right. Physiologically, this can occur in tall and thin individuals. Pathologically, conditions such as a left-sided pneumothorax and lung hyperinflation (e.g. COPD) can cause rightwards displacement of the heart. The congenital condition of dextrocardia results in right axis deviation. Diagnosis In general, a positive (upwards) deflection of an ECG trace demonstrates an electrical activity that moves towards the measuring electrode, whereas a negative (downwards) deflection of an ECG trace demonstrates an electrical activity that moves away from the measuring electrode. The electrical heart axis can be estimated from the ECG by using the quadrant method or degree method. Quadrant Method: Leads I and II are usually observed. If lead I is positive (translating to 0° on the hexaxial reference system) and lead II is positive (translating to 60°), the electrical heart axis is estimated to fall in the left lower quadrant within the normal range. On the other hand, as shown in Figure 2, if lead I is negative (translating to 180°) and lead II is positive, the electrical heart axis is estimated to fall in the right lower quadrant suggesting a right axis deviation. Similarly, leads I and aVF can be used. Degree method: First, identify the lead with the smallest QRS complex or isoelectric (flat) QRS complex (lead a). After locating the axis of the lead on the hexaxial reference system, identify the lead which is perpendicular to it (lead b). If lead b is positive, the electrical heart axis can be estimated to lie within the quadrant between axis of lead a and lead b. A simple tool to quickly identify axis deviation (Figure 3) is the popular mnemonic; Reaching for Right Axis Deviation and Leaving for Left Axis Deviation. This refers to the appearance of leads I and III. If the QRS complex is negative in lead I and positive in lead III, the QRS complexes appear to be "reaching" to touch each other. This signifies right axis deviation. Conversely, if the QRS complex is positive in lead I and negative in lead III. the leads have the appearance of "leaving" each other. If the QRS complex in lead II is also negative, this confirms a left axis deviation. See also Left axis deviation References Heart diseases Medical mnemonics