Teaching Rounds

Clinical pearls for lifelong learners

[teachingrounds]

Q. What's a U wave on an EKG?

A. U waves are seen best in V2 and V3. They should be 1-2mm high and going the same direction as the T wave. Causes include bradycardia and severe hypOkalemia (K<2.7), +/- hypOcalcemia, hypOmagnesemia, hypOthermia, increased intracranial pressure, LVH, HCOM, and some cardiac drugs.

An inverted U wave (opposite deflection to the T wave) suggests CAD, including MI, HTN, valvular disease, congenital heart defect, cardiomyopathy, and/or hyperthyroidism. Source: LITFL

Pro-Tip: The slower the heartrate (<65 bpm), the taller the U wave will be.

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Q. Are inverted T waves ever normal?

A. In healthy adults, the T wave should be upright in all leads except aVR and V1. Inverted T waves are normal in children in the R precordial leads because of RV dominance; as a persistent juvenile T-wave pattern in V1-3, especially in young Afro-Caribbean women; and can be normal variant in lead III. However, NEW T-wave inversions are always abnormal and suggest acute MI, bundle branch block, ventricular strain from hypertrophy, pulmonary embolism, hypertrophic cardiomyopathy, or raised intracranial pressure. Pathological T wave inversions are usually symmetrical and deep (>3mm). Source: LITFL

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Q. Is a J point the same as a J wave on an EKG?

A. No, the letter J on the EKG defines 2 totally different and unrelated events. The J point is a point in time marking the end of the QRS and the onset of the ST segment present on all EKGs. The J wave is a much less common, slow deflection of uncertain electrophysiological origin that was originally described in relation to hypothermia (T<30C) and is sometimes called an Osborn wave. Fairly specific for hypothermia (rules it IN), an Osborne or J wave can also been seen in hypERcalcemia, LVH due to HTN, myocarditis or Takotsubo cardiomyopathy, acute MI, or just early repolarization. Source: LITFL.

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Q. What is "poor R-wave progression" on an EKG anyway?

A. Early ventricular depolarization is reflected in the first upward deflection after the P wave (which represents atrial depolarization). Usually the size of the R wave increases from V1 to V3 If the R wave in lead V3 is shorter than expected (<3mm), then you should consider a prior anteroseptal MI, left ventricular hypertrophy, inaccurate lead placement (V1 and V3 swapped?), a normal variant, or dextrocardia.

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Q. Are Q waves always pathological?

A. A Q wave is any negative deflection before an R wave and is normal in leads I, aVL, V5, and V6. Deeper Q waves (>2 mm) may be seen in leads III and aVR as a normal variant, but under normal circumstances, Q waves are not seen in the right-sided leads (V1-3). Q waves are considered pathological if:

40 ms (1 mm) wide

2 mm deep

25% of depth of QRS complex

Seen in leads V1-3

Pathological Q waves usually indicate current or prior myocardial infarction. Source: LITFL

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Q. What does a P wave on an EKG signify?

A. The P wave represents atrial depolarization. It should have an upward direction in leads I and II but inverted in aVR. You can detect right atrial enlargement by a taller than normal P wave in lead II, and left atrial enlargement by a notched P wave in lead II. It is normal for the P wave to be biphasic in lead V1.

Source: LITFL

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Can you guess what this week's topic is?

Image courtesy of Medical Humor (21 Dec. 2011).

[teachingrounds]

Q. Why should people taking anti-seizure medications have their vitamin D levels checked?

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A. Many anti-epileptic drugs like phenobarbital and phenytoin accelerate vitamin D metabolism, and the body may not be able to make enough endogenously to keep up.

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Q. How often should you monitor vitamin D levels after starting supplementation?

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A. If the patient is consistent with taking the supplement, there's no need for monitoring labs. It may be worth rechecking to see if they should go back on a supplement they are not taking.

HOWEVER, it is wise to check calcium levels 1 month after starting a supplement, because it can unmask primary hyperparathyroidism if the parathyroid hormone (PTH) level is not suppressed --> increased calcium DESPITE the sudden vitamin D load.

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Q. Should you prescribe vitamin D2 or vitamin D3 supplements for vitamin D deficiency?

