1 / 53

Electrocardiogram

Electrocardiogram. Wendy Blount, DVM Nacogdoches TX. ECG – What it Detects. Heart chamber enlargement Eccentric hypertrophy Dilation and growth of heart chambers Due to volume overload Concentric hypertrophy Wall thickening of heart chambers Due to pressure overload

audi
Download Presentation

Electrocardiogram

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electrocardiogram Wendy Blount, DVM Nacogdoches TX

  2. ECG – What it Detects Heart chamber enlargement • Eccentric hypertrophy • Dilation and growth of heart chambers • Due to volume overload • Concentric hypertrophy • Wall thickening of heart chambers • Due to pressure overload Conduction Disturbances

  3. ECG – What Doesn’t Detect Type of Heart chamber enlargement • Eccentric vs. Concentric hypertrophy • Congestive Heart Failure A Short ECG won’t detect many arrhythmias • Arrhythmias can be intermittent • 10 minutes is <1% of the day

  4. ECG – When to Do • Pulse deficits detected on exam • Chaotic heart sounds (arrhythmia) detected on exam • Tachycardia • Bradycardia • Episodes of weakness or collapse • Pre-anesthetic in sick or geriatric animal • Abdominal mass (especially spleen) • Heart murmur

  5. ECG – When to Do Event Recorders • Owner/witness starts recording during an event Holter Monitors • Continuously record ECG for 24 hours • Can rent for Dr. Kate Meurs at Washington State Vet School http://www.vetmed.wsu.edu/deptsVCGL/holter/requestform.aspx

  6. ECG – Helpful Hints • Always in right lateral recumbency • Patient on a towel or rubber mat • Metal tables are more problematic • Limbs perpendicular to body • Place leads at the elbow and knee • No one moves while the ECG is being recorded • Enhance lead contact with gel or alcohol Alcohol is FLAMMABLE!!

  7. ECG – Helpful Hints Which lead goes where • “Snow and Grass are on the ground” • White and green leads are on the bottom (R) • “Christmas comes at the end of the year” • Red and green are on the back legs • “Read the newspaper with your hands” • White and black are on front legs White – RF Green – RR (ground) Black – LF Red – LR

  8. ECG – The Cardiac Cycle P wave • SA node fires • Atrial depolarization (contraction) • HS4 2. Iternodal tracts (shortcut to AV node)

  9. ECG – The Cardiac Cycle PR interval • Beginning of P wave to beginning of QRS • AV node • *most of the PR interval is here* • Bundle of HIS • bundle branches (R&L) • Purkinje fiber network

  10. ECG – The Cardiac Cycle QRS complex • ventricular depolarization (systole) • Q wave 1st negative deflection • R wave 1st positive deflection • S wave 2nd negative deflection

  11. ECG – The Cardiac Cycle QRS complex • HS1 • AV valves closing • beginning of QRS • HS2 • Semilunar valves closing (AoV, PV) • end of QRS • Pulse is generated

  12. ECG – The Cardiac Cycle T wave • Ventricular repolarization (diastole) • HS3 • Ventricular filling • if myocardium is stiff

  13. ECG – The Cardiac Cycle QT interval • beginning of QRS to end of T wave • ventricular depolari- zation & repolarization • HS1, HS2, HS3 • Pulse generated

  14. ECG – The Cardiac Cycle ST segment • Between S & T waves • Between ventricular contraction (depolarization – systole) and ventricular relaxation (repolarization – diastole) • Isn’t measured per se • But it’s relationship with baseline is noted

  15. ECG – 6 Leads Bipolar leads • I – LF+ RF- • II – LR+ RF- • III – RR+ LF- Unipolar leads • aVR – RF+ (summation lead III)- • aVL – LF+ (summation lead II)- • aVF - LR+ (summation lead I)-

  16. ECG – Systematic Interpretation • Heart Rate and Rhythm • Measurements of the parts • P wave - width and height • PR interval - length • QRS - width and height • QT interval – length • ST segment – relative to PR interval • T wave - width and height • Mean Electrical Axis Form

  17. ECG – Measurements • Take 3-5 measurements and average • All measurements done in lead II • Use calipers • Measure from the center of the line

  18. ECG – Heart Rate At 25 mm/sec, 150mm = 6 sec • “Bic Pen Times Ten” • Accurate within 10 beats per minute At 50 mm/sec, 300mm = 6 sec • A Bic Pen times Twenty • Accurate within 20 beats per minute

