UCONN Emergency Medicine Interest Group

Posts Tagged ‘ECG’

Pearl/Pitfall: Right-sided MI

In PEARL/PITFALL on July 11, 2011 at 12:40 AM

From didactics with Dr. Regan:

Understanding the presentation of posterior MI on EKG is not that complicated, and need not require any mirrors or special tricks! It can be relatively easily understood simply by recalling the coronary anatomy and lead placement. Remember that anatomically, the right coronary artery takes a path that goes to the posterior portion of the heart, then the inferior portion of the heart. This means that a posterior MI must* have an associated inferior MI; if the inferior leads (II, III, aVF) do not show signs of MI on EKG, then there is no posterior MI. Recall also that the chest leads V1-V6, just like the other leads, measure a vector of electrical activity pointing anteriorly. This implies that the vector goes from posterior to anterior. So, it should be expected that posterior MI should show reciprocal ST-T changes in the anterior chest leads. If they do not, this implies that the MI is a more distal pure inferior MI (which has a significantly better prognosis). If the chest leads do show reciprocal changes, right sided chest leads should be placed to obtain a right-sided EKG to determine if the obstruction is more proximal, resulting in a complete right sided MI, or more distal, resulting in a posteroinferior MI. In other words, the right-sided EKG should demonstrate ST-T changes consistent with MI if there is a complete right-sided MI (eg. ST elevation).  If they do not, the diagnosis is posteroinferior MI (again, remember that a posterior MI requires there to be an accompanying inferior MI).

* Note: as with everything in medicine, there are exceptions to the rule, and so it is possible for variants in coronary anatomy to make this idea not always hold. However, Dr. Regan informs me that he has only seen this occur several times in his nearly 20 years of practicing EM.

** Note: please remember that not all MI present with EKG changes. In fact, the sensitivity of the first EKG in acute MI is only 13-69%, and considering the evolution of all EKG abnormalities (ST, T, Q waves, LBBB) over time, the sensitivity is  87%.

References:
http://www.bestbets.org/bets/bet.php?id=75
http://www.uptodate.com/contents/electrocardiogram-in-the-diagnosis-of-myocardial-ischemia-and-infarction?source=search_result&selectedTitle=4~150

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Journal Article Synopsis: Prewired Electrodes for ECG

In JOURNAL CLUB on May 11, 2011 at 5:42 PM

Summary for “Comparison of the Use of Conventional and Prewired Electrodes for Electrocardiography in an Emergency Setting: The Spaghetti Study” by Frederic Lapostolle et al. in Annals of Emergency Medicine Vol 57 (4); pp 357 -361

What is already known on this topic:
ECG’s are a routine procedure commonly encountered in the Emergency Department and integral to the diagnosis and disposition of a wide variety of patients. The two most important factors in the usefulness of an ECG are its quality and the duration of time it takes to be performed. A poorly done ECG done promptly can be just as useless as a well-done ECG received too late. Therefore, improvements in the speed and quality of ECG recording are highly sought after.

The quality and promptness of an ECG are heavily influenced by the user. It is not uncommon for errors to occur in the placement of ECG leads, in particular reversal of the leads. These types of mistakes can lead to a significant loss in time and accuracy of interpretation of ECG’s. Unfortunately, these types of errors are more common in the acute settings, such as those often seen in Emergency Departments. This study involved the use of pre-wired electrodes, rather than conventional electrodes that are placed and then hooked up to the series of wires. These prewired electrodes are disposable, pre-wired, pre-gelled, and numbered for ease and elimination of ambiguity in placement.

What questions this study addressed:
Is there a difference in the quality of ECG recordings obtained with conventional versus prewired electrodes ? How easy is the use of the prewired electrodes in an emergency setting?

What was the study design:
Prospective, randomized, open comparison study including 105 patients undergoing ECG’s. Time to make recordings was measured, and both a prewired and conventional recording was performed. These were then analyzed and scored by 3 blinded reviewers, on the basis of artifacts and baseline instability.

What this study adds to our knowledge:
The ECG’s performed with the prewired electrodes took 20% less time than those done with conventional electrodes (average 118 seconds versus 144 seconds). Signal noise and baseline instability were significantly reduced with prewired electrodes regardless of the endpoint considered (whether number of unstable leads, max signal noise, baseline instability score, etc). There was no significant difference found in the prevalence of p-wave or QRS complex abnormalities.

How this is relevant to clinical practice:
The recordings done with prewired electrodes were accomplished significantly faster than those with conventional – and this did not include the time necessary to disinfect and untangle the lead wires (a daunting task, at times). In addition, recordings with prewired electrodes were significantly better than those made with conventional electrodes. The number of artifact-free recordings was nearly twice as high, and the level of signal noise and baseline instability was significantly lower.

Other considerations:
It would be interesting to examine this from a cost-benefit perspective. Although prewired electrodes are faster and provide better recordings, they are also more expensive – would they pay for themselves with faster and better quality care?

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