How to diagnose and manage a patient with a pacemaker (permanent artificial cardiac pacemaker) presenting with symptoms suggestive of ST-Elevation Myocardial Infarction (STEMI), considering the use of Scarbossa criteria (ECG interpretation criteria)?

Diagnosing STEMI in Patients with Pacemakers Using Scarbossa Criteria

In patients with pacemakers presenting with symptoms suggestive of STEMI, proceed directly to emergency coronary angiography with a view to primary PCI without relying on ECG criteria alone, as ventricular pacing prevents reliable interpretation of ST-segment changes. 1

Immediate Diagnostic Approach

Primary Strategy: Bypass ECG Interpretation

• Ventricular pacing fundamentally prevents interpretation of ST-segment changes, making traditional STEMI criteria (including Scarbossa criteria) unreliable for diagnosis. 1
• Emergency coronary angiography is required to confirm diagnosis and initiate therapy when persistent ischemic symptoms occur in the presence of ventricular paced rhythm. 1
• Do not delay invasive investigation while attempting ECG interpretation in pacemaker patients with ongoing chest pain or other ischemic symptoms. 1

Consider Pacemaker Reprogramming (Only if Non-Dependent)

• Reprogramming the pacemaker to allow evaluation of ECG changes during intrinsic heart rhythm may be considered in patients known NOT to be pacemaker-dependent. 1
• This should never delay invasive investigation—proceed to the catheterization laboratory while attempting reprogramming if feasible. 1
• Most patients requiring permanent pacing are pacemaker-dependent, making this option impractical in the majority of cases. 1

Adjunctive Diagnostic Tools

Point-of-Care Troponin Testing

• A positive point-of-care troponin test 1-2 hours after symptom onset in patients with paced rhythm helps decide whether to perform emergency angiography with a view to primary PCI. 1
• However, do not wait for troponin results if clinical suspicion is high—activate the catheterization laboratory immediately based on symptoms alone. 1

Echocardiography (Only if Immediately Available)

• Rapid confirmation of segmental wall-motion abnormalities by two-dimensional echocardiography may assist in decision-making, as regional wall-motion abnormalities occur within minutes following coronary occlusion. 1
• Wall-motion abnormalities are not specific to acute MI and may be due to ischemia, old infarction, or ventricular conduction defects. 1
• The absence of wall-motion abnormalities excludes major myocardial infarction. 1
• This should only be performed if immediately available at bedside and should never delay transfer to the catheterization laboratory. 1

Management Algorithm

Step 1: Clinical Assessment

• Patient presents with symptoms suggestive of ongoing myocardial ischemia (chest pain, dyspnea, diaphoresis, nausea) AND has ventricular paced rhythm on ECG. 1

Step 2: Immediate Actions

• Activate cardiac catheterization laboratory immediately for emergency coronary angiography. 1
• Administer aspirin 160-325 mg (non-enteric coated, chewed) unless contraindicated. 2
• Establish IV access and initiate continuous monitoring. 2
• Draw point-of-care troponin but do not wait for results. 1

Step 3: Pacemaker Assessment

• Determine if patient is pacemaker-dependent (review pacemaker interrogation records, underlying rhythm). 1
• If non-dependent: Consider reprogramming during transport to catheterization laboratory (do not delay transfer). 1
• If dependent: Proceed directly to angiography without attempting ECG interpretation. 1

Step 4: Reperfusion Strategy

• Primary PCI is the definitive treatment and should be performed as soon as possible. 2, 3
• Target door-to-balloon time <90 minutes from first medical contact, though this is often delayed in pacemaker patients (average 280 minutes vs 85 minutes in non-paced patients). 4

Critical Pitfalls to Avoid

Do Not Rely on Scarbossa Criteria

• While Scarbossa criteria were developed for diagnosing MI in the presence of left bundle branch block, they are not validated or mentioned in major guidelines for ventricular paced rhythms. 1
• The European Society of Cardiology explicitly states that ventricular pacing prevents interpretation of ST-segment changes, making any ECG-based criteria unreliable. 1

Do Not Delay Angiography for Additional Testing

• Pacemaker patients with acute MI represent a high-risk group with doubled crude mortality (11.3% vs 4.6%) compared to patients without pacemakers. 4
• Diagnosis is difficult and results in markedly delayed treatment (door-to-balloon time 280 minutes vs 85 minutes). 4
• Treatment algorithms for MI with paced rhythm should be adapted to those used for STEMI or new left bundle branch block—meaning immediate catheterization laboratory activation based on symptoms alone. 4

Do Not Dismiss Symptoms Due to Non-Diagnostic ECG

• Ongoing suspicion of myocardial ischemia despite medical therapy is an absolute indication for emergency coronary angiography with a view to revascularization, even in patients without diagnostic ST-segment elevation. 1
• Some patients with genuine acute coronary occlusion may present without ST-segment elevation and be denied reperfusion therapy, resulting in larger infarction and worse outcomes. 1

Be Aware of Pacemaker Lead Complications

• Pacing failure of the right ventricular lead can occur in patients with anterior STEMI if the left anterior descending artery wraps around to supply the right ventricular apex. 5
• Elevation of pacing threshold due to myocardial infarction at the lead site can cause pacemaker malfunction and life-threatening arrhythmias. 5

Special Considerations

High-Risk Features Requiring Immediate Action

• Hemodynamic compromise (hypotension, cardiogenic shock). 1
• Persistent ischemic symptoms despite medical therapy. 1
• Positive point-of-care troponin in the appropriate clinical context. 1
• New or worsening heart failure (Killip class >2). 4

Patient Characteristics

• Pacemaker patients with MI are typically older (average age 78.2 years vs 65.4 years), have more comorbidities (Charlson Index >1 in 54.0% vs 21.1%), and higher rates of heart failure upon presentation. 4
• These factors contribute to higher crude mortality, but when adjusted for age and comorbidities, mortality is similar to non-paced patients (11.2% vs 10.5%). 4