**Core Concept**
The patient's presentation of sudden onset unrelenting chest pain with loss of peripheral pulses suggests an acute cardiovascular event, particularly aortic dissection or pulmonary embolism. However, the clear lung fields and normal air entry help to rule out pulmonary embolism, pointing towards a more common cardiovascular emergency.

**Why the Correct Answer is Right**
Given the patient's history of smoking and sudden onset chest pain, aortic dissection is a likely diagnosis. Aortic dissection occurs when there is a tear in the inner layer of the aorta, allowing blood to flow between the layers of the aorta and potentially leading to aortic rupture. The loss of peripheral pulses suggests compromised blood flow to the lower extremities, which is consistent with aortic dissection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pulmonary embolism typically presents with abnormal lung fields and decreased air entry, which is not consistent with the patient's presentation.

**Option B:** This option is incorrect because myocardial infarction typically presents with electrocardiographic changes and elevated cardiac biomarkers, which are not mentioned in the patient's presentation.

**Option C:** This option is incorrect because cardiac tamponade typically presents with muffled heart sounds and elevated jugular venous distension, which are not consistent with the patient's presentation.

**Clinical Pearl / High-Yield Fact**
Aortic dissection often presents with sudden onset, severe chest pain radiating to the back, and loss of peripheral pulses. The "Three Ps" of aortic dissection are pain, pulselessness, and pallor.

**Correct Answer:** C. Aortic dissection.