 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

 Bundle Branch Blocks Right Bundle Branch Block

 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

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

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

 Left Bundle Branch Block

 Right Bundle Branch Block

 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

 Right Atrial Enlargement

 Left Atrial Enlargement

 Right Ventricular Hypertrophy

 Left Ventricular Hypertrophy

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