Sunder, a young male was diagnosed as suffering from acute myeloid leukemia. He was started on induction chemotherapy with a doxorubicin-based regimen. Induction regimen was successful. Two months later, he presents to OPD with swelling of both the feet and breathlessness on climbing the stairs. He also complains he had to wake up many times because of breathlessness. Which of the following is most likely responsible for this patient’s symptoms?

**Core Concept**
Acute myeloid leukemia (AML) treatment with doxorubicin-based chemotherapy can lead to cardiotoxicity, characterized by left ventricular dysfunction and subsequent heart failure.

**Why the Correct Answer is Right**
The patient's symptoms of breathlessness on exertion, nocturnal dyspnea, and bilateral lower limb edema suggest congestive heart failure. Doxorubicin is an anthracycline antibiotic that can cause cardiotoxicity by generating free radicals, leading to lipid peroxidation and mitochondrial damage in cardiac myocytes. This results in left ventricular dysfunction and eventually heart failure.

**Why Each Wrong Option is Incorrect**
* **Option A:** Pulmonary embolism would cause sudden onset of breathlessness, often with chest pain and hemoptysis, which is not the case in this patient.
* **Option B:** Acute respiratory distress syndrome (ARDS) would present with hypoxemic respiratory failure, often in the context of sepsis or severe infection, which is not mentioned in the patient's history.
* **Option C:** Acute coronary syndrome (ACS) would cause chest pain, ST-segment elevation on ECG, and elevation of cardiac enzymes, which are not mentioned in the patient's symptoms.

**Clinical Pearl / High-Yield Fact**
Doxorubicin-induced cardiotoxicity is a well-known side effect of anthracycline chemotherapy, and patients should be closely monitored for signs of cardiac dysfunction, including echocardiography and cardiac biomarkers.

**Correct Answer:** C. Doxorubicin-induced cardiotoxicity leading to congestive heart failure.

✓ Correct Answer: C. Dilated cardiomyopathy