Second-degree AV block (type 1) is also known as Mobitz type 1 AV block or Wenckebach phenomenon. First-degree heart block (AV block) Second-degree heart block (type 1) First-degree heart block (AV block)įirst-degree heart block involves a fixed prolonged PR interval (>200 ms). Prolonged PR interval (>0.2 seconds)Ī prolonged PR interval suggests the presence of atrioventricular delay (AV block). The PR interval should be between 120-200 ms (3-5 small squares). If P waves are absent and there is an irregular rhythm it may suggest a diagnosis of atrial fibrillation. If P waves are absent, is there any atrial activity? Do the P waves look normal? – check duration, direction and shapeĤ. If so, is each P wave followed by a QRS complex?ģ. The next step is to look at the P waves and answer the following questions:Ģ. Left axis deviation is associated with heart conduction abnormalities.Lead I has the most positive deflection.Typical ECG findings for left axis deviation: Right axis deviation 2 Left axis deviation Right axis deviation is associated with right ventricular hypertrophy.Lead III has the most positive deflection and lead I should be negative.Typical ECG findings for right axis deviation:

Lead II has the most positive deflection compared to leads I and III.Typical ECG findings for normal cardiac axis: Read our cardiac axis guide to learn more. To determine the cardiac axis you need to look at leads I, II and III. In a healthy individual, the axis should spread from 11 o’clock to 5 o’clock. Measure the R-R intervals to assess if the rhythm is regular or irregular 1Ĭardiac axis describes the overall direction of electrical spread within the heart. As you move along the rhythm strip, you can then see if the PR interval changes, if QRS complexes are missing or if there is complete dissociation between the two. If you are suspicious that there is some atrioventricular block (AV block), map out the atrial rate and the ventricular rhythm separately (i.e.

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