Abnormalities of P Waves, QRS Complexes and T Waves

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Abnormalities of P waves, QRS complexes and T waves



When interpreting an ECG, identify the rhythm first. Then ask the following questions – always in the same sequence:



Remember:





ABNORMALITIES OF THE QRS COMPLEX


The normal QRS complex has four characteristics:




ABNORMALITIES OF THE WIDTH OF THE QRS COMPLEX


QRS complexes are abnormally wide in the presence of bundle branch block (see Ch. 2), or when depolarization is initiated by a focus in the ventricular muscle causing ventricular escape beats, extrasystoles or tachycardia (see Ch. 3). In each case, the increased width indicates that depolarization has spread through the ventricles by an abnormal and therefore slow pathway. The QRS complex is also wide in the Wolff-Parkinson-White syndrome (see p. 79, Ch. 3).



INCREASED HEIGHT OF THE QRS COMPLEX


An increase of muscle mass in either ventricle will lead to increased electrical activity, and to an increase in the height of the QRS complex.



Right ventricular hypertrophy


Right ventricular hypertrophy is best seen in the right ventricular leads (especially V1. Since the left ventricle does not have its usual dominant effect on the QRS shape, the complex in lead becomes upright (i.e. the height of the R wave exceeds the depth of the S wave) – this is nearly always abnormal ( Fig. 4.3). There will also be a deep S wave in lead V6.



Right ventricular hypertrophy is usually accompanied by right axis deviation (see Ch. 1), by a peaked P wave (right atrial hypertrophy), and in severe cases by inversion of the T waves in leads V1 and V2, and sometimes in lead V3 or even V4 ( Fig. 4.4).




Pulmonary embolism


In pulmonary embolism the ECG may show features of right ventricular hypertrophy ( Fig. 4.5), although in many cases there is nothing abnormal other than sinus tachycardia. When a pulmonary embolus is suspected, look for any of the following:




However, do not hesitate to treat the patient if the clinical picture suggests pulmonary embolism but the ECG does not show the classical pattern of right ventricular hypertrophy. If in doubt, treat the patient with an anticoagulant.



Left ventricular hypertrophy


Left ventricular hypertrophy causes a tall R wave (greater than 25 mm) in lead V5 or V6 and a deep S wave in lead V1 or V2 ( Fig. 4.6) – but in practice such ‘voltage’ changes alone are unhelpful in diagnosing left ventricular enlargement. With significant hypertrophy, there are also inverted T waves in leads I, VL, V5 and V6, and sometimes V4, and there may be left axis deviation. It is difficult to diagnose minor degrees of left ventricular hypertrophy from the ECG.


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Jul 26, 2016 | Posted by in CARDIOLOGY | Comments Off on Abnormalities of P Waves, QRS Complexes and T Waves

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