What does isoelectric QRS in leads V5 and V6 suggest?

What does isoelectric QRS in leads V5 and V6 suggest?

• A. Rightward rotation in the horizontal plane
• B. Leftward rotation in the horizontal plane
• C. Narrowing of the QRS complex
• D. Complete heart block

Answer: (B)

The presence of an isoelectric QRS complex in leads V5 and V6 suggests leftward rotation in the horizontal plane. This is associated with a normal axis deviation in the setting of a leftward rotation, as these leads correspond to the left lateral wall of the heart.

In a normal EKG, the QRS complexes in these leads are expected to be predominantly positive when the heart's electrical axis is oriented in a leftward or normal fashion. When the QRS is isoelectric, it indicates that the electrical forces are not strongly directed towards either lead V5 or V6; instead, they are balanced. This can occur in certain conditions, such as left ventricular hypertrophy or in patients with specific anatomical configurations that alter the vector of depolarization.

While rightward rotation would typically yield more positive QRS complexes in V5 and V6 or an upward deflection, isoelectric QRS indicates that the electrical activity is not predominantly directed to the left, therefore suggesting a leftward rotation. Other options, such as narrowing of the QRS complex or complete heart block, would not typically result in an isoelectric pattern specifically in these leads.