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Classic Catch - ECG Case #3
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Here is a classic ECG case not usually caught on a 12-lead ECG.
Below, a progression of four ECGs helps to teach one of the most important ECG lessons any practicing health care professional needs to know in order to act quickly and save lives.
This previously healthy 50-year-old female collapsed while walking. She had been having some "indigestion" for a few hours earlier in the day. Her blood pressure is 70/40 with a heart rate of 180 beats per minute. Here is her first ECG in the ER:
Oh my! Now what? Looks like a wide-complex tachycardia in a left bundle branch block pattern. When the patient does not look well, always assume ventricular tachycardia (VT) is the cause until proven otherwise, and institute ACLS protocols.
This ECG is a good example of VT. Note the wide QRS complex and fast rate. There are two possibilities when you see a wide-complex tachycardia: ventricular tachycardia or supraventricular tachycardia with "aberrancy" (such as a plain, ordinary right or left bundle branch block with a fast heart rate). So is it VT or not VT? That is the question. There are criteria to figure this out called the "Brugada criteria." The ACC/AHA has a similar algorithm. Here are three questions to ask first. If the answer is "yes" to any of them, the rhythm is ventricular tachycardia:
1. Do you see concordance present in the precordial leads (leads V1-V6)?
Our above ECG does not have concordance, which means all pointing in the same direction. Positive concordance would mean all the QRS complexes are pointing up in V1-V6, and negative concordance would have all QRS complexes downward. Also sometime explained as the absence of an RS complex, concordance is diagnostic of VT. This ECG does not show concordance since the QRS is down (negative) in V1-V3 but up (positive) in V4-V6. Below is an example:
2. Is the R to S interval > 100 ms in any one precordial lead?
If present, then VT is the diagnosis. Our patient's ECG does indeed have a long RS interval, as seen below. Simply use calipers to measure the distance between the R wave to S wave in each precordial lead and see if it exceeds 100 ms. This ECG has an R to S interval of 200 ms, so VT it is! Measure from the start of the R wave (hard to tell sometimes) to the bottom of the S wave. The image below is taken from our patient's ECG. We could have started measuring even earlier in the upstroke of the R wave:
3. Do you see atrioventricular (AV) dissociation?
AV dissociation occurs when the P wave (representing atrial depolarization) is seen at different rates than the QRS complexes (ventricular depolarization). This is present in only a small percentage of ventricular tachycardia ECG tracings; however, it is diagnostic of VT. Our patient's ECG does not have AV dissociation. Frequently, this is difficult to see due to the fast rate of the QRS complex. Below is an ECG strip from a patient with ventricular tachycardia. See the P-P interval when in sinus rhythm, then march out the P waves within the wide QRS complex to find the AV dissociation that is present, thus confirming the diagnosis of ventricular tachycardia:
4. Morphology Criteria
If the answer to questions one through three was "no," then look at the shape (morphology) of the QRS complex. Let's go on to the rest of the case, but you can go back and review the morphology criteria here later.
Why is ventricular tachycardia so dangerous?
This is why. Here is her second ECG, just a few seconds after the first:
This is ventricular fibrillation, a universally fatal arrhythmia unless immediate electrical cardioversion is performed. Ventricular tachycardia can "degenerate" into ventricular fibrillation. We don't usually take the time to get a 12-lead ECG of this. The ventricular rate exceeds 400 beats per minute, the blood pressure drops to zero and this is why people die during heart attacks. In this setting, virtually no forward cardiac output occurs.
So what is the cause of all of this?
She is successfully cardioverted and looks good. Vitals are back to normal, she is awake and alert, but she is complaining of chest pains. A third ECG is done and can explain everything. Here it is:
Now we know she has an anterior ST elevation MI. Coronary angiography showed that she had a 100% occlusion in her left anterior descending, which was opened up. There happens to also be a right bundle branch block (RBBB) on this ECG. The ST elevation is most dramatic in leads V2 and V3, indicating an anterior ST elevation MI (STEMI). Check out this post on the Top 5 MI ECG Patterns You Must Know if you are still learning to recognize an MI on ECG.
It's crazy, but I always tell patients that the people who die from heart attacks are the people who don't come in. Dozens of times I have been in the ER telling a patient "OK sir, you are having a heart attack. That means a blood clot in your ... CODE BLUE!" ... Then ventricular fibrillation, shock ..."coronary artery. We have to do an angioplasty and stent procedure now." The patient says, "Wait a second, something weird just happened." My response is, "You just died. Glad you came in and didn't ignore the symptoms. We got you back, though. If you were at home, you would not have made it."
Did we save the heart muscle?
If the coronary artery is not opened up with angioplasty and stenting quickly enough, permanent scarring can develop and lead to congestive heart failure. Here is her last ECG:
Note the big Q waves in lead V1-V3. This indicates an old myocardial infarction in the anterior and anteroseptal walls. You can review the ECG findings of anterior MI including an old MI here. Unfortunately, she did have permanent damage done, and her ejection fraction (measure of systolic function of the heart) remains at 30% (normal 55% to 65%).
There are two major lessons to learn. First, wide complex tachycardia is ventricular tachycardia until proven otherwise. If the patient is unstable, shock right away. If the patient is stable, you have time to think about the ECG and figure out if it is ventricular tachycardia or supraventricular tachycardia with aberrancy. The second lesson is, don't take the time to get a 12-lead ECG of ventricular fibrillation just because it looks cool.
Editor’s note: This Blog was originally published on learntheheart.com.
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