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Dr. B. Uma

Cardiac Rhythm and Anaesthesia : Basics of ECG Abnormal rhythms relevant to anaesthetic practice Antidysrhythmic agents Management of perioperative arrhythmias Abnormal rhythms relevant to anaesthetic practice Management of perioperative arrhythmias Antiarrhythmic agents. Dr. B. Uma.

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Dr. B. Uma

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  1. Cardiac Rhythm and Anaesthesia: Basics of ECGAbnormal rhythms relevant to anaesthetic practiceAntidysrhythmic agentsManagement of perioperative arrhythmiasAbnormal rhythms relevant to anaesthetic practiceManagement of perioperative arrhythmiasAntiarrhythmic agents Dr. B. Uma University College of Medical Science & GTB Hospital, Delhi

  2. Basics of ECG

  3. Objectives • What is an ECG • ECG indications • Review of the conduction system • ECG recording ECG paper ECG leads 5. ECG interpretation

  4. What is an ECG? • The electrocardiogram (ECG) is a graphic recording of the electrical potentials generated by the heart. The signals are detected by means of metal electrodes attached to the extremities and chest wall and are then amplified and recorded by the electrocardiograph • Introduced by William Einthoven in 1901

  5. ECG Indications • Monitoring • Diagnosis

  6. ECG Indications… Preoperative period • Risk Assessment • Assess the baseline cardiac status • Information regarding MI, conduction or rhythm abnormalities • Reveals findings related to life threatening metabolic disturbances or susceptibility to sudden cardiac death

  7. ECG Indications… Intraoperative period • Monitoring to detect changes in rate and rhythm or myocardial ischaemia • Monitoring of proper function of pacemakers or implantable cardiac defibrillators in patients undergoing surgery with these devices in place

  8. ECG Indications… Postoperative period • Monitoring • Important in high risk patients when new ischemic or rhythm changes are suspected

  9. ECG Paper

  10. The Normal Conduction System

  11. P wave caused by atrial depolarization Right atrial activation reflected by ascending limb of P wave Duration=0.02-0.04s Left atrial activation reflected by descending limb of P wave Duration=0.05-0.06s Hence, total duration=0.08- 0.10s (maximum duration=0.11s) Maximum normal amplitude=2.5mm

  12. QRS complexiscaused by the ventriculardepolarization • QRS duration0.05 - 0.11 sec • QRS amplitude • S amplitude in V1 + R amplitude in V6 < 3.5 millivolt (mV) • R in V5 or V6 < 2 mV

  13. The ST segment and T wave reflect ventricular repolarization ST segment duration=0.08-0.12s T wave duration=0.16 s T wave should be at least ⅛th but less than ⅔rd of the amplitude of the corresponding R wave

  14. ECG Leads Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)

  15. ECG Leads The standard ECG has 12 leads: 6 Frontal plane leads 6 Horizontal plane leads Frontal plane leads - oriented in frontal or coronal plane of the body and consist of standard leads I, II, III and augmented limb leads AVR, AVL, AVF. Horizontal plane leads - oriented in transverse or horizontal plane of the body and are formed by precordial leads V1-V6.

  16. Standard Limb Leads

  17. Standard Limb Leads

  18. Augmented Limb Leads

  19. All Limb Leads

  20. Precordial leads

  21. Summary of Leads

  22. Anatomic Groups(Summary)

  23. 3 Electrode ECG monitoring • Electrodes placed on the torso to reduce artifacts from limb movement • RA/LA electrodes placed in right and left infraclavicularfossae • LL leg electrode below the left rib cage • Most common mode in OR and ICU • Good enough to detect HR and VF • Inadequate for detecting complex arrhythmias and ST segment monitoring

  24. 5- Electrode ECG monitoring

  25. Modified Chest leads • Modified chest leads (MCL) are useful in detecting bundle branch blocks and premature beats. • Lead MCL1 simulates chest lead V1 and views the ventricular septum. • Lead MCL6 simulates chest lead V6 and views the lateral wall of the left ventricle • CS5 (RA electrode placed under the right clavicle and LA electrode placed in the V5 position)for detection of anterior myocardial wall ischaemia • CB5 (RA electrode over the center of the right scapula and LA electrode in the V5 position) for detection of ischaemia and supraventricular arrhythmias

  26. Ten-Electrode, Twelve-Lead ECG Monitoring

  27. The Right-Sided 12-Lead ECG • The limb leads are placed as usual but the chest leads are a mirror image of the standard 12-lead chest placement • Clinical significance: Patients with an acute inferior MI should have right-sided ECGs to assess for possible right ventricular infarction

  28. Invasive Electrocardiographic Monitoring Esophageal electrocardiogram: • Much closer to atria. Hence better option when p waves recording is uncertain • Detection of posterior wall ischaemia • Esophageal electrodes incorporated into esophageal stethoscopes and welded to conventional electrocardiographic wires

