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(BQ) Part 2 book ECG workbook presents the following contents: Axis deviation, ischaemia, injury and necrosis, sites of infarction, bundle branch blocks, chamber enlargement, hemiblocks, bifascicular blocks and trifascicular blocks, paced rhythms, a systematic approach to ECG interpretation.
ECG chapters 8–11:Layout 10/09/2014 11:06 Page 47 Chapter Axis deviation We have already learned about the normal pathway of the impulse as it travels through the conducting system We have also seen how the direction of this impulse and the position of electrodes around the heart affect the polarity of the limb leads However, there may be times when the normal pathway of the impulse is disrupted, e.g by a piece of damaged tissue as the result of a heart attack Such a disruption may cause the pathway of the impulse to deviate to the left or the right or in extreme cases back up to the direction from which it came This is known as axis deviation This disruption will affect the polarity of the limb leads If something is causing the impulse to travel back from where it came, the aVR may be positive on the ECG, rather than negative, because the impulse is now travelling towards the aVR Meanwhile Lead II may be negative, as the impulse is now travelling away from the lead One way of working out axis deviation is therefore by looking at the polarity of two of the limb leads This can be most easily done by assessing Lead I and the aVF In a normal ECG, as we know, all the limb leads should be positive except aVR Therefore, if the ECG shows a normal axis deviation (meaning that there is no disruption of the normal pathway of electrical activity) both Lead I and the aVF should look positive (see fig 8.1) Figure 8.1: Normal cardiac axis demonstrated by both Lead I and the aVF being positive 47 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 48 The ECG workbook If there is an extreme axis deviation (severe disruption of the electrical pathway) the opposite will occur – Lead I and the aVF will look negative (see fig 8.2) Figure 8.2: Extreme axis deviation Lead I and the aVF lead are negative Note that the aVR is positive; the electrical impulses are therefore moving in the opposite direction from normal If the impulse deviates to the left, there is left axis deviation, Lead I is positive and the aVF is negative This can be easily remembered by thinking about the tips of the QRS complexes of these two leads as leaving each other or leaving the page: LEFT and LEAVING (start with the same letter!) (see fig 8.3) Figure 8.3: Left axis deviation Lead I is positive and the aVF is negative 48 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 49 Axis deviation In right axis deviation, Lead I is negative and the aVF is positive The tips of the QRS complexes reach for each other: RIGHT and REACHING (see fig 8.4) Figure 8.4: Right axis deviation Extreme axis deviation is the most worrying for a patient, then right axis deviation, and then left In practice, axis deviation does not necessarily require any treatment in itself However, it raises the question of what has caused the axis deviation in the first place For the clinician, the axis deviation will indicate how the patient’s condition may be affecting the pathway of the impulse through the conducting system, and thus how likely the patient is to become unstable and have arrhythmias Using the above method, axis deviation can be assessed at a glance as the ECG is coming out of the ECG machine 49 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 50 The ECG workbook SUMMARY: Axis deviation I Normal +ve Left +ve aVF +ve -ve (leaving) Right -ve +ve (reaching) Extreme -ve -ve Occasionally, in more advanced cardiology, it may be necessary to talk about axis deviation in terms of degrees of deviation, rather than just in terms of normal, left, right or extreme This can be done by plotting the axis on a graph called the Hexaxial Reference System (see fig 8.5) If an ECG shows a right axis deviation of +95 degrees, for example, it is not as serious as a right axis deviation of +170 degrees The first method that we learned will be adequate for the majority of ECGs that you will encounter However, calculating axis deviation using the Hexaxial Reference System is useful if you encounter a Lead I and aVF that are equiphasic (equally positive and negative) In addition, some complex arrhythmias can be distinguished from one another by the degree of axis deviation