Can an electrocardiogram (ECG) show a normal sinus rhythm without ST-segment changes?

Can an ECG Show Normal Sinus Rhythm Without ST-Segment Changes?

Yes, an ECG can absolutely show normal sinus rhythm without ST-segment changes, and this occurs commonly in clinical practice—even in patients who are actively experiencing acute coronary syndrome (ACS). This is a critical clinical reality that demands vigilance and serial evaluation.

Key Clinical Reality

A normal or nonspecific ECG does not exclude ACS or acute myocardial infarction. 1 In fact:

• 1-6% of patients with a completely normal ECG are ultimately proven to have had an acute myocardial infarction (by definition, an NSTEMI) 1
• At least 4% will be found to have unstable angina despite a normal initial ECG 1
• Up to 6% of patients with evolving ACS are inappropriately discharged from the emergency department with a normal ECG 1

Why This Happens: The "Electrically Silent" Problem

Several anatomic and physiologic factors explain why serious cardiac events can present with normal ECGs:

• Left circumflex or right coronary artery occlusions may produce posterior wall ischemia that is "electrically silent" on standard 12-lead ECG 1
• Approximately 4% of acute MI patients show ST elevation only in posterior chest leads (V7-V9), which are "hidden" from standard 12-lead recordings 1
• The ECG represents only a snapshot in time of a dynamic ischemic process 1

Critical Management Algorithm

When You See a Normal ECG in Suspected ACS:

1. Never rely on a single normal ECG to exclude ACS 1

2. Obtain serial ECGs, especially if:

   • Symptoms persist or recur 1
   • Clinical condition changes 1
   • The patient experiences new chest pain episodes 1

3. Consider supplemental leads V7-V9 when posterior MI is suspected (reasonable recommendation, Class IIa) 1

4. Combine ECG findings with cardiac biomarkers:

   • Serial troponin measurements at 6-12 hours are essential 1
   • Biomarker measurements have higher diagnostic yield than serial ECGs alone 1
   • However, ECG changes (not biomarkers) remain the principal criterion for emergency reperfusion therapy 1

5. Compare with previous ECGs when available 1

   • Patients with an unchanged ECG have reduced risk of MI and very low risk of life-threatening complications 1

Risk Stratification Based on ECG Patterns

A gradient of risk exists based on ECG findings 1:

• Highest risk: Bundle branch block, paced rhythm, or LV hypertrophy (confounding patterns) 1
• High risk: ST-segment deviation (elevation or depression) 1
• Lowest risk: Isolated T-wave inversion or normal ECG patterns 1

However, this prognostic information does not eliminate the need for comprehensive evaluation in patients with normal ECGs and concerning symptoms 1

Critical Pitfall to Avoid

Patients who are symptomatic during acquisition of a normal or nonspecific ECG have rates of adverse cardiovascular events similar to those without symptoms during ECG acquisition 2. This means:

• Do not be falsely reassured by the absence of ECG abnormalities during active symptoms 2
• The timing of ECG relative to symptoms does not reliably predict outcomes 2

Bottom Line for Clinical Practice

Management should never be based solely on a single normal or nondiagnostic ECG 1. The decision pathway must integrate:

• Clinical history and physical examination findings 1
• Serial ECG monitoring 1
• Serial cardiac biomarkers 1
• Risk stratification tools 1
• Consideration of stress testing or anatomic imaging when initial workup is nondiagnostic 1

Serial ECGs should be performed until the disease process stabilizes or other diagnostic testing definitively rules out ACS 1.