As is the case for hyperkalemia - You have NO IDEA as to what this patient’s true “baseline” ECG looks like until you repeat the ECG after you have corrected serum electrolytes (ie, It could be that the reason for ST flattening rather than ST depression in this case - is that baseline ST elevation has been attenuated by the ST segment lowering effect of superimposed hypokalemia!). Doing so allows you to follow the evolution of ST-T wave and U wave changes as serum electrolytes are corrected. PEARL #4 - I have found it insightful ( when possible) to follow patients like this who have severe electrolyte disorders, with serial ECGs.

As emphasized above - in light of this patient’s presenting complaint of “weakness” - this tracing is perfectly consistent with moderate-to-severe hypokalemia. CLINICAL IMPRESSION: There are no acute changes on this tracing.Regarding Q-R-S-T Changes - there are small sepal q waves - normal transition ( that occurs between leads V3-to-V4 ) - and nonspecific ST-T wave flattening in multiple leads + a long QT and/or a long QU, as previously discussed.If the patient is not a young adult - then there is probable LVH, given the very deep anterior S waves ( IF interested in My Take on the ECG diagnosis of LVH - CLICK HERE). Regarding chamber enlargement - there is LAA ( deep negative component to the P wave in lead V1 ).There is slight left axis deviation ( about -10 degrees, given greater negativity than positivity in lead aVF ).BOTTOM Line: U waves are present in this ECG - and either the QT and/or QU interval is markedly prolonged - which for practical purposes means that we need to think of the short LIST of Potential Causes of QT Prolongation = i ) Drugs ii ) Lytes ( ie, low K+/low Mg++ and/or low Ca++ ) and/ or, iii ) some CNS Catastrophe ( For more on this LIST, see My Comment in the Mapost).Does the T wave have a double hump? - or, is this 2nd ‘hump” the initial part of the U wave? Or, is the U wave biphasic ( neg-pos )? My Guess - is that the answer is some combination of these possibilities. But there is also an extra “hump” in lead V2 ( GREEN arrow in this lead ).This upsloping deflection must be part of the U wave ( since it clearly occurs after the T wave - but before the P wave ). Note in simultaneously-obtained leads V1, V2 and V3 - that there is a small, upsloping deflection seen before the onset of the P wave ( BLUE arrows that clearly occur before the vertical BLUE line). I therefore drew a vertical BLUE line at precisely the onset of the P wave. I believe we clearly see the beginning of the P wave in the long lead II ( RED arrow ). The problem I had was distinguishing T wave from U wave.Given the fairly rapid heart rate - one might think from lead aVL that the QT is prolonged.This is because the end point of the T wave is not distinct. Confession: I found it very difficult to measure the QT interval.This is important - because serum Mg++ levels are not necessarily included in chem profiles unless specifically ordered. PEARL #3 - In my experience - Hypomagnesemia produces virtually identical ECG changes as hypokalemia.PEARL #2 - IF U waves are so large that they become bigger than ( or almost as big as) T waves - then the ECG becomes much more reliable for predicting significant hypokalemia ( Panels E and F in Figure-1).That said - when U waves are present, and the clinical history is consistent with ( or suggestive of) hypokalemia ( as in a patient with vomiting, or the weakness that both patients in this case had) - prompt assessment of serum electrolytes becomes essential! PEARL #1 - The finding of U waves is not specific for hypokalemia! U waves may also be found in patients with LVH and/or bradycardia, and occasionally as a normal variant.That said - with more severe degrees of hypokalemia, the ECG tends to do much better in its prediction, and the ECG is very unlikely to be “normal”. Thus, in my experience - the ECG is less than optimally sensitive or specific as a tool for detecting mild-to-moderate hypokalemia. I’ve also seen patients with mild-to-moderate hypokalemia who did not manifest any of the signs in Figure-1. I’ve seen many patients with all of the ECG findings shown in Figure-1 who had normal serum K+.

Hyperkalemia ecg u wave