From the Guidelines
Normal ECG values include a heart rate of 60-100 beats per minute, PR interval of 120-200 milliseconds, QRS duration of 70-110 milliseconds, QT interval of 350-440 milliseconds (corrected for heart rate), and a normal sinus rhythm with P waves preceding each QRS complex. Management of abnormal findings depends on the specific abnormality, as outlined in the 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guideline for the evaluation and diagnosis of chest pain 1.
Key Abnormalities and Management
- Bradycardia (heart rate <60) may require atropine 0.5mg IV (repeated up to 3mg) or temporary pacing if symptomatic.
- Tachycardia (>100) treatment varies by type—supraventricular tachycardia often responds to vagal maneuvers, adenosine 6mg IV followed by 12mg if needed, or beta-blockers like metoprolol 5mg IV.
- Ventricular arrhythmias may require amiodarone 150mg IV over 10 minutes, followed by infusion.
- Heart blocks are managed based on severity—first-degree blocks typically need monitoring only, while complete heart blocks often require permanent pacemaker implantation.
- ST-segment elevation >1mm in two contiguous leads suggests myocardial infarction requiring immediate reperfusion therapy, following STEMI guidelines as recommended by 1.
- QT prolongation (>470ms in females, >450ms in males) requires discontinuation of offending medications and electrolyte correction.
ECG-Directed Management
The 2021 guideline 1 provides an algorithm for ECG-directed management of chest pain, emphasizing the importance of serial ECGs and consideration of new electrocardiographic changes or other diagnostic testing. For patients with a normal or nondiagnostic initial ECG, serial ECGs should be performed, and management should be guided by new electrocardiographic changes or other diagnostic testing. The timing for repeat ECG should also be guided by symptoms, especially if chest pain recurs or a change in clinical condition develops.
Considerations for Specific Conditions
- ST-elevation on the initial ECG should be managed following STEMI treatment algorithms.
- ST depression identified on the initial ECG should be managed following NSTE-ACS guidelines.
- A normal ECG may be associated with left circumflex or right coronary artery occlusions and posterior wall ischemia; therefore, right-sided ECG leads should be considered when such lesions are suspected, as suggested by 1.
These guidelines and management strategies are based on the most recent and highest quality evidence available, prioritizing morbidity, mortality, and quality of life outcomes.
From the Research
Normal ECG Values
Normal ECG values typically include:
- A heart rate of 60-100 beats per minute
- A PR interval of 120-200 milliseconds
- A QRS duration of less than 120 milliseconds
- A QT interval of less than 440 milliseconds
- A P wave axis of 0 to 75 degrees
- A QRS axis of -30 to 100 degrees
- A T wave axis of 0 to 75 degrees
Abnormal ECG Findings
Abnormal ECG findings can indicate various heart conditions, including:
- ST-segment elevation, which can indicate acute myocardial infarction 2
- ST-segment depression, which can indicate subendocardial ischemia 2
- Q waves, which can indicate previous myocardial infarction
- Arrhythmias, such as atrial fibrillation or ventricular tachycardia 3
Management of Abnormal ECG Findings
Management of abnormal ECG findings depends on the specific condition and may include:
- Antiplatelet therapy, such as aspirin, for patients with acute coronary syndrome 4
- Anticoagulation therapy, such as heparin or low-molecular-weight heparin, for patients with acute coronary syndrome 4
- Fibrinolytic therapy, such as tPA, for patients with ST-segment elevation myocardial infarction 4, 5
- Percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) for patients with acute coronary syndrome 4
- Antiarrhythmic drug therapy, such as beta-blockers or amiodarone, for patients with arrhythmias 3
- Implantable cardioverter-defibrillator (ICD) therapy for patients with life-threatening arrhythmias 3