that is present Figure 8.5: The Hexaxial Reference System The purpose of including the Hexaxial Reference System within this text is simply to help make sense of what looks like a complex diagram in many ECG books Such diagrams can make learners think they have reached their limit with ECG interpretation! The Hexaxial Reference System is divided into 30-degree segments The numbers at the bottom of the Hexaxial Reference System are positive and those at the top half, negative If you look at Figure 8.5 you will see which portion of the diagram represents which type of axis deviation Here the heart is superimposed onto the Hexaxial Reference System In normal circumstances, the pathway of the impulse would flow through the conducting system directly towards Lead II This falls within the normal axis deviation quadrant of the Hexaxial Reference System Anything deviating between +90 degrees and -30 degrees is considered normal axis deviation If the pathway of the impulse deviates to the patient’s left it would fall in the upper right- 50 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 51 Axis deviation hand quadrant (as you look at the page) of the Hexaxial Reference System If deviation is to the right, it would fall in the lower left-hand quadrant And if the pathway of the impulse goes back to where it came from, it would travel towards the upper left quadrant, which represents extreme axis Figure 8.5a: Normal electrical conduction; deviation the impulses move towards Lead II Figure 8.5c: Right axis deviation; the impulses now move in the direction of Lead III Figure 8.5b: Left axis deviation; the impulses move in the approximate direction of Lead aVL Figure 8.5d: Extreme axis deviation; all electrical activity is moving in the opposite direction to normal Calculating axis deviation in degrees using the Hexaxial Reference System Here is a step-by-step method to follow: Look at the ECG and decide, by looking at Lead I and Lead aVF, if it is a normal, left, right or extreme axis deviation If lead is equiphasic (a complex that is as positive as it is negative), it is sufficient at this stage to say that it is either a left or a normal axis, for example Now look at the Hexaxial Reference System and remind yourself in which quadrant of the Reference System the axis will fall (For instance, if it is a normal axis deviation it will fall between +90 degrees and -30 degrees.) Look back at the ECG and find the smallest, equiphasic complex (the smallest complex that is both positive and negative) in the limb leads Remember: the smallest limb lead complex may not be equiphasic; you need to choose the lead that is both small and equiphasic 51 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 52 The ECG workbook Once you have found this lead, go to the Hexaxial Reference System and find the positive pole of that electrode From this electrode, move 90 degrees around the Hexaxial Reference System towards the quadrant that you first decided your axis would fall in (see step above) Look at the lead that you have arrived at and the degree of axis deviation that it represents This is the axis deviation of the ECG For example, Figure 8.1 shows a normal axis deviation of +60 degrees Lead aVL is the smallest, equiphasic complex in the limb leads Moving 90 degrees towards the quadrant that represents normal axis deviation takes us to Lead II and +60 degrees Why move 90 degrees? We have already learned that if an impulse travels towards an electrode we get a positive deflection, and if it travels away from an electrode we get a negative deflection If we travel at 90 degrees to an electrode, we get an equiphasic complex (see fig 8.6) Figure 8.6: How the direction of the electrical current affects the shape of the QRS complex The equiphasic complex is recorded when the direction of the axis is around 90 degrees to the lead In effect, the current is moving towards and then away from the lead so it will be displayed on the ECG as being equally positive and negative 52 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 53 Axis deviation Measuring cardiac axis can be a tricky skill to learn at first, so don’t worry if you feel as though you haven’t quite got the hang of it yet The good news is that, with a little practice, you will soon be able to estimate the cardiac axis on a 12 lead ECG quickly and easily The activity for this chapter will give you more opportunity to practise this skill When you have completed this activity you should be