Myocardial Infarction in the Perioperative Setting

Background:

In Sweden, over 800 000 patients undergo surgery each year. Worldwide, the number of surgical procedures yearly is over 310 million. Surgical care is an essential part of the advancement in treating disease, associated with increased life expectancy and improved quality of life. However, as surgical volume continues to grow, the number of patients who suffer postoperative complications will also increase.

More specifically the project aims to answer the following questions:

1. How common is perioperative acute myocardial infarction following non-cardiac surgery?
2. What are the preoperative and intraoperative risk factors for peroperative AMI?
3. Does perioperative AMI affect mortality and morbidity, Length of stay and days at home?
4. Is the risk of AMI affected by the type of hospital, region or calendar year of surgery?

Orbit - surgical planning system:

The study population was identified from 23 hospitals of all levels (university-, County- and district hospitals) in Sweden, that use the same software program to administer surgical procedures, between 1999 and 2015. The Orbit surgical planning system obligatory includes Swedish identity number, patient demographics, elective or non-elective status, date, type, extent and duration of anesthesia and surgery. Information of the American Society of Anesthesiologists (ASA) physical status classification was often available.

National Patient Register:

To obtain information on discharge dates, covariates and drug exposure, records of surgeries will be linked to the national patient register using the unique Swedish personal identification number assigned to all at birth or at immigration. The national registers have close to complete coverage. The Swedish cause of death registry includes the deaths of all Swedish citizens and residents with a national identity number; it is highly reliable with over 99% of all deaths reported. The Swedish Prescribed Drug Register became operational in July 2005 and contains data on all dispensed prescription of drugs in the Swedish population.

Swedeheart:

To identify all incident cases of myocardial infarctions, the surgical cohort will be linked to Swedeheart, a National Quality Registry containing data on all patients with acute myocardial infarction and all patients undergoing angiographic coronary intervention and heart surgery. The Swedeheart registry was developed in January 1995 and has a present coverage of 95% among incident cases of myocardial infarction treated at a cardiology department.

The National Board of Health and Welfare:

The National Board of Health and Welfare publishes statistics in the areas of health and medical care and social services, including data on acute myocardial infarction. The statistics include all persons aged 20 years and above who have had an acute myocardial infarction reported at the Hospital Discharge Register or the Cause of Death Register. Statistics are presented by year, sex, age and geographical area, information of incidence per 100 000 inhabitants is provided. These data were used to obtain information of expected cases of MI, for standardized incidence ratios (SIR) to be calculated.

Study Participants:

Patients aged 18 years or older undergoing elective or non-elective inpatients surgery between January 1, 2007 and December 31, 2014 were included. Exclusion criteria were surgeries in ambulatory care, cardiac surgery, obstetric- and minor surgical procedures. Patients were also excluded if the surgery was performed prior to 2007 or after 2014, and if a valid surgery code in Orbit - or if a corresponding surgery code in NPR - was lacking.