  29. : Intracardiac electrocardiogram: • Multipurpose pulmonary artery catheter with 3atrial and 2ventricular electrodes for intracavitary ECG • Relatively insensitive to electrocautery Endotracheal electrocardiogram: • Endotracheal tube with 2 electrodes embedded • Diagnosis of atrial arrhythmias in pediatrics Intracoronary electrocardiogram: • Coronary guide wire during angioplasty is used • Greater detection of acute ischaemia

  30. ECG Interpretation • Rate • Rhythm • QRS axis • P Wave • PR Interval • QRS Complex • QT Interval • ST Segment

  31. Documentation: name of the patient and the date and time it was recorded. Calibration signal: The amplifier gain is normally adjusted so that a 1 millivolt signal through the ECG amplifier results in a vertical deflection of 10 mm (two large ECG squares). All voltage measurements on the ECG depend entirely on the accuracy of this calibration signal.

  32. Determining the Heart Rate • Rule of 1500 Heart rate=1500/no. of small boxes between adjacent RR intervals • Rule of 300 Heart rate=300/no. of big boxes between adjacent QRS complexes • 6/3 second rule No. of RR intervals in 3sec multiplied by 20 or No. of RR intervals in 6sec multiplied by 10

  33. What is the heart rate? 1500/30 = 50 bpm www.uptodate.com

  34. What is the heart rate? Count number of large boxes between first and second R waves=7.5. 300/7.5 large boxes = rate 40

  35. What is the heart rate? Count 30 large boxes, starting from the first R wave. There are 8 R-R intervals within 30 boxes. Multiply 8 x 10 = Rate 80

  36. Rhythm • Normal: Each QRS preceded by a P wave with a regular PR and RR interval and a rate between 60 and 100 bpm • Irregular • Regularly Irregular • Irregularly Irregular

  37. The QRS Axis • The QRS axis represents the net overall direction of the heart’s electrical activity • Direction of the axis determined on the basis of the hexaxial reference system

  38. The QRS Axis • By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°. • -30° to -90° is referred to as a left axis deviation (LAD) • +90° to +180° is referred to as a right axis deviation(RAD)

  39. Movement of the electrical impulse towards the positive electrode will result in a positive deflection on the ECG. Movement of the electrical impulse towards the negative electrode will result in a negative deflection on the ECG. Movement of an electrical impulse perpendicular to a line between the positive and negative electrodes results in a biphasic deflection on the ECG.

  40. Determining the Axis Predominantly Positive Predominantly Negative Equiphasic

  41. The Equiphasic Approach 1. Determine which limb lead contains the most equiphasic QRS complex. The fact that the QRS complex in this lead is equally positive and negative indicates that the net electrical vector (i.e. overall QRS axis) is perpendicular to the axis of this particular lead. 2. Examine the QRS complex in whichever lead lies 90° away from the lead identified in step 1. If the QRS complex in this second lead is predominantly positive, than the axis of this lead is approximately the same as the net QRS axis. If the QRS complex is predominantly negative, than the net QRS axis lies 180° from the axis of this lead.

  42. Equiphasic Approach: Example 1 The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/ Equiphasic in aVF  Predominantly positive in I  QRS axis ≈ 0°

  43. Equiphasic Approach: Example 2 The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/ Equiphasic in II  Predominantly negative in aVL  QRS axis ≈ +150°

  44. Two lead approach • Look for net QRS deflection in leads I and aVF • If both +ve – Normal axis • If I +ve & aVF predominantly –ve – Left axis deviation • If I –ve & aVF +ve – Right axis deviation

  45. Calculation of Axis – Third Approach • Calculate the net QRS deflection in lead I and aVF • E.g. in lead I, Q wave measures 3 small squares & R wave measures 6 small squares - net deflection is +3 • Similarly, net deflection in aVF is -5 • Cardiac vector is thus sum of individual vectors from leads I and aVF

  46. P Wave • Best evaluated in standard lead II and lead V1 • In standard lead II P wave is pyramidal with a rounded apex • In lead V1 biphasic P wave with an initial positive and a terminal negative deflection • Axis within 40°to 60°

  47. P Wave – Clinical Significance • P Pulmonale -Tall peaked P wave -Amplitude in lead II >2.5 mm -Duration WNL -Expression of right atrial enlargement • P Mitrale -Double peaked, notched or camel humped P wave -Negative deflection in V1> 1mm -Duration of notch > 0.04s -Expression of left atrial enlargement

  48. PR Interval • PR interval - between beginning of P wave and beginning of QRS complex • Duration = 0.12 to 0.20 sec • Reflects time taken for conduction of impulse from SA node to the ventricles through the AV node • Long PR interval: first degree heart block, hyperkalemia • Short PR interval: WPW syndrome

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