Comparing 12-Leads: Discussion

This is the discussion for Comparing 12-Leads: Common Error or Common Disease? All of our readers were on the right track, and many were spot on!

Sometimes, troubleshooting an ECG is more than just lead placement. In this case report, we had three 12-Lead ECG's, all featuring a similar pattern: inappropriate R-wave progression.

You Take the Lead - Inappropriate R-wave Progression

Initially, when reviewing the first of these ECG's, I had believed it to be lead placement error. The most likely cause of inappropriate R-wave progression and low voltage in a precordial lead is the placement of the electrode on the mammary tissue or on the abdomen.

After reviewing two more ECG's from two different shifts, it became evident that the problem was more likely with the equipment than operator.

Two of the paramedics on duty were alerted to the possibility of a malfunctioning cardiac monitor, and the same was taken out of service for testing. During their investigation, it was found that the cables themselves were at fault.

The following is a 12-lead ECG acquired from one of the Paramedics using the current set of malfunctioning LP15 cables:

You Take the Lead - 12-Lead Comparison: Bad Cables

A set of LP12 cables was then connected to the same Paramedic and then connected to the same cardiac monitor:

You Take the Lead - 12-Lead Comparison: Good Cables

The difference in these 12-Lead ECG's is striking.

Remember, R-waves should progress in a continuous fashion from V1 through V6. Usually with a transition from negative to positive around leads V3 and V4. This is known as good R-wave progression.

R-Wave Progression - The Textbook of Medical Physiology 9e; © 1996 Guyton AC, Hall JE; WB Saunders.

With Paced Rhythms, RBBB, LBBB, RVH, LVH, or myocardial infarctions this zone of transition and R-wave progression may be early or delayed. You'll often hear about poor R-wave progression or an early or late transition. These refer to the change in dominant polarity across the precordial leads, whether from positive to negative or vice versa.

In any case, the changes must be continuous. Any discontinuity indicates a problem in acquisition.

Whenever you review a 12-Lead, be sure to consider the validity of the tracing beyond simple interpretation. You should be checking for baseline wander, excessive artifact, and electrode placement.

  • What types of machine failures have you seen that have gone unnoticed?
  • Do you have a QA program in place to assess the quality and accuracy of 12-Lead ECG acquisition?
  • Does your department discuss data quality issues during training?

See also:

Precordial Leads – The Transition, R-Wave Progression, R/S Ratio in Lead V1

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