able to: ● recognise normal, left and right axis deviation; ● estimate the degrees of axis deviation on a 12 lead ECG Activity 8.1: Measuring cardiac axis Time required to complete this activity: 15 minutes Answers are provided on p 92 Activities Chapter activities Look at the three ECGs below and estimate the cardiac axis for each one Use both the methods that you have been shown in this chapter This should enable you to fill in the boxes under each ECG, choosing one of the words in brackets when they are given Once you have done this, and have checked your answers, you should go and practise some more You could start by looking at the ECG that you recorded back in Chapter Remember: the more you practise, the easier it will become! Figure 8.7: ECG Lead I is (positive or negative) Lead aVF (positive or negative) Therefore the axis is (left, right or normal) Lead is the smallest equiphasic lead Lead Therefore, the cardiac axis is is 90 degrees to the most equiphasic lead degrees 53 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 54 Activities The ECG workbook Figure 8.8: ECG Lead I is (positive or negative) Lead aVF (positive or negative) Therefore the axis is (left, right or normal) Lead is the smallest equiphasic lead Lead Therefore, the cardiac axis is 54 degrees is 90 degrees to the most equiphasic lead ECG chapters 8–11:Layout 10/09/2014 11:06 Page 55 Chapter Ischaemia, injury and necrosis Animal experiments have played a major part in the development of ECG knowledge over the years Fye (1994) describes how, as far back as 1790, Luigi Galvani used electrical stimulation to make a dead frog’s leg dance This was the first step in making a connection between electrical stimulation and the heart’s contraction and it led on to the discovery of links between the heart’s conducting system and myocardial contraction Ischaemia Much later, Bayley (1944) identified ECG changes by means of experiments performed on dogs If a tourniquet is tied around a dog’s coronary artery while it is connected to an ECG, and the coronary artery is occluded for a few minutes, a startling change occurs on the ECG trace The T waves turn upside down (T wave inversion) This is known as an ischaemic change The term ischaemia refers to a condition where there is insufficient oxygenated blood reaching the myocardium (heart muscle) When the tourniquet is released the T waves turn upright again Ischaemia is therefore a reversible change We can relate this to patients with angina Angina is a condition in which the supply of blood to the myocardium does not match its demand for oxygen The process may be reversed by giving the patient a tablet of Glyceryl trinitrate (GTN) GTN reduces the amount of blood flowing into the heart (its preload) and therefore lowers the heart’s workload, reducing the myocardial need for oxygen – a similar effect to that gained by releasing the tourniquet There are two other ischaemic changes that we may see on an ECG: ST depression (where the second part of the QRS complex and the T wave are depressed below the baseline); and T wave flattening Figure 9.1: ST depression The amount of ST depression is measured from between the J point (the end of the S wave) and the isoelectric line 55 ECG chapters 8–11:Layout 10/09/2014 11:06 Page 56 The ECG workbook Figure 9.2: T wave inversion It is useful to record an ECG when a patient is experiencing chest pain Often one of these ischaemic changes will be present and this may confirm that the patient’s pain is cardiac in origin An exercise treadmill test is sometimes used to quantify a patient’s symptoms during aerobic exercise As the patient exerts themselves on the treadmill, the myocardium demands more oxygen and the patient may show symptoms The development of ST depression on the ECG recorded during this procedure may indicate that the heart is becoming ischaemic, as the demand for oxygen increases with exercise ST depression is measured from the bottom of the ECG’s baseline to the ST segment Injury Following the Bayley experiment, scientists examined what would happen if the tourniquet was left on the dog’s coronary artery a little longer When this was tried, another startling change occurred The second half of the QRS complex became elevated above the baseline Known as ST elevation, this is the change that is often seen when the patient is having a heart attack (acute myocardial infarction) This is known as the injury stage and it can still be reversed if it is treated early enough The