Its vey unfortunate to hear your daughter story. There are two issues here. 1.Your daughter may have what we call postpartum cardiomyopathy. But with fourth pregnancy and with previous normal deliveries(which I presume, may be a remote cause. Or she had Myocarditis and then became pregnant. So if I had more information about her past medical and conception history ,I may be able to answer your question with more authority. 2.Azitromycin is a drug which belong to group called macrolides. All Macrolides including azithromycin can predispose to irregular fast heat beat which we call arrhythmias, especially in group of predisposed patients. In 2013,the FDA issued a warning as well regarding azithromycin can cause abnormal changes in the electrical activity of heart that may lead to fatal irregular heart rhythm. The warning indicated that people with pre-existent conditions are at particular risk, such as those with QT interval prolongation, low blood levels of potassium or magnesium, a slower than normal heart rate, or those who use of certain drugs used to treat abnormal heart rhythms, or arrhythmias.