. For example, if the P is tallest in the lead II, the electrical axis is parallel to the lead II {normal) (fig 5 11 7a), if R is tallest m lead I the

Axis determinations, are made by finding the amplitudes of the R waves in the bipolar limb leads. For example, if the P is tallest in the lead II, the electrical axis is parallel to the lead II {normal) (fig 5 11 7a), if R is tallest m lead I the axis is parallel! to the lead I (Left axis deviation) (5 11 7b), where as when the R is tallest in lead III the axis is parallel to the lead III and there is right axis deviation (fig.5.11.7c) APPLIED PHYSIOLOGY Myocardiaf infarction. Common findings (fig 5.11.8) are - (i) elevation (in acute stage) or depression (in sub acute or chronic stage) of the ST segment, (mi) presence of Q wave where it should be normally absent or big O wave where Ft should be normally present, and (iii) inversion of T wave (iv) normally the height of R wave progresses from V1 to VS but in myocardial infarction this progressive increase jn height does not occur (see also fig. 5 21 6) Fig. 5 11 8 An etevated ST segment in acute infarction of heart muscle Myocardial ischemia Common finding is depression of ST segment which may or may not be associated with other signs. Presence of a normal ECG, however, does not rule out cardiac ischemia. 3 Hypertrophy Left ventricular hypertrophy is usually associated with larger R in V5, V6, deeper S in V1 V2 and ft anix deviation These changes may or may not be associated with inversion of T wave and depression of ST A Heart Block In AV block the PR interval is more than 0.2 sec In bundle branch block the duration of QRS is more than 0.11 sec. Presence of RSR' (in V1) pattern denotes right bundle branch block (fig 5.11.9 a) whereas a sluired and broad ORS to V5 andV6 denote left bundle branch block (fig.5.11.9 b) Wolf-Parkinson-While (WPW) Syndrome This syndrome (-=disease] is raie but academically important In WPW syndrome, there is an additional connecting (in addi­tion, to the normal AV jurrctional tissue connection) path between the atria and ventricle. and this additional path is called "bundle of Kent.'As a result of the presence of bundle of Kent, conduction between hyper and the ventncle is abnormally rapid, the characlenstic ECG features are (i) short PR interval, value around 0.1 sec (ii) broader ORS camplex 6. Hyparkalemia and hypokalemia The causes of hyper and hypokalemia wilh their pathophysiology have been described elsewhere in this book (chap 3 sec VIII) Here only ECG signs will be