EMS is called to a local medical clinic to transport an 81 year old male to the emergency department.
The patient had experienced an episode of chest discomfort the day prior that was accompanied by palpitations and tachycardia.
He described the pain as a “pressure” in the center of his chest without radiation that resolved on its own after he sat down in a chair.
His primary care physician is concerned about “changes on his ECG.”
Past medical history: HTN, asthma, atrial fibrillation, cardiac stents
Medications: Albuterol, aspirin, warfarin, loratadine, avodart, furosemide, diltiazem, flunisolide
- RR: 20
- HR: 130
- NIBP: 142/80
- SpO2: 97% on room air
Skin: Pink, warm and dry
Breath sounds are clear bilaterally.
At the time of EMS evaluation he has no complaints.
The cardiac monitor is attached.
A 12-lead ECG is captured (which is similar to the 12-lead ECG taken at the doctor’s office).
Stephen Smith, M.D. ofÂ Dr. Smith’s ECG BlogÂ has a decision rule to help distinguish LVA from acute anterior STEMI by looking at the T/QRS ratio in leads V1-V4.
A high T/QRS ratio indicates acute STEMI. A low T/QRS ratio indicates LVA.
To come up with the T/QRS ratio you measure the amplitude of the T wave and divide by the depth of the S-wave.
If there is one lead in V1-V4 with a T/QRS ratio > 0.36, then STEMI is likely.
Or, if the sum of the T-waves in V1-V4 divided by the sum of the S-waves in V1-V4 > 0.22, then STEMI is likely.
Let’s look at the current case.
Lead V4 shows a T/QRS ratio of 0.38 which is suggestive of acute STEMI.
Let’s try the more complicated calculation (TV1+TV2+TV3+TV4 divided by SV1+SV2+SV3+SV4).
1+1.5+6+5 = 13.5
11+13+18+13 = 55
13.5/55 = 0.24 (T/QRS ratio)
Remember, the cut-off is 0.22 so this is very close but favors acute STEMI.
Finally, let’s consider another of Dr. Smith’s ECG interpretation tips: the rule of proportionality.
Lead V5 in this case shows a little bit of ST-elevation but the QRS complex is small. Let’s consider the ST/QRS ratio in this lead.
Here we use PowerPoint to “stretch” the QRS complex while preserving the ST/QRS ratio.
Another finding that supports acute STEMI is the well formed R-waves in leads V3 and V4.
Typically LVA shows QS-complexes in leads V1-V4.
Diagnosis: Acute anterior STEMI (confirmed with angiography)
T/QRS ratio best distinguishes ventricular aneurysm from anterior myocardial infarction.Â Am J of Emerg MedÂ 2005 May; 23(3):279-287.