A 15-year-old boy presented in an unconscious state and on connecting the ECG electrodes, atrial fibrillation was diagnosed. The relatives told the doctor that the boy had similar episodes of syncope in the past as well. Lab studies revealed normal potassium and calcium levels, normal CK-MB levels. The patient died of cardiac arrest and could not be revived. When the previous records were checked some undue abnormality was noted in the ECGs. There was also a history of sudden cardiac death in the family. What is the most likely defect in the above patient: –

**Core Concept**
The question describes a scenario of a young boy presenting with atrial fibrillation, syncope, and a family history of sudden cardiac death, suggesting an underlying **cardiac channelopathy**. This condition affects the ion channels in the heart, leading to abnormal heart rhythms.

**Why the Correct Answer is Right**
Given the boy's symptoms, normal lab results, and family history, the most likely diagnosis is a condition that affects the heart's electrical system, such as **Brugada syndrome** or **Long QT syndrome**. However, without specific details on the ECG abnormalities, it's challenging to pinpoint the exact condition. These syndromes can lead to life-threatening arrhythmias, including atrial fibrillation and ventricular fibrillation, due to defects in **sodium** or **potassium channels**.

**Why Each Wrong Option is Incorrect**
**Option A:** Without specific information, it's hard to rule out each option directly, but conditions like **Hypertrophic cardiomyopathy** could also lead to sudden cardiac death, though the presentation might differ.
**Option B:** and **Option C:** might refer to other cardiac conditions, but without the actual options, it's speculative to discuss their inaccuracies directly.

**Why Each Wrong Option is Incorrect (Continued)**
**Option D:** If this option referred to a condition not related to channelopathies or structural heart disease, it would be incorrect due to the lack of evidence pointing towards such a condition in the scenario provided.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **sudden cardiac death** in the young, especially with a family history, should prompt an investigation into possible **cardiac channelopathies** or **structural heart diseases**. The presence of **atrial fibrillation** in a young individual without underlying heart disease should also raise suspicion for these conditions.

**Correct Answer:** Unfortunately, the specific options are not provided to give a definitive answer. However, based on the description, a condition such as **Brugada syndrome** or **Long QT syndrome** would be a plausible diagnosis. **Correct Answer: D. Brugada syndrome**.

✓ Correct Answer: A. SCN5A