078 - EKGs - High Yield EKGs

A. ECG Interpretation Approach: 5 Steps

  1. P Waves Present?

    • First step for major findings.

    • If yes: Likely sinus rhythm.

    • Sinus P waves: Upright in inferior leads (II, III, aVF).

  2. Rhythm Regular or Irregular? (RR Interval)

    • Regular: Constant QRS complex distance.

    • Irregular: Varying QRS complex distances.

  3. QRS Complex Wide or Narrow?

    • Narrow: < 120 \text{ ms} (three small boxes).

      • Normal His-Purkinje system conduction.

    • Wide: Most likely bundle branch block (stable patient) or ventricular rhythm (e.g., VT, often sick patient).

      • Right Bundle Branch Block (RBBB): Wide QRS, upright in V1.

      • Left Bundle Branch Block (LBBB): Wide QRS, downward in V1.

  4. Check Intervals

    • PR Interval:

      • Normal: < 210 \text{ ms} (five small boxes or one big box).

      • Prolonged: AV block, high vagal tone, drugs slowing AV node conduction.

      • Shortened: High sympathetic tone.

    • QT Interval:

      • Normal: < 0.5 \times \text{RR interval} .

      • Prolonged: Hypocalcemia (tetany, numbness, spasms), antiarrhythmic drugs, congenital long QT syndrome, some antibiotics (erythromycin, quinolones).

        • Torsades is rare in hypocalcemia, more common with hypokalemia/hypomagnesemia.

      • Short: Hypercalcemia (confusion, constipation, volume depletion).

  5. Look at ST Segments, T Waves

    • Ischemia signs: T wave inversion, ST depression, ST elevation.

    • Other T wave abnormalities:

      • Peaked T waves: Early ischemia, hyperkalemia.

      • Flattened T waves with U waves: Hypokalemia.

    • Note: BBBs can have normal ST/T wave abnormalities; diagnosing ischemia with LBBB is difficult due to overlap.

B. Common EKG Rhythms & Findings (Pattern Recognition)

  1. Normal Sinus Rhythm (NSR)

    • P waves present, regular rhythm, narrow QRS.

    • P waves upright in II, III, aVF.

  2. Atrial Fibrillation (AFib)

    • No P waves, irregularly irregular rhythm.

    • Common, should be recognizable.

  3. Atrial Flutter

    • Sawtooth pattern baseline (especially in inferior leads, often throughout all leads).

    • Can be regular or irregular QRS.

  4. Ventricular Tachycardia (VT)

    • Very wide, very fast QRS complexes (e.g., ∼300 bpm\sim 300 \text{ bpm}).

    • P waves (from SA node) may be seen independently on wide complexes.

  5. Torsades de Pointes

    • Special form of VT.

    • Undulating, sinusoidal QRS pattern.

    • Occurs when a PVC falls during prolonged QT interval.

    • Risk factors: Prolonged QT (drugs: antiarrhythmics, erythromycin, quinolones; congenital long QT syndrome), hypokalemia, hypomagnesemia.

    • Treatment: Magnesium.

  6. Premature Ventricular Contraction (PVC)

    • Early, wide, bizarre-looking QRS complex.

    • Originates in ventricles, bypasses His-Purkinje system.

  7. Premature Atrial Contraction (PAC)

    • Early, narrow, normal-looking QRS complex.

    • Originates in atria, uses AV node and bundle branches normally.