EKG for Dummies

This is by no means a comprehensive guide to reading EKGs. The goal of this checklist is to serve as a quick and efficient way to scan for abnormalities that warrant further evaluation (ie cardiology please help!)

Small box: 0.04 s | 40 ms | 1 mm

Big box: 0.2 s | 200 ms | 5 mm

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Rate:

• Take 300 divided by the number of big boxes OR

• Count down 300 | 150 | 100 | 75 | 60 | 50 for each big box

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Rhythm: Is it sinus?

• Is there a P before each QRS? QRS after each P?

• Are P waves upright in leads I and II, inverted in aVR?

• Are the PR intervals constant

• Are the QRS complexes narrow (< 100 ms wide or approximately 3 small boxes)

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Axis:

Use leads I and AVF

• Is QRS above/below baseline?

  • If above, it’s considered “+”

  • If below, it’s considered “-“

• If I = +, and AVF = +, NORMAL axis

• Thumbs trick: The left thumb is lead I and the right thumb is AVF.

  • If both thumbs are + (“thumbs up”), then normal axis

  • If L thumb +, R thumb -, then LAD

  • If R thumb +, L thumb -, then RAD

    • RAD can be a normal finding at birth and usually resolves by 6 months of age.

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Intervals:

• PR (3-5 small boxes: 0.12 - 0.2s)

  A prolonged or changing (esp lengthening) PR interval indicates AV block.

  • First-degree: PR >0.2s

  • Second-degree (Mobitz Type-1 Wenckenbach): Longer, longer, longer then a drop

  • Second-degree (Mobitz Type-2): P’s can’t get through

  • Third-degree: P’s and Q’s don’t agree

  Shortened PR intervals can be because of WPW, or a junctional rhythm.

• QRS (<3 small boxes: 0.12s)

  A widened QRS width indicates some sort of conduction defect with the left or right bundle branches.

• QTc = (QT x 0.04 / Sqrt( Previous R-R x 0.04)

  Normal <440 in men or <460 in women

Ischemia

• Look for Q waves (deeper or wider than1 small box (1 mm) or >1/3 QRS amplitude)

• Look for ST depressions, ST elevations, and T wave inversions

• Scan EKG for contiguous leads. Findings are only real if they occur in 2 or more contiguous leads

  • Inferior leads: II, III, aVF

  • Anterior leads: V1 - V4 (make sure the inverted T wave in V1 gradually becomes positive)

  • Lateral leads: V5, V6, I, aVL

Waves:

• P-wave (Lead II): Any peaked P's (>2.5 small boxes) or bifid P waves?

  • Right atrial enlargement produces peaked P waves (>2.5 small boxes)

  • Left atrial enlargement produces bifid P waves in lead II.

• QRS (V1 and V6): Are R or S waves >20 in V1? Are R waves >20 in V6? Are S waves >5 in V6?

  To assess for hypertrophy, use the “20,20,20,5” trick for normal values

  • R < 20 mm in V1

  • S < 20 mm in V1

  • R< 20 mm in V6

  • S < 5 mm in V6

  If break 20,20,20,5 rule, then compare to normal values in Harriet Lane

  RVH:

  • Tall R waves in V1 and deep S waves in V6

  • R/S ratio >1 in V1

  • R/S ratio <1 in V6

  LVH:

  • Tall R waves in V6 and deep S waves in V1

  • R/S ratio > 1 in V6

  • R/S ratio <1 in V1

• T-wave (All leads): Any inversions (except in aVR and V1)? Any larger than 1 big box in limb leads or <3 big boxes in precordial leads?

  Look in ALL leads for T-waves

  Should be upright in all leads except aVR and V1.

  • Inversions: MI, BBB, LVH/RVH, PE, HoCM

  • Can be normal in children

  Amplitude <1 big box (<5mm) in limb leads and <3 big boxes (<15 mm) in precordial leads.

  • Peaked: Hyperkalemia

  • Flattened: Hypokalemia, Ischemia

  • Biphasic: Hypokalemia, MI

  • Hyperacute (broad, asymmetric): STEMI