supply of oxygen to the myocardium has been occluded and the occlusion therefore needs to be removed in order to reinstate the blood supply – again, like releasing the tourniquet This is done by mechanically opening the vessel in a procedure called primary angioplasty and then inserting a coronary stent This procedure is carried out in a specialist Angiography Suite It is performed by introducing a catheter up through the femoral artery to the heart This enables a balloon to be inflated in order to open up the artery Alternatively, a metal structure (a stent) can be used to keep the artery open The criteria for primary angioplasty are that the patient’s ECG should show: ● mm or more ST elevation in at least two chest leads; ● or mm or more ST elevation in two or more of the limb leads (Springings et al 1995); ● or have a posterior myocardial infarction (see Chapter 10); ● or new left bundle branch block (see Chapter 11) The longer the treatment is delayed, the more likely the myocardium is to die from lack of oxygen This is why the public are being educated to report symptoms of chest pain and seek help early Once they have called for help, the patient’s transfer to hospital for primary angioplasty should be as quick as possible (the ‘call-to-balloon’ time) The time between their arrival at hospital and the time they receive their primary angioplasty should also be as quick as possible (the ‘door-to-balloon’ time) In order to try to reduce deaths from coronary heart disease, current guidelines for the treatment of ST-segment elevation myocardial infarction recommend a door-to-balloon time of 90 minutes or less for patients undergoing primary percutaneous coronary intervention (Menees 2013) Necrosis To continue with the Bayley experiment, our experimenters then wondered what would happen if the tourniquet was left on the dog’s coronary artery for even longer? What happened was that after about six hours of occluding the blood supply to the myocardium, the myocardium started to die 56 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 96 The ECG workbook Right (reaching) Extreme (both negative) ● Choose the smallest equiphasic complex in the limb leads ● Find the corresponding lead Move 90 degrees towards the appropriate section ● R wave progression (V1–V6) Good or poor? Is there: ● Ischaemia (ST depression, T wave inversion, T wave flattening) ● Injury (ST elevation) ● Or necrosis? (Q waves, indicate full thickness MI) ● Which leads are affected? Myocardial infarction? ● Posterior MI Suspect if ST depression or tall R waves in V1 and V2 ● Non ST elevation MI Non-resolving T wave inversion or ST depression and Troponin rise ● Diagnosis Which coronary vessels are affected? Bundle branch block ● Wide QRS complexes ● Look at V1 and V6 ● Left bundle branch block (WILLIAM) ● Right bundle branch block (MARROW) Ventricular hypertrophy 96 ● Left V4, V5, V6 high voltage R wave in V5 or V6 >25 mm R wave in V5 or V6 plus the S wave >35 mm R wave in V5 >20 mm Left axis deviation, ST depression, T inversion in V4–V6 P-mitrale (P wave m-shaped) ● Right R wave >S in V1 >5 mm R wave in V1 plus the S wave in V5 or V6 >10 mm Right axis deviation, ST depression, T inversion in V1–V3 P-pulmonale (P wave is peak-shaped) ECG chapters 12–15:Layout 10/09/2014 11:05 Page 97 Activity 2.1 The ECG records electrical impulses as they pass through the specialised cells of the conducting Answers Answers to activities system As the electrical impulses pass across these cells, myocardial contraction occurs Normally, all electrical impulses originate from the sino-atrial node in the right atrium After spreading across the atria, the impulses then pass through the atrioventricular node and into the Bundle of His The impulse spreads through the interventricular septum via the right and left bundle branches Finally, the impulse conducts across the ventricular myocardium, causing contraction The ECG is made up of a number of parts, each of which relates to a different part of the conduction system The first part of the normal ECG complex is the P wave This represents the impulses that arise from the sino-atrial node and spread across the atria towards the atrioventricular node As the impulse spreads across the ventricular myocardium, the ECG records a large wave called the QRS complex The spread of impulse across the atria and ventricles is often referred to as depolarisation The total time that it takes for depolarisation to spread from the SA node to the