  19. ECG – Heart Rate Normals • Giant dogs 60-140 Med-Lg dogs 70-160 • Toy dogs 80-180 Puppies 70-220 • Cats 100-240 Get Baseline heart rates for individuals on every visit

  20. ECG – Rhythm Normal Sinus rhythm • Regular heart rate • Measure from one P wave to the next with calipers • P, QRS and T waves in each complex Respiratory Sinus Arrhythmia • heart rate regularly irregular • Speeds up with inhale, slows with exhale (vagal tone variance, in a regular cycle) • P, QRS and T waves in each complex • Variable P wave – wandering pacemaker • Heart rate less than 200 Arrhythmia

  21. ECG – Rhythm Respiratory Sinus Arrhythmia

  22. ECG – P Wave Measurements • Atrial depolarization (contraction) • Normal Dog: <0.4 mV x <0.04 sec <0.5 sec in giant breeds • 4 boxes tall • 25 mm/sec 1-1.25 boxes wide • 50 mm/sec 2-2.5 boxes wide • Normal Cat: <0.2 mV x <0.04 sec • 2 boxes tall

  23. ECG – P Wave Measurements • Wide P wave (Sometimes Notched) • 25 mm/sec > 1 box wide • 50 mm/sec > 2 boxes wide • LA enlargement • Tall P wave (often spiked) • Dog > 4 boxes tall, cat > 2 boxes tall • RA enlargement • Variable P wave – normal variation • “wandering pacemaker” – increased vagal tone • Lack of P wave • Atrial standstill

  24. ECG – P Wave Measurements Wandering pacemaker

  25. ECG – PR Interval

  26. ECG – PR Interval Conduction from atria to ventricles (AV node) Establishes the ECG baseline Normal Dog: 0.06-0.13 sec Normal Cat: 0.05-0.09 sec

  27. ECG – PR Interval Conduction from atria to ventricles (AV node) Establishes the ECG baseline Normal Dog: 0.06-0.13 sec Normal Cat: 0.05-0.09 sec

  28. ECG – PR Interval • Short PR Interval (tachycardia) • AV node is bypassed • “Accessory pathway” (Wolff-Parkinson-White) • Congenital or acquired • Treated in people by radioablation of the pathway • Sudden onset of tachycardia in a dog • Can try calcium channel blockers • Diltiazem SR (Plumb dose) • If you don’t treat right away, the myocardium will poop out & rapidly progressive CHF will ensue

  29. ECG – PR Interval Normal Dog: 0.06-0.13 sec Normal Cat: 0.05-0.09 sec • Long PR Interval • Slow conduction through abnormal AV node • AV Blocks

  30. ECG – PR Interval Normal Dog: 0.06-0.13 sec Normal Cat: 0.05-0.09 sec 1st degree AV Block • Every P wave is followed by a QRS • Due to increased vagal tone • Non-pathogenic 50 mm/sec

  31. ECG – PR Interval

  32. ECG – PR Interval 2nd degree AV Block Some P waves not followed by a QRS • Mobitz type I – PR progressively longer until QRS dropped (Wenkebach Phenomenon)

  33. ECG – PR Interval 2nd degree AV Block Some P waves not followed by a QRS • Mobitz type 2 – no pattern • PR interval does not change • P-P interval is consistent, so SA node is working fine • PR interval may be prolonged and may be normal • Occasionally, a P wave is not followed by a QRS • Not necessarily pathogenic

  34. Physiology - Cardiac Pacemakers Automatic cells in the heart • Depolarize on their own during phase 4 of the cardiac cycle • Rate of depolarization affected by autonomic nervous system • SA node (60-180 beats/min dog) (100-240 cat) • AV node (40-60 beats/min dog) (80-130 cat) • Purkinje fibers (20-40 beats/min) • Bundle of HIS (20-40 beats/min) • Ventricular myocytes (20-40 beats/min)

  35. Physiology - Cardiac Pacemakers Automatic cells in the heart • The fastest functioning pacemaker in the heart takes over, by default • The closer to the AV node, the more the escape beat will resemble normal QRS • The closer to the ventricle, the more wide and bizarre the QRS will appear • Escape rhythm – pacemaker other than SA node takes over, because SA node fails to fire

