What are the current procedures to diagnose and manage suspected heart block or myocardial infarction (MI) in a remote patient, out-patient department, and in-patient setting?

Diagnostic Procedures for Heart Block and Myocardial Infarction Across Clinical Settings

Remote/Pre-Hospital Setting

Patients with suspected cardiac symptoms should immediately call 9-1-1 for ambulance transport rather than self-transport or use private vehicles, as approximately 1 in 300 patients with chest pain transported by private vehicle experiences cardiac arrest en route. 1

Patient Recognition and Initial Response

• Patients experiencing chest discomfort/pain that is unimproved or worsening 5 minutes after onset should call 9-1-1 immediately 1
• For patients previously prescribed nitroglycerin: take ONE sublingual dose; if symptoms are unimproved or worsening 5 minutes after taking nitroglycerin, call 9-1-1 1
• For chronic stable angina patients: if symptoms significantly improve after one nitroglycerin dose, repeat every 5 minutes for total of 3 doses and call 9-1-1 if symptoms have not totally resolved 1
• Patients should NOT seek someone else's nitroglycerin (from neighbors, friends, or relatives) 1

EMS/Ambulance Capabilities

• Emergency medical technicians and paramedics can provide life-saving interventions including early CPR and defibrillation if cardiac arrest develops 1
• Ambulance arrival is significantly associated with early reperfusion therapy in STEMI patients 1

Out-Patient Department/Emergency Department Setting

All patients presenting with chest discomfort or symptoms suggestive of MI should be considered high-priority triage cases and evaluated based on a predetermined, institution-specific chest pain protocol. 1

Immediate Actions (Within 10 Minutes)

• Place patient on continuous cardiac monitor immediately with emergency resuscitation equipment and defibrillator nearby 1, 2
• Obtain 12-lead ECG within 10 minutes of ED arrival 1, 3
• ECG must be evaluated by experienced emergency medicine physician within 10 minutes 1
• For inferior MI: add right-sided leads (V1R-V6R) to standard 12-lead ECG to identify right ventricular infarction, which occurs in 35.9% of cases and carries significantly higher mortality (18.5% vs 2.1%) 3

ECG Interpretation for MI

• STEMI diagnosis: ST-segment elevation in contiguous leads warrants decision for reperfusion therapy within 10 minutes of ECG diagnosis 1, 4
• Posterior MI: horizontal ST-segment depression with upright precordial T-waves in ≥2 contiguous leads V1-V4 should be treated as STEMI-equivalent requiring immediate reperfusion 4
• Inferior MI: ST-segment elevation ≥1 mm in leads II, III, aVF 3

ECG Interpretation for Heart Block

• Complete heart block (CHB) risk scoring: sum individual risk factors including first-degree AV block, Mobitz type I, Mobitz type II, left anterior hemiblock, left posterior hemiblock, right bundle branch block, and left bundle branch block 5
• CHB risk scores of 0,1,2, or ≥3 are associated with CHB incidences of 1.2%, 7.8%, 25.0%, and 36.4% respectively 5
• Mobitz type II second-degree AV block has site almost always below the AV node and is more likely to progress to complete heart block and Stokes-Adams arrest 6
• Heart block occurs in approximately 12% of inferior MI patients receiving thrombolytic therapy 7

Cardiac Biomarkers and Serial Testing

• Do NOT delay reperfusion waiting for cardiac biomarkers—ECG findings alone warrant immediate treatment 3
• Use combination of cardiac biomarkers, short-term observation, diagnostic imaging, and provocative stress testing for unclear cases 1
• Serial ECGs should be obtained for evolving patterns 1

Immediate Pharmacologic Management for MI

• Administer aspirin 160-325 mg orally immediately (chew if possible) unless contraindicated 2, 3
• Give sublingual nitroglycerin unless systolic BP <90 mmHg, heart rate <50 or >100 bpm 3
• CRITICAL PITFALL: Avoid nitrates completely in right ventricular infarction—these patients depend on high preload 3
• Provide supplemental oxygen only if oxygen saturation <90% 2, 3
• Titrated IV morphine for pain relief (note: delays oral antiplatelet absorption) 4, 2

Structured Diagnostic Approach

• Use multidisciplinary, standardized, structured protocols/checklists/critical pathways—this approach provides clinical and cost-effective benefit regardless of whether institution designates itself a chest pain center 1
• One randomized trial confirmed safety, efficacy, and cost-effectiveness of structured decision-making versus standard unstructured care 1

Cardiology Consultation

• Immediate cardiology consultation is advisable when initial diagnosis and treatment plan are unclear or not covered by institutional protocol 1

In-Patient Setting

Continuous Monitoring for Heart Block

• Patients with new or indeterminate bifascicular block (RBBB with LAFB or LPFB, or LBBB) with first-degree AV block require transcutaneous pacing patches applied with system ready to activate 1
• Mobitz type II second-degree AV block requires transcutaneous standby pacing 1
• Bilateral bundle branch block (alternating BBB or RBBB with alternating LAFB/LPFB) at any age requires standby pacing 1

Indications for Temporary Transvenous Pacing (Class Ia)

• RBBB with LAFB or LPFB (new or indeterminate) 1
• RBBB with first-degree AV block 1
• LBBB, new or indeterminate 1
• Incessant ventricular tachycardia for atrial or ventricular overdrive pacing 1
• Recurrent sinus pauses (>3 seconds) not responsive to atropine 1
• Sinus bradycardia (rate <50 bpm) with symptoms of hypotension (systolic BP <80 mmHg) unresponsive to drug therapy 1
• Symptomatic bradycardia including sinus bradycardia with hypotension not responsive to atropine 1

Transvenous Access Routes

• Percutaneous access through internal/external jugular, subclavian, or femoral veins 1
• Brachial veins percutaneously or by cutdown 1
• Target: right ventricular apex 1

Indications for Permanent Pacing Post-MI

• Persistent second-degree AV block in His-Purkinje system with bilateral BBB or complete heart block after acute MI 1
• Transient advanced (second- or third-degree) AV block with associated BBB 1
• Symptomatic AV block at any level 1

Echocardiography

• Perform echocardiography to assess left ventricular function and exclude mechanical complications 2

Ongoing Pharmacologic Management

• High-intensity statin therapy initiated as early as possible 2
• Beta-blockers if heart failure or LVEF <40% 2
• ACE inhibitors within 24 hours if heart failure, LV dysfunction, diabetes, or anterior wall involvement 2
• Aspirin 75-100 mg daily continued indefinitely 2
• P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) 3

Monitoring Duration

• Patients with Type 2 MI should be admitted to monitored bed with duration matching Type 1 MI protocols given equivalent arrhythmia and mortality risk 2

Critical Pitfalls to Avoid

• Do not withhold reperfusion therapy based solely on ST-depression if clinical suspicion for posterior MI exists 4
• Fibrinolytic therapy in undifferentiated ST-depression patients (without confirmed posterior MI) may increase mortality 4
• Do not give nitrates or diuretics to patients with right ventricular infarction 3
• Do not underestimate inferior MI as "low risk"—mortality reaches 18.5% with RVI involvement 3
• Do not miss lateral wall extension—check for ST-elevation in leads I, aVL, V5-V6, which predicts worse outcomes 3
• Heart block developing after thrombolytic therapy carries 21-day mortality of 9.9% versus 2.2% without heart block 7
• Complete heart block with anterior MI has significantly higher mortality than with inferior MI 8