Diagnostic Features of ECGs Flashcards Preview

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Flashcards in Diagnostic Features of ECGs Deck (19):
1

Steps of cardiac conduction/depolarization

  • sinoatrial (SA) node = pacemaker
  • Electrical impulses initiated @ SA node --> internodal tracts --> wave of depolarization in the atrium --> atrioventricular (AV) node.
  • @ AV node: brief delay --> impulses to Bundle of His and activate the ventricles through the right and left bundles
  • bundles --> Purkinje fibers --> activate ventricular myocardial cell depolarization and contraction.

2

Main clinically relevant components of EKG (6)

  • P wave
  • PR interval
  • QRS complex
  • QT interval
  • T wave
  • U wave

3

P wave fxnl action

atrial depolarization

4

PR interval fxnl significance

  • measure of AV node conduction time
  • normal = 0.12 - 0.20 secs

5

QRS fxnl significance

  • ventricular depolarization
  • normal duration = 0.06 - 0.10 secs
  • Q: negative
  • R: positive
  • S: late negative deflection

6

QT interval fxnl significance

  • lasts from begin of Q to end of T
  • total duration of depolarization and repolarization

7

T wave fxnl significance

ventricular repolarization

8

U wave fxnl significance

  • not always seen
  • follows T wave
  • possibly repolarization of purkinje fibers or papillary muscles

9

Line measurements/speed of EKG paper

  • paper speed = 25mm/sec
  • vertical lines = 0.04 sec
  • thick vertical lines = 0.2 sec

10

Calculation of heart rate from EKG

HR=300/# of heavy lines between P waves

11

EKG changes produced by ventricular hypertropy

  • both left and right ventricular hypertrophy result in greater muscle mass --> greater voltage associated with depolarization and repolarization of the myocardium.
    • ecg ventricular hypertrophy is seen as a R wave with greater amplitude.
  • Left ventricular hypertrophy: large positive deflections (R waves) in V5 and V6 and large negative deflections (S waves) in V1.


  • Right ventricular hypertrophy: high voltage in V1 and V2.





     

12

EKG changes caused by myocardial ischemia

  • Ischemic changes alter ventricular repolarization and affect the ST segment and the T wave.
  • Ischemia due to sudden high oxygen demand in the presence of a fixed coronary obstruction causes depression of the ST segment. 

    • In some patients a resting ekg is normal, but ST depression is only visible during exercise due to transient ischemia. 

  • Ischemia due to acute coronary artery obstruction during low oxygen demand can cause T wave inversion.


  • Normally, T waves are in the same direction of the QRS complex.


    Inversion of a T wave→myocardial ischemia
     

     

13

EKG changes in acute myocardial infarction


  • ST elevation is a sign of transmural injury in an acute coronary syndrome, usually with a clot due to platelet aggregation obstructing a coronary artery. 

  • Sizeable (>0.04 s) Q waves can be a sign of transmural necrosis. Infarcts usually involve only the left ventricle.


    • Inferior leads (II, III, aVF): inferior infarcts 




    • V1-V4: anterior wall infarct 






    • I, aVL and V5, V6: lateral wall infarcts.
       

 

 

14

Evolution of transmural acute myocardial infarct


  • Giant upright “hyperacute” T wave 




  • T wave inverts and ST segment rises. 




  • Sometimes, ST elevation precedes of occurs simultaneously with T inversion.

  • Q waves are usually the last to develop.

     

15

Transmural vs. subendocardial acute myocardial infarction


  • Transmural—involves the entire thickness of the LV 




  • Subendocardial—localized to the inner layer of the LV wall. 




    • Subendocardial infarcts do not have Q waves or ST elevation.

    • They do have persistent ST depression.

       

16

EKG changes in hypercalcemia


  • shortened QT interval 

  • often associated with hyperparathyroidism. 

17

EKG changes in hypocalcemia



  • lengthened QT interval 


  • may be associated with life threatening ventricular arrhythmias
     








 

18

EKG changes associated with hyperkalemia

  • increased T wave voltages with a distinctive peaked, symmetrical appearance
  • At higher levels, the P waves may be flattened and the QRS and T waves widened.
  • broad S wave often appears.
  • At very high levels, a sinusoidal pattern appears without P or R waves.

19

EKG changes associated with hypokalemia

  • QT interval is generally prolonged
  • prominent U waves are frequent
  • T waves may be inverted