Cardio1- EKG

  1. Graphic representation of summed electrical activity of the heart.
  2. ******What is the standardization for voltage measurement (calibration) with EKG paper?
    small squares= 1mm; (((1cm)))= 1mV; therefore, 10 small squares or (((2cm/2 large squares)))= 1mV
  3. What is the baseline on an EKG?
    line immediately prior to P wave
  4. What is the most important/most common information that can be obtained from an EKG?
    cardiac rhythm and conduction
  5. What information can be obtained from an EKG? (5)
    heart rate, cardiac rhythm and conduction, info about heart muscle (hypertrophy, ischemia), pericardial diseases, effects of extracardiac diseases on the heart
  6. Describe the electrocardiographic system as a function of the body.
    • heart- current generator as cardiac cell depolarize
    • torso- volume conductor of current with resistance
    • Current flowing across the heart in sheets of dipoles creates depolarization boundaries with an instantaneous electrical field measured as potential difference
  7. ________ form leads.
    Connected electrodes
  8. The potential for current flow between electrodes is measured by a _____________, and _____________ is displayed as the EKG.
    galvanometer (electrocardiograph); potenital difference
  9. The QRS complex represents the summed _____________ across the ___________.
    phase 0 depolarizations; ventricular myocytes
  10. The T wave represents the summed ___________ of the ___________.
    phase 3 repolarizations; ventricular myocytes
  11. As far as action potential, the ST interval is the __________.
    phase 2 plateau
  12. The EKG is the test of choice for...
    the identification of heart rhythm and conduction disturbances (arrhythmias).
  13. The EKG CANNOT measure...
    mechanical activity or contractility of the can be nearly dead with a normal EKG tracing.
  14. What are the x and y-axes on EKG paper?
    • x-axis: time in seconds or milliseconds
    • y-axis: potential difference in millivolts
  15. Determine the time duration for a canine P-wave measuring 3.5mm boxes wide, with an EKG recording speed of 50mm/sec.
    • chart?chf=bg,s,00000000&cht=tx&chl=3.5mm%20%5Ctimes%20%5Cfrac%7B1sec%7D%7B50mm%7D%20&chs=232x66  
    • 0.07sec
    • Normal P wave duration for a dog is <0.04s, but it is often longer in giant breeds.
  16. Determine the amplitude of a feline R-wave in lead II, when the distance from the top pf the baseline to the tip of the R-wave measures 14.5mm and the calibration is "standard".
    • 2cm=1mV<--is this the right conversion??
    • chart?chf=bg,s,00000000&cht=tx&chl=14.5mm%20%5Ctimes%20%5Cfrac%7B1cm%7D%7B10mm%7D%20%5Ctimes%20%5Cfrac%7B1mV%7D%7B2cm%7D%3D%200.725mV&chs=518x66
    • Normal feline R wave amplitude for lead II or aVF is <0.7mV. R wave amplitude suggestive of LV dilation or hypertrophy is 1.0mV in cats; therefore, this value is normal.
  17. Conduction current across the heart is _________.
  18. Areas of lower electrical resistance, through which current flows between most heart muscle cells; allow one cell to initiate depolarization in adjacent cells.
    gap junctions
  19. Potential at which the cell membrane has opened voltage-gated channels to undergo depolarization (phase 0).
  20. What are the 3 major exceptions to the rule of rapid cell-to-cell conduction speed?
    SA node, AV node, and ischemic tissues
  21. Describe the pattern by which current spread through the heart.
    initiated in SA node (pacemaker)--> across atria and internodal pathways--> down AV node and Bundle of His--> traverses the ventricular Purkinje system to reach ventricular myocardium
  22. Describe the Purkinje penetration of dogs/cats/rodents versus large animals/birds.
    dogs/cats/rodents penetrate ~1/4-1/2 of the distance into the myocardium; large animals/birds penetrate completely across the wall (transmural penetration)
  23. What cells discharge to rescue the heart when the sinus node fails or if there is a block of conduction, creating "escape" discharges?
