Heart Failure and Electrical Conduction Changes During Trastuzumab Treatment

What happened, in summary

A 70-year-old woman had been diagnosed almost a year earlier with grade 2 HER2-positive, oestrogen-receptor-positive ductal breast cancer. She underwent lumpectomy, completed paclitaxel chemotherapy and was nearly 6 months into adjuvant trastuzumab. Routine echocardiograms had shown normal heart function, and she had no previous cardiovascular disease. She came to the emergency department with shortness of breath, cough and chest pain and tested positive for influenza A and H1N1, with lung changes concerning for secondary infection. Her ECG showed a new left bundle branch block. During intensive-care treatment for respiratory failure, she developed a prolonged QT interval, torsades de pointes and cardiac arrest, requiring cardioversion and antiarrhythmic treatment. After initial improvement, she developed recurrent chest pain, flash pulmonary oedema and left bundle branch block. Echocardiography showed a new reduction in left ventricular ejection fraction to 40%. Cardiac MRI and coronary catheterisation excluded myocarditis, infiltrative disease and obstructive coronary disease. The clinical team concluded that trastuzumab-induced cardiotoxicity was the most unifying diagnosis. Trastuzumab was suspended, and she started lisinopril and torsemide for systolic heart failure, with propranolol to reduce recurrent arrhythmia risk. She was discharged with a wearable defibrillator and close cardio-oncology follow-up. Four weeks later, her ejection fraction had recovered, and ECG showed normal rhythm without left bundle branch block or QT prolongation.