12-LEAD ECG's - A "Web Brain" for Easy Interpretation

                          

  
   

Analyze an ECG
Applying the Systematic Approach

Use the following as a guide for your descriptive analysis, then formulate your clinical impression. Whenever possible, WRITE OUT your findings (even when time is short, be systematic)!

Rate

  • Divide 300 by the number of boxes in the R-R Interval (review).

 

Rhythm

  • Are there P waves?

  • Are P waves "married" to the QRS?

  • P waves should always be upright in lead II if there is sinus rhythm (unless there is lead reversal or dextrocardia)

Remember: for Rhythm, you must watch your P's & Q's, & the 3 R's

 

Intervals

  • Be sure to look at intervals early in the process!

  • The PR Interval is prolonged if >0.20-0.21 second (if clearly more than a LARGE box in duration).

  • The QRS Complex  is wide if >0.10 sec. (if more than half a large box).

  • The QT Interval is prolonged if clearly more than half the R-R interval (provided that heart rate is not more than 100 beats/ minute).

 KEY Point - If the QRS complex is wide, STOP and find out why (i.e., RBBB, LBBB, IVCD, or WPW) before proceeding further. (review causes of wide QRS)

 

Axis

  • Axis is determined by looking at lead I (at 0°) and lead aVF (at +90°)

  • The axis is normal if net QRS deflection is positive in leads I and aVF.

  • There is RAD if net QRS deflection is negative in lead I, but positive in aVF.

  • There is LAD if the net QRS is positive in lead I, but negative in aVF.

  • There is pathologic LAD (LAHB) if net QRS is more negative than positive in lead II.

  • The axis is indeterminate if net QRS deflection is negative in I and aVF. (review of Axis determination)

 

Hypertrophy

  • The "magic numbers" for LVH are 35 (deepest S in V1 or V2 plus tallest R in V5 or V6, in a patient at least 35 years of age) and 12 (for the R in lead aVL).  True chamber enlargement is much more likely if "strain" is also present!

  • There is RAA (P Pulmonale) if P waves are prominent (> 2.5 mm tall) and peaked (i.e., "uncomfortable to sit on") in the pulmonary leads (II, III, and aVF).

  • There is LAA (P Mitrale) if P waves are notched ("m"- shaped) in mitral leads (I, II, or aVL) or if the P in V1 has a deep terminal negative component.

  • Consider pulmonary disease if there is RAA, RAD (or indeterminate axis), incomplete RBBB (or rSr' pattern in lead V1), low voltage, or persistent precordial S waves.

  • Consider RVH if there is also a tall R wave in V1 and right ventricular "strain".

 

Infarct (QRST changes)

Look at all leads (except aVR) for the following:

  • Q Waves -  Small (normal septal Q waves) are commonly seen in lateral leads (I, aVL, V4, V5, V6); moderate or large- sized Q waves are normal (as an isolated finding) in leads III, aVF, aVL, and V1.

  • R Wave Progression - Does transition occur from V2-V4? Is there a tall R wave in V1? Is there a rSR' pattern in V1?

  • ST Segments - More than the amount of ST segment deviation, concentrate on shape ("smiley" or "frowny") of the ST segment.

  • T Waves - May normally be inverted in leads III, aVF, aVL, and V1.

 

 12-LEAD ECG's - A "Web Brain" for Easy Interpretation