This week we'll focus primarily on the information contained by the P wave.
1.What is a practical way of considering arrhythmias?
2.What P wave information should be assessed?
3.What are characteristics of a normal P wave?
4.What do biphasic, isoelectric, or inverted P waves suggest?
5.What leads should be utilized to analyze P wave information?
1 实践中是如何认定心律失常的？
2 应该如何评估P波提供的信息？
3 正常P波的特征有哪些？
4 双向、等电位或倒置P波提示什么？
5 分析P波信息时应该使用哪个导联？
参考答案（请批评指正）
1 实践中是如何认定心律失常的？
对心律失常进行系统化分析可揭示心律失常的病因学,这些步骤包括:
1).确认P波存在，包括有无P波、P波速率、P波形态
2).观察P 波和QRS丛之间的关系
3).观察QRS丛形态
2 应该如何评估P波提供的信息？
P波代表心房的的去极化。如果P波缺失和QRS 丛不规则，最有可能发生防颤。相反，如果在QRS丛规则或变窄时P波缺失，通常提示存在房室节折返激动通路存在。
P波存在时，成人心率应在60-100次／分 (bpm)。房性或房室节折返性心动过速时心律通常在140-220 bpm。如果心律在260-320 bpm之间提示房扑存在。
最后，应该P波和QRS丛之间的关系。如果P波多于QRS 丛，提示存在房室传导传导阻滞。如果QRS 丛多于P波则存在交界性或室性逸搏。如果二者比率是1:1，则可应用PR间期进行判断。
3 正常P波的特征有哪些？
心房去极化时向量呈向下向左方向，在下肢导联(II, III, aVF) P波呈正向波型，V1导联呈双向。PR 间期在健康成人静息时基本恒定，在0.11-0.21 s之间。PR 间期过长或过短提示房室传导阻滞或室性预激。此外，当房和室存在各自启搏点时，P波和QRS丛呈分离现象。
4 双向、等电位或倒置P波提示什么？
如上所述，V1导联P波可以呈双向。如果下肢导联(II, III, aVF) P波双向且PR间期正常，提示心房增大或异位心房去极化。如果在下肢导联QRS 丛后P 波倒置，同时伴恒定PR间期，提示心房激动由房室交界或室性激动点激发。
5 分析P波信息时应该使用哪个导联？
如果发生心律失常，至少应从如下导联分析P波：II、 III、aVF、V1。据报道P波可通过食道、静脉或心外膜导联进行描记。最近有研究者建议P波信号均位性心电图可作为发现和预测潜在房性心律失常的有效方法。12导心电图可用来评估是否发生心律失常以支持诊断。
英文参考答案
1 What is a practical way of considering arrhythmias?
A systematic approach to the analysis of arrhythmias can unveil their etiologies (1). These steps include:
1).Identification of the P wave including presence, rate, and morphology
2).Establishing the relationship between the P wave and QRS Complex
3).Examining the QRS morphology.
2 What P wave information should be assessed?
The P wave represents the depolarization of the atria. If P waves are absent and the QRS complex is irregular, atrial fibrillation is most likely present. By contrast, if P waves are absent in the presence of regular and narrow QRS complexes, this is commonly due to a AV nodal reentry pattern.
In the presence of P waves, the rate should be between 60-100 beats per minute (bpm) in adults. Rates in the 140-220 bpm range are usually atrial or AV nodal reentrant tachycardias, and in the 260-320 bpm range most likely represent atrial flutter.
Finally, the P wave should be considered in relation to the QRS complex. If more P waves than QRS complexes exist, then an AV block is present. If more QRS complexes than P waves, than a junctional or ventricular origin exists. If the relationship in 1:1, then the PR interval can be useful.
3 What are characteristics of a normal P wave?
Atrial depolarization occurs in a caudad and leftward orientation, producing upright P waves in the inferior limb leads (II, III, aVF) and a biphasic P wave in V1. The PR interval remains fairly constant, with a range of 0.11-0.21 s in resting, healthy adults. Longer or shorter PR intervals suggest AV heart blockade or ventricular prexcitation, respectively. In addition, when the atria and ventricles have independent pacemaker foci, the P waves appear to march "in and out" of the QRS complex.
4 What do biphasic, isoelectric, or inverted P waves suggest?
As mentioned above, biphasic P waves can be normal in lead V1; however, when present in the inferior limb leads (II, III, aVF) with a normal PR interval, these alterations can suggest atrial enlargement or ectopic atrial depolarization. Inverted P waves after the QRS complex, again with a constant PR interval, and observed in the inferior limb leads, can suggest retrograde atrial activation from a AV junctional or ventricular foci.
5 What leads should be utilized to analyze P wave information?
Should dysrrhythmias occur, at least one of the following leads should be analyzed to maximize P waves: II, III, aVF, V1. Of note, improvements in P wave tracings can be demonstrated via esophageal, transvenous, or epicardial leads (2). Most recently, P wave signal-averaged electrocardiograms have been advocated as an effective means of identifying and potentially predicting the risk of atrial dysrhythmias (3). Strip chart recordings or a 12 lead ECG should be evaluated should dysrrhythmias occur to assist in diagnosis and documentation.
References:
1.Hollenberg SM, Dellinger RP. Noncardiac surgery: Postoperative arrhythmias. Crit Care Med 2000; 28suppl) N145-50.
2.Atlee JL. Perioperative cardiac dysrhythmias: diagnosis and management. Anesthesiology 1997;86:1397-424.
3.Tuzcu V, Ozkan B, Sullivan N, Karpawich P, Epstein ML. P wave signal-averaged electrocardiogram as a new marker for atrial tachyarrhythmias in postoperative Fontan patients. J Am Coll Cardiol 2000;36(2):602-7.
