From the Guidelines
The P wave in lead V1 is biphasic due to the sequential activation of the right and left atria, resulting in an initial positive deflection followed by a terminal negative deflection. This phenomenon occurs because the electrical impulse from the sinoatrial node first depolarizes the right atrium, creating a positive deflection in V1, and then spreads to the left atrium, producing a negative deflection as it moves away from the lead V1 position [ 1 ]. The normal biphasic P wave in V1 has a positive initial component less than 1.5 mm in height and a negative terminal component with an area less than 0.04 mm·sec.
Key Points to Consider
- The P wave duration of 120 ms or more can indicate left atrial abnormality [ 1 ].
- A widely notched P wave (40 ms or more) also appears to have equal value in indicating left atrial abnormality [ 1 ].
- The product of the amplitude and the duration of the terminal negative component of the P wave in lead V1 (the P terminal force) is a useful criterion for left atrial abnormality [ 1 ].
- Conduction delay is more closely linked to left atrial abnormality than to right atrial abnormality, often representing delay in the specialized interatrial pathway (Bachmann’s bundle) [ 1 ].
Clinical Implications
The biphasic nature of the P wave in V1 is a critical aspect of electrocardiogram interpretation, as changes in its morphology can indicate atrial enlargement or abnormality. Recognizing the normal and abnormal patterns of the P wave is essential for accurate diagnosis and management of cardiac conditions. The information provided by the P wave can guide further diagnostic testing and influence treatment decisions, ultimately impacting patient outcomes in terms of morbidity, mortality, and quality of life.
From the Research
P Wave Morphology
The P wave represents the depolarization of the atria, and its morphology can provide valuable information about atrial function and structure.
- A biphasic P wave in lead V1 can be a normal finding, but it can also be associated with various cardiac conditions.
- The biphasic morphology in lead V1 is often related to the depolarization of the right and left atria 2.
Interatrial Block and Atrial Enlargement
Interatrial block (IAB) is a condition characterized by a delayed conduction between the left and right atria, resulting in a prolonged P wave duration (>120 ms) and a biphasic morphology in inferior leads 3.
- Advanced IAB can lead to atrial remodeling, dyssynchrony, and enlargement, increasing the risk of atrial fibrillation, stroke, and mortality 3.
- Left atrial enlargement (LAE) can be a consequence of prolonged elevation of atrial pressure due to various underlying conditions, including IAB, diastolic dysfunction, and valvular heart disease 3.
Clinical Significance
The identification of a biphasic P wave in lead V1 has prognostic implications and should trigger the search for associated conditions, such as interatrial block, atrial enlargement, and cardiac valve disease 2.
- The presence of a biphasic P wave in lead V1 can be associated with an increased risk of supraventricular tachyarrhythmias, stroke, left ventricular dysfunction, and mortality 2.
- The evaluation of P wave morphology, including the presence of a biphasic P wave in lead V1, can provide valuable information for the diagnosis and management of cardiac conditions 4, 5, 6.