How to diagnose and manage STEMI (ST-Elevation Myocardial Infarction) in patients with a paced rhythm?

Diagnosis and Management of STEMI in Patients with Paced Rhythm

In patients with ventricular paced rhythm and suspected STEMI, urgent cardiac catheterization is required to confirm diagnosis and initiate appropriate therapy, as pacemaker rhythm prevents reliable interpretation of ST-segment changes. 1

Diagnostic Challenges in Paced Rhythm

Ventricular pacing creates significant challenges for ECG interpretation in suspected STEMI:

• Standard ST-elevation criteria cannot be applied due to altered ventricular depolarization
• Paced beats typically show discordant ST changes (ST elevation opposite to QRS direction)
• Baseline ECG abnormalities mask acute ischemic changes

Modified Sgarbossa Criteria for Paced Rhythms

The modified Sgarbossa criteria have been validated for ventricular paced rhythms with high specificity (82-94%) 2:

1. ST-segment elevation ≥1 mm concordant with the QRS complex (sensitivity 18%, specificity 94%)
2. ST-segment depression ≥1 mm in leads V1-V3 (highly specific for AMI)
3. ST/S ratio ≤-0.25 in leads with discordant ST elevation (replacing the original criterion of ST-segment elevation ≥5 mm discordant with QRS)

Management Algorithm

Step 1: Initial Assessment

• Obtain 12-lead ECG immediately when STEMI is suspected in a patient with paced rhythm
• Apply modified Sgarbossa criteria to the ECG
• Consider additional posterior leads (V7-V9) to detect posterior wall involvement

Step 2: Decision Making

• If any Sgarbossa criterion is positive: Activate cardiac catheterization laboratory immediately 2
• If criteria negative but clinical suspicion remains high:
  • Obtain serial ECGs
  • Check cardiac biomarkers (troponin)
  • Consider urgent angiography if symptoms persist despite medical therapy

Step 3: Additional Considerations

• In non-pacemaker dependent patients, consider reprogramming the pacemaker to allow evaluation of intrinsic rhythm 1
• Do not delay invasive investigation while waiting for pacemaker reprogramming
• Do not wait for troponin elevation if modified Sgarbossa criteria are positive 2

Reperfusion Strategy

Once STEMI is confirmed in a patient with paced rhythm:

• Primary PCI is the preferred reperfusion strategy 1
• If primary PCI cannot be performed in a timely manner (within 120 minutes from STEMI diagnosis), consider fibrinolytic therapy within 12 hours of symptom onset 1
• For patients with resuscitated cardiac arrest and ECG consistent with STEMI, primary PCI is recommended 1

Special Considerations

• Pre-hospital management: Regional networks should be designed to deliver reperfusion therapy expeditiously, with direct transfer to PCI-capable centers 1
• ECG monitoring: Continuous ECG monitoring with defibrillator capacity is essential in all patients with suspected STEMI 1
• Echocardiography: Can be useful to detect regional wall motion abnormalities when ECG diagnosis is unclear 1
• False positives: Be aware that misinterpretation of ECGs is a common cause of inappropriate catheterization laboratory activation 3, 4

Pitfalls to Avoid

1. Delayed diagnosis: Do not wait for biomarker results before activating the catheterization laboratory when clinical suspicion is high
2. Over-reliance on ECG alone: Consider the entire clinical picture, as absence of Sgarbossa criteria does not rule out STEMI
3. Ignoring persistent symptoms: Ongoing chest pain despite medical therapy warrants urgent angiography even without diagnostic ECG changes 1
4. Missing posterior MI: Consider posterior leads (V7-V9) when suspecting posterior wall involvement 2

By following this approach, clinicians can optimize the diagnosis and management of STEMI in patients with paced rhythm, potentially improving morbidity and mortality outcomes through timely reperfusion therapy.