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The length of time between a diagnosis of ST-segment elevation myocardial infarction (STEMI) and cath lab activation is a strong predictor of door-to-balloon time (D2B), according to a study published online September 4, 2012, ahead of print in Circulation: Cardiovascular Quality and Outcomes. Moreover, successfully achieving a ‘door-to-activation’ time of 20 minutes or less appears imperative to maintaining D2B times within existing guidelines.

For the study, James M. McCabe, MD, of Brigham and Women’s Hospital (Boston, MA), and colleagues looked at registry data from 347 consecutive patients diagnosed with STEMI in the emergency departments of 2 San Francisco, CA, area hospitals between October 2008 and April 2011. Investigators broke down door-to-balloon time into the following categories:

• Door-to-activation time (emergency department)
• Activation-to-lab time (emergency department)
• Lab-to-balloon time (cath lab)

Median D2B time was 78 minutes, while the median door-to-activation time was 19 minutes. Door-to-activation time was substantially associated with D2B time (r = 0.97), but D2B time was not correlated with activation-to-laboratory time (r = 0.08) or laboratory-to-balloon time (r = 0.47). Additionally, door-to-activation time accounted for 93% of the variability in D2B time.

A total of 89% of patients who had door-to-activation times of 20 minutes or less achieved a guideline-recommended D2B time of 90 minutes or less, while only 28% of patients with a door-to-activation time of more than 20 minutes did so (P < 0.001). Door-to-activation time had no effect on activation-to-balloon time (P = 0.118).

Multivariate analysis found that typical angina symptoms and ambulance prehospital ECG use were associated with 33% and 61% shorter door-to-activation times, respectively. On the other hand, use of CT scans in the emergency department and Asian race were associated with 245% and 56% longer door-to-activation times, respectively. However, after sensitivity analyses excluded Asian patients requiring a translator, there was no longer an association. Independent predictors of substantial changes in D2B times were prehospital ECG use (18% shorter; P = 0.002) and CT scan use in the emergency department (75% longer; P < 0.001).

All-comers Registry Provides Real World Data

“Our findings are unique because large registry studies do not collect the time and motion data needed to parse out the components of door-to-balloon time for more detailed analysis,” the authors write. “In addition, large registries, such as the Centers for Medicare and Medicaid services’ STEMI database, allow for broad exclusion of patients or rely on hospital discharge diagnosis codes and procedural codes in the catheterization laboratory for classification of a STEMI rather than the diagnosis established in the ED.”

In a telephone interview with TCTMD, Jeffrey W. Moses, MD, of Columbia University Medical Center/Weill Cornell Medical Center (New York, NY), said the all-comers study paints a more real-world picture of what actually happens in the emergency department. “The emergency room MI question is a lot messier than it looks from some registries that exclude shock or intubation, so I like the fact that this gives a much broader picture of the diversity of issues that come up in the emergency room and impact long activation times,” he said.

Despite adoption of other best practice measures, Dr. McCabe and colleagues write that “door-to-activation times remain the key determinant of door-to-balloon times.” Rather than focus on out-of-hospital care and STEMI receiving-center networks, “continued emphasis on the triage and diagnostic period in the [emergency department] is paramount to establishing consistently lower time to reperfusion therapy,” they say.

While the “magnitude of change in door-to-balloon time seen with prehospital ECG use in our registry is highly consistent with other larger registries’ data,” there is little information regarding the use of CT scans before primary PCI, the investigators report. In most cases, CT scans were used to exclude other diagnoses and “rarely altered the course of care,” they write.

The Case for Prehospital ECGs

In a telephone interview with TCTMD, Dr. McCabe said the data suggest that “the process of determining who has a STEMI and who doesn’t is not always as black and white as has been previously portrayed, and it can be very challenging for first responders and people in the emergency room setting to determine who has a real culprit occlusion and STEMI and who is instead just at high risk, or who has chest plain complaints that don’t ultimately pan out to require emergent angioplasty.”

Because D2B times are generally “quite good,” he continued, the overall process “works extremely well.” What deserves the most attention going forward, he added, is dedicating resources ‘upstream’ to the triage and diagnosis time interval rather than to patients who are already known to have a STEMI.

Breaking down the overall process into small sections is key to shortening D2B times even more, according to J. Lee Garvey, MD, of the Carolinas Medical Center (Charlotte, NC). “I think that hospitals would benefit by building out a detailed map of their process and then using that to study where they have opportunities for improvement,” he told TCTMD in a telephone interview. “The more you get into the detail of the process that you’re working with, the more opportunity you’ll have to identify spots that are ripe for improvement . . . and to shave small segments off each process that can add up to many minutes overall.”

Because of the small nature of the study, Dr. Moses said the results should be confirmed in a broader group. But the main message reinforced by this dataset, he concluded, is that “prehospital ECGs are important and should be the standard of care,” noting that there have been difficulties enforcing them uniformly.

Study Details

Patients with door-to-activation times longer than 20 minutes tended to be slightly younger, were more likely to undergo a CT scan in the emergency department, and were less likely to be brought by ambulance, have a prehospital ECG, and have a culprit lesion.

Source:

McCabe JM, Armstrong EJ, Hoffmayer KS, et al. Impact of door-to-activation time on door-to-balloon time in primary percutaneous coronary intervention for ST-segment elevation myocardial infarction. Circ Cardiovasc Qual Outcomes. 2012;Epub ahead of print.

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