Effects of Drugs on the ECG

by Joseph Alpert, MD

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    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.

    About the Lecture

    The lecture Effects of Drugs on the ECG by Joseph Alpert, MD is from the course Electrocardiogram (ECG) Interpretation.

    Included Quiz Questions

    1. ST-segment depression (rounded shape)
    2. QT interval prolongation
    3. Cardiac arrest
    4. Torsades de pointes
    5. Ventricular fibrillation

    Author of lecture Effects of Drugs on the ECG

     Joseph Alpert, MD

    Joseph Alpert, MD

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