**Core Concept:**
The clinical presentation of an young boy with history of breathlessness on exertion, auscultation findings, and ECG interpretation are important in assessing and diagnosing patients with heart conditions. The auscultation findings (ejection systolic murmur in the left 2nd intercostal space, normal S1, wide and fixed split S2) suggest pulmonary hypertension, which can be caused by various conditions such as right-to-left shunts, congenital heart diseases, or hypertension. ECG is a useful tool to assess cardiac electrical activity and wall motion.

**Why the Correct Answer is Right:**
The ECG findings in this case would be consistent with pulmonary hypertension and right heart strain. Option D ("Right ventricular hypertrophy") is the most likely finding in the ECG report, as it reflects the adaptation of the right ventricle to the increased workload due to elevated pulmonary artery pressure. Right ventricular hypertrophy can be seen on ECG as increased R wave amplitude in leads II, III, and aVF.

**Why Each Wrong Option is Incorrect:**
Option A ("Left ventricular hypertrophy") is incorrect because pulmonary hypertension primarily affects the right side of the heart, not the left side. Option B ("Atrial arrhythmia") is incorrect because the ECG changes would be different for atrial arrhythmias, which are not the main concern in this case. Option C ("Right bundle branch block") is incorrect because it would be expected in cases of severe right ventricular hypertrophy or heart failure, not pulmonary hypertension.

**Why the Correct Answer is Right:**
The correct answer, D ("Right ventricular hypertrophy"), is right because it is a common ECG finding in pulmonary hypertension and right heart strain, which is the most probable diagnosis based on the clinical presentation and auscultation findings.

**Clinical Pearl:**
In cases of pulmonary hypertension, the ECG findings should raise suspicion for right heart strain, leading to further evaluation and diagnosis confirmation. If these findings are present in a patient with breathlessness on exertion and auscultation findings, this can help guide further diagnostic tests and management strategies, such as echocardiography and right heart catheterization.