ventricular myocardium is measured on the ECG as the PR interval When the ventricles recover from depolarisation, the final part of the ECG complex is recorded This is the T wave and represents repolarisation of the ventricles Activity 3.1 Scenario What is the rate? 140bpm Is it regular or irregular? Irregular Is there atrial activity? (P waves) No Is there ventricular activity? (QRS complexes) Yes Are the QRS complexes broad or narrow? Narrow Is there a relationship between the atrial activity and the ventricular activity? NA – there are no P waves Are the PR intervals normal? NA – there are no P waves Name/description? Atrial fibrillation 97 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 98 Answers The ECG workbook Scenario What is the rate? 120bpm Is it regular or irregular? Regular Is there atrial activity? (P waves) Yes Is there ventricular activity? (QRS complexes) Yes Are the QRS complexes broad or narrow? Narrow Is there a relationship between the atrial activity and the ventricular activity? Yes Are the PR intervals normal? Yes Name/description? Sinus tachycardia Activity 4.1 ECG ECG ECG Is there atrial activity? Yes Yes Yes Are the P waves regular? Yes Yes Yes Is the ventricular activity regular? No Yes Yes Is the PR interval constant or does it vary? Constant before QRS complexes Varies Constant If the PR interval is constant, is it normal? Yes N/A No Are there missed QRS complexes? Yes No No Second degree (Mobitz type II) Complete Heart Block First degree What is this heart block? Activity 4.2 The ECG represents… A The structure of the heart B Movement of electrical impulses through the heart ✔ C Movement of blood through the heart D The state of the coronary arteries Electrical conduction of the heart’s cells is also known as… A Polarisation B Repolarisation C Depolarisation D Defibrillation 98 ✔ ECG chapters 12–15:Layout 10/09/2014 11:05 Page 99 Answers to activities ECG paper speed should be… Answers A 25cm/s B 2.5mm/s C 2.5m/s D 25mm/s ✔ millivolt is represented as… A large squares on the vertical axis ✔ B cm on the horizontal axis C large square on the horizontal axis D cm on the vertical axis One small square on the horizontal axis of the ECG paper is… A 0.4 seconds B 0.04 seconds ✔ C second D 0.2 seconds One large square on the horizontal axis of the ECG paper is… A 0.04 seconds B second C 0.2 seconds ✔ D 0.02 seconds Which of these will not cause artefact on an ECG? A Patient movement B Electrical apparatus C Palpitations ✔ D Poor electrode contact Lead V4 is positioned… A In the fourth intercostal space on the right sternal border B In the fourth intercostal space on the left sternal border C In the fifth intercostal space on the midaxillary line D In the fifth intercostal space on the mid-clavicular line ✔ The width of the QRS should be… A < 0.12 seconds ✔ B > 0.12 seconds C 0.12–2.0 seconds D > seconds 99 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 100 Answers The ECG workbook 100 10 An ECG is ‘Sinus’ if … A It has a QRS complex B It has a P wave ✔ C It has a T wave D The ventricular rate is regular 11 Lead position Lead In the fourth intercostal space left sternal border V1 In the fourth intercostal space right sternal border V6 Anterior axillary line on the same horizontal plane as V4 V4 In the fifth intercostal space on the midclavicular line V2 Midaxillary line on the same horizontal plane as V4 V5 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 101 Answers to activities 12 Answers QRS T P PR Activity 5.1 A Ventricular tachycardia B Atrial flutter C Ventricular fibrillation D Atrial fibrillation E Supraventricular tachycardia Activity 6.1 Figure 6.3a: Ventricular (3rd complex) Figure 6.3b: Atrial (complexes 2, and 6) Figure 6.3c: Ventricular (5th complex) 101 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 102 Answers The ECG workbook Activity 7.1 V2 V6 V4 V1 V3 V5 Activity 8.1 ECG Lead aVF + + (positive or negative) Therefore the axis is normal (left, right or normal) Lead I is Lead (positive or negative) aVL is the smallest equiphasic lead Lead II is 90 degrees to the most equiphasic lead Therefore, the cardiac axis is +60 degrees ECG Lead I is Lead aVF Therefore the axis is Lead + _ (positive or negative) (positive or negative) left (left, right or normal) aVR is the smallest equiphasic lead Lead Therefore, the cardiac axis is -60 degrees 102 III is 90 degrees to the most equiphasic lead ECG chapters 12–15:Layout 10/09/2014 11:05 Page 103 Answers to activities Activity 