SNOWMASS, COLO. – An ECG can offer a handful of easily interpreted clues that raise to 99% the certainty of diagnosing ventricular tachycardia as the cause of a patient’s wide complex tachycardia, according to Dr. Samuel J. Asirvatham.
The first thing to realize about wide complex tachycardias (WCTs), as defined by a heart rate in excess of 100 bpm and a QRS duration greater than 120 milliseconds, is that the cause is ventricular tachycardia (VT) rather than supraventricular tachycardia in 80% of cases, he said at the Annual Cardiovascular Conference at Snowmass.
Dr. Samuel J. Asirvatham
“When you diagnose wide complex tachycardia as not VT, you’re much more likely to make a mistake than if you just closed your eyes and said VT,” said Dr. Asirvatham, professor of medicine and pediatrics at the Mayo Clinic, Rochester, Minn.
The history also provides a valuable clue: “If there’s anything wrong with the heart – a prior MI, structural disease, a scar on the heart from previous surgery, sarcoid – there’s a 95% chance that the WCT is due to VT,” he said.
Key ECG features will boost the diagnostic certainty of VT from 95% to 99%. Here are Dr. Asirvatham’s favorites:
• Atrioventricular dissociation. When the ventricular rate is faster than the atrial rate, the result is atrioventricular dissocation. In the setting of WCT, it’s highly specific for VT, and it’s present on the ECGs of up to 50% of affected patients.
“This is a very useful clue. I like looking for this. If you see it, you can be convinced the patient has VT,” he said.
• The wide QRS. The wider the wide QRS, the more likely it’s VT.If the QRS duration is greater than 150 milliseconds, there’s nearly a 98% likelihood of VT.
• Northwest axis. If both lead I and the inferior leads show negative deflection – that is, the electrical wave is moving away from the positive electrodes located over the left shoulder and closest to the feet – that means the wave is moving toward the northwest on the frontal plane axis. The odds are extremely high that this is VT.
• Chest lead concordance. If all of the chest leads V1-6 are positive or they’re all negative, that’s “powerful information” indicating VT, according to Dr. Asirvatham.
• Time from onset of R wave to S wave nadir. Even if chest concordance isn’t present, VT can be diagnosed with near-absolute certainty simply by measuring the time from onset of the R wave to the lowest point on the S wave. If it’s longer than 100 milliseconds, that finding strongly favors VT.
“Remember these ECG features and 99% of the time you will correctly diagnose VT,” the cardiologist said.
Dr. Asirvatham reported serving as a consultant to a dozen medical device companies.