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P波在各导联中的正负方向取决于P波的电轴方向。正常窦性P波额面平均电轴在0°～+90°之间,一般在+50°左右,所以P波在Ⅰ、Ⅱ、avF导联中直立,在aVR中绝对倒置。当额面P电轴为+90°时,P_Ⅰ平坦或低小,P_(aVR、aVL)倒置,P_(Ⅱ、Ⅲ、VF)直立。反之,当P电轴为0°时,P_(aVF)呈低小或平坦,P_(Ⅲ、aVR)倒置,P_(Ⅰ、Ⅱ、aVL)直立。由此看来,P波在aVR中的绝对倒置是诊断窦性P波不可缺少的条件。但是,属于房室交界区的逆行P波则在Ⅱ、Ⅲ、aVF中倒置,在aVR中总是直立的。额面平均P电轴在-60°～-90°之间,P_Ⅰ和P_(V6)不倒置,因为P波向量在横面上向左,这是和左房心律鉴别的要点,左房心律时P的额面平均电轴在-60°～-150°之间,P向量在横面上向右。近二年来,我们发现少数患者心电图上各导联的P波朝向有所变异,即不是我们所熟悉的直立的窦性P波,也不是典型的逆行P波,而是介于二者之间。即:P_(Ⅱ、Ⅲ、aVF)轻度倒置,P_(aVR)亦倒置,P_(Ⅰ、aVL)直立,P_(V_5)轻度倒置、平坦或低小。P波电轴一般在-30°～-45°(0°～-60°之间)。P波时限在正常范围内,平均0.08秒。因为它在aVR中总是倒置的,所以这是一种P波电轴极度左偏的窦
The positive and negative directions of the P wave in each lead depend on the direction of the electrical axis of the P wave. Normal sinusoidal P-wave surface average electric axis between 0 ° ~ + 90 °, usually about +50 °, so the P wave in Ⅰ, Ⅱ, avF lead upright, absolute inversion in aVR. P_ (aVR, aVL) is upside down and P_ (Ⅱ, Ⅲ, VF) is upright when the frontal plane P axis is + 90 °. On the contrary, P_ (aVF) is low or flat when P axis is 0 °, P_ (Ⅲ, aVR) is reversed and P_ (Ⅰ, Ⅱ, aVL) is upright. From this, the absolute inversion of P wave in aVR is an indispensable condition for the diagnosis of sinus P wave. However, retrograde P waves belonging to the atrioventricular junction are inverted in II, III, aVF and are always upright in aVR. Frontal average P axis between -60 ° ~ -90 °, P_I and P_ (V6) is not inverted, because the P wave vector to the left in the horizontal plane, which is the main point and the left atrial rhythm identification, left atrial rhythm When P the average frontal plane electric axis between -60 ° ~ -150 °, P vector on the horizontal to the right. The past two years, we found that a small number of patients ECG lead P wave changes in the direction, that is, we are not familiar with the upright sinus P wave, nor is it a typical retrograde P wave, but in between the two . That is, P_ (Ⅱ, Ⅲ, aVF) is slightly inverted, P_ (aVR) is also inverted, P_ (Ⅰ, aVL) is upright, P_ (V_5) is slightly inverted, flat and low. P wave axis is generally -30 ° ~ -45 ° (0 ° ~ -60 °). P wave duration within the normal range, an average of 0.08 seconds. Because it is always inverted in the aVR, this is a sinusoid with a P-axis extreme left deviation