When the heart rate doesn't decrease after a nuclear stress test, this may be caused by complications such as allergic reaction to radioactive dye, abnormal heart rhythms due to medication, or a heart attack, according to the Mayo Clinic. Stress test complications, especially heart attacks, are rare.
It is not unusual for doctors to detect irregular heart rhythms, known as abnormal ventricular beats, during a stress test. While the heart rate is high during exercise, these irregular beats don't normally pose any substantial risk to the patient. Studies show that a small percentage of people whose hearts refused to completely decrease after exercise suffered a fatal heart attack within five years, as reported by Harvard Medical School. Likewise, a study of 200 heart attack survivors who also took stress tests found that patients who had slow heart rate recovery times were four times more likely to have a fatal heart attack. Doctors can continue monitoring high-risk patients with abnormal ventricular beats by treating high blood pressure, high cholesterol, obesity and smoking addiction.
Stress tests are commonly used to diagnose conditions such as coronary heart disease and heart arrhythmias, according to Mayo Clinic. Doctors may also use the test to monitor the progress of ongoing treatments for heart conditions, and to determine if surgery is needed.