Here is an interesting case submitted by Billy Eskridge.
EMS is called to an assisted living facility to evaluate a 94 year old female complaining of chest pain. History of present illness:
Approximately 1 hour prior to EMS arrival, the patient had complained of a headache. A nurse gave the patient a Lortab. About 15 minutes later the patient started complaining of chest discomfort.
The nurse gave the patient two 0.4 mg NTG tablets over 20 minutes with no relief of the chest pain. The patient requested to be seen by a physician.
Patient is slightly confused and lethargic but states that she feels "sick all over." The nurse states this is unusual for the patient.
Past medical history:
Complex medical history including hypertension, aortic stenosis, and mitral regurgitation
Resp: 24 Pulse: 68 BP: 184/72 SpO2: 85 on RA
The cardiac monitor is attached.
A 12-lead ECG is captured.
Here are the computer measurements and interpretive statements.
Billy Eskridge asks the following questions:
Since this patient has an internal pacemaker and wide QRS complexes, is it possible to identify the ST/T changes of ischemia or acute injury?
I have also observed that not every beat is paced, and that there are come supraventricular beats which are also wide complex, showing a LBBB.
I know that there are certain tricks for diagnosing acute MI in LBBB, but I'm not familiar with them.
I am also aware that normal ST changes in wide complex rhythms can be used for diagnosis of MI if an old 12 lead is available to compare the current one to, but is this valid for both paced and supraventricular rhythms with a BBB?
If this rhythm was paces every beat without any apparent conduction abnormality can you scan it for AMI?
In the first place, even though the pacing spikes seem to "disappear" occasionally in the rhythm strip, it shows 100% pacing. I suspect that the pacing spikes are simply lining up perfectly with the lines on the graph paper, but regardless, we can rest assured that it's 100% paced because there is no change whatsoever in the R-R interval or QRS morphology.
In this case, the 12-lead ECG shows a fairly typical looking paced rhythm consistent with a pacing lead in the apex of the right ventricle. Namely, it shows LBBB morphology in lead V1 with a left axis deviation. It also shows negative concordance in the precordial leads, which is a common finding with paced rhythms.
You will note that the ST-segments and T-wave are deflected opposite the main deflection of the QRS complex (which is also the terminal deflection of the QRS complex). This is consistent with a "normal" paced rhythm and the "rule of appropriate T-wave (and ST-segment) discordance" with LBBB or paced rhythm.
Another important finding is that the larger the QRS complex, the more pronounced the secondary ST-T wave abnormality in the opposite direction. This is also true with strain patterns with left ventricular hypertrophy (LVH).
However, there are limits as to the expected amount of discordant ST-segment elevation in the presence of LBBB or paced rhythm.
According to Sgarbossa's Criteria, discordant ST-elevation (that's ST-elevation that is opposite the main deflection of the QRS complex -- in other words, ST-elevation in a lead with a negative QRS complex) > 5 mm is suggestive of AMI.
The problem is that QRS complexes with extremely deep QRS complexes will show more ST-elevation, and that's normal for LBBB and paced rhythm. For example, if you have a QRS complex in the right precordial leads with an S-wave that is 50 mm deep, you can have 5 mm of discordant ST-elevation and the ST-elevation is only 10% the depth of the QRS complex, which is fine.
Dr. Smith and colleagues from Hennepin County Medical Center propose a modified rule for discordant ST-elevation where you look for discordant ST-elevation that is 0.25 (or 1/4) the depth of the QRS complex.
Regardless, this 12-lead ECG shows a normal looking paced rhythm with appropriate T-wave discordance and ST-segments that are normal looking within the context of paced rhythms.
To learn more about Sgarbossa's Criteria and the "rule of appropriate T-wave discordance" see these previous posts: