ABSTRACT: Rapid evaluation and reperfusion following ST-segment elevation myocardial infarction determines outcome and mortality rate.

CME OBJECTIVE: The reader will be aware of the rationale for rapid intervention following myocardial infarction and the best approach based on clinical findings and local therapeutic options.
Silvio E. Papapietro, MD, no conflicts of interest

Each year, an estimated 1.6 million Americans suffer from an acute coronary syndrome, sudden chest pain caused by a spectrum of clinical conditions ranging from unstable angina to non-Q-wave or Q-wave myocardial infarction (MI). Yet, a 2005 study found clinicians provided optimal treatment to less than half of patients with an acute coronary syndrome because existing guidelines were lengthy, complex, and difficult to implement in local settings (JAMA. 2005;293:349-357).

For the 500,000 people with an acute coronary syndrome who present to emergency departments with ST-segment elevation MI (STEMI) in any given year, rapid triage to restore coronary blood flow is crucial to prevent permanent myocardial damage. “In patients with STEMI, treatment delayed is effectively treatment denied,” says UAB Acute Chest Pain Center Director Silvio E. Papapietro, MD. “Shortening time to reperfusion in patients with STEMI limits myocardial damage and significantly reduces mortality. Up to a 50% reduction in mortality can be achieved if ischemic myocardium is reperfused within 30 to 45 minutes of symptom onset.”

Classic symptoms of STEMI include crushing chest pain or pressure, usually lasting more than 5 minutes, dyspnea, weakness, and nausea. Other symptoms include sweating and chest discomfort that may radiate to the arms, back, neck, jaw, or abdomen.

“Early angiography shows about 90% of patients with STEMI have a coronary thrombus, which often occludes the infarct artery, compared with thrombus formation in 35% to 75% of patients with non-STEMI or unstable angina and 1% of patients with stable angina. Therefore, it is critical to promptly reperfuse the occluded infarct-related artery through pharmacological or catheter-based interventions,” he says.

Prompt Protocols
The American College of Cardiology (ACC) and the American Heart Association (AHA) have revised practice guidelines to shorten the time from symptom onset to reperfusion (J Am Coll Cardiol. 2004;44:E1-E211). Updated guidelines advise physicians to complete a directed history and physical examination within 5 to 10 minutes so a rapid two-stage decision can be made: Is reperfusion indicated, and if so, which reperfusion strategy is most effective?

“The new guidelines are designed to improve triage and management decisions by first responders, emergency medical technicians, emergency department staff, and cardiologists,” says Papapietro, who, in December 2005 implemented UAB’s 3-level chest pain directive system for rapid patient management. Patients with STEMI are considered the most emergent, followed by those with non-STEMI/unstable angina, then persons experiencing chest pain of probable cardiac origin.

“Whenever STEMI is suspected, the goal is to perform a 12-lead electrocardiogram (ECG) within 10 minutes of patient presentation. ST-segment elevation identifies those most likely to benefit from reperfusion,” he says. “Every minute delayed is precious time wasted, because heart muscle is dying. We must try to reperfuse the artery and restore blood flow in a very short period of time.”

In emergency departments across the nation, physicians evaluating STEMI patients must rapidly decide whether to treat patients with immediate fibrinolysis or transfer them to a tertiary cardiac care center for percutaneous coronary intervention (PCI). Primary PCI achieves complete reperfusion in more than 90% of patients and is associated with less risk of stroke than fibrinolysis. However, only 20% of US hospitals have cardiac catheterization laboratories, and fewer provide PCI, an approach that requires significant cost and expertise.

“At UAB we emphasize two critical goals from the updated guidelines: no more than 30 minutes from ‘door to needle’ — ie, from emergency department arrival to fibrinolysis — and no more than 90 minutes from arrival to PCI — the time from ‘door to balloon,’” he says. “Each 30-minute delay from symptom onset to balloon inflation increases 1-year mortality by 7.5%. Waiting 6 hours for enzyme levels, such as troponin and creatinine kinase, may be useful when chest pain patients present with atypical ECG findings, but the delay is unacceptable for patients with ST-segment elevation, when a delay of 3 to 5 hours leads to significant, irreversible myocardial damage.”

A 2005 review of the National Registry of Myocardial Infarction found average door-to-balloon times for Americans transferred for primary PCI was close to 3 hours, far beyond proposed limits (Circulation. 2005;111:761-767). PCI centers with rapid-management chest pain protocols, such as those at UAB, can provide 90-minute door-to-balloon times if patients can be transferred within 1 hour. But across the rural South, where transport times to the closest hospital with PCI capability may extend far beyond the guidelines’ 60 minute limit, initial fibrinolysis may be a better strategy.

“Fibrinolytic therapy is effective in up to 75% of patients, and it is most beneficial when given within 3 hours of symptom onset, when fresh clots are more likely to dissolve,” he says. “Tissue plasminogen activator requires an infusion, whereas tenecteplase and the recombinant plasminogen activator reteplase can be administered in bolus form; all are equally effective, although there are differences in fibrin selectivity and drug half-life.”

Relative Risks
Fibrinolytic therapy must be given within 12 hours of symptom onset to benefit functional outcomes or mortality. Because of the serious risk of hemorrhage, fibrinolysis is contraindicated when patients have any prior known structural cerebral vascular lesion or intracranial hemorrhage, suspected aortic dissection, active bleeding or bleeding diathesis, recent closed head trauma, or severe uncontrolled hypertension.

“Patients on anticoagulants with no other contraindications may need to stop these medications and receive fibrinolysis,” Papapietro says. “When transport times surpass guideline recommendations and patients are ineligible for fibrinolysis, they should be transferred for PCI as quickly as possible.”

PCI may have limited benefit over fibrinolysis if performed more than 3 hours after symptoms begin, yet it remains the preferred route for certain high-risk patients such as those older than 75 years or those who cannot receive fibrinolytics. Patients who are transferred to an acute cardiac care facility and determined ineligible for PCI due to coronary anatomy, mechanical MI complications, or other issues may still benefit from hemodynamic support with an intraaortic balloon pump or coronary artery bypass grafting.

Combining Therapies
A recent review of reperfusion strategies suggests STEMI patients who receive pharmacologic fibrinolysis may benefit from transfer to a PCI-capable facility if the therapy fails to restore blood flow to infarcted myocardium. In addition, most patients with STEMI who undergo successful reperfusion with fibrinolytics will benefit from subsequent coronary angiography and PCI if there is significant residual stenosis in the infarcted artery that may lead to recurrent ischemia.

“The most important message from the revised guidelines is to realize that simplified, evidence-based protocols are in place for clinicians at every level to streamline reperfusion and improve outcomes for patients with STEMI,” Papapietro concludes.

For more information
Dr. Silvio Papapietro
1.800.UAB.MIST
mist@uabmc.edu