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ECG’s and ABG’s Raghul Rajchandar rr1222@ic.ac.ukTILO'S COVERED I. Cardiovascular and respiratory systems II. Cardiac disorders: Summarise the regulation: Outline the regulation of the pathophysiology, presentation and cardiovascular and respiratory systems. management of arrhythmias, valve disorders, and cardiac tissue disorders. III. Cardiovascular and respiratory IV. Cardiovascular and respiratory systems investigations: Outline and interpret integration: Outline the relationship clinical tests for cardiovascular and between cardiovascular and respiratory respiratory diseases. systems.LECTURE TIMELINE 1. ECG Introduction 2. ECG Abnormalities 3.ABG Introduction 4. ABG Summary + Interpretation + CardiacAxis + Interpretation + QuestionsIntroduction to ECG’s • Allow you to visualise depolarisation wave, based on the electrodes used. • Consist of various leads, which are specific combinations of electrodes recording electrical activity from different angles. o 12 leads; 6 in coronal plane, 6 in axial plane. o Standard limb leads – bipolar o Precordial (chest) leads o Augmented limb leads – unipolar • These leads look at voltage difference between 2 electrodes + provide graphical representation of electrical activity from –ve to +ve.Electrode Placement + Reading th V1 – right sternal border, 4 intercostal space V2 – left sternal border, 4 intercostal space V3 – halfway between V2 and V4 V4 – mid-clavicular line, 5 intercostal space V5 – anterior axillary line, at the level of V4 V6 – mid-axillary line, at the level of V4 L RULE: Lead ONE – right arm to Left arm • Leads are read left -> right, top -> bottom, Lead TWO – right arm to Left Leg just like English. Lead THREE – Left arm to Left Leg • First electrode of each bipolar pair you read is always the –ve electrode.Visualising each wave:Interpreting ECG’s 1. Confirm patient details – name, DOB, date. 2. (Verify voltage and paper speed.) 3. Calculate heart rate Name: John Smith DOB: 21/01/59 Date: 28/02/24 4. Assess rhythm – is it sinus? • Regular/irregular • P wave before every QRS • PR interval • Broad/narrow QRS 5. Screen for cardiac axis deviation. 6. Assess ST segment.Interpreting ECG’s 1. Confirm patient details – name, DOB, date. Name: John Smith DOB: 21/01/59 Date: 28/02/24 2. (Verify voltage and paper speed.) 3. Calculate heart rate ➢ 300 / no. of large squares between 2 P-waves ➢ E.g. 300/4.4 -> 68bpm ➢ OR: no. of QRS complexes x 6 ➢ 12*6= 72bpm • Normal HR: 60-100 BPM • <60: bradycardia • >100: tachycardia Assessing Sinus Variations SINUS RHYTHM: • P:QRS = 1:1 • Rate is regular (even R-R intervals) + normal. SINUS BRADYCARDIA: • P:QRS = 1:1 • Rate is regular (even R-R intervals) + slow. • Healthy in athletes, caused by medication/vagal stimulation. SINUS TACHYCARDIA: • P:QRS = 1:1 • Rate is regular (even R-R intervals) + fast. • Can be a physiological response via sympathetic activation. SINUS ARRHYTHMIA: • P:QRS = 1:1 • Rate is irregular (variable R-R intervals) + semi-normal. • R-R interval varies with breathing cycle; vagal stimulation slows. Assessing Atrial Arrhythmias ATRIAL FIBRILLATION: • Asynchronous contraction of atria (not together). • SA node overrides by many mini contractions – “fibrillations”. • Irregular rhythm, slow rate. • No discernible P waves; instead, an oscillating baseline. • Pattern of turbulent flow may increase clot risk. • Manageable, as atria are not essential for cardiac cycle. ATRIAL FLUTTER: • High rate of atrial contractions caused by recurrent signals • Regular saw-tooth pattern in leads II, III, aVF. • Due to relatively long refractory period of AV node. • Atrial: ventricular beats >= 2:1/3:1, as not every atrial contraction can cause ventricular. Assessing Ventricular Arrhythmias VENTRICULAR TACHYCARDIA: • Hidden P-waves; dissociated atrial rhythm. • Regular rhythm, fast rate. • High risk of deteriorating into