Survival to 30 days after PCI is reported, using life status data provided by the Office of National Statistics. Factors that determine survival after PCI are often not related to the treatments given and procedures performed, but are influenced by the patient’s general state of health and the condition with which they present. For example some patients admitted with a heart attack may die because of extensive damage to the heart and in spite of excellent care including PCI. Most heart attacks are associated with a mortality of about 5%. If a patient presents with a very big heart attack and is in a state of ‘cardiogenic shock’, then in spite of excellent care and a high quality PCI procedure there is about a 50% risk of death (see below)
Nevertheless outcome will also depend on the quality of care given and the timeliness of treatment. For this reason the analysis attempts to account for the differences in how sick patients are when they present, so that what remains of the variation in outcomes might be explained by the care received.