ECG notes

Pulmonary Circulation

  • Flow of Blood: Blood travels from the pulmonary veins back to the heart.
    • Pathway: left atrium → mitral valve → left ventricle → aortic valve → rest of the body
    • Both atria fill first, pushing blood into the ventricles; ventricles then pump blood to designated areas, resulting in heart sounds S1 and S2.
    • Visual Aid: Cartoon representation can help to clarify the pathway of blood flow through the heart.

Electrophysiology of the Heart

  • SA Node: Known as the sinus node; the natural pacemaker of the heart with a firing rate of 60 to 100 beats per minute.
  • AV Node: Receives signals from the SA node to coordinate atria contraction; inherent rate is about 40 to 60 beats per minute.
  • Bundle of His: Receives signals from the AV node, leading to the Purkinje fibers where depolarization and repolarization occur.
    • Definitions:
    • Depolarization: Contraction of the ventricles and atria.
    • Repolarization: Relaxation and filling of the ventricles and atria.
  • Refractory Period: The period during which heart muscle cannot be depolarized again. The relative refractory period requires a stronger than normal stimulus to generate a heartbeat.

Electrocardiography (ECG)

  • ECG Definition: A graphic tracing of the electrical activity of the heart.
  • Measurement Leads: Imaginary lines/electrodes between heart conductivities; common methods of monitoring include three lead and five lead systems.
    • Standard Monitoring: Continuous monitoring via three or five lead systems, whereas a twelve lead provides a snapshot of heart health but involves further training for interpretation.
  • Standards of Leads: Lead placement involves ensuring leads are positioned correctly to avoid interference with signals from muscle or bone.
  • Common Methods: Acronyms exist to help remember proper placement, e.g., "Smoke Over Fire" for white (right arm) over black (left arm).

12 Lead ECG Analysis

  • Composition: Includes six frontal leads and six precordial leads, mainly reflecting the left ventricle's electrical activity.
  • Lead Configuration:
    • Lead I: Right arm to left arm
    • Lead II: Right arm to left leg (most common for monitoring)
    • Lead III: Left arm to left leg
  • Tracings: Different leads provide various perspectives on heart activity, confirming correct lead placement ensures accurate readings.

Electrocardiogram Waveforms

  • Components of the ECG:
    • P Wave: Represents atrial depolarization; positive wave facing upwards.
    • PR Segment: Represents atrial repolarization.
    • QRS Complex: Represents ventricular depolarization; consists of downward deflection (Q), upward spike (R), followed by downward deflection (S), ending at the isoelectric line, from Q to S.
    • ST Segment: Represents the isoelectric period indicating the refractory period; followed by the T wave indicating ventricular repolarization.

Measurement Timing in ECG

  • ECG Timing:
    • X-axis represents time (0.04 seconds for small boxes, 0.2 seconds for large boxes).
    • Y-axis represents amplitude (voltage).
    • Counting methods can vary and are vital when analyzing heart rate on the strips.
  • Box Count Methodology:
    • Determining heart rate can be done through the small box method, big box method, or 6 seconds strip method.

Analyzing Heart Rhythms

  • Normal Sinus Rhythm:
    • Defined by a consistent PR interval (0.12 to 0.2 seconds), P wave before every QRS complex, and a heart rate between 60 and 100 bpm.
  • Bradycardia and Tachycardia:
    • Bradycardia: Heart rate less than 60 bpm, but maintains P waves and narrow QRS complexes.
    • Tachycardia: Heart rate above 100 bpm, with P waves corresponding to each QRS complex.
  • Atrial Fibrillation:
    • Characterized by quivering atria leading to ineffective blood flow, highly increases risk of clotting, necessitating blood-thinning medications (e.g., Warfarin).
  • Ventricular Arrhythmias:
    • Ventricular Tachycardia (VT): Marked by a rapid heart rate with wide QRS complexes and potential loss of P waves.
    • Pulseless Electrical Activity (PEA): Occurs without effective heartbeat despite electrical activity—critical to assess patient.
    • Ventricular Fibrillation: Disorganized electrical activity resulting in no effective heart contractions, requiring immediate CPR.

Final Notes and Practical Application

  • Understanding heart rhythms entails assessing the patient’s physical state in conjunction with their ECG readout.
  • Intervention Preparedness: Maintaining an understanding of equipment setup, patient interaction, and potential medication responses is crucial in practical and emergency situations.
  • Interactive activities, like rhythm recognition exercises, can boost comprehension and application of ECG readings in clinical environments.