9.1 N for ‘no’ or Y for ‘yes’, as appropriate Q waves? ST elevation? ST depression? T wave inversion? T wave flattening? Likely cause/s (ischaemia, injury, necrosis) I N N Y N N ischaemia II N Y N N N injury III N Y N N N injury aVR N N N Y N lead not used to access these criteria aVL N N Y N N ischaemia aVF N Y N N N injury V1 N N N Y N ischaemia V2 N N Y N N ischaemia V3 N N Y N N ischaemia V4 N N Y N N ischaemia V5 N N Y N N ischaemia V6 N N Y N N ischaemia Answers ECG lead NB: The ischaemic changes seen in the chest leads are most likely to be reciprocal changes from the inferior ST elevations (II, III and aVF) Activity 10.1 Myocardial region ECG leads Anterior ST elevation in II, III and aVF Lateral ST depression and tall R waves in V1–V2 Inferior ST elevation in V1–V6 Septal ST elevation in I, aVL V5–V6 Posterior ST elevation in V3–V4 103 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 104 Answers The ECG workbook Activity 10.2 ECG 1: Anterior Septal; ST elevations in Leads V1–V3 ECG 2: Inferior; ST elevation in Leads II, III, aVF Activity 11.1 V1 Analysis RSR complex in V1 RsR’ complex in V6 V6 WiLLiaM pattern = LBBB Analysis RsR complex in V1 (note the slight notch in the downstroke) RS complex (very subtle notch in the downstroke) in V6 WiLLiaM pattern= LBBB Activity 12.1 Rate 200bpm Regular No obvious P waves QRS present but narrow Name: Narrow complex tachycardia or Supraventricular tachycardia (SVT) Normal axis deviation +60 degrees Ischaemic changes I II III aVL V2–V6 Deep S waves V1–V3 ?left ventricular enlargement Activity 12.2 Atrial enlargement is shown on the ECG by changes to the P wave Notably, the changes will affect the height and the morphology (or shape) of the wave When the right atrium is enlarged, the P wave is often > 2.5 mm in height and is peaked in appearance This is sometimes referred to as P-pulmonale When the left atrium is enlarged, the P wave is often notched and has the appearance of an M shape This is sometimes referred to as P-mitrale 104 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 105 References References Bayley, R.H (1944) Electrocardiographic changes (local ventricular ischaemia and injury) produced in the dog by temporary occlusion of a coronary artery, showing a new stage in the evolution of a myocardial infarction The American Heart Journal 27, 164 Davis, D (1985) How to Quickly and Accurately Master ECG Interpretation Philadelphia: J.B Lippincott Company Eriksson, P., Wilhelmsen, L and Rosengren, A (2005) Bundle-branch block in middle-aged men: risk of complications and death over 28 years The Primary Prevention Study in Göteborg, Sweden European Heart Journal 26 (21), 2300–306 doi: 10.1093/eurheartj/ehi580 Fye, W.B (1994) A history of the origin, evolution and impact of electrophysiology The American Journal of Cardiology 73, 937–49 Kourtesis, P (1976) Incidence and significance of left anterior hemiblock complicating acute inferior myocardial Infarction Circulation 53, 784 Menees, D.S., Peterson, E.D., Wang, Y., Curtis, J.P., Messenger, J.C., Rumsfeld, J.S and Gurm, H.S (2013) Door-toBalloon Time and Mortality among Patients Undergoing Primary PCI New England Journal of Medicine 369, 901–909 doi: 10.1056/NEJMoa1208200 Menown, I.B., Mackenzie, G., Adgey, A.A (2000) Optimizing the initial 12-lead electrocardiographic diagnosis of acute myocardial infarction European Heart Journal 14 (4), 275–83 doi: 10.1053/euhj.1999.1748 Mingels, A.M., Joosen, I.A., Versteylen, M.O., Laufer, E.M., Winkens, M.H., Wildberger, J.E., Van Dieijen-Visser, M.P., Hofstra, L (2012) High-sensitivity cardiac troponin T: risk stratification tool in patients with symptoms of chest discomfort Public Library of Science (PLoS) One (4), e35059 Springings, D., Chambers, J and Jeffrey, A (1995) Acute Medicine Oxford: Blackwell Science Ltd 105 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 106 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 107 Glossary Glossary aneurysm A dilatation or protrusion of the ventricular or arterial wall anterior axillary line An imaginary anatomical line that extends vertically down one side of the chest, starting from the crease between the arm and the chest arrhythmia A disturbance in the heart’s normal rhythm artefact Interference that makes it difficult to analyse an ECG trace accurately atria The smaller of the four heart chambers that sit above the ventricles The right atrium receives deoxygenated blood from the venous circulation and the left