I would strongly advise taking it right after 2nd year. While there is some clinical content on Step 1, it's all in the context of basic science underpinnings of clinical material. The content on shelf exams looks similar and there may be a modicum of overlap, but in reality shelf questions are testing a different knowledge base. I think the points lost to forgetting M1/M2 content would greatly overshadow any of the points you would pick up from studying for a few shelf exams.
To illustrate the difference between shelf/step 2ck and step 1 questions, here is an example of the difference:
Shelf Question:
A 38 year old female presents to the ED complaining of chest pain and shortness of breath. The chest pain began yesterday morning and subsided after 2 hours, but returned 2 hours ago and is 7/10 in severity and now accompanied by shortness of breath. She has no known past medical history and takes no medication other than OCPs. She smokes 0.5 packs per day with occasional alcohol use. Her father had an MI at age 52 and her mother had a stent placed at age 58. On exam her vitals signs are T 37.2 P 123 RR 32 BP 143/87 O2 94% on room air. She has a 1/6 systolic mumur best heard at the lower left sternal border. Her lungs were clear to auscultation. He abdomen is soft and nontender. Her lower extremities are warm and non-tender to palpation. All distal pulses 2+ bilaterally. An EKG shows sinus tachycardia with no ST elevation or depression. ABG shows pH of 7.48 and a pCO2 of 32 with a PO2 of 64. What is the best next step in management of this patient?
a) Check troponin
b) Check CK-MB
c) Order spiral CT
d) Give 2 liters of oxygen by nasal cannula
e) Start empiric warfarin
Step 1 Question:
A 38 year old female presents to the ED complaining of chest pain and shortness of breath. The chest pain began yesterday morning and subsided after 2 hours, but returned 2 hours ago and is 7/10 in severity and now accompanied by shortness of breath. She has no known past medical history and takes no medication other than OCPs. She smokes 0.5 packs per day with occasional alcohol use. Her father had an MI at age 52 and her mother had a stent placed at age 58. On exam her vitals signs are T 37.2 P 123 RR 32 BP 143/87 O2 94% on room air. She has a 1/6 systolic mumur best heard at the lower left sternal border. Her lungs were clear to auscultation. He abdomen is soft and nontender. Her lower extremities are warm and non-tender to palpation. All distal pulses 2+ bilaterally. An EKG shows sinus tachycardia with no ST elevation or depression. A right sided pulmonary embolism is visible on CT. Which of the following best describes the mechanism of the first line treatment for this condition?
a) Competitive inhibition of epoxide reductase
b) Binds to and inhibits Factors IX and X
c) Potentiates the activity of antithrombin III
d) Increases production of thromboxane A1
e) Antagonism of endothelin 1 and potentiation of bradykinin
So, the second question does expect you to know that heparin is the initial therapy for a PE, but the question gets more at the basic science of it. The answer choices are such that even if you can't decide btw warfarin and heparin, you can reason your way to the right answer. The Shelf question expects you to recognize likely PE from the vignette (vitals, history, risk factors, no MI by EKG, ABG) and order the appropriate diagnostic text.
