What is the role of primary angioplasty (percutaneous coronary intervention) in the treatment of acute myocardial infarction (AMI) based on the PAMI (Primary Angioplasty in Myocardial Infarction) trials?

Primary Angioplasty in Acute Myocardial Infarction: The PAMI Trials

Primary percutaneous coronary intervention (PCI) is superior to thrombolytic therapy for acute myocardial infarction when performed by experienced operators within 90 minutes of first medical contact, reducing mortality, reinfarction, and stroke based on the PAMI trial series. 1

Key Findings from PAMI Trials

Short-Term Outcomes (30 Days)

The original PAMI trial demonstrated clear superiority of primary angioplasty over tissue plasminogen activator (t-PA):

• Combined death or nonfatal reinfarction occurred in 5.1% with primary angioplasty versus 12.0% with t-PA (p=0.02) 1
• Recurrent ischemia was significantly reduced with angioplasty compared to thrombolysis 1
• In high-risk patients (age >70 years, anterior infarction, or tachycardia), mortality was only 2% with primary angioplasty versus 10% with thrombolysis (p=0.01) 1
• The survival benefit was partly attributed to excessive cerebrovascular hemorrhage deaths in the thrombolytic group, though cardiac-related deaths were similar 1

Long-Term Outcomes (2-5 Years)

The durability of primary angioplasty's benefit was confirmed in extended follow-up:

• At 2 years, primary angioplasty resulted in less recurrent ischemia (36.4% vs 48%, p=0.026), lower reintervention rates (27.2% vs 46.5%, p<0.0001), and reduced hospital readmissions (58.5% vs 69.0%, p=0.035) 2
• The combined endpoint of death or reinfarction at 2 years was 14.9% for angioplasty versus 23% for t-PA (p=0.034) 2
• At 5-year follow-up, mortality was 13% with angioplasty versus 24% with streptokinase (relative risk 0.54,95% CI 0.36-0.87) 3
• Nonfatal reinfarction occurred in 6% versus 22% respectively (relative risk 0.27,95% CI 0.15-0.52) 3

Meta-Analysis Confirmation

A quantitative review of 10 randomized trials involving 2,606 patients confirmed these findings:

• 30-day mortality was 4.4% with primary angioplasty versus 6.5% with thrombolysis (34% reduction, OR 0.66,95% CI 0.46-0.94, p=0.02) 4
• Death or nonfatal reinfarction occurred in 7.2% versus 11.9% (OR 0.58,95% CI 0.44-0.76, p<0.001) 4
• Total stroke was reduced (0.7% vs 2.0%, p=0.007) and hemorrhagic stroke was markedly reduced (0.1% vs 1.1%, p<0.001) 4

Critical Implementation Requirements

Time-Dependent Benefit

Primary angioplasty performed within 2 hours of symptom onset showed a striking 53% relative reduction in 30-day mortality compared to procedures performed 2-6 hours later (4.3% vs 9.2%, p<0.04) 1

The current guideline-recommended time targets are:

• Door-to-device time ≤90 minutes for patients presenting directly to PCI-capable hospitals 1
• First medical contact-to-device time ≤90 minutes as a system goal 1
• Primary PCI should be performed within 120 minutes of STEMI diagnosis by experienced teams 1

Operator and Center Experience Requirements

Primary PCI should only be performed at hospitals with established interventional cardiology programs and experienced teams, including skilled supporting staff 1

Critical caveats about generalizability:

• Lower mortality rates are observed in centers with high volumes of PCI procedures 1
• The excellent PAMI trial results were attributed to: extensive operator experience, enthusiastic protocol commitment, institutional dedication, and capability to perform PCI within short time frames (≤60 minutes) 1
• Only 20% of U.S. hospitals have cardiac catheterization laboratories capable of performing emergency PCI, limiting applicability as primary therapy 1

Community Hospital Considerations

The PAMI-No SOS study addressed safety at hospitals without on-site cardiac surgery:

• Primary angioplasty at hospitals without cardiac surgery on-site achieved TIMI 3 flow in 96% of patients with 30-day mortality, reinfarction, and disabling stroke occurring in only 5% 5
• On-site primary angioplasty was faster than transfer (120 vs 187 minutes, p<0.0001) with similar or better outcomes 5
• However, institutions without PCI capability should not feel compelled to develop such services based on available data 1

Transfer Strategy Evidence

For patients presenting to non-PCI-capable hospitals, transfer for primary PCI is superior to in-hospital thrombolysis when transfer time is reasonable:

• The DANAMI-2 trial showed that transfer for primary PCI (median transport time <32 minutes, median time from community hospital arrival to PCI <2 hours) reduced the combined endpoint of death, reinfarction, and stroke from 14.2% to 8.5% (p<0.002) 1
• However, the CAPTIM study comparing pre-hospital fibrinolysis with primary PCI found no significant difference in combined endpoints (8.2% vs 6.2%), with 30-day mortality actually 1% higher in the primary PCI arm (3.8% vs 4.8%) 1

The key determinant is whether primary PCI can be performed within 90 minutes of first medical contact; if not, immediate fibrinolytic therapy should be considered 1

Stenting in Primary PCI

The STENT-PAMI trial evaluated routine stenting versus balloon angioplasty alone:

• The combined endpoint of death, reinfarction, disabling stroke, or target-vessel revascularization at 6 months was significantly reduced with stenting (12.4% vs 20.1%, p<0.01) 1
• This benefit was driven entirely by reduced target-vessel revascularization (7.5% vs 17%, p<0.0001) 1
• Concerning, there were more deaths in the stent group (4.2%) than balloon angioplasty alone (2.7%), though not statistically significant 1
• Routine stenting decreases need for target-vessel revascularization but is not associated with significant reductions in death or reinfarction rates 1

Economic Considerations

Primary angioplasty resulted in lower total medical charges compared to thrombolytic therapy ($16,090 vs $16,813, p=0.05) over 5 years of follow-up 3

This was achieved through:

• 30% fewer coronary angiograms 1
• 15% fewer coronary angioplasties 1
• 13% lower costs after 3 years 1
• Reduced hospital readmissions for ischemia and heart failure 3

Contradictory Evidence

One large community-based registry study (12,331 patients) found no mortality benefit with primary angioplasty versus thrombolytic therapy in real-world practice (5.5% vs 5.6%, p=0.93), with 30% fewer procedures and 13% lower costs in the thrombolytic group 6

This highlights the critical importance of operator experience and institutional commitment—benefits seen in controlled trials may not translate to all community settings without these elements 1, 6

Current Guideline Recommendations

Primary PCI is the recommended method of reperfusion when it can be performed in a timely fashion by experienced operators (Class I, Level of Evidence: A) 1

Specific indications:

• Primary PCI should be performed in patients with STEMI and ischemic symptoms <12 hours duration (Class I, Level of Evidence: A) 1
• Primary PCI is the preferred treatment for patients in cardiogenic shock 1
• For patients <75 years with STEMI who develop cardiogenic shock within 36 hours and can undergo revascularization within 18 hours of shock onset, primary PCI is recommended (Class I, Level of Evidence: A) 1