Causes of Tall R Wave in V1

Tall R Wave in V1: ECG Interpretation and Clinical Significance

A tall R wave in lead V1 is an important ECG finding that often reflects altered ventricular depolarization. Normally, V1 shows a small R wave and a deep S wave because left ventricular forces dominate. When the R wave in V1 becomes tall (R/S ratio >1 or R ≥7 mm), it suggests either increased right ventricular forces, altered cardiac position, conduction abnormalities, or mirror-image changes from infarction.

Common Causes of Tall R Wave in V1

1. Right Ventricular Hypertrophy (RVH)

RVH produces increased right-sided electrical forces, resulting in a dominant R wave in V1–V2. Associated findings include right axis deviation, right atrial enlargement, and strain pattern in right precordial leads. Common etiologies include pulmonary hypertension, chronic lung disease, and congenital heart disease.

2. Duchenne Muscular Dystrophy

Patients with Duchenne muscular dystrophy often demonstrate tall R waves in V1–V2 due to selective posterolateral left ventricular myocardial involvement, creating unopposed anterior forces. This ECG finding can precede overt cardiomyopathy.

3. Incorrect Lead Placement (V1–V2 Too Low)

Placing V1 and V2 lower than the fourth intercostal space exaggerates R-wave amplitude, mimicking pathological tall R waves. This is a frequent and important technical cause that should always be excluded before clinical interpretation.

4. Wolff–Parkinson–White (WPW) Syndrome Type A

In WPW type A, a left-sided accessory pathway causes early activation of the left ventricle, generating a tall R wave in V1 that can mimic posterior myocardial infarction. A short PR interval and delta wave help in diagnosis.

5. Normal Variant in Children and Young Adults

In infants, children, and some young adults, right ventricular dominance is physiological. This can result in a relatively tall R wave in V1 without pathological significance.

6. Dextrocardia

In dextrocardia, the heart is positioned on the right side of the chest. Standard left-sided precordial leads record reversed electrical forces, often producing tall R waves in V1 with poor R-wave progression across the chest leads.

7. Posterior Myocardial Infarction

Posterior MI produces reciprocal ECG changes in anterior leads. A tall R wave in V1 acts as a mirror image of a Q wave in the posterior wall. It is usually associated with ST depression in V1–V3 and upright T waves. Posterior leads (V7–V9) confirm the diagnosis.

8. Lateral Myocardial Infarction

Loss of lateral left ventricular forces due to infarction (leads I, aVL, V5–V6) may leave unopposed right ventricular forces, manifesting as a relatively tall R wave in V1.

9. Chest Wall Abnormalities

Conditions such as pectus excavatum, kyphoscoliosis, or post-surgical chest changes alter heart orientation within the thorax, modifying electrical vectors and sometimes producing a tall R wave in V1.

10. Ebstein’s Anomaly

Ebstein’s anomaly involves apical displacement of the tricuspid valve with atrialization of the right ventricle. ECG findings commonly include tall R waves in V1, right atrial enlargement, and association with accessory pathways.

11. Brugada Syndrome

Brugada syndrome may show a prominent R wave or r′ in V1–V2, particularly in type 1 and type 2 patterns. This reflects abnormal right ventricular outflow tract depolarization and is associated with a risk of malignant ventricular arrhythmias.

12. Arrhythmogenic Right Ventricular Dysplasia (ARVD)

ARVD causes fibrofatty replacement of right ventricular myocardium, leading to delayed RV activation. ECG features include tall R waves in V1, epsilon waves, T-wave inversion in V1–V3, and ventricular arrhythmias of RV origin.

Clinical Approach to Tall R Wave in V1

• First exclude lead misplacement and normal age-related variants

• Assess QRS duration, PR interval, and delta waves for conduction abnormalities

• Look for associated axis deviation, ST-T changes, and R-wave progression

• Correlate clinically and use imaging (echo, cardiac MRI) when structural disease is suspected

Summary

A tall R wave in V1 is a valuable ECG clue rather than a diagnosis. It reflects right ventricular dominance, altered conduction, abnormal cardiac position, or reciprocal infarction changes. Systematic evaluation helps differentiate benign variants from serious structural or electrical heart disease.

Source: Braunwald’s Heart Disease, Hurst’s The Heart