1. Understanding Cardiac Electrophysiology
BY NICOLE BROOKER

2. TABLE OF CONTENTS Electrical conduction system
Electrical conduction pathway
Conduction components:
The sinoatrial node (SA)
Bachmann’s bundle
Internodal tracts
Atrioventricular node (AV)
Right and Left Bundle branches
Perkinje fibers
Ventricles
Basic electrocardiograph (EKG) waveform:
P wave
PR interval
QRS complex
ST segment
T wave
QT interval

3. Electrical Conduction System of the Heart
The heart is supplied with an electrical conduction system that generates and conducts electrical impulses along specialized pathways
Contraction is sequence specific so the atria contracts before the ventricle and the ventricle contracts from apex to base for efficient ejection of blood.

4. ELECTRICAL CONDUCTION PATHWAY

5. CONDUCTION COMPONENTS
Sinoatrial (SA) node
Interatrial tract (Bachmann’s bundle)
Internodal tracts, the atrioventricular (AV) node
Bundle of His
Right and left bundle branches
Purkinje fibers.

6. THE SINOATRIAL NODE (SA)
The SA node, located in the upper right atrium, is the primary pacemaker of the heart (60 to 100 beats).
If the SA node fails to generate impulses or if those impulses are blocked, pacemaker cells in other sites can assume control, but at a slower rate.

7. BACHMANN’S BUNDLE INTERNODAL TRACTS
Bachmann’s bundle conducts impulses to the left atrium, while the internodal tracts conduct impulses to the AV node, located in the lower R atrium near the interatrial septum.

8. ATRIOVENTRICULAR NODE
Primary function- slow conduction of electrical impulses coming from the atria, allowing time for the atria to contract and empty their contents into the ventricles.
It can function as a backup pacemaker (40 to 60 beats). When the atrial rate is rapid, the AV node blocks some of the impulses being conducted to the ventricles, protecting them from dangerously fast rates.

9. RT AND LT BUNDLE BRANCHES
From the AV node, the electrical impulse moves rapidly through the bundle of His and to the R bundle branch (R ventricle) and L bundle branch ( L ventricle).

10. PURKINJE FIBERS
The impulse then enters the Purkinje system where Purkinje fibers conduct the impulse to myocardial cells of the ventricle, causing ventricular depolarization and contraction.

11. THE VENTRICLES
The ventricles also have pacemaker cells (30 to 40 beats) that take over if impulses are not being transmitted by the SA or AV nodes.
Repolarization follows.

12. Basic ECG Waveform
The heart’s electrical activity is represented by an ECG tracing by three basic waveforms: the P wave, the QRS complex, and the T wave.

13. BASIC ECG WAVEFORM
Between the waveforms are the following segments and intervals: the PR interval, the ST segment, and the QT interval. A U wave is sometimes present.

14. THE P WAVE
P wave - atrial depolarization, or the spread of the impulse from the SA node throughout the atria.

15. THE PR INTERVAL
PR interval - the time required for the impulse to leave the SA node, travel through the atria, AV node, bundle of His, bundle branches, and Purkinje fibers.

16. THE QRS COMPLEX
QRS Complex-represents ventricular depolarization and is represented by three waves: Q, R and S.

17. THE T WAVE
T wave - the latter phase of ventricular repolarization, and the vulnerable period of repolarization (R on T phenomenon).

18. THE ST SEGMENT
ST segment - represents the end of ventricular depolarization and the beginning of ventricular repolarization.

19. THE QT INTERVAL
QT interval - the time between the onset of ventricular depolarization and the end of ventricular repolarization
Includes the QRS complex, ST segment, and T wave