The Septal R Wave in V1 and V2: Anatomy, Physiology, and Clinical Relevance

One of the subtle but critical features on the ECG is the septal R wave in the right precordial leads (V1 and V2). This small deflection often gets overlooked, but it reflects a very specific sequence of cardiac activation and provides important insight into normal conduction and anatomy. Understanding the septal R wave requires us to revisit the anatomy of the interventricular septum and the physiology of ventricular depolarization.

Related Topics:

• Understanding the Biphasic P Wave in V1

The Anatomy of the Interventricular Septum

The interventricular septum isn’t uniform—it has two distinct parts:

1. Muscular septum – the thick lower portion that makes up the majority of the septum.

2. Membranous septum – the thinner upper portion near the atrioventricular junction.

Embedded within the septum is the conduction system:

• The bundle of His courses through the membranous septum before dividing.

• The left bundle branch splits into anterior and posterior fascicles that spread across the left ventricle.

• The right bundle branch runs down the right side of the septum.

This anatomic arrangement explains why septal depolarization begins left to right, producing the small R waves in V1–V2.

Physiology of Septal Activation

Stepwise Depolarization:

1. Impulse from the His bundle enters the left bundle branch slightly before the right.

2. Septal depolarization begins left-to-right, activating the mid-septum toward the right ventricle.

3. This left-to-right vector is captured in the right precordial leads (V1–V2) as a small positive deflection: the septal R wave.

4. Almost immediately after, the large mass of the left ventricle depolarizes, producing a dominant S wave in V1–V2.

Key Concept:

The septal R wave is not about right ventricular activation—it’s about the earliest left-to-right depolarization of the interventricular septum.

ECG Appearance of the Septal R Wave

• Leads: Seen in V1 and V2.

• Size: Small, typically <3 mm in amplitude.

• Duration: Narrow, as it reflects a brisk conduction across the septum.

• Morphology: Appears as an rS complex (small r followed by deep S).

When the Septal R Wave is Abnormal

Loss or alteration of the septal R wave can be an important clinical clue:

1. Left Bundle Branch Block (LBBB)

   • The septum depolarizes right-to-left instead of left-to-right.

   • Result: Septal R wave disappears in V1–V2 (deep QS complex).

2. Anterior Myocardial Infarction

   • Infarction of the septum (often LAD territory) can eliminate the septal vector.

   • Result: Pathologic Q waves or absence of septal R waves in V1–V2.

3. Ventricular Pre-excitation (WPW)

   • Accessory pathway conduction may bypass the normal His-Purkinje sequence.

   • Septal activation becomes abnormal, altering or abolishing the expected septal R.

4. Right Ventricular Hypertrophy or Conduction Delay

   • May exaggerate or distort the rS pattern in V1–V2.