The results of new research has shown that patients given high doses of beta blocker drugs following non-cardiac surgery were more likely to have a stroke or die. However they were less likely to suffer a heart attack.
Beta blockers are drugs which decrease the force and rate of the heart's contractions, which lowers blood pressure and reduces the heart's demand for oxygen.
Worldwide, about 100 million adults undergo non-cardiac surgery every year to treat a range of conditions which affects how well the heart functions such as atherosclerotic disease (hardening of the arteries), coronary artery bypass graft (CABG) surgery or angioplasty, atrial fibrillation, a type of irregular heartbeat, hypotension, low blood pressure that requires medical treatment and bardycardia, a low heart rate that needs medical treatment.
One million of such patients will suffer major complications associated with the surgery which results in an increase in heart-rate, blood pressure, and fatty acid concentrations, which in turn increases the oxygen demands made on the heart.
Beta blockers are thought to help reduce such effects and prevent cardiovascular complications, however previous research on this theory has produced mixed results.
An international trial led by Canadian researchers involving 8,351 patients set out to test the theory.
All the patients either had or were at risk of atherosclerotic disease and were about to undergo non-cardiac surgery; 4,174 patients were randomly chosen to receive a beta blocker metoprolol succinate and 4,177 were given a placebo.
Dr P. J. Devereaux, from McMaster University in Hamilton and his colleagues conducted the POISE (PeriOperative ISchemic Evaluation) study to investigate the effects of peri-operative beta blockers.
The study was done in 190 hospitals across 23 countries including the UK, Australia, Canada, New Zealand, Argentina, Hong Kong, Malaysia, Singapore, Brazil, China, Colombia, Ecuador, Finland, Hungary, India, Mexico, Norway, Peru, Spain, Sweden, Thailand, Cuba, El Salvador.
The researchers found that 244 patients in the beta blocker group experienced non-fatal heart attack, or non-fatal cardiac arrest or cardiovascular death as against 290 in the placebo group.
However there were more deaths in the beta blocker group (129) than the placebo group (97) and more patients had a stroke in the beta blocker group (41) than the placebo group (19).
The researchers say their results highlights the risk of assuming that beta blockers offer benefits without the risk of substantial harm and in view of the large numbers of people undergoing such surgery and the high risk of cardiovascular complications, more large trials are needed urgently.
They say most patients are unlikely to accept the risk associated with a perioperative beta blocker regimen.
Experts say the POISE study clearly shows that high dose beta blocker therapy in the perioperative period is associated with greater risk than benefit but they suggest that a low dose beta blocker regimen has in other research established a beneficial effect on post operative outcome without an increased incidence of stroke.
The study is reported in the current issue of The Lancet medial journal.