Dysrythmias

Understanding the Electrical Properties of the Heart

Overview of Cardiac Electrical Conduction

  • Impulse Movement Through the Heart:

    • Begins at the SA node (Sinoatrial node), located in the right atrium.

    • Travels across both atria to initiate contraction.

    • Reaches the AV node (Atrioventricular node) where there is a brief pause.

    • After the AV node, the impulse continues to the Bundle of His (His bundle), divides into right and left bundle branches, and finally reaches the Purkinje fibers.

    • This pathway allows for coordinated contraction of the ventricles after atrial contraction.

Depolarization and Repolarization

  • Definitions:

    • Depolarization: The process by which ions exchange across the cell membrane, leading to heart muscle contraction.

    • Repolarization: The return of ions to their original state, leading to muscle relaxation, though it is important to note that repolarization itself does not equal relaxation, but rather leads to it.

  • Remembering the Terms:

    • Repolarization leads to relaxation.

    • After ventricular repolarization, the ventricles will relax and precede the next phase of depolarization.

Mnemonic Device:

  • Light Switch Analogy:

    • Depolarization: Flipping on the light switch (contraction occurs).

    • Repolarization: Shutting off the light switch (leads to relaxation).

Sequence of Cardiac Events

  • Atrial Depolarization:

    • Occurs first as the impulse spreads through both atria, leading to atrial contraction that pushes blood into the ventricles.

    • After depolarization, atria contract via the AV node allowing blood flow through the valves.

  • Ventricular Activation:

    • Next, the impulse travels through the AV node to the Bundle of His, both bundle branches, and finally reaches the Purkinje fibers.

    • Ventricular Depolarization:

    • This event causes the ventricles to contract.

  • Repolarization of the Ventricles:

    • The ventricles must repolarize to allow for relaxation, marking the transition back to a resting state.

Understanding EKG Strips

  • EKG Waveforms:

    • P Wave: Represents atrial depolarization (contraction of atria).

    • QRS Complex: Represents ventricular depolarization (contraction of ventricles);

    • Notably larger spike compared to the P wave due to greater muscle mass of ventricles.

    • T Wave: Represents ventricular repolarization (ventricles relaxing).

  • U Wave (Less Common):

    • Rarely visible; thought to represent a rebound effect during ventricular relaxation.

    • It is usually not an abnormal finding, but can be confused with the P wave.

Commonly Confused Cardiac Rhythms

  • Most Confused Rhythms:

    1. Sinus Tachycardia (STT): Narrow QRS complexes (~0.04 seconds).

    2. Ventricular Tachycardia (V-Tach): Wide QRS complexes (appear very different from STT).

Pharmacological Considerations

  • Treatment for Fast Heart Rates (SVT):

    • Adenosine: First-line treatment for SVT to lower heart rate.

    • Confusion with Atropine:

    • Atropine is used to treat bradycardia (slow heart rate).

    • Important distinction as atropine increases heart rate, whereas adenosine decreases it.

  • Amiodarone:

    • Often used as a catch-all medication for various dysrhythmias.

    • First-line treatment for ventricular dysrhythmias.

Important Notes on Medications:

  • Diltiazem: Used primarily for supraventricular dysrhythmias.

  • Awareness on Medication Effects:

    • Adenosine causes a brief asystole period (heart stops for about 5 seconds).

    • Be aware of specific side effects for each medication and general education points regarding their use.

Conclusion

  • Recognizing the importance of the electrical conduction system of the heart and the physiological processes involved in heart rhythm is crucial for understanding cardiac function. Ensuring clarity between depolarization and repolarization is fundamental in both clinical assessments and monitoring through EKG readings.