View source for WBR1089

 {{WBRQuestion
|QuestionAuthor= {{MM}}
|ExamType=USMLE Step 3
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|MainCategory=Primary Care Office
|MainCategory=Primary Care Office
|SubCategory=Cardiovascular, Electrolytes
|Prompt=A 57-year-old male comes to your office for follow up.  He is a newly diagnosed lung cancer patient, and undergoes his first round of cisplatin.  He has insignificant past medical history.  On examination, his BP is 100/80 mmHg, irregular heart rate 50 beat per minute, temperature 37 C (98.6 F), respiratory rate is 17/minute.  His laboratory tests are: 

:Sodium 135 
:Potassium 6.8
:Chloride 108
:CO2 20
:BUN   35
:Creatinine 3.4
:Glucose 152
:Calcium 7.5

What would be the most likely finding on this patient’s EKG?
|Explanation=The patient has [[tumor lysis syndrome]]. The destruction of malignant cells by chemotherapeutic agents will lead to the release of intracellular contents, including [[potassium]], [[phosphorus]], and [[uric acid]] (from nucleic acids). This can result in [[hyperkalemia]], [[hyperuricemia]], and [[hyperphosphatemia]].

[[Hyperkalemia]] will produce significant EKG abnormalities, including peaked [[T waves]] and widened [[QRS complexes]]. The presence of [[bradycardia]] and irregular heart rate on physical examination are suggestive of the cardiac effects of [[hyperkalemia]], which can lead to life threatening [[arrhythmias]] if not managed properly.
|AnswerA=Shortened P-R segment
|AnswerAExp=Incorrect
[[Hyperkalemia]] does not cause shortened P-R segment.  The most common causes of shortened P-R segment include AV junctional rhythm, and [[Wolff-Parkinson-White syndrome]].
|AnswerB=Abnormally prominent U waves
|AnswerBExp=Incorrect
Abnormally prominent [[U waves]] are characteristically seen in severe [[hypokalaemia]].  U waves are prominent if > 1-2mm or 25% of the height of the [[T wave]].  The most common cause of prominent [[U waves]] is [[bradycardia]].
|AnswerC=Widened QRS complexes
|AnswerCExp=Correct
[[Hyperkalemia]] will produce significant EKG abnormalities, including [[peaked T waves]] and widened [[QRS complexes]]
|AnswerD=Flattened T waves
|AnswerDExp=Incorrect
Flattened [[T waves]] may indicate [[myocardial ischemia]], or [[hypokalemia]].
|AnswerE=Atrial fibrillation
|AnswerEExp=Incorrect
[[Hyperkalemia]] will produce significant EKG abnormalities, including [[peaked T waves]] and widened [[QRS complexes]].  [[Bradycardia]] and irregular heart rate on physical examination are suggestive of the cardiac effects of [[hyperkalemia]].
|EducationalObjectives=[[Hyperkalemia]] due to [[tumor lysis syndrome]] will produce significant EKG abnormalities, including peaked [[T waves]] and widened [[QRS complexes]].
|References=http://www.wikidoc.org/index.php/Tumor_lysis_syndrome
|RightAnswer=C
|WBRKeyword=[[Tumor lysis syndrome]]
|Approved=No
}}