2.  AV Blocks  First-Degree AV Block PR interval >0.21 seconds  Second-Degree AV Block (Mobitz I) Progressive delay until conduction blocked  Second-Degree AV Block (Mobitz II) Conduction of selected impulses through the AV node  Third-Degree AV Block No atrial impulses are conducted through the AV node Atria and ventricles fire at their intrinsic rates

3.  Bundle Branch Blocks Right Bundle Branch Block

4.  The Turn-Signal Rule  QRS >0.12 seconds throughout the ECG  Look at the QRS in V1  Identify the J point  Draw a horizontal line  Triangle pointing up indicates RBBB  Triangle pointing down indicates LBBB

5.  Hemiblocks  Left Posterior Hemiblock  Principal finding is a rightward shift in the QRS axis

6.  Hemiblocks  Left Anterior Hemiblock  Principal abnormality is a shift in the QRS axis far to the left

7.  Left Bundle Branch Block

8.  Right Bundle Branch Block

9.  Chamber Enlargement  Atrial Enlargement  Ventricular Hypertrophy  Causes Right-sided enlargement and hypertrophy Secondary to long-term pulmonary disease Left-sided enlargement and hypertrophy Secondary to long-term hypertension

10.  Right Atrial Enlargement

11.  Left Atrial Enlargement

12.  Right Ventricular Hypertrophy

13.  Left Ventricular Hypertrophy

15.  Cardiac Conductive System  ECG Recording  ECG Leads  Mean QRS Axis Determination  The Normal 12-Lead ECG  Disease Findings  Conduction Abnormalities  Prehospital ECG Monitoring