4 Unique properties of cardiomyocytes Electrical syncytiumThis means that the cells are coupled together in a way that permits rapid conduction of electrical impulsesAutomaticityThis describes the ability of cardiomyocytes to spontaneously depolarise. Under normal conditions the cells of the sinoatrial node have the fastest rate of spontaneous depolarisation and therefore are the dominant pacemaker cells.
5 What is the ECG measuring? Electrical activity detected at the body surfaceCardiac tissueNeuromuscular tissue (= movement)Movement artefact such as trembling results in irregular baseline movement as shown below:
6 Einthoven’s triangleDr Einthoven invented the first practical ECG in 1903Einthoven’s triangle refers to the imaginary equilateral triangle formed by the 3 standard limb leadsLeft forelimb Left hindlimb- Lead III +- Lead IILead IThe dots demonstrate the standard electrode positions
7 Anatomy of the intracardiac conduction system Sinoatrial node (SAN)Bundle of HisAtrioventricular node (AVN)Left bundle branchRight bundle branchRight Left
8 Origin of -QRS-T P ECG: -VE (Right forelimb in lead II) P Wave of depolarisation moves from sinoatrial node across atria from right to left thereby creating a flow in current towards the positive electrode+VE(Left hindlimb in lead II)Right Left
9 Origin of P- RS-T Q ECG: -VE (Right forelimb in lead II) P Q Small delay as impulse traverses AVN hence trace returns to baseline.Depolarisation of the proximal interventricular septum then creates a small negative deflection – the Q wave.+VE(Left hindlimb in lead II)Right Left
10 Origin of P- Q S-T R ECG: -VE (Right forelimb in lead II) P QR Wave of depolarisation moves rapidly through the conduction system to the heart apex thereby creating a flow in current towards the positive electrode – the R wave+VE(Left hindlimb in lead II)Right Left
11 Origin of P- QR -T S ECG: -VE (Right forelimb in lead II) P Q R S Wave of depolarisation moves from the cardiac apex towards the heart base+VE(Left hindlimb in lead II)Right Left
12 Origin of P- QRS- T ECG: -VE (Right forelimb in lead II) P QRS T Wave of depolarisation moves from sinoatrial node across atria from right to left thereby creating a flow in current towards the positive electrode+VE(Left hindlimb in lead II)Right Left
13 Section 2 - Indications for obtaining an ECG Common indications:Document heart rate and rhythmDysrhythmia on auscultationLess common indications:Electrolyte abnormalitiesSuspected drug toxicitySuspected cardiac chamber enlargement
15 Patient set up for conscious ECG Patient calm and stillGood electrical contactClips over bony areas to reduce muscle artefact50mm/s in leads I, II, III, aVL, aVR and aVF25mm/s rhythm strip for 1-5 minutes
16 Machine set up for conscious ECG Is this the machine that is commonly used in the clinics?If so then I can expand on order of button pressing.If not then prob more helpful if we use the machine that is in the clinics for the images / movie of actually taking the ECG.
17 Set up for monitoring ECG Multi-parameter monitorsTape ensures good contact between electrode and pad
18 Muscle movement artefact A common artefact seen on ECG is movement artefact caused by electrical activity present in moving muscles being detected by the ECGThis results in rapidly undulating baseline movement which does not disrupt the superimposed heart rhythm.
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