Sunday, September 14, 2014

Massive Excessively Discordant Anterior ST Elevation in a Paced Rhythm

This patient has a standard DDD pacer, with RV pacing (not biventricular pacing), severe chronic nonischemic cardiomyopathy with EF of 10% (partly due to many years of having an RV pacemaker), severe systolic dysfunction, 3rd degree heart block from penetrating trauma, mild to moderated aortic stensosis, multiple LV thrombi, and a standard RV pacemaker.  He has had previous angiograms showing "large vessels" and "no significant coronary disease." 

He presented with chest pain, not relieved by nitro, pain reproducible on exam and centered around the pacemaker insertion site.  Here is his ED ECG
There is RV Pacing.  There is a very large amount of ST elevation in leads V1-V6.  It is out of proportion to the preceding S-wave, with a maximum ratio in leads V3 and V4 of 10/33 =  0.30.   

In LBBB, a ratio of greater than 0.25 is very specific for STEMI, and there is some evidence, as well as rationale, that a paced rhythm behaves similarly.
Here is one case of anterior STEMI in a paced rhythm.
Here is a case of lateral STEMI in a paced rhythm.

Here is his ECG one month prior, on admission for chest pain at that time also:
Similar ratios.  LV Ejection Fraction at the time of this hospitalization was 10%.

At that previous visit, he had had some mildly elevated troponins, but mostly had severe heart failure from very poor systolic function and aortic stenosis.

There was an ECG from 2 months prior as well, at which time the EF was 30%.  Here it is:
Here the maximum ratio is in lead V3 and is 7/42 = 0.167 (normal ratio).


Thus, the top two ECGs with excessively discordant ST elevation are false positives. During both presentations, the patient was fluid overloaded, and had decompensated heart failure with a very low ejection fraction.  It is likely that severe cardiomyopathy and loading conditions result in false positives.

How could you suspect that this is false positive?  
1) there was a previous ECG to compare with
2) there was a recent normal angiogram
3) the chest pain was fully reproducible
4) decompensated heart failure can affect the ECG.

In both presentations, the treating physicians were not fooled by the excessive ST elevation, though they did not comment on it.

Lesson:

1. There are false positives in every situation, whether normal conduction, LBBB, or pacing, or other.  Use all the information at your disposal to assess the situation. 
2. Severe decompensated cardiomyopathy likely can exaggerate the ST elevation associated with paced rhythm, and probably also LBBB.

1 comment:

  1. This is purely anecdotal, but it has also been my experience that paced EKG's are more likely to show false-positives by your criteria than LBBB's. I still run through paced EKG's looking for concordance or excessive discordance and believe there's definitely merit behind the idea of crossing the criteria over from LBBB to pacers, but it seems that the structural heart disease and scarring from old MI's that necessitate the implantation of many PM's really screw with our ability to analyze the ST-segments and T-waves.

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