Coronary heart disease (CHD) remains a significant cause of death, accounting for 1 in 10 deaths worldwide and 1 in 7 deaths in the United States, even though medical advances have reduced mortality rates from CHD in developed nations. Acute myocardial infarction (AMI), which leads to myocardial injury and necrosis, is a common initial presentation of CHD and may recur over the course of the disease.1
Cardiac ischemia may occur via many mechanisms, such as coronary thrombosis due to atherosclerotic plaque rupture, endothelial dysfunction, hypotension, and coronary embolism. Complications of AMI, particularly ST-segment elevation MI (STEMI), include cardiogenic shock, ventricular fibrillation, and heart failure, which can be serious and potentially fatal.1
The management of AMI aims to reduce myocardial ischemia and subsequent morbidity and mortality. International guidelines recommend improving myocardial perfusion or decreasing the cardiac workload using a combination of therapies known as MONA: morphine, oxygen, nitrates, and aspirin.1,2
Oxygen for AMI: Current Practice
Oxygen, via face mask or nasal cannula, is often administered to patients with suspected AMI in an attempt to increase myocardial oxygenation and decrease infarct size.1
According to Dion Stub, MBBS, PhD, from The Alfred Hospital in Melbourne, Australia, treating AMI with oxygen has its roots in practices dating back more than a century. “Oxygen was first administered to patients with suspected ACS in 1900, and to this day is given to [more than] 90% of patients with cardiac emergencies. Whilst other medical practices from the early 1900s — such as starvation diets for aneurysms and mercury as a treatment for infections — were quickly discarded, the routine use of oxygen in cardiac emergencies has remained a pervasive component of first medical response,” Dr Stub told Cardiology Advisor.
While treating AMI with oxygen makes sense from a physiologic standpoint, no studies have convincingly demonstrated that oxygen therapy improves outcomes in AMI.1 In addition, recent data suggest that this practice may even be harmful. Oxygen therapy may decrease cardiac blood flow and perfusion, reduce cardiac output, and increase coronary vascular resistance.1,3,4 If myocardial reperfusion is achieved, oxygen may have a paradoxical effect by inducing reperfusion injury through production of oxygen free radicals.5
In 2010, Juan Cabello, MD, PhD, from Hospital General Universitario de Alicante in Spain, and colleagues published a review of the literature for oxygen therapy in AMI conducted to determine whether this practice is helpful or harmful. They found that robust evidence to support the use of oxygen to treat AMI was lacking. 6 A 2013 update of the 2010 review included data from 1 new trial, and results were similarly inconclusive.7