In sinus rhythm, what is the typical morphology of the P wave in leads I and II?

In sinus rhythm, what is the typical morphology of the P wave in leads I and II?

• A. Inverted
• B. Upright
• C. Biphasic
• D. Variable

Answer: (B)

In sinus rhythm, the P wave represents atrial depolarization and is formed by the electrical activity traveling through the atria before triggering ventricular contraction. Typically, in leads I and II of an electrocardiogram (ECG), the P wave is upright. This upright morphology indicates that the electrical depolarization is moving toward the positive electrode in these leads, which is characteristic of a normal sinus rhythm. In lead I, which views the heart from a horizontal plane, the P wave should be upright because the electrical impulse from the sinoatrial (SA) node spreads towards both atria and then down towards the ventricles. Similarly, in lead II, which resonates closely with the overall direction of cardiac electrical activity from the SA node to the AV node (and then to the ventricles), the P wave is also expected to be upright. The inversion and biphasic forms of the P wave are indicative of other conditions or abnormal rhythms, suggesting either an abnormal atrial activation sequence or other cardiac issues. Thus, in a healthy individual with a typical sinus rhythm, observing an upright P wave in leads I and II confirms normal atrial electrical conduction.

In sinus rhythm, the P wave represents atrial depolarization and is formed by the electrical activity traveling through the atria before triggering ventricular contraction. Typically, in leads I and II of an electrocardiogram (ECG), the P wave is upright. This upright morphology indicates that the electrical depolarization is moving toward the positive electrode in these leads, which is characteristic of a normal sinus rhythm.

In lead I, which views the heart from a horizontal plane, the P wave should be upright because the electrical impulse from the sinoatrial (SA) node spreads towards both atria and then down towards the ventricles. Similarly, in lead II, which resonates closely with the overall direction of cardiac electrical activity from the SA node to the AV node (and then to the ventricles), the P wave is also expected to be upright.

The inversion and biphasic forms of the P wave are indicative of other conditions or abnormal rhythms, suggesting either an abnormal atrial activation sequence or other cardiac issues. Thus, in a healthy individual with a typical sinus rhythm, observing an upright P wave in leads I and II confirms normal atrial electrical conduction.