atrium receives oxygenated blood from the lungs bifascicular block A blockage of the right bundle branch and one of the fascicles of the left bundle branch bigeminy An arrhythmia in which every other beat is a ventricular ectopic bradyarrhythmia An abnormal heart rhythm that is slower than 60 beats per minute bradycardia A heart rate that is slower than 60 beats per minute (the rhythm is otherwise normal) calibration A means of correcting the measurements taken by an ECG machine capture When the tissue in the chamber being paced has been depolarised clavicle Also known as the collarbone The clavicle extends from the shoulder to the breast bone demand pacing When a pacemaker is programmed to adjust the discharge rate in response to the body’s demands depolarisation When the cells of the heart become electrically charged ECG complex A graphic representation of the electrical activity in a complete heartbeat echocardiogram A diagnostic imaging technique that uses sound waves to show the structure of the heart ectopics/extrasystoles Ectopic beats are extra heartbeats that arise from a focus other than the sino-atrial node and occur early in the cardiac cycle They are also commonly referred to as extrasystoles or premature contractions endocardium The innermost layer of the heart epicardium The outermost layer of the heart equiphasic An ECG complex that has both positive and negative deflections in approximately equal proportions fibrosis Thickening or hardening of tissue haemodynamic The movement of blood through the cardiovascular system Haemodynamics refers to both pressures and volumes of blood heart block A disturbance in the passage of electrical current between the atria and ventricles, as it moves through the conduction system hemiblock A blockage in one of the fascicles of the left bundle branch hyperkalaemia A high level of potassium in the blood hypertrophy Enlargement and thickening of part of an organ (in this case, the myocardium) hypokalaemia Low potassium levels in the blood (typically under 4.0mmol/l in cardiac patients) hypotension Low blood pressure inhibited When a pacemaker function does not emit an impulse if activity is sensed within the pacemaker’s escape interval intercostal space The space between two adjacent ribs ischaemia Reduction in the supply of oxygenated blood to part of the myocardium 107 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 108 The ECG workbook isoelectric line Also known as the ‘baseline’ The line on an ECG trace from which all positive and negative deflections deviate midaxillary line An imaginary anatomical line that extends vertically down the chest, starting from the centre of the armpit multifocal ectopics Ectopics coming from different foci within the heart myocardium The middle (muscular) layer of the heart occluded Blocked so that blood cannot flow pacemaker spike A vertical line on the ECG which indicates that the pacemaker has fired pericarditis Inflammation of the pericardium (the outermost layer of the heart) polarity Relating to the electrical poles (positive and negative) of the cardiac cell primary angioplasty An invasive technique for opening up occluded blood vessels The procedure is performed by introducing a catheter up through the femoral artery to the heart This enables a balloon to be inflated in order to open up the artery (balloon angioplasty) Alternatively, a metal structure (stent) can be used to keep the artery open pro-arrhythmic Putting the patient at risk of arrhythmias R on T phenomenon This occurs when a ventricular ectopic falls so early that its R wave interrupts the T wave of the preceding complex, resulting in a high risk of ventricular tachycardia or fibrillation The apex of the T wave is a vulnerable phase in the ventricular cycle If stimulated by an ectopic, it may produce repeated ventricular responses, leading to life-threatening arrhythmias repolarisation When a depolarised cell starts to return to its resting state revascularisation A procedure to open up occluded blood vessels This can be achieved by primary angioplasty or by thrombolysis senses When a pacemaker monitors the heart’s natural electrical activity If a pacemaker senses a natural heartbeat, it will not stimulate the heart septum The wall of myocardium that lies between the atria and the ventricles sick sinus syndrome An umbrella term for a group of arrhythmias caused by a malfunction of the sinus node stent A stent is a tube placed in the coronary arteries to keep the arteries