  36. ECG – PR Interval 3rd degree AV Block (complete AV block) No relationship between P waves and QRS • P waves have their own rate (faster), determined by the normal SA node • QRS has its own rate (slower), determined by the automaticity of the fastest remaining functioning pacemaker • Treatment • pacemaker • Prognosis • Cats – without anesthesia, potentially very good • Dogs – eventual asystole is likely, if no pacemaker implanted

  37. ECG – PR Interval 3rd degree AV Block (complete AV block) • Pacemaker above bifurcation of bundle of His • Pacemaker left ventricle

  38. ECG – QRS Complex Measurements Normal Dog: <40 lbs: <0.05sec x <3.0 mV • 30 boxes tall • 25 mm/sec 1.25 boxes wide • 50 mm/sec 2.5 boxes wide >40 lbs: <0.06sec x <3.0 mV • 25 mm/ sec 1.5 boxes wide • 50 mm/sec 3 boxes wide Normal Cat: <0.04sec x <0.9 mV • 9 boxes tall • 25 mm/sec 1 box wide • 50 mm/sec 2 boxes wide

  39. ECG – QRS Complex Measurements R wave measured from baseline to top • Tall R wave, wide QRS • LV enlargement • Left Bundle branch block • Deep S wave in leads I, II & III • RV enlargement

  40. ECG – Bundle Branch Blocks • Depolarization wave through myocardium rather than through Purkinje network on affected side • takes longer • “appears bigger” on ECG • Can be persistent or intermittent • Intermittent often precipitated by increased heart rate (delayed refractory period) • Left side, right side or both • Bilateral BBB looks like 3rd degree AV block

  41. ECG – Bundle Branch Blocks Right Bundle Branch Block (RBBB) • Causes: • primary conduction system disease • Disruption of moderator band • RV enlargement • Congenital (especially beagles) • ECG • Deep S wave leads I, II, III, aVF • Wide QRS • May cause a split S2

  42. ECG – Bundle Branch Blocks Left Bundle Branch Block (RBBB) • Causes: • primary conduction system disease • Widespread LV myocardial disease • Unlike RBBB, not usually benign • ECG • Tall R wave • Wide QRS • Looks like a VPC, but follows normal PR interval

  43. Ventricular Premature Complexes • Depolarization wave through myocardium rather than through Purkinje network on affected side • takes longer • “appears bigger” on ECG

  44. Ventricular Premature Complexes • VPCs are like escape beats in that they both originate from the ventricular myocardium • VPCs are abnormal due to primary LV pathology or secondary to metabolic disease • Escape beats are the normal life saving response to a failure of upline pacemaker • VPCs can be persistent or intermittent • Intermittent often precipitated by increased heart rate (delayed refractory period) • Multiform VPCs are more serious • Multifocal areas of LV pathology

  45. ECG – ST Segment ST segment depression or elevation • >0.2mV between baseline and ST • hypothermia • hypokalemia • Digitalis toxicity • Bundle branch block • Myocardial infarction • Rare in dogs • Can be seen in feline HCM

  46. ECG – Mean Electrical Axis (MEA) • when a wavefront spreads toward an electrode, the largest possible deflection will occur • When a wavefront spreads perpendicular to a lead, the smallest or no deflection occurs • ECG shows the sum of all wavefronts relative to the lead being used to measure (MEA) • Isoelectric lead • lead with the smallest deflection • Perpendicular to the MEA

  47. ECG – Mean Electrical Axis (MEA) • The normal MEA is 40o to 100o in the dog • Lead II is most perpendicular to the normal MEA • largest deflections • best for measurements • aVL is most often the isoelectric lead • Approximates MEA in normal dogs

  48. ECG – Mean Electrical Axis (MEA) Calculating MEA by graph • Calculate the net deflection in lead I • Graph on “x axis” • Calculate net deflection in head aVF • Graph on “y axis” • Draw the vector between the two (MEA)

  49. ECG – Mean Electrical Axis (MEA) +3 - 5 = -2 +10 -1.5 = +8.5 - + MEA = 105o

  50. ECG – Mean Electrical Axis (MEA) Estimating MEA • Find the isoelectric lead • NOT the lead with smallest deflections • Lead with smallest NET DEFLECTION • MEA is perpendicular to that, in the direction of net deflection

More Related