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ECG/EKG Interpretation: What Heart Rhythm Readings Reveal About Cardiac Electrical Activity

Electrocardiogram (ECG/EKG) records the heart's electrical activity via surface electrodes. Key diagnostic information:

  1. Heart Rate & Rhythm: Beats per minute (normal 60–100 at rest); regularity (sinus rhythm vs. arrhythmias).
  2. Electrical Conduction Pathway: SA node → atria → AV node → bundle of His → bundle branches → Purkinje fibers → ventricles. Each step has a characteristic waveform.
  3. Intervals & Segments:
    • PR interval (AV conduction): 120–200 ms.
    • QRS complex (ventricular depolarization): <120 ms.
    • QT interval (repolarization): corrected (QTc) <440 ms (men), <460 ms (women).
    • ST segment (ischemia/injury): elevation or depression.
  4. Arrhythmia Detection: AFib, flutter, SVT, VT, VF, heart blocks, PVCs, PACs — morphology and context guide management.
  5. Ischemia / Infarction: STEMI (ST↑), NSTEMI (ST↓/T↑), Q waves (old MI), reciprocal changes.
  6. Conduction Defects: BBB (LBBB/RBBB), AV blocks (1°, 2° Mobitz I/II, 3°), WPW (delta wave, short PR).

Clinical Utility

  • Non-invasive, immediate, repeatable.
  • Guides acute intervention (STEMI → cath lab, unstable arrhythmia → cardioversion).
  • Monitors drug effects (QT-prolonging), electrolyte shifts, device function (pacemaker/ICD).

Interpretation requires systematic approach (rate, rhythm, axis, intervals, morphology) and clinical correlation.

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