Nov 2, 2015
Torsades de pointes is very bad. It easily degenerates into Ventricular Fibrillation (VF) and that’s sudden cardiac death. How many cases of torsades have you seen in your career? Are your ready for it when you see it? Let’s see, there’s magnesium...uh, and then I seem to recall that drug isoproterenol (that I’ve never used) and then..oh yeah...I’m supposed to do ‘OVERDRIVE pacing’. Got it. Ummm, how do you do overdrive pacing? How does it work? DOES it work?
First. Let's set the record straight: emergency doctors don’t do overdrive pacing. How do I know that? Because there is only one indication for “overdrive pacing” in the ED: torsades de pointes. But the rate of torsades is 150-250 BPM. And the most commonly used pacemaker in US ED’s is the Medtronic single-chamber Pacer, which has a maximum RATE of 180 BPM. So how were you planning to OVERDRIVE Torsades, which is running at 250 BPM, when your max pacer rate is 180? See? You can’t even DO overdrive pacing. What are you really supposed to do?
Ventricular Tachycardia: 2 flavors
Torsades de Pointes = Polymorphic VT with long QT
The QT is heart rate-dependent. When the heart rate is slower, the QT is longer, and vice versa. In order to determine whether your patient truly has a long QT, the QTc was developed as a calculation that that attempts to normalize the QT interval to a rate of 60 BPM.
The bottom line: the QTc is number you should look at. There are several calculations available- even MDCalc has one. But just look at the top of the EKG. It turns out the EKG computer does a fine job of calculating the QTc. Use the QTc.
The dirty definition: Long QT = QT > 500 ms
Beware the patient with syncope or near-syncope with a QTc longer than 500. You might be staring straight at a patient who just had polymorphic VT with long QTc. You might be staring at torsades. Torsades likes to degenerate into VF, and VF is a less than desirable rhythm.
**Transvenous Pacing: RATE = 110 BPM
Bonus: Hollywood Weingart