Keeping Score on STEMIs

How well does your system perform?

Among the handful of cases for which EMS has the potential to make a truly measureable difference in outcomes are the heart attacks known as ST elevation myocardial infarctions (STEMI). EMS has the potential to identify STEMI cases in the field and, working in close collaboration with receiving hospitals, set actions into motion that can significantly reduce the time from the onset of symptoms until flow in the patient’s obstructed coronary artery is restored.

 

How well does your EMS system and your community’s overall system of care for STEMI perform? How does that performance compare to other EMS systems and systems of STEMI care? Unless your EMS system and your community’s STEMI care system have well-designed measures of performance, your level of performance is going to very hard to quantify. Unless your EMS system and community are measuring performance in the same way as other EMS systems and communities, it’s going to be difficult to compare performance levels and identify best practices to learn from.

 

EMS and the emergency healthcare community faced a similar challenge when trying to quantify and compare levels of performance in cases of cardiac arrest. The issue was addressed by developing a standard way of categorizing cases and developing a standard way of measuring performance in those categories. The categorization and performance measurement process came to known as the àœtstein template.

 

As I began working with EMS providers and hospitals in Kent County, Mich., to quantify their performance in STEMI care, I looked for an àœtstein-style template for STEMI. Not finding one, we began to build one for use in Kent County, trying to take design cues from the way the àœtstein template for cardiac arrest works. If your system is trying to address the same questions, this account of our efforts in Kent County may provide some tips and ideas.

Scope

The first challenge in designing an àœtstein-style template for STEMI is defining the group of patients to be measured. In the case of cardiac arrest, the focus was on cases of presumed cardiac etiology rather than trying to measure all cases. The cardiac arrest template also has separate versions for out-of-hospital and in-hospital resuscitations.

 

For STEMI, it might have been a bit easier to limit the scope of the template to just those cases that are treated by EMS. That would have left out the cases in which public education efforts failed to convince patients to call 9-1-1 if they suspect a heart attack. It also would have been a bit easier to begin the template at the time when someone called 9-1-1 to respond to the suspected heart attack. That would have left out the often significant delays between the time that symptoms began and when 9-1-1 was called or when they arrived at a hospital or other type of healthcare facility or office. This was a difficult issue to resolve and will probably be revisited in future versions. For the first version, it was adjusted back and forth as the template was developed.

 

For patients who enter the healthcare system via a call to 9-1-1 and who are subsequently seen by EMS personnel, the inclusion criteria chosen in this first version were those for whom the crew obtained a 12-lead ECG. In future versions, this might be expanded to include all cases where a cardiac problem was suspected so that cases that should have had a 12-lead, but did not, would also be counted.

Diagnostic process measurement: True & false positives & negatives

The performance of a diagnostic process is commonly measured by counting true and false positives and negatives. In the context of STEMI, the following definitions would apply:

  • True Positives–Cases in which a STEMI diagnosis or field impression was declared and it was true–a STEMI was found in the cath lab.
  • True Negatives–Cases in which a STEMI diagnosis or field impression was not declared and it was true–a STEMI was not found in the cath lab.
  • False Positives–Cases in which a STEMI diagnosis or field impression was declared and it was false–a STEMI was not found in the cath lab.

The false positives should be kept to a reasonable minimum to reduce unnecessary expenses and hassle to the cath lab team. The false negatives represent a risk to patients and the system: There was a STEMI and the process failed to detect it.

 

EMS and hospitals deal with the same issues in trauma care. If the criteria are too stringent, there is a risk that seriously injured patients do not get care at a trauma center. When the criteria are too loose, there are too many cases that unnecessarily go the trauma center. Over time, EMS and hospitals should be working together to measure the true and false positives and negatives to find the right balance between the two.

 

EMS false negatives can be tricky to measure. You will need to look at hospital data for all STEMIs received via ambulance and find which ones did not have an EMS STEMI alert (or equivalent).

Criteria for cath lab activation

STEMIs are not the only types of cases that may be appropriate for cath lab activation. In fact, there are some cases for which the 12-lead ECG will have every indication that a myocardial infarction is taking place, but when the patient is examined in the cath lab, no obstructions are found in the coronary arteries. How should EMS and systems of care for STEMI deal with this and similar situations?

 

Is there consensus in the cardiology community regarding which cases, other than STEMI, should result in cath lab activation? Rokos and colleagues recently addressed this question in a paper entitled “Appropriate Cardiac Cath Lab Activation: Optimizing Electrocardiogram Interpretation and Clinical Decisionmaking for Acute ST-Elevation Myocardial Infarction” published in the December 2010 issue of the American Journal of Cardiology.1 They offer a set of criteria to use, adapted in Table 1 (below):

 

Table 1: Classification of Appropriate vs. Inappropriate Cath Lab Activation

Appropriate Cath Lab Activation = Ideal
  • Angiography and PPCI performed.
Appropriate Cath Lab Activation = Reasonable
  • Angiography without PPCI performed.

–Surgical revascularization indicated

–Coronary anatomy is not amenable to PPCI intervention (i.e., medical therapy)

–”Unavoidable angiography” per index ECG and/or clinical scenario as documented by the real-time clinicians (e.g., Tako-tsubo, myocarditis)

–No PPCI target-lesion identified but cardiac markers become elevated

 
  • Before angiography, true STEMI per index ECG dies suddenly
  • Angiography ± PPCI for ROSC following witnessed OHCA from a shockable rhythm. Some ROSC patients may deteriorate and die before angiography.
Inappropriate Cath Lab Activation = Goal
  • No angiography performed (cath lab activation cancelled by a physician)
     
  • Angiography without a PPCI target-lesion identified and normal cardiac markers:

–”Avoidable angiogram” based upon erroneous ECG interpretation

 
  • Advanced co-morbidities: Patient is not a PPCI candidate.
Classification based on retrospective and multidisciplinary peer review of all index clinical data.

Outcome & time interval measures

Measurement of the performance of a process of care for life-threatening medical conditions is not limited to getting the right diagnosis or getting care in the right setting. The àœtstein-style STEMI template should also measure mortality as the rate of survival to hospital discharge. Other helpful measures may include the length of stay. The length of stay can also be used as a surrogate for the cost of care. If you can get an average cost of care per additional hospital days after the initial cath lab day on STEMI cases, you can do value quotient calculations.2

 

Time interval performance is also commonly measured. Commonly used targets are 30 minutes from the time the 9-1-1 call was received to arrival in the emergency department. Thirty minutes is the target for ED arrival to cath lab arrival. Thirty minutes is also the target for cath lab arrival to balloon inflation or similar device activation to open the coronary obstruction. The total 9-1-1 activation to balloon time interval (E2B interval) target is 90 minutes.

 

As you try to monitor and improve the performance of your STEMI process of care over time, consider measuring your progress by watching:

  • E2B time interval & its three components;
  • False positive rate (by EMS and the ED);
  • False negative rate (by EMS and the ED);
  • Survival-to-hospital discharge rate;
  • Length of stay;
  • Cost of stay (based on average cost per additional hospital days for STEMI cases); and
  • STEMI process value quotient (survival rate / cost of stay).

For those interested in getting a copy of our STEMI template, please contact me at mic.gunderson@gmail.com. It’s a work in progress, but we’ll be happy to share what we have so far.

References

  1. Rokos IC, French WJ, Matu A, et al. Appropriate cardiac cath lab activation: optimizing electrocardiogram interpretation and clinical decisionmaking for acute ST-elevation myocardial infarction. Am Heart J. 2010;160:995—1003.e8. www.ahjonline.com/article/S0002-8703(10)00758-1/abstract.
  2. Gunderson MR. Value quotient–Looking at the combined effects of cost and quality. JEMS. March 2009. 34(3):36.
 

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