The P-wave can be divided into 2 halves, the initial and the terminal portions. The product of the peak height and peak duration is termed the force.
initial force =
= (maximum height in mm for the initial half of the P-wave) * (duration for the initial half in seconds)
terminal force =
= (maximum height in mm for the terminal half of the P-wave) * (duration for the terminal half in seconds)
where:
• A wave extending below baseline has the peak height that is a negative number.
Interpretation:
• A terminal force in V1 < -0.03 is abnormal.
• In left atrial enlargement due to mitral valvular disease, the P wave in V1 may be positive in the initial phase, then show a deep and prolonged deflection in the terminal phase, giving an abnormal terminal force value.
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