fibrillation -> cardiac arrest. • Shockable. VENTRICULAR FIBRILLATION: • Irregular rhythm, fast rate. • Ventricles aren’t contracting in a co-ordinated manner; unable to generate a cardiac output. • Shockable. Atrio-Ventricular Heart Blocks FIRST DEGREE: • PR interval prolonged due to slower AV conduction – delayed. • Regular rhythm, P:QRS = 1:1 • Benign, but pathological progression with ageing. SECOND DEGREE – MOBITZ I: • Gradual PR interval prolongation -> eventually beat skipped. • Diseased AV node causing regularly irregular rhythm. • Some P waves are not followed by QRS; this pattern is consistent. SECOND DEGREE – MOBITZ II: • Regular, un-delayed P waves with intermittent dropping of beat. • No PR prolongation; can be regularly irregular OR random. • Can rapidly deteriorate into 3 degree heart block. THIRD DEGREE: • P+QRS waves both regular, but no relationship. • P waves often hidden within bigger vectors – complete signal block. • Non-sinus rhythm compensated by ventricular pacemakers. Assessing ST Variations ST ELEVATION: • Visible P waves, P:QRS = 1:1 • Rate and rhythm is regular and normal. • Elevation of ST-segment by >2mm above iso-electric line. • Caused by infarction -> inadequate blood supply leading to tissue death. ST DEPRESSION: • Visible P waves, P:QRS = 1:1 • Rate and rhythm is regular and normal. • Depression of ST-segment by >2mm above iso-electric line. • Caused by myocardial ischaemia -> inadequate O2 supply to the heart. Where is the ST Elevation (MI) ? Location of MI Leads showing ST elevation Coronary arteryaffected LATERAL I, aVL, V5, V6 Left Circumflex Artery INFERIOR II, III, aVF Right Coronary Artery SEPTAL V1, V2, V3, V4 Left Anterior Descending Artery ANTERIOR V1, V2, V3, V4 Left Anterior Descending Artery Cardiac Axis • Net direction of the depolarisation wave travelling through the myocardium. • Takes into account pairs of perpendicular leads between limb and augmented. • Normal cardiac axis is -30 degrees to + 90 degrees. • Lead I is given as 0 degrees; clockwise is +ve, anti-clockwise is –ve. ———————————————————————————————————— • Most precise way to calculate is by comparing lead I with aVF. • Alternatively, could use lead II/aVL OR lead III/avR. • Two methods of calculating QRS axis: o Approximation using overall net deflection. o Precise trigonometric calculation of QRS angle. QRS Axis Methods: To quickly check if an axis deviation exists, look at lead I and lead II -> if both have a net +ve deflection, then cardiac axis is normal. • The overlap between 2 depolarisations is our range for the QRS axis. Quadrant method: 1. Look at Lead I’s net QRS deflection; no. of squares above vs. below isoelectric line and approximate an angle. 2. Look at aVF’s net QRS deflection and do the same. • The more +ve the deflection is, the closer the angle is to the direction of the lead. • The more –ve the deflection is, the closer the angle is to the opposite direction of the lead. 3. To estimate, combine the 2 overall angles between lead I and aVF and visualise the overlap – this is your range for the overall QRS axis. RECOMMENDED – Watch James Moss’ tutorial; well-explained with worked examples.QRS Axis Cheatsheet:QRS Axis Methods: Example Lead I: more squares above the iso-electric line than below, so overall +ve deflection; because there are still some negative deflection, angle is not exactly 0; instead around -50 degrees. Lead aVF: there are only squares below the iso- electric line, so overall –ve deflection of -90 degrees. QRS axis range is average between 2 individual angles of -50 and -90, so: -70 degrees.ECG Questions 3. What ECG abnormality can be identified in the image above? 1. Calculate the heart rate of the 2. Estimate the cardiac axis of ECG above: the ECG above: a) 62bpm a) -25˚ b) 44bpm b) 145˚ c) 88bpm c) -42 4. What ECG abnormality can be identified d) 108bpm d) 42˚ in the image above? e) 58bpm e) -130˚ECG Answers 3. What ECG abnormality can be identified in the image above? 