A 58-year-old man with no prior cardiac history presents to the emergency department with symptoms of retrosternal chest pain starting at rest and lasting 30 minutes. The pain radiates to the left arm and is associated with diaphoresis and dyspnea.On physical examination, his blood pressure is 150/90 mm Hg, pulse is 100/min, the heart sounds are normal, and the lungs are clear to auscultation. Which of the following is the next most appropriate investigation?

## **Core Concept**
The patient's presentation of retrosternal chest pain radiating to the left arm, associated with diaphoresis and dyspnea, is highly suggestive of **acute coronary syndrome (ACS)**, specifically **myocardial infarction (MI)**. The immediate goal is to confirm the diagnosis and assess the severity of the condition.

## **Why the Correct Answer is Right**
The most appropriate next investigation in a patient with suspected acute coronary syndrome (ACS) is an **electrocardiogram (ECG)**. An ECG is crucial because it:
- Provides immediate information about the heart's electrical activity.
- Helps diagnose **ST-elevation myocardial infarction (STEMI)**, **non-ST-elevation myocardial infarction (NSTEMI)**, or **unstable angina**.
- Guides immediate management, including the decision for **thrombolysis** or **primary percutaneous coronary intervention (PCI)** in the case of STEMI.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While a **chest X-ray** can provide useful information about the lungs and cardiac silhouette, it is not the immediate next step in diagnosing ACS.
- **Option B:** A **complete blood count (CBC)** may provide supportive information but is not diagnostic for ACS.
- **Option C:** **Troponin levels** are critical for diagnosing MI but take time to result and should not delay immediate ECG evaluation.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that in the setting of ACS, **time is muscle**. Early diagnosis and intervention significantly impact outcomes. The American College of Cardiology (ACC) and American Heart Association (AHA) guidelines emphasize the importance of rapid ECG interpretation in ACS.

## **Correct Answer:** .

✓ Correct Answer: D. ECG