What factors make myocardial infarction worse?

Many. The location is a major factor: left main blockage is most likely to be fatal. Proximal left anterior descending is also often fatal. Patient factors such as on-going tobacco use, uncontrolled hypertension, diabetes, anemia, pre-existing heart or kidney failure and advanced age all raise the risk.
Myocardiainfarction. Arriving to the hospital later rather than earlier can decrease the chance of early intervention to open the artery that saves heart muscle to be effective.