Internal Diseases · MU Sofia

Practical · 27. ECG - diagnostic evaluation

Explains what an ECG records and how the 12-lead set-up is arranged, then takes the reader step by step through interpretation: rate, rhythm, P wave, PR interval, QRS complex with axis, ST segment, T wave and QT interval. A table links common diagnoses such as myocardial infarction, atrial fibrillation, hyperkalaemia and pulmonary embolism to their characteristic ECG findings, and closes with notes on axis calculation, R wave progression and voltage criteria for hypertrophy.

Inside: 6 sections · 2 labelled pictures · 1 table · 14 flashcards · 2 min

Topic 84 of 88 in the MU Sofia syllabus for Internal Diseases (Dental Medicine, Year 4). The free AceMed note covers it in 6 sections, about 207 words (2 min of reading), with 14 flashcards.

In this note

  1. ECG: Diagnostic Evaluation
  2. I. What is ECG?
  3. II. Standard 12-Lead ECG Setup
  4. III. Steps in ECG Interpretation
  5. IV. Common ECG Diagnoses
  6. V. Additional Notes

I. What is ECG?

Electrocardiography (ECG) is a non-invasive test that records the electrical activity of the heart via surface electrodes. It is essential for the diagnosis of arrhythmias, ischemia, infarction, electrolyte disturbances, and structural heart diseases.

II. Standard 12-Lead ECG Setup

  • Limb Leads (6 total):
  • Bipolar: I, II, III
  • Augmented unipolar: aVR, aVL, aVF
  • Chest Leads (6 total): V1–V6

III. Steps in ECG Interpretation

  1. 1. Rate
  • Normal: 60–100 bpm
  • Tachycardia: >100 bpm
  • Bradycardia: <60 bpm
  1. 2. Rhythm
  • Regular vs irregular
  • Sinus rhythm = P wave before each QRS, regular PR interval
  1. 3. P wave
  • Atrial depolarization
  • Abnormal in atrial enlargement or ectopic atrial rhythm
  1. 4. PR interval (0.12–0.20 sec)
  • Prolonged = 1st-degree AV block
  • Short = pre-excitation (e.g., WPW)
  1. 5. QRS complex (< 0.12 sec)
  • Widened in bundle branch block, ventricular rhythm
  • Axis deviation:
  • Left axis: -30° to -90° → LVH, LBBB
  • Right axis: +90° to +180° → RVH, PE
  1. 6. ST segment
  • Elevation: acute MI, pericarditis
  • Depression: ischemia
  1. 7. T wave
  • Inversion: ischemia, PE
  • Peaked: hyperkalemia
  • Flattened: hypokalemia
  1. 8. QT interval (QTc)
  • Prolonged: risk of Torsades de Pointes
  • Shortened: hypercalcemia

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