2nd degree heart block 1. Calculate the heart rate of the 2. Estimate the cardiac axis of ECG above: the ECG above: a) 62bpm a) -25˚ b) 44bpm b) 145˚ c) 88bpm c) -42 4. What ECG abnormality can be identified in the image above? Atrial flutter d) 108bpm d) 42˚ e) 58bpm e) -130˚ ABG Introduction • Measures acid-base components and pressure of gases in arterial blood. Consists of: o Oxygen -> PaO2 -> Amount of O2 in arterial blood o pH -> [H+]: o Acidosis pH <7.35 o Normal 80 – 100 mmHg (10 – 14 kPa) o Normal pH 7.35 – 7.45 o Alkalosis pH >7.45 o Base Excess: o Normal: -2 to +2 o Bicarbonate -> [HCO3]-: o Base -> can combine with H+ to remove from solution o Normal 21 – 28 mEq/L o Carbon Dioxide -> PaCO2 -> Amount of CO2 dissolved in arterial blood o Normal 35 – 45 mmHg (4.5 – 6.0 kPa)Regulating a Constant pH • A buffering system that ensure that pH is within range to prevent protein desaturation. • Works through HCO3-H2CO3 system; dissociation of carbonic acid into protons (H+) and bicarbonate ions. • CO2 + H2O -> H2CO3 -> H+ + HCO3- FAST RESPONSE – LUNGS: • Rapid changes brought about by altering respiratory rate. • Acidosis (too much CO2) -> resp. rate increases -> more CO2 cleared out through hyperventilation • Alkalosis (not enough CO2) -> resp. rate decreases -> less CO2 cleared out through hypoventilation SLOW RESPONSE – KIDNEYS: • Gradual changes brought about by selective excretion/retention of H+/HCO3- to alter pH. • Acidosis -> excess H+ is cleared out, so pH increases. • Alkalosis -> more HCO3- is reabsorbed and retained, so pH increases. Acidosis vs. Alkalosis ACIDOSIS ALKALOSIS Metabolic: Metabolic: ▪ Increased Acid Production: ▪ Excess Acid Removal: ▪ e.g. lactic acidosis, (Diabetic) ketoacidosis, ▪ E.g. excess vomiting/antacids, prolonged gastric Increased ingestion of acids. suctioning, excess Sodium Bicarbonate administered parenterally. ▪ Decreased Acid Elimination: ▪ e.g. renal failure, increased base elimination (excess diarrhoea). Respiratory: ▪ Excess CO2 removal Respiratory: ▪ Many causes -> Hyperventilation ▪ Many causes -> increased CO2 retention ▪ E.g. Fever, thyrotoxicosis, psychogenic responses ▪ E.g. respiratory depression, respiratory muscle (anxiety, fear, pain) impairment, pneumonia, pulmonary oedema. Mixed: Mixed: ▪ PaCO2 high and Base Excess low. ▪ PaCO2 low and Base Excess highInterpreting ABG’s 1. pH – is it high or low? 4. O2 – is this normal? 7.35-7.45 10-13.5kPa Acidosis (low) or alkalosis (high) Normoxaemaia/hypoxia 2. CO2 – does it fit w/ the pH? 5. Is there any compensation? 4.7-6.0 Partial or Complete? Respiratory if CO2 does not follow pH [TIP – partially compensated if HCO3- and CO2 go together.] Compensation if it does Mnemonic: ROME 3. HCO3 – does it fit w/ the pH? 22-28mmol/L Respiratory = opposite Metabolic = equal Metabolic if HCO3- follows Low pH + high CO2 Low pH + low bicarbs Compensation if it does not High pH + high bicarbs High pH + low CO2ABG Summary ABG Questions Interpret the following ABG results: pH: 7.56 (7.35-7.45) pH: 7.30 (7.35-7.45) pO2: 10.7 (10-14) pO2: 7.8 (10-14) pCO2: 5.0 (4.5-6.0) pCO2: 7.9 (4.5-6.0) HCO3: 31 (22-26) HCO3: 32 (22-26) pH: 7.38 (7.35-7.45) pH: 7.51 (7.35-7.45) pO2: 7.9 (10-14) pO2: 7.5 (10-14) pCO2: 7.8 (4.5-6.0) pCO2: 2.9 (4.5-6.0) HCO3: 34.1 (22-26) HCO3: 24 (22-26) ABG Answers Interpret the following ABG results: pH: 7.56 (7.35-7.45) Uncompensated pH: 7.30 (7.35-7.45) Partially pO2: 10.7 (10-14) pO2: 7.8 (10-14) compensated pCO2: 5.0 (4.5-6.0) Metabolic pCO2: 7.9 (4.5-6.0) Respiratory HCO3: 31 (22-26) Alkalosis HCO3: 32 (22-26) Acidosis pH: 7.38 (7.35-7.45) Completely pH: 7.51 (7.35-7.45) pO2: 7.9 (10-14) compensated pO2: 7.5 (10-14) Uncompensated Respiratory pCO2: 7.8 (4.5-6.0) Respiratory pCO2: 2.9 (4.5-6.0) Alkalosis HCO3: 34.1 (22-26) Acidosis HCO3: 24 (22-26)Thank You! 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