ECG Guide for Surgeons

There is an old saying that two surgeons and an ECG form a double-blind-study. Then, there’s a protocol for surgeons intended for humor:

  1. All spikes up: Operate
  2. All spikes down: Call Medics
  3. All spikes missing:
    • Recently: Call Anesthetist
    • A long time ago: Complete death certificate
ECG interval

So, let’s think of heart as a cefazolin pump and ECG as “A RARE P-QRS-T” thing and approach the ECG to interpret it.

Mnemonic: A RARE P-QRS-T (V. Dimov approach)

1. Age

2. Rate:

  • Atrial rate (between same points in 2 P waves) and Ventricular rate (between 2 R waves)
  • <3 squares between each QRS complex = >100 bpm (tachycardia)
  • >6 squares between each QRS complex = <50 bpm (bradycardia)

You can use the 300 method (large boxes) or 1500 method (small boxes) or use a sequence of 300, 150, 100, 75, 60, 50 for rapid estimation of the heart rate.

3. Axis:

Axis can be crudely determined with the thumb rule looking at only 2 leads – I and aVF. Imagine that your left thumb is lead I and right thumb is lead aVF. Thumbs up represent positive deflections and thumbs down represent negative deflections.

Left thumb (Lead I)Right thumb (Lead aVF)Interpretation
🠕↓Left axis deviation
↓🠕Right axis deviation
↓↓Indeterminate axis

4. Rhythm:

  • Is it regular (same no. of squares between each QRS) or irregular (variable no. of squares between each QRS)?
  • Check for P before each QRS and QRS after each P (to see if the rhythm is sinus, i.e. the rhythm starts in SA node).

5. Evaluate each ECG elements:

a. P:

Wave (lead II)InterpretationIntervalInterpretation
<3 squares in width & <2.5 squares in height; may be biphasic in V1 (up an down)Normal P wave3-5 boxesNormal PR interval
Taller than 2.5 sqaures (P pulmonale)Right atrial enlargement (usually due to pulmonary hypertension)Longer than 5 sqauresHeart block (AV node block)
Longer than 3 squares +/- notch i.e. bifid (P mitrale)Left atrial enlargement (P. mitrale in mitral stenosis)Shorter than 5 sqauresAccessory pathway between atria and ventricle (WPW syndrome); AV nodal rhythm
Inverted (Retrograde)Non-sinus rhythm (AV nodal rhythm)
Variable morphologyMultiple ectopic pacemakers
AbsentSinus arrest, AVNRT
Flutter (saw-tooth) wavesAtrial flutter
FibrillationsAtrial fibrillation
>1 P wave before QRSHeart block

b. QRS:

  • Width:
    • 1.25-3 boxes: Normal
    • >3 boxes: Broad/Wide QRS (Slow conduction in ventricle or AV nodal/ventricular origin of electrical activity)
      • Bundle branch block
      • Hyperkalemia
      • Hypothermia
      • WPW syndrome
    • <1.5 boxes: Narrow/Supraventricular QRS (Supraventricular origin of conduction
      • Normal P waves: Sinus tachycardia
      • Regular flutter waves: Atrial flutter
      • No P waves: AV nodal tachycardia
  • Height:
    • 5 boxes (in >/=1 standard lead) or 10 boxes (in >/=1 precordial lead) – 25 boxes: Normal voltage
    • Low voltage: Damping effect of fluid/flat/air or loss of viable myocardium or restrictive heart disease
      • Fluid: Effusion (Pericardial or Pleural)
      • Fat: Obesity
      • Air: Emphysema, Pneumothorax
      • Loss of viable myocardium: Infarction or Cardiomyopathy
      • Infiltrative disorders: Myxedema, Constrictive pericarditis, Restrictive myocarditis
    • High voltage:
      • Voltage criteria: S wave depth in V1 + tallest R wave height in V5-V6 > 35 mm (Left ventricular hypertrophy)
    • Alternans (alternating in height): Massive pericardial effusion

c. T:

T WaveInterpretationST segmentInterpretation
Same direction as R wave (usually upside down in aVR and lead I), <5 boxes tall and <10 boxes tall in precordial leadNormalLevel with baseline; upto 1 box elevation or depression from baseline; upto 3 box elevation in V2-V3Normal
Asymmetric and not narrow tall T wavesNormal variantConvex, straight upsloping, straight horizontal or straight downsloping ST elevationMyocardial infarction
Symmetric, narrow based, pointing tall T wavesHyperkalemiaConcave ST elevationPericarditis
Symmetric, broad based, non-pointing tall T wavesHyperacute ischemia
Asymmetric inverted T waveStrain pattern
Symmetric inverted T waveIschemia (Old if no ST depression)
Gigantic/deep inverted T wavesCerebrovascular insult

To confirm STEMI we can use algorithm proposed from Stephanie et all. (2012), which involves four simple steps:

1. Is there ST elevation of at least 1 to 2 mm in 2 anatomically oriented leads)?

2. Is sum of the Q wave in lead V1/V2 + R-wave in lead V5/V6 less than 35 mm?

3. Is the QRS complex less than 0.12 second in width?

4. Is there ST-segment depression present in at least 1 lead?

In cases where all four criteria of this algorithm are fulfilled, diagnosis of STEMI is confirmed. In cases where even only one criterion isn’t fulfilled, then a diagnosis of STEMI can be in some degree of doubt.

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