What is the appropriate ICD‑10 code for an ECG showing sinus tachycardia, normal electrical axis, S1‑S2‑S3 pattern, incomplete right bundle‑branch block, possible right‑ventricular hypertrophy, and ST‑T changes suggesting septal ischemia?

ICD-10 Coding for Complex ECG Findings

For this ECG showing sinus tachycardia, incomplete right bundle branch block, possible right ventricular hypertrophy, and ST-T changes suggesting septal ischemia, code the most clinically significant finding first: I25.10 (atherosclerotic heart disease without angina) or I24.9 (acute ischemic heart disease, unspecified) for the ST-T changes suggesting ischemia, followed by I45.4 (nonspecific intraventricular block) for the incomplete RBBB, and I51.7 (cardiomegaly) if right ventricular hypertrophy is confirmed.

Prioritization Algorithm for Multiple ECG Abnormalities

Code the finding with the highest morbidity and mortality risk first, which in this case is the ST-T abnormality suggesting septal ischemia 1.

Primary Diagnosis: ST-T Changes (Septal Ischemia)

• I25.10 - Atherosclerotic heart disease of native coronary artery without angina pectoris (if chronic ischemia suspected) 1
• I24.9 - Acute ischemic heart disease, unspecified (if acute presentation) 1
• I25.6 - Silent myocardial ischemia (if asymptomatic) 1

The ST-T abnormalities suggesting ischemia represent the most critical finding requiring immediate clinical correlation, as they may indicate active myocardial injury or infarction 1.

Secondary Diagnosis: Incomplete Right Bundle Branch Block

• I45.4 - Nonspecific intraventricular block 1

Incomplete RBBB is defined by QRS duration between 110-120 ms in adults with terminal rightward deflection in V1 1. While often benign, particularly in athletes, it requires clinical context evaluation 1, 2, 3.

Tertiary Diagnosis: Right Ventricular Hypertrophy (If Confirmed)

• I51.7 - Cardiomegaly 1, 4
• I27.89 - Other specified pulmonary heart diseases (if secondary to pulmonary pathology) 4

Right ventricular hypertrophy criteria include right axis deviation (present with S1S2S3 pattern), tall R waves in V1, and ST-T abnormalities in right precordial leads 1, 4. The S1S2S3 pattern indicates right axis deviation, supporting possible RVH 5, 4.

Additional Diagnosis: Sinus Tachycardia

• R00.0 - Tachycardia, unspecified 1

Code only if clinically significant or symptomatic, as sinus tachycardia may be physiologic or secondary to the underlying cardiac pathology 1.

Critical Clinical Context Considerations

• Verify lead placement before finalizing codes, as improper electrode positioning can create artifactual patterns mimicking pathology 5, 6
• The S1S2S3 pattern indicates right axis deviation (≥90°), which is required for RVH diagnosis in nearly all cases 1, 5, 4
• Incomplete RBBB with right axis deviation may indicate right ventricular strain from pulmonary hypertension, congenital heart disease, or atrial septal defect 1, 2, 3
• ST-T changes in the setting of RBBB reduce diagnostic accuracy for ischemia, but should not be dismissed without further evaluation 1

Common Coding Pitfalls to Avoid

• Do not code "consider" findings - only code confirmed diagnoses or findings requiring clinical correlation 1
• Do not use R94.31 (abnormal ECG) as primary code when specific abnormalities are identified 1
• Do not overlook the ischemic changes - these carry the highest mortality risk and should be coded first 1
• Incomplete RBBB is not coded as I45.10 (right bundle branch block, unspecified) - use I45.4 for nonspecific intraventricular block instead 1

Documentation Requirements

• Specify QRS duration to differentiate incomplete (110-119 ms) from complete RBBB (≥120 ms) 1
• Document frontal plane axis - the S1S2S3 pattern suggests right axis deviation between 90-180° 1, 5
• Correlate with clinical presentation - symptoms, risk factors, and prior cardiac history determine whether ischemic changes warrant acute versus chronic coding 1
• Note if echocardiography confirms RVH - ECG criteria have low sensitivity but high specificity when multiple criteria are present 1, 4