From the Guidelines
The QRS horizontal axis values provided (-24, -19, -42, -33, and -40 degrees) indicate a left axis deviation pattern on the electrocardiogram (ECG), suggesting that the electrical activation of the ventricles is occurring in a more leftward direction than normal, as defined by the American Heart Association electrocardiography and arrhythmias committee 1.
Key Points to Consider
- A normal QRS axis typically falls between -30° and 90°, so most of these measurements are at the leftward edge of normal or beyond, according to the guidelines set by the American College of Cardiology Foundation and the Heart Rhythm Society 1.
- Left axis deviation can be a normal variant in some individuals but may also indicate underlying cardiac conditions such as left anterior fascicular block, left ventricular hypertrophy, or inferior myocardial infarction.
- The axis deviation occurs because the electrical impulses are traveling through altered conduction pathways in the heart, changing the overall vector of ventricular depolarization, as explained in the scientific statement from the American Heart Association electrocardiography and arrhythmias committee, council on clinical cardiology 1.
Clinical Implications
- No immediate treatment is required based solely on these axis measurements, but clinical correlation is necessary to determine the underlying cause of the left axis deviation.
- The patient should undergo a complete cardiac evaluation including a full 12-lead ECG interpretation, cardiac history, physical examination, and possibly additional cardiac testing depending on symptoms and other ECG findings, as recommended by the American Heart Association and the American College of Cardiology Foundation 1.
- It is essential to consider the patient's age, as the normal QRS axis range varies throughout childhood, with a rightward QRS axis at birth that shifts gradually leftward throughout childhood, as noted in the study published in the Journal of the American College of Cardiology 1.
From the Research
QRS Horizontal Axis Deviation
The provided QRS horizontal axis deviations are -24 deg, -19 deg, -42 deg, -33 deg, and -40 deg.
- These values indicate left axis deviation, as a normal QRS axis is typically defined as -30° to 90° 2.
- Left axis deviation is a common ECG abnormality that may be associated with underlying structural heart disease 3.
- Studies have shown that left axis deviation can be an independent predictor of poor prognosis in patients with heart failure and left bundle branch block 2, 4.
Mechanisms of Left Axis Deviation
- Left axis deviation in patients with left bundle branch block may be due to electrophysiological abnormalities rather than structural factors or cardiac anatomic axis 5.
- Total activation times are longer in patients with left axis deviation, and left ventricular activation is from apex to base, in contrast to a circumferential pattern of activation in patients with normal axis 5.
Clinical Impact
- Left axis deviation has been associated with a higher risk of adverse cardiovascular events and mortality in various patient populations 2, 4.
- The prognostic impact of QRS axis deviation has been assessed in patients with and without conduction block, and left axis deviation has been shown to be a significant predictor of poor outcomes 2, 4.