ecg Flash Cards

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Title: ecg
Description: ECG
Number of Cards: 21
Save Count: 0
Author: frankie_lorford13
Created: 2011-06-02
Tags: ecg
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    • Question
    • Answer
    • Side 3
    • Describe the rules on the nature of the signal - upward, downward and amplitude.
    • Depolarisation going towards to electrode - upward signal
      Depolarisation going away from electrode - downward signal.
      Repolarisation going towards the electrode - downward signal.
      Repolarisation going away from the electrode - upward signal

      Amplitude is decided by how many myocytes are changing potential and how directly the impulse is going to or away from electrode.
      - Directly towards/away electrode = large signal
      - Obliquely towards/away from electrode = small signal
      - Right angles to electrode - NO SIGNAL!
    • What is P wave? When are these absent?
    • P wave is the depolarisation of the atria. Repolarisation of atria is not seen as it is masked by QRS complex.
      P waves usually are followed by QRS complexes.
      P waves are absent in atrial fibrilation and an irregular base line is seen.
    • What is PR segment? What is normal? What problems can cause an abnormal PR segment?
    • PR interval is the conduction time from atria to ventricles. It is how long the AV node holds the impulse.
      PR intervals are usually 120-200ms (3-5 squares)
      They are prolonged in first degree heart block and erratic in 2nd degree heart block
    • What is QRS complex?What is normal?When is it abnormal?
    • The QRS complex is ventricular depolarisation.
      - Q wave -septal depolarisation spreading to ventricle
      Pathological Q waves - larger downward deflection than 2mm
      - R wave - main ventricular depolarisation
      - S wave - end ventricular depolarisation

      The QRS complex is usually 120ms (3 large squares).
      The QRS complex is NARROWED in supraventricular tachycardias. Any abnormality of conduction will take longer to depolarise ventricles causing a widened QRS.
      The hight of R wave should not exceed 25mm or ventricular hypertrophy.
    • What is T wave? When are these abnormal?
    • T wave is repolarisation of the ventricle.
      T waves are always inverted in lead VR and usually in lead 1.
      In black people there may be inverted T waves in leads V3 and v4.
      Inverted T waves sometimes indicate MI or pulmonary embolism ( in leads VI-V4 if accompanied with right cardiac axis deviation)
    • What is ST segment? when is it abnormal?
    • ST segment the repolarisation delay. It is raised in MI and depressed in ischaemia in the leads looking at infarcted/ischaemic myocardium. ST elevation is present in every lead of someone with pericarditis.
    • How long does each large and small square represent? How do you calculate rate?
    • Each large square (5mm) represents 200ms.
      Each small square represents 40ms.

      To calculate the rate you divide 300 by the RR interval ( number of large squares).
      Also you can count the number of QRS complexes in 30 large squares and multiply by 10.
    • What is sinus rhythm? sinus bradycardia/tachycardia?
    • Sinus rhythm is when each P wave is followed by a QRS complex.
      SInus bradycardia is a sinus rhythm of rate below 60bpm.
      Sinus tachycardia is a sinus rhythm of rate below 100bpm.
    • Where do leads v1-6 look at?
    • V1-V2 looks at the right ventricle
      V3-v4 looks at the interventricular septum
      V5-V6 looks at the left ventricle
    • Where do leads I,II,III,VL,VR,VF look at?
    • leads VL, I and II look at the left side of the heart.
      Leads III and VF look at the inferior surface of the heart - right ventricle
      Lead VR looks at right atrium
    • Describe the cardiac axis and left and right axis deviation.
    • A normal cardiac axis will show upward deflection in leads I, II and III.
      Right axis deviation will show a downward deflection in lead I and a more upward deflection in lead III.
      - This is caused by right ventricular hypertrophy or by pulmonary conditions eg PE

      Left axis deviation is a downward deflection in leads 2 &3 but an upward deflection in lead 1.
      - This is usually caused by a conduction defect
    • Describe Right bundle branch block.
    • Right bundle branch block will indicate a normal heart if QRS complex is less than 120ms ( 3 small squares). Otherwise it may indicate an atrial septal defect or PE.

      MarroW
      - M - V1 - RSR
      - W - V6 - QRS

      The conduction is blocked in the right bundle branch so the left ventricle is depolarised first and then the right is causing a second R wave.
    • Describe left bundle branch block.
    • A left bundle branch block can NEVER be normal and will indicate ischaemia, aortic stenosis, hypertension or cardiomyopathy.

      WilliaM
      - W -V1 -QRS
      - M -V6 -RSR
      Conduction is blocked in left bundle branch so septa is depolarised right to left, with the right ventricle depolarised first.
    • What doe electrodes detect?
    • Electrodes detect changes in membrane potential - depolarisation or repolarisation.
      Sometimes they detect skeletal muscle signals if limb leads are placed on limbs which twitch.
    • What is seen in myocardial infarction?
    • STEMI
      - ST elevation, inverted T waves, pathological Q waves
      - troponin and creatine kinase
      NSTEMI
      - ST depression, pathological Q waves may be present from previous infarct
      - no enzymes or cardiac markers
    • Describe first degree heart block.
    • Prolonged PR interval - greater than 200ms.
    • Describe 2nd degree heart block.
    • Erratic PR intervals
      Mobitz - occasional non conducted beats
      wenckebach - PR interval becomes increasingly prolonged until a beat is dropped, QRS does not follow a P wave.
      2:1, 3: 1 block - indicates 2/3 P waves per QRS complex
    • Describe 3rd degree heart block
    • Complete heart block - there is no relation between P waves and QRS complexes. Usually wide QRS complexes result with rate less than 50bpm.
    • Describe ventricular tachycardia and ventricular fibrilation
    • Ventricular tachycardia - an ectopic pacemaker in the ventricle depolarises with high frequency. The QRS complexes are wide and abnoramal and T waves are hard to find.
      Ventricular fibrilation - the ventricular muscle fibres contract independently so there is no QRS complex and ECF is totally disorganised.
    • Describe wolff-parkinson white syndrome.
    • Wolff parkinson white syndrome is a re-conduction loop. There is an accessory conducting bundle between the atria and ventricle so the impulse can travel down the septa via the bundle of his and back into the atria via the accessory conducting bundle to re-activate atrium. During re-entry tachycardia no p waves can be seen.
    • When is QT prolonged?
    • QT is prolonged with some electorlyte abnormalites and by some drugs. If greater than 450ms, it may lead to ventricular tachycardia.