EKG Systematic Approach Lecture Notes

Introduction to EKG Basics

• Purpose: Understand how to systematically interpret a 12-lead EKG.
• Key Components: Deflections and segments in EKG signals.

Basic Components of EKG Waveform

• P Wave:

  • Definition: Represents atrial depolarization.
  • Location: Generated by the SA node in the atria.

• PR Segment:

  • Definition: Time between the end of the P wave and the beginning of the QRS complex.
  • Function: Indicates AV node depolarization.

• PR Interval:

  • Definition: Time span from SA node firing to the readiness of sending action potentials to ventricles.

• QRS Complex:

  • Components: Q (downward), R (upward), S (downward).
  • Function: Represents ventricular depolarization.

• ST Segment:

  • Definition: Time during which ventricles are depolarized and awaiting repolarization.

• T Wave:

  • Definition: Represents ventricular repolarization.

• QT Interval:

  • Definition: Time period for ventricular depolarization and repolarization.

EKG Lead Placement and Electrical Activity

• Leads:
  • Inferior Leads: II, III, aVF (focus on right and left ventricles).
  • Lateral Leads: I, aVL, V5, V6 (lateral wall of the left ventricle).
  • Right Ventricular Leads: V1, V2, aVR.
  • Anterior and Septal Leads: V1 to V4.

Understanding EKG Paper

• Box Size:
  • Large Box: 5mm x 5mm = 0.5mV in height, 0.2s in width.
  • Small Box: 1mm x 1mm = 0.1mV in height, 0.04s in width.

Determining Rate and Rhythm on a 12-lead EKG

• Normal Heart Rate: 60-100 beats/min.

  • Bradycardia: <60 bpm.
  • Tachycardia: >100 bpm.

• Methods to Determine Rate:

  • Box Method: Count boxes between R waves.
  • R Wave Times 6: Count R waves in a 10s strip, multiply by 6.

• Rhythm Assessment:

  • Check R-to-R intervals: Regular vs. Irregular.

• QRS Appearance:

  • Narrow: <0.12s, Wide: >0.12s.

Sinus P Waves and PR Interval

• Sinus Rhythm:

  • P wave must precede QRS, upright in lead II, inverted in aVR.

• PR Interval:

  • Normal: <0.20s, Prolonged: >0.20s.

ST Segment Analysis

• ST Segment Elevation:

  • Criteria: 1mm elevation in leads (except V2-V3: needs 2mm).
  • Differentiation: STEMI, benign early repolarization, pericarditis, etc.

• ST Segment Depression:

  • Types: Downsloping, horizontal, upsloping.
  • Significance: Horizontal depression indicates ischemia.

T Wave Abnormalities

• T Wave Types:
  • Inversions: Sign of ischemia, notably in AVL.
  • Hyperacute Waves: Tall, broad, peaked waves indicating early STEMI.
  • Biphasic T Waves: Potential sign of Wellens syndrome (ischemia).
  • Flat T Waves: Impending ischemia, check potassium levels.

QRS Complex Evaluation

• Width:

  • Wide QRS: >0.12 seconds, consider bundle branch blocks, hyperkalemia, VT.

• Bundle Branch Blocks:

  • Left Bundle Branch Block (LBBB): Deep S in V1/V2, M shape in V5/V6.
  • Right Bundle Branch Block (RBBB): RSR' pattern in V1/V2.

Pathological Q Waves

• Definition:
  • Q wave >0.04s or >2mm depth, significant in V1-V3 indicates ischemia.

Low Voltage QRS Complexes

• Criteria: R waves in I, II, III <15mm or V1, V2, V3 <30mm.
• Concern for pericardial effusion or heart failure.

R Wave Progression

• Normal Progression: Increase in R wave amplitude from V1 to V6.
• Poor Progression: Suggests anterior MI or right ventricular hypertrophy.

QT Interval Evaluation

• Prolonged QT: >460ms in females, >450ms in males.

• Risks: Torsades de Pointes (ventricular tachycardia).

• Causes for Prolonged QT: Medications, electrolyte imbalances, ischemia.

• Short QT: <350ms, associated with hyperkalemia, hypermagnesemia, digoxin toxicity.

P Wave and PR Interval Abnormalities

• Right Atrial Enlargement: Tall P waves in lead II.
• Left Atrial Enlargement: Bifid P waves in lead II.
• PR Interval: Short <0.12s (WPW) or prolonged >0.20s (heart blocks).

Cardiac Axis Assessment

• Normal Axis: R wave positive in lead I and aVF.
• Left Axis Deviation: Lead I positive, aVF negative.
• Right Axis Deviation: Lead I negative, aVF positive.
• Extreme Right Axis Deviation: Both Lead I and aVF negative.

Conclusion

• Summary: Systematic approach crucial for accurate EKG interpretation.
  • Rate and Rhythm, ST Segment, T Waves, QRS, QT Interval, P Waves, Cardiac Axis analysis are all important.