Mechanical shifts that cause LAD are expiration or raised diaphragm from pregnancy, ascites (fluid accumulation in the abdomen), abdominal tumor, or enlarged liver or spleen. Pre-excitation syndrome as well as congenital heart diseases such as atrial septal defect, endocardial cushion defects can also cause LAD on ECG. Conduction defects such as left bundle branch block or left anterior fascicular block can cause LAD on the ECG. Normal variation causing LAD is an age-related physiologic change. These include normal variation, left ventricular hypertrophy, conduction defects, inferior wall myocardial infarction, preexcitation syndrome, ventricular ectopic rhythms, congenital heart disease, hyperkalemia, emphysema, mechanical shift and pacemaker-generated paced rhythm. There are several potential causes of LAD. On the other hand, if QRS complex is negative in lead II, then this is a LAD.Another method of determining LAD is called the Isoelectric lead, which allows for a more precise estimation of the QRS axis. If the QRS complex is positive in lead II, then this is a normal axis. To determine a true LAD, examine QRS in lead II. If lead I is positive and lead aVF is negative, then this is a possible LAD. First, examine the QRS complex in both leads I and avF and determine if the QRS complex is positive (height of R wave > S wave), equiphasic (R wave = S wave), or negative (R wave < S wave). The easiest method is the quadrant method, where one looks at lead I and lead aVF. There are several methods to determining the ECG axis. Determining left axis deviation ĭetermining the electrical axis can provide insight into underlying disease states and help steer the differential diagnosis. In contrast to that, left axis deviation (LAD) is defined as QRS axis between −30° and −90°, and right axis deviation is defined as QRS axis greater than +90°, while extreme axis deviation occurs when QRS axis is between -90° and 180°. In a normal axis, QRS is between -30° and +90°. Usually, left ventricles makes up most of the heart muscles, so a normal cardiac axis is directed downward and slightly to the left. To interpret the cardiac axis, one has to determine the relationship between the QRS axis and limb leads of the ECG. Symptoms and treatment of left axis deviation depend on the underlying cause.Ĭardiac axis in electrocardiography represents the sum of depolarization vectors generated by individual cardiac myocytes. Some of the causes include normal variation, thickened left ventricle, conduction defects, inferior wall myocardial infarction, pre-excitation syndrome, ventricular ectopic rhythms, congenital heart disease, high potassium levels, emphysema, mechanical shift, and paced rhythm. This is reflected by a QRS complex positive in lead I and negative in leads aVF and II. In electrocardiography, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°. The hexaxial reference system is a diagram that is used to determine the heart's electrical axis in the frontal plane.
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