Effects of Drugs on the ECG

00:01 So, let's look at a few drugs.

00:02 The most famous drug for changing the ECG is digitalis preparations.

00:07 Usually these days just Digoxin. You get a rounded depression of the ST segment.

00:13 And I think I showed this way back in one of the earliest lectures when we were getting intervals and various other definitions of the EKG straight.

00:22 Also, antipsychotic drugs, such as Thorazine and a whole bunch of others can prolong the QT interval.

00:29 And by the way as I mentioned in an earlier lecture, can set up the situation for Torsades de Pointes and cardiac arrest.

00:36 There's a long list of drugs that can lengthen the QT interval and predispose patients to Torsades de Pointes and cardiac arrest. It isn't just antipsychotic drugs.

00:48 There's now a whole website with dozens of drugs listed that can prolong the QT interval and set up this dangerous situation where you might get Torsades de Pointes.

00:59 So, here is a typical ECG from a patient who's getting digitalis.

01:04 Notice the rounded sort of smoothly rounded ST segment denoted by the green arrows.

01:12 This is typical digitalis effect.

01:15 Sometimes their EKG will be read by - as none specific ST-T changes.

01:20 But this one really looks to me like the patient's on digitalis. Here's the long QT interval in two little diagrams.

01:28 You'll notice to the left, here's the normal ECG, P-wave, QRS and T-wave and you can see the length of the QT interval.

01:36 Notice the long QT on the right-hand side.

01:40 The P and the QRS are normal, but there's a long pause between the development of the QRS and the occurrence of the T-wave.

01:49 There's prolonged repolarization in the ventricle and this sets up the situation for a reentrant malignant ventricular arrhythmia.

01:58 Prolonged QT, many drugs are capable of doing this.

02:02 Here's a patient receiving an antipsychotic drug. Notice, long QT interval.

02:08 This could be very worrisome.

02:10 The dose might need to be changed or a different drug might need to be instituted.