When I started in EMS, it was drilled into me. I had ten minutes on scene for trauma and 20 minutes for medicals. If I took longer, I had to explain why. If I did it quicker, all was good.
Evidence – based medicine wasn’t in our vocabulary then. We believed whole-heartedly in the golden hour of trauma. Times have changed. For trauma, studies have shown the golden hour has no scientific basis and that EMS time intervals have little to no effect on outcomes in trauma.
But what about medicals, and in particular what about ST-elevation myocardial infarctions(STEMIs)? The American Heart Association says that for patients having ST-Elevation MIs, who go to the cath lab to have their occlusions cleared, the systems goal should be a first medical contact–to-balloon time within 90 minutes.*
So 90 minutes is the goal? But is there anything magic about the 90 minute time? And how much better or worse does someone do if they get to the cath lab earlier or later than the 90 minutes?
A recent study in the British Medical Journal, Association of door-to-balloon time and mortality in patients admitted to hospital with ST elevation myocardial infarction: national cohort study., asks: Is mortality higher with successively longer times to treatment? And does mortality plateau after two or more hours of delay?
To answer this, the investigators analyzed the National Cardiovascular Data Bank, sponsored by the American College of Cardiology, which collects standardized data from 600 participating cath labs.
They hypothesized that any increase in door-to-balloon time would be associated with increased mortality and that this mortality risk would persist irrespective of the length of the delay in treatment.
For a study sample they looked at the records for 2005-2006, counting the patients presenting within 12 hours of symptom onset, who had lab and ECG evidence of STEMI, and who underwent the cath procedure.
They excluded transferred patients, patients who received fibrinolytic therapy first, patients under 18 or over 99, and patients at facilities that did less than 5 procedures a year.
They further excluded patients who had missing times, who had door-to-balloon times of less than 15 minutes (excluded due to possible incorrectly coded times) and excluded patients with door-to-balloon times of > 6 Hours (excluded because PCI was presumably not the primary reperfusion strategy). This left a total of 43,801 patients.
In the study the median door-to-balloon time was 83 Minutes. 57.9% were treated within 90 Minutes.
Women, nonwhites, older patients, and patients with comorbidities had proportionally longer door-to-balloon times. Patients with shorter door-to-balloon times were treated between 8AM and 4 PM, at urban hospitals, and had lower incidences of cardiogenic shock.
Mortality was 4.6%. Patients who died had a 14 minute longer median door-to-balloon time. Mortality was 2.8% for patients with 30 minutes, 9.8% for door-to-balloon times of 240. When patients with shock were excluded, longer door-to-balloon times continued to be associated with mortality.
When plotted out on a graph, there was a steadily rising minute by minute mortality curve.
The results are pretty easily explained: Patients with longer door-to-balloon times will experience longer periods of ischemia and more necrosis than patients with shorter time to treatment.
The clinical implications are also clear:
“Any minute of delay is associated with an increased risk of mortality.”
“There is no ‘floor’ to the mortality reduction that can be achieved by reducing time to treatment.”
Reducing D2B from 90 to 60 minutes could reduce mortality from 4.3% to 3.5%.
Rather than settling for 90 minutes as the standard, the standard should be “As soon as possible.”
As far as limitations, the study did not assess time from onset of symptoms to arrival at hospital, nor did the study assess door-to-balloon and subsequent mortality at 30 days, 1 year. It did not examine morbidity.
The bottom line:
Door-to-balloon time is associated with mortality.
Any delay in door-to-balloon time is associated with increased mortality.
This is an excellent study with a large patient sample. I cannot help but think if mortality can be improved by such a great percent, the morbity improvement must be even more substantial.
Here’s what I will try to do and what I will tell other medics to do:
Cast a wide net with your 12-lead. Get a clear 12-lead as soon as possible.
Once you recognize a STEMI, call the hospital right away so they have all the necessary equipment and personnel ready to go as you hit the doors.
Get going. Don’t dawdle on scene. Don’t wait for the patient’s daughter to arrive. Don’t let the patient take his time going about gathering his toothbrush and pajamas. Get on your way. Lights and sirens if needed for traffic, but drive safely.
Do serial 12-leads.
Don’t forget the Aspirin.
* 2007 Focused Update of the ACC/AHA 2004 Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction