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Upstream activation of the catheterization laboratory by emergency medical services (EMS) technicians and emergency department physicians for patients suspected of suffering an ST-segment elevation myocardial infarction (STEMI) is appropriate most of the time, according to data from a North Carolina STEMI network. But the authors of the study, published online December 6, 2011, ahead of print in Circulation, say improvements are still needed to reduce inappropriate decisions and avoid overburdening cath lab personnel.

Investigators led by J. Lee Garvey, MD, of the Carolinas Medical Center (Charlotte, NC), analyzed activation of the cath lab and management of 3,973 patients with suspected STEMI at 14 primary PCI hospitals participating in the Reperfusion of Acute Myocardial Infarction in North Carolina Emergency Departments (RACE) initiative from December 2008 through December 2009. The cohort included patients presenting directly to the PCI center and those transferred from 85 non-PCI hospitals.

ECG Interpretation Key

Activation of the cath lab was based primarily on paramedic or emergency physician interpretation of patient ECGs. Activation was considered to be appropriate if catheterization was performed, or was cancelled due to a change in patient status, such as resolution of symptoms or ST elevation, or death. Activation was considered inappropriate if catheterization was cancelled due to ECG reinterpretation or if the patient was deemed not to be a candidate for cardiac catheterization.

Overall, the cath lab was appropriately activated for 85% of patients. PCI was performed in 76.9% of these cases and in 65% of total activations. Surgical revascularization was performed in 3.5% of all activations. In terms of outcomes, 10.8% of those who underwent angiography were found not to have occlusive CAD.

Among instances of inappropriate cath lab activation, the most common reason for cancellation was reinterpretation of EMS ECG readings (72%; 6% of all activations). Most of the other cancellations were because patients were deemed inappropriate for cath lab management (28%; 4.3% of all activations). For example, such patients were too old (> 90 years) or had active bleeding, a known terminal illness, or severe comorbidities.

STEMI system activation was fairly evenly distributed among EMS agencies (28.9%), non-PCI hospitals (38.9%), and PCI centers (32%). About two-thirds of patients were transported to their initial hospital by EMS, and EMS cath lab activation after EMS transport was the most common combination of system activation and mode of arrival (28.9%).

Appropriateness Influenced by Who Makes the Call

The likelihood of appropriate vs. inappropriate activation varied according to the combination of who triggered it and how patients came to the hospital. Using EMS activation plus EMS transportation to the hospital as the reference, non-PCI center activation with either EMS or walk-in arrival was about 2 times more likely to be appropriate and PCI center activation with either mode of arrival was more than 3 times more likely to be appropriate (table 1).

Table 1. Appropriateness of Cath Lab Activation by Mode of Activation, Presentation

^a All P < 0.01.

In addition, a multivariable model showed that Caucasians were more likely to receive appropriate activation than other ethnic groups (adjusted OR 2.4; 95% CI 1.9-3.0).

In a telephone interview with TCTMD, Harlan M. Krumholz, MD, SM, of the Yale School of Medicine (New Haven, CT), said the study data provide a good starting point for a broader assessment of STEMI system activation.

Determining an acceptable level of activation is a matter of balancing sensitivity and specificity, Dr. Krumholz observed. “You have to accept that you’re not going to have perfect [accuracy in] ascertainment of ST elevation,” he said. “[If you did,] you’d likely miss some cases. The question is, how do you minimize false-positives?”

Overactivation Hard on the Cath Lab

Overactivation of the STEMI system is a potential downside of efforts to reduce door-to-balloon times that should not be overlooked, Dr. Krumholz noted. “Sometimes people think, ‘Well, it doesn’t hurt the patient, and if it turns out to be unnecessary, at least cardiologists are there to provide a consultation.’ They don’t realize that [activation] requires people’s time and effort, and it can be exhausting, especially in the middle of the night.”

It is reassuring to see a relatively low rate of inappropriate activations in a state (North Carolina) that emphasizes transfer for primary PCI, Dr. Krumholz said, but the fact that most instances involved ECG interpretation suggests that the rate could still be reduced without jeopardizing treatment of true STEMI patients. “Our challenge is to figure out how we can drive down the rate by improving ECG interpretation or getting second opinions quickly when [emergency personnel] are trying to figure out whether or not to activate the system.”

One approach is to look for patterns of ECG misinterpretation and focus on correcting them with better training, Dr. Krumholz suggested. Another useful step would be to provide a way for EMS technicians or emergency doctors who are uncertain about an ECG reading to get a second opinion quickly, perhaps by taking a picture of the ECG with a mobile phone and sending it to a cardiologist.

A Team Responsibility

Unfortunately, many STEMI systems do not know their false-positive activation rate, Dr. Krumholz said. And too often they do not work together as a team. The key is to have EMS personnel, emergency department physicians, and cardiologists sit down periodically to review activation decisions and provide feedback. “If there are members of the team who could do better, it’s everyone’s responsibility to make sure that they get better,” Dr.Krumholz commented.

“This is the kind of study that every [system] should be doing,” he continued, “because no doubt there are some places where the rate [of inappropriate activation] is much higher [than in North Carolina]. The bottom line is if you don’t have a low false-positive rate, the system is not sustainable. If you exhaust your team, eventually it will affect patient outcomes. [Cath lab] people will get frustrated, and their overall performance will deteriorate because they won’t trust that people are making the right decisions.”

 

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Source:
Garvey JL, Monk L, Granger CB, et al. Rates of cardiac catheterization cancelation for ST elevation myocardial infarction after activation by emergency medical services or emergency physicians: Results from the North Carolina Catheterization Laboratory Activation Registry (CLAR). Circulation. 2011;Epub ahead of print.

 

 

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