From the Guidelines
To determine axis deviation on an ECG, look at leads I, II, and aVF, as these leads provide the most relevant information for assessing the heart's electrical axis. The approach to determining axis deviation involves checking the polarity of the QRS complex in lead I and aVF, as this will indicate whether the axis is normal, left deviated, or right deviated 1.
Key Leads for Axis Deviation
- Lead I: runs horizontally from right to left
- Lead aVF: runs vertically from superior to inferior
- Lead II: can be used as a reference to confirm the axis deviation
Steps to Determine Axis Deviation
- Check lead I: if the QRS complex is positive (upright), the axis is either normal or left deviated; if negative, it's right deviated.
- Examine lead aVF: if positive with positive lead I, the axis is normal; if negative with positive lead I, it's left axis deviation.
- For right axis deviation, lead I will be negative and aVF positive.
- In extreme right axis deviation, both leads I and aVF are negative.
Importance of Axis Deviation
Understanding axis deviation is crucial as it can indicate various cardiac conditions, such as left anterior fascicular block, pulmonary embolism, or right ventricular hypertrophy 1. The normal cardiac axis is between -30° and +90°, with left axis deviation being less than -30° and right axis deviation greater than +90°. By analyzing leads I, II, and aVF, healthcare professionals can quickly assess the heart's electrical axis and make informed decisions about patient care.
From the Research
Axis Deviation Leads
To determine axis deviation, several leads are examined on an electrocardiogram (ECG). The leads used for this purpose include:
- Lead I: measures the difference in electrical potential between the left and right arms 2
- Lead II: measures the difference in electrical potential between the right arm and the left leg 2
- Lead III: measures the difference in electrical potential between the left arm and the left leg 2
- The precordial leads (V1-V6): provide information about the electrical activity of the heart from a horizontal plane 2
Importance of Baseline ECG
Baseline ECG alterations can be identified before arrhythmia development, and early recognition of these alterations is crucial for starting appropriate preventive therapies and stratifying the risk according to patients' outcomes 3.
Clinical Tools for Assessing Cardiac Electrical Events
The primary clinical tool for assessing cardiac electrical events is the electrocardiogram (ECG), which provides global and regional information on rate, rhythm, and electrical conduction as well as changes in electrical activity associated with cardiac disease 2.
Advances in Cardiac Electrophysiology
Recent advances in cardiac electrophysiology have increased our understanding of arrhythmia mechanisms and diagnosis, and new therapies have been developed, including new technologies and techniques for atrial fibrillation ablation 4.