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
πŸ •πŸ •Normal
πŸ •β†“Left axis deviation
β†“πŸ •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.

2 Viewpoints πŸ’¬ on “ECG Guide for Surgeons”

  1. Thank u for the breakdown on each wave, but for each explanation I think it should be followed by graphical example of what each wave would look like on the ECGgraph for better understanding

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