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A. This is a trick question! When supplementing at high doses for vitamin D DEficiency, we use 50,000 IU of vitamin D2 (ergocalciferol) once a week. It is produced by fungi or by irradiation in a lab; the process is safe but the result is less active. For vitamin D INsufficiency or as maintenance therapy after repletion for DEficiency, we usually prescribe 1,000 IU of vitamin D3 (cholecalciferol). It is more biologically active, but vegans may object to having an animal-based supplement.

Pro-tip: Both forms are available as tablets, capsules, and liquid solutions.

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Q. What does the obesity epidemic have to do with vitamin D levels?

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A. Because vitamin D is one of the four fat-soluble vitamins (the others are A, E, and K), adipose tissue (body fat) sequesters it, making it less bioavailable to perform its job of increasing calcium and phosphate absorption from the gastrointestinal tract.

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Vitamin D is made by a multi-step process in the human body:

In the skin: 7-dehydrocholesterol (provitamin D3) --*sunlight*--> previtamin D3 --> vitamin D3 (cholecalciferol).

In the liver: vitamin D3 (cholecalciferol) --hydroxylation--> 25-hydroxyvitamin D3 = stable form for storage that circulates in the blood. THIS is what we test for in "vitamin D deficiency."

In the kidney: 25-hydroxyvitamin D3 --hydroxylation--> 1,25-hydroxyvitamin D3 (calcitriol) = short-lived, biologically active form.

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Q. What IS vitamin D, and where does it come from?

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A. The "sunshine vitamin" is a derivative of cholesterol; because it is a lipophilic molecule, it can enter the cell nucleus to modify gene transcription and suppression. There are two natural sources of vitamin D:

Sunlight: Your body can actually make its own vitamin D with 5-30 minutes of exposure to ultraviolet B waves per day. Variables that affect this process include the strength of the sun's rays, the amount of melanin in your skin, and whether you're wearing clothes or sunblock.

Food: There are only a small number of foods that naturally contain vitamin D. Some of the best sources include liver, oily fish, mushrooms, and egg yolks. Other foods are artificially fortified with vitamin D, like cereals and milk.

Source: GoodRx

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Q. So, how much vitamin D do we need, anyway?

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A. The Endocrine Society, the National and International Osteoporosis Foundation, and the American Geriatric Society define vitamin D deficiency as the level of 25-hydroxyvitamin D (25 OH D) of <30 ng/mL. The Endocrine Society recommends 40-60 ng/mL. To maintain this level, the Endocrine Society recommends an intake of 400-1000 International Units (IU) daily for infants <1 year old, 600-1000 IU for children and adolescents 1-18, and 1500-2000 IU for all adults.

Source: StatPearls

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We close this week on malignancies that metastasize to bone with a wry bit of medical student humour courtesy of Reddit: Cookies_72 complained, "I pay £9250 yearly for this medical education" and shared a screen shot of their lecture notes:

-All the "Bs" go to bone

-Breast, bung, bidney, byroid, brostate

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Q. We interrupt this week of posts on bone metastases to ask, "Where did this lung metastasis come from?"

A. Statistically speaking it is most likely to be a carcinoma (colon, kidney, breast, testicle, thyroid), a sarcoma (bone), or melanoma. However, if it is a peripheral interstitial abnormality described as lymphangitic, it is more likely to be an adenocarcinoma (lung, breast, GI), melanoma, or lymphoma/leukemia.

Pro-Tip #1: Endobronchial mets are classically from renal cell carcinoma.

Pro-Tip #2: A miliary pattern should make you think of metastasized non-small cell carcinoma of the lung.

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Among patients age 40 and older presenting with radiographically aggressive-appearing bone lesions, metastatic ϲаrϲinоma is the most likely diagnosis, followed by multiple myelοma and lуmрhoma, with primary bone sarcomas being distinctly less likely. However, the possibility of ѕаrсоma has to be kept foremost in consideration until a tissue diagnosis is established, because the surgical treatment for primary sarcomas is different from that for metastatic tumors. Diagnosis <40 represents just 2% of all MM patients. Despite low incidence and low pre-test probability, must keep MM on your radar when working up pathologic fracture.

Weber, J Am Acad Orthop Surg 2010;18: 169-179, https://upload.orthobullets.com/journalclub/free_pdf/20190107_20190107.pdf