    AV nodal/junctional region and His-Purkinje system
  24. What process leads to the P-wave?
    atrial depolarization starting in the SA node--> right atrium and atrial septum--> left atrium
  25. The ventricular activation process of dogs and cats can be divided into what 4 distinct phases?
    • 1- initial activation of IVS, Q wave
    • 2- mutually cancelling boundaries spread around the heart and return deflection back to baseline
    • 3- depolarization boundary spreads across LVFW, R wave
    • 4- tracing returns to baseline with a smaller basilar oriented boundary
  26. How is the ventricular activation of horses and ruminants different from dogs to cats and why?
    due to greater penetration of purkinje cells, ventricular activation is dominated by a prominent depolarization and a deep S wave
  27. What is the PR interval?
    slow conduction across cells of theAV node
  28. What is the P wave?
    depolarization started by the SA node discharge but cause by activation of fast sodium channels (phase 0) in atrial myocytes
  29. What is the QRS complex?
    ventricular depolarization dictated by the bundle branches and Purkinje system
  30. What is the J point?
    the junction between the QRS complex and the ST segment
  31. What are the ST segment and T wave?
    ventricular repolarization
  32. What is the QT interval?
    time required for ventricular depolarization and repolarization
  33. What is "wandering pacemaker"?
    atrial arrhythmia that occurs when the natural cardiac pacemaker site shifts between the sinoatrial node (SA node), the atria, and/or the atrioventricular node (AV node) that occurs when vagal tone is high--> normal in dogs and horses
  34. Whether the P wave is positive or negative depends on...
    where the electrode is oriented (looking at the same thing from different aspects).
  35. What are the 4 wavefronts/boundaries of depolarization?
    • Boundary 1- ventricular septum (left to right, dorsal to ventral)
    • Boundary 2- mutually cancelling boundary (endocardium to epicardium)
    • Boundary 3- left ventricular free wall (left and caudal)
    • Boundary 4- base of the heart (dorsally)
  36. What do the 4 wavefronts/boundaries of depolarization correspond to on the EKG?
    • Boundary 1- Q wave
    • Boundary 2- back to baseline
    • Boundary 3- R wave
    • Boundary 4- S wave
  37. What is the difference in EKG between small animals and horses/ruminants?
    In small animals, boundary 3 is the predominant boundary (left ventricular free wall); in large animals, boundary 4 is dominant (base of heart)
  38. The biggest boundaries of repolarization occur during the _________.
    T wave
  39. QT interval is inversely related to _________, but the relationship is not ___________; QT also depends somewhat on the ___________.
    HR; linear; size of the animal
  40. What species is it normal to have a positive and quite notched P wave?
  41. What boundaries are picked up by a given probe and which are not?
    boundaries traveling perpendicular to the lead are NOT recorded; waveforms going parallel to the lead are recording [if traveling at an angle, partially picked up]
  42. What is the difference between a unipolar and bipolar lead?
    Unipolar- mainly recording the potential at one electrode compared to the average of the other two or to zero; Bipolar- compares potential at one electrode to another.
  43. How do you determine the lead axis of a unipolar lead versus a bipolar lead?
    • With a unipolar lead, the lead axis can be estimated by drawing a line b/w the surface electrode (the + end of the lead) and the center of the heart.
    • With a bipolar lead, the lead axis is determined by connecting the 2 surface electrodes.
  44. When determining the effects of boundaries on the EKG deflection, you must consider... (4)
    size of boundary, direction, lead axis, and cancellation from other boundaries.
  45. What are the frontal plane leads used in clinical EKG?
    • bipolar leads I, II, III
    • augmented unipolar leads aVR, aVL, aVF
    • precordial/ chest leads- V leads
  46. What lead is typically used to monitor heart rhythm in small animals?
    lead II
  47. What lead is typically used to monitor heart rhythm in large animals?
    base-apex lead [+ left apex to right jugular furrow]