open while coronary artery disease is being treated A stent is used in a procedure called percutaneous coronary intervention (PCI) or angioplasty sternal notch A depression that is felt at the top of the sternal bone in the front, centre of the chest wall syncope A transient loss of consciousness caused by transient global cerebral hypo-perfusion, characterised by rapid onset, short duration and spontaneous complete recovery tachyarrhythmia An abnormal heart rhythm that is faster than 120 beats per minute tachycardia A heart rate that is faster than 100 beats per minute thrombolysis The administration of a powerful drug to dissolve the clots that occlude the arteries tricuspid valve The heart valve that lies between the right atrium and the right ventricle trifascicular block A blockage in the right bundle branch and the two fascicles of the left bundle branch triggered Delivery of a pacing stimulus in response to sensing a cardiac event troponin A small component of the myocardial cell that is released into the blood when myocardial injury occurs Troponin is not normally present in the blood so measurement of troponin is a useful means of diagnosing myocardial infarction vena cava The major veins that bring venous blood back to the heart The superior vena cava brings blood from the upper body and the inferior vena cava brings blood from the lower body ventricles The two larger heart chambers that eject the blood into the arteries The right ventricle ejects blood into the pulmonary artery and the left ventricle ejects blood into the aorta 108 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 109 uploaded by [stormrg] Index Index Acute coronary syndrome 58, 60 Anterior myocardial infarction 63–68, 96 Anterior fascicule 85 Arrhythmias 27–33 Artefact 3, 24, 77 Atrial ectopics 36 Atrial fibrillation 27 Atrial flutter 28, 29 Axis deviation 47, 50, 53, 85, 86 - extreme 48, 50 - normal 47, 50 - left 48, 50 - right 49, 50 Bifascicular block 88 Bundle branch blocks 73–77, 85, 88, 96 - left 73, 74, 77, 78 - right 75–77, 78 Chest leads 39, 41, 44 Chamber enlargement 79–84 Conducting system 7–9, 47, 73–75 Differential diagnosis 59 Ectopics 35–38 Evolving pattern of myocardial infarction 55–59 Extrasystoles 35–38 Heart blocks 13, 19–23, 85 - first degree 19 - second degree 19 Wenkebach 19 Mobitz Type II 20 - third degree 20 Hemiblocks 85 - Diagnosis of 87 - Left anterior 86 - posterior 86, 87 Hexaxial Reference System 50–52 Hypertrophy 79–84 - left atrial 81 - left ventricular 79–80, 96 - right atrial 81 - right ventricular 80, 96 Inferior myocardial infarction 63, 64, 65, 67, 96 Injury 55, 56, 59, 65, 96, 103 Intervals 15 Ischaemia 55, 59, 65, 73, 96, 103 Lateral myocardial infarction 63, 96 Lead positions 4, 5, 25 Limb leads 4, 5, 39, 40, 41 Necrosis 55, 57, 59, 65 Non ST segment elevation myocardial infarction 58 Paced rhythms 91–94 Pacemakers 91 - Malfunctions of 93 Paper speed P-mitrale 81, 96, 104 Polarity of limb leads 4, 39, 95 Posterior fascicule 85 Posterior myocardial infarction 56, 68, 96 P-pulmonale 81, 96 PR interval 8, 13, 15, 17, 19–21, 23, 95, 97, 98 P wave 8, 10, 13–15, 20, 81, 95, 104 QRS complex 8, 11–17, 24, 26, 39, 41, 42, 45, 73–79, 95, 104 QT interval 14 Q wave 8, 10, 41, 57, 58, 73–77, 96 Reciprocal changes 65–66 R wave 41–45, 68, 80, 96 R wave progression 42–45, 96 Septal Myocardial Infarction 63 Sinus rhythm 24, 79 Sites of infarction 63–70 Standardisation ST elevation 56, 57–59, 63, 65, 66–69, 103 ST depression 55,59, 66–69, 80, 96, 103 Strain pattern 80 Supraventricular tachycardia 29, 30 Thrombolysis 77 Trifascicular block 89 Troponin 58 T wave 8, 77 - flattening 55, 59, 96 - inversion 55, 57–59, 80, 96 Ventricular Ventricular Ventricular Ventricular ectopics 35 fibrillation 31, 32 paced rhythms 92 tachycardia 31 Wandering baseline 109 ECG chapters 12–15:Layout 10/09/2014 11:05 Page 110 ... 8–11:Layout 10/09 /20 14 11:06 Page 71 Sites of infarction Figure 10.6: ECG Activities 10 71 ECG chapters 8–11:Layout 10/09 /20 14 11:06 Page 72 72 Figure 10.7: ECG Activities 10 The ECG workbook ECG chapters... necrosis) ECG chapters 8–11:Layout 10/09 /20 14 11:06 Page 61 Figure 9.6: A 12 lead ECG with a number of abnormal ECG changes on it 61 Activities ECG chapters 8–11:Layout 10/09 /20 14 11:06 Page 62 ECG. .. bundle branch block 73 74 The ECG workbook ECG chapters 8–11:Layout 10/09 /20 14 11:06 Page 74 Figure 11 .2: Left bundle branch block ECG ECG chapters 8–11:Layout 10/09 /20 14 11:06 Page 75 Bundle branch