia (11%), atrial flutter (15%), and atrial fibrillation (7%) 2
• The ACC/AHA guidelines recommend electrophysiological study for documented or suspected supraventricular arrhythmia, with consideration for radiofrequency catheter ablation 1
• Right atrial enlargement predisposes to atrial tachycardias and creates stasis that increases thrombus formation risk, particularly with atrial fibrillation 1, 4

Right Axis Deviation

• Right axis deviation is present in 42% of patients, reflecting right ventricular hypertrophy 2
• Right ventricular hypertrophy is documented in approximately 50% of cases 2

Clinical Correlation and Diagnostic Utility

ECG as a Diagnostic Tool

• The ECG is valuable in the diagnosis of Ebstein's anomaly and should be part of the initial evaluation alongside chest X-ray and echocardiography-Doppler (Class I recommendation) 1
• ECG changes suggestive of right heart enlargement are important for primary care physicians to recognize when patients present with reduced effort tolerance 5

Important Pitfalls

• Do not confuse Ebstein's anomaly with other causes of right heart enlargement: tricuspid valve dysplasia, tricuspid valve prolapse, traumatic tricuspid changes, arrhythmogenic RV cardiomyopathy, tricuspid endocarditis, or carcinoid heart disease all require differentiation 1, 6
• The severity of tricuspid regurgitation may be underestimated on physical examination due to subtle findings and the compliant right atrium accepting regurgitant flow with minimal pressure rise 1

When to Pursue Electrophysiology Study

• Obtain EP study before surgical repair in any patient suspected of having an accessory pathway, allowing localization and attempted catheter ablation 1
• EP study is useful (Class IIa) for history or ECG evidence of accessory pathways, with subsequent ablation considered if clinically feasible 1
• If catheter ablation is unsuccessful (success rates are lower and recurrence rates higher than in structurally normal hearts), surgical interruption can be performed intraoperatively 1

Context for Patients with Acute MI and T2DM

In a patient with Ebstein's anomaly who develops acute myocardial infarction, the baseline ECG abnormalities (QR pattern in V1-V4, RBBB, inverted T waves) may obscure typical MI changes. Coronary angiography should be performed before any surgical intervention if there is suspicion of coronary artery disease, particularly in men ≥35 years, premenopausal women ≥35 years with coronary risk factors, and all postmenopausal women 1. The presence of type 2 diabetes mellitus increases coronary artery disease risk and lowers the threshold for angiographic evaluation in these patients.