  48. Describe the orientation of Lead I according to Einthoven's triangle.
    left arm minus right arm: potential difference b/w the + LA and -RA
  49. What is a lead axis?
    a straight line b/w the 2 electrodes
  50. Describe the orientation of Lead II according to Einthoven's triangle.
    Left foot minus right arm: potential difference b/w the +LF and -RA
  51. Describe the orientation of Lead II according to Einthoven's triangle.
    Left foot minus left arm: potential difference b/w +LF and -LA
  52. Describe the orientation of Lead aVR according to Einthoven's triangle.
    right arm minus the average of the left arm+left foot: potential difference b/w +RA and -avg of LA & LF
  53. Describe the orientation of Lead aVL according to Einthoven's triangle.
    Left arm minus the average of the right arm and left foot; potential difference b/w +RA and the -avg of RA & LF
  54. Describe the orientation of Lead aVF according to Einthoven's triangle.
    Left foot minus the average of left arm and right arm; potential difference b/w the +LF and -avg of LA & RA
  55. Describe the lead axis of chest leads. What are they comparing?
    lead axis: electrode --> center of the heart; comparing electrode potential to Wilson's central terminal (zero)
  56. What is the base to apex lead used for in large animal medicine?
    monitoring heart rhythm in large animals
  57. Describe the orientation of the base to apex lead in large animals and what it "sees"?
    "sees" ventral to dorsal basilar activation; electrode going dorsally, so normal QRS is negative deflection
  58. What is the purpose of a Holter EKG?
    heart rhythm data for 24 hours (ambulatory EKG that is worn like a sweater)--> find short periods of abnormal heart rhythm
  59. What is the purpose of an "event monitor"?
    like Holter EKG, it is worm and record for 24 hours, BUT it only save data that is a recording of an "event" (fainting spells, collapsing)
  60. What is the purpose of telemetry EKG monitoring?
    intensive care settings as well as for exercise EKG recordings
  61. What is the standard position of the patient for recording an EKG in small animals?
    right lateral recumbancy
  62. What is the standard position of the patients for recording an EKG in large animals?
    standing with left forelimb advanced
  63. What colored lead cables are attached to the hindlimbs?
    red and green (green is ground)
  64. What colored lead cables are attached to the forelimbs?
    black and white
  65. What color are chest leads?
    usually brown
  66. What does a sine wave at 60 cycles/second indicate on EKG tracing?
    artifact: electrical interference from the outlet
  67. What does a non-rhythmic undulation of the baseline indicate? What can be done?
    muscle tremoring; filtering cleans up the trace but reduces the overall voltage displayed
  68. What happens to the heartbeat if the heart becomes denervated?
    A denervated heart fills with blood and pumps as any other normal heart because the SA node has intrinsic pacemaker activity. However, a denervated heart takes longer to increase HR with exertion and slows more gradually with rest because it is not under the influence of the CNS.
  69. What are normal HR ranges for horses, cows, dogs, and cats?
    • Horses- 44-50bpm
    • Cows- 75-80bpm
    • Dogs- 60-180bpm
    • Cats- 140-240bpm
  70. Does the size of the QRS complex relate directly to myocardial contractility?
    NO. The EKG cannot measure mechanical activity or contractility of the heart; you can be nearly dead and have a normal EKG tracing!
  71. Calculate the HR for a regular heart rhythm based on the R-R interval of 20mm; the paper speed is 25mm/s.
    If the heartbeat is regular, count the number of 1mm boxes b/w two consecutive R waves and divide it by the paper speed to get the R-R interval; then divide 60 by the R-R interval to get bpm.

    • chart?chf=bg,s,00000000&cht=tx&chl=20mm%20%5Ctimes%20%5Cfrac%7B1s%7D%7B25mm%7D%20%3D%200.8s&chs=326x66
    • chart?chf=bg,s,00000000&cht=tx&chl=%5Cfrac%7B60%7D%7B0.8%7D%20%3D%2075bpm&chs=188x66
  72. How is HR calculated with heart rhythm is irregular?
    count the number f QRS complexes per 3s (or 6s) then multiply by 20 (or 10).
  73. What does isoelectric mean?
    flat or nearly at baseline
  74. What is a normal sinus rhythm?
    inspiration decreases vagal activity and causes HR to increase; expiration decreases HR as it causes vagal activity to resume. [Vagal tone decreases HR by inhibiting firing of the SA node].
Card Set
Cardio1- EKG
vetmed cardio1