Effects of Electrolyte Abnormalities on the ECG

by Joseph Alpert, MD

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    00:01 Welcome back to the ECG lecture series.

    00:03 We're gonna be talking about the effect of electrolyte abnormalities in the blood and various drugs on the ECG recording.

    00:11 This is actually one of the things that makes ECG reading difficult in that things beside heart disease can affect the EKG and makes it difficult for you to determine, "Is this change in the ECG to heart - due to heart disease or is it due to an electrolyte abnormality?" However, some of these electrolyte abnormalities give you a warning that something bad is happening as I will show you in a moment.

    00:35 So, let's first talk about electrolyte abnormalities, and then we'll talk about drugs.

    00:41 So, one of the different types of electrolyte abnormality, one can have hyper or hypokalemia, in other words, hyper; elevated potassium or hypo; low potassium in the blood.

    00:53 Similarly, one can have hyper or hypocalcemia that is elevated calcium in the blood or low calcium in the blood or one can have low-sodium in the blood and then of course finally a variety of drugs which we'll talk about right at the end.

    01:08 But first we're gonna talk about electrolyte disturbances because they're so common, they happen all the time, and they cause abnormalities in the ECG that are nonspecific.

    01:19 That is, they don't say to you, "Oh, this is hypokalemia." Let's talk about hyper and hypokalemia first, all right? This is an example of hyperkalemia.

    01:30 Notice how sharp and pointed the T waves are.

    01:34 In fact, my resident who was teaching me when I was an intern used to say, "Think of hyperkalemia when you wouldn't wanna sit on the T waves." You can imagine it would hurt to sit on that T wave.

    01:46 They're elevated and they're markedly pointed. Here's another example.

    01:52 Notice, markedly pointed and elevated T waves.

    01:56 And in this patient the potassium was 6.9.

    02:01 Normal is generally 3.5 to 5.5, although we start to get nervous when we get up into the fives, this was almost 7.

    02:09 What happens if the potassium continues to rise, is eventually you lose the form of the QRSs and you get what's like a sine wave like this. The blood pressure falls and it can be fatal.

    02:21 So, here we see what happens to the ECG when the potassium in the blood is low.

    02:27 In green up at the top is a normal QRS P-wave and T wave.

    02:33 Notice the normal P-wave, normal PR interval, normal QRS, normal ST segment and then a normal T-wave.

    02:40 You may have an abnormal U wave; some normal people will have that but it is also often seen in hypokalemia.

    02:50 Notice down below in pink, this is a hypokalemic change.

    02:54 First of all, the PR interval is prolonged as opposed to normal above.

    02:59 The QRS maybe a little bit widened or slightly abnormal in shape.

    03:04 The ST segment is abnormally down sloping.

    03:07 The T wave is shallow and there's often a prominent - a U wave, although that doesn't have to be present.

    03:14 So again, a longer PR interval, depressed ST segment, inverted T waves and a U wave in some cases.

    03:23 Unfortunately, these changes are not specific for hypokalemia and they're often read as nonspecific ST-T changes cuz as I'll show you in a moment, they can be caused by other electrolyte abnormalities or drugs.

    03:35 So, this doesn't give you a diagnostic information, "Oh, the potassium is low," as the way the hyperkalemia T waves do give you a diagnosis.

    03:46 Again, here's another ECG with a patient with hypokalemia.

    03:50 You'll notice with the blue arrow the T wave is inverted.

    03:54 The green arrow, you'll see that the - there's a U wave after the T wave and there's a depressed ST segment in the green box and the serum potassium here is 2.8.

    04:07 Again, this is a nonspecific ECG. This could occur in patients that have multiple electrolyte abnormalities.

    04:16 Let's talk about hyper and hypocalcemia, elevated and depressed serum calcium - blood calcium.

    04:24 So, the ECG changes are modest in hypercalcemia with some shortening of the ST segment and the QT interval, so not very specific findings.

    04:35 Again, you'll notice there's a short ST segment, the blue arrow and the QT interval is short.

    04:42 Notice the T wave comes early.

    04:44 So, this is a short ST segment and a short QT interval, otherwise, the ECG is not remarkable. In hypocalcemia, the ECG changes are even more modest, they include slight lengthening of the ST segment and lengthening of the QT interval.

    05:02 And here we see a little more extreme example.

    05:05 You'll notice in the green box there's a prolonged ST segment and a late T wave leading to a prolonged QT interval.

    05:14 And here is another example, this shows you a prolonged ST segment and a prolonged QT interval.

    05:24 So unfortunately, patients don't show up neatly packaged.

    05:30 You don't have a patient, "Oh, this patient just has hyperkalemia.

    05:33 Oh, this patient just has hyponatremia. Oh, this patient just has hypercalcemia." Unfortunately, multiple electrolyte abnormalities occur at the same time which also makes the EKG not specific in these findings.

    05:48 So again with multiple electrolyte abnormalities, one can get very nonspecific changes.

    05:54 As I said, often called nonspecific ST-T changes or diffused ST-T changes and it doesn't make the diagnosis.

    06:04 It just tells you that there's something disturbing the electrical activity, could be combined hypokalemia and hyponatremia, a variety of other things.

    06:13 And so here we see a typical example.

    06:15 Notice in this first part of the ECG that there's abnormal ST segment sort of down sloping and you see that in a number of the leads.

    06:25 For example, lead V2 and V3 also have an abnormal ST segment.

    06:30 And then you'll notice in the green box, very abnormal T wave, sort of a funny looking T wave following the abnormal ST segment.

    06:38 This is nonspecific ST-T wave changes, multiple changes can do this, hypoxia can do this, electrolyte abnormalities. You can't make a diagnosis based on this ECG.

    06:50 So, as I said, there are many things that can cause these nonspecific ST-T changes.

    06:56 Sometimes its ischemia, sometimes drugs will do it, hypoxia, low oxygen in the blood can do it, certain infections can do it, certain CNS diseases, and there's a whole raft of others which is why we call it nonspecific because we can't make a diagnosis.

    07:12 Remember, this is quite different from hyperkalemia with the big sharp T waves that you wouldn't wanna sit on that's very diagnostic of hyperkalemia.

    07:21 These EKG changes really just say, "There's something going on but we can't tell you exactly what it is but there's abnormalities." Look at the electrolytes, look at the oxygen and the blood and so forth.

    About the Lecture

    The lecture Effects of Electrolyte Abnormalities on the ECG by Joseph Alpert, MD is from the course Electrocardiogram (ECG) Interpretation. It contains the following chapters:

    • Effects of Electrolyte Abnormalities on the ECG
    • Hyper- and Hypokalemia
    • Hyper- and Hypocalcemia

    Included Quiz Questions

    1. A prolonged PR segment
    2. Prominent T waves
    3. A short ST segment
    4. A short QT interval
    5. ST segment elevation
    1. A short QT interval
    2. A prolonged QT interval
    3. Prominent U waves
    4. A depressed ST segment
    5. Prominent T waves
    1. A prolonged QT interval
    2. A short QT interval
    3. Prominent U waves
    4. A depressed ST segment
    5. Prominent T waves

    Author of lecture Effects of Electrolyte Abnormalities on the ECG

     Joseph Alpert, MD

    Joseph Alpert, MD

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