Door-to Balloon (D2B) time is a time measurement that starts with patient arrival to the emergency department (door) and ends when a catheter crosses a culprit lesion in the cardiac cath lab (balloon). The benefit of prompt primary percutaneous coronary intervention over thrombolytic therapy for acute ST elevation myocardial infarction is very well established. Because of this “time is muscle” strategy, the American College of Cardiology (ACC) launched a national Door to Balloon (D2B) initiative in November 2006. The purpose of this was to recommend a D2B time of no more than 90 minutes. Currently, there is quite a bit of effort put into this guideline by cardiology and emergency medicine, but are we measuring the right thing?
What are some proven strategies that do help reduce D2B time? 
- 365 surveyed hospitals
|STRATEGY||MEAN REDUCTION in D2B TIME|
|ED physician activated the cath lab||8.2 min|
|Single call activation system to activate the cath lab||13.8 min|
|Prehospital ECG activation of cath lab||15.4 min|
|Cath lab team is available within 20 min of being paged||19.3 min|
|Attending cardiologist always on site||14.6 min|
|Prompt data feedback between EM and Cardiology staff||8.6 min|
Does D2B time decrease significantly if multiple strategies are used? 
- 365 surveyed hospitals
- 0 strategies = avg D2B time 110 min
- 1 strategy = avg D2B time 100 min
- 2 strategies = avg D2B time 88 min
- 3 strategies = avg D2B time 88 min
- 4 strategies = avg D2B time 79 min
So if the above strategies are evidence based, have been shown to reduce D2B times, and “time is muscle,” then this should be standard of care, right? Currently, D2B times of 90 minutes or less (Class I recommendation) have become a performance measure and the focus of regional/national quality improvement initiatives. More importantly, does this measure reduce morbidity/mortality? Recently, in the September 2013 NEJM  a retrospective, observational study looked at this exact question.
How large was this NEJM study?
- 95,007 patients accounted for 96,738 admissions for primary PCI of STEMI
- 515 hospitals participating in the CathPCI Registry
- Conclusion: The study was very large
How were the D2B times in this study?
- 2005 – 2006 mean D2B time 83 minutes
- 2008 – 2009 mean D2B time 67 minutes
- There was an increase from 59.7% to 83.1% of patients having D2B times ≤90 minutes over the course of the study
- Conclusion: D2B time decreased over the course of the study
So does lower D2B correlate with decreased mortality?
- Overall, unadjusted mortality if D2B ≤90 minutes: 4.8% in first year of study
- Overall, unadjusted mortality if D2B >90 minutes: 4.7% in the last year of the study
- When these were risk adjusted, there was no statistical difference in mortality
- Conclusion: No difference in mortality despite improved D2B times
Take Home Message
So despite reductions in D2B times across the nation, we have not impacted 30 day in hospital mortality. Maybe what we should be measuring is symptom onset to balloon time?