ABC OF CLINICAL ELECTRO - CARDIOGRAPHY FRANCIS MORRIS JUNE EDHOUSE WILLIAM J BRADY JOHN CAMM BMJ Books ABC OF CLINICAL ELECTROCARDIOGRAPHY [...]... analysis should include measurement of the ventricular rate, assessment of the ventricular rhythm, identification of P F, or f waves , , measurement of the atrial rate, and establishment of the relation of P waves to the ventricular complexes Sinus tachycardia 13 ABC of Clinical Electrocardiography the absence of an obvious underlying cause should prompt consideration of atrial flutter or atrial tachycardia... at least 1/8 but less than 2/3 of the amplitude of the corresponding R wave; T wave amplitude rarely exceeds 10 mm T wave Complex showing T wave highlighted 7 ABC of Clinical Electrocardiography QT interval The QT interval is measured from the beginning of the QRS complex to the end of the T wave and represents the total time taken for depolarisation and repolarisation of the ventricles V1 aVL QT interval... elevation of the ST segment, and this is known as “high take-off.” Non-pathological elevation of the ST segment is also associated with benign early repolarisation (see article on acute myocardial infarction later in the series), which is particularly common in young men, athletes, and black people Interpretation of subtle abnormalities of the ST segment is one of the more difficult areas of clinical electrocardiography; ... Sinus arrest with pause of 4.4 s before generation and conduction of a junctional escape beat 9 ABC of Clinical Electrocardiography Escape rhythms are the result of spontaneous activity from a subsidiary pacemaker, located in the atria, atrioventricular junction, or ventricles They take over when normal impulse formation or conduction fails and may be associated with any profound bradycardia Atrioventricular... PR interval is 0.12-0.20 s (three to five small squares) 5 ABC of Clinical Electrocardiography it is measured from the beginning of the P wave to the first deflection of the QRS complex (see next section), whether this be a Q wave or an R wave The normal duration of the PR interval is three to five small squares (0.12-0.20 s) Abnormalities of the conducting system may lead to transmission delays, prolonging... initiated by an extrasystole and involves two pathways of conduction with differing electrical properties The re-entry circuits that support ventricular tachycardia can be “micro” or The electrophysiology of a re-entry circuit was described in last week’s article 21 ABC of Clinical Electrocardiography “macro” in scale and often occur in the zone of ischaemia or fibrosis surrounding damaged myocardium... block 11 ABC of Clinical Electrocardiography In the normal heart, septal depolarisation proceeds from left to right, producing Q waves in the left chest leads (septal Q waves) In left bundle branch block the direction of depolarisation of the intraventricular septum is reversed; the septal Q waves are lost and replaced with R waves The delay in left ventricular depolarisation increases the duration of the... The information from these 12 leads is combined to form a standard electrocardiogram Wave of depolarisation Wave of depolarisation Shape of QRS complex in any lead depends on orientation of that lead to vector of depolarisation V1 V2 V3 V4 V5 V6 aVR aVL Position of the six chest electrodes for standard 12 lead electrocardiography V1: right sternal edge, 4th intercostal space; V2: left sternal edge,... syndrome x Pulmonary embolus 60˚ II Hexaxial diagram (projection of six leads in vertical plane) showing each lead’s view of the heart 3 ABC of Clinical Electrocardiography Several methods can be used to calculate the cardiac axis, though occasionally it can prove extremely difficult to determine The simplest method is by inspection of leads I, II, and III I aVR II aVL III aVF Calculating the cardiac... abnormal direction of wave of depolarisation, giving rise to bizarre axis Axis change Change in axis with onset of monomorphic ventricular tachycardia in lead aVR Broad complex tachycardia—Part I QRS complex in lead aVR is entirely positive the tachycardia originates close to the apex of the ventricle, with the wave of depolarisation moving upwards towards the base of the heart Direct evidence of independent . ABC OF CLINICAL ELECTRO - CARDIOGRAPHY FRANCIS MORRIS JUNE EDHOUSE WILLIAM J BRADY JOHN CAMM BMJ Books ABC OF CLINICAL ELECTROCARDIOGRAPHY