ECG Flashcards
What is an electrocardiogram?
electrical changes during the cardiac cycle being recorded via electrodes placed on limbs and chest wall, transcribed onto graph paper.
Action potentials of heart are affected by external factors. what are they?
- ANS (parasympathetic) via vagus nerve innervating SAN.
- physical activity increases HR and increase in sympathetic efferent activity to SAN.
explain the conduction orchestrated by the SAN.
- fastest depolarisation of heart, suppressing other pacemakers.
- Intrinsic firing rate 60-100/min.
- sets heart at sinus rhythm.
explain conduction and the AVN.
- slows conduction giving atria time to contract fully.
- intrinsic firing rate w/o simulation is 40-60/min.
explain conduction and the ventricles. specifically RBB and LBB.
- intrinsic firing rate usually not manifested.
- 20-40/min so extremely slow.
what is escape rhythm or junctional rhythm?
- heart rate of 40-60 bpm by AVN in extreme instances of sinus bradycardia or complete heart block affecting SAN.
briefly outline path of electrical activity in the heart.
- initiated at SAN, depolarising RA+LA.
- hits AVN at inter-atrial septum near tricuspid and slows down.
- AVN to bundle of HIS through annulus fibrosis (prevents conduction directly from atria)
- enters ventricular septum via RBB exciting RV and LBB excited LV.
- Purkinje conducts depolarisation through ventricles.
how do we obtain 12 leads (views of heart) using 10 electrodes?
- there are 2 types of leads ; unipolar and bipolar which uses a positive and negative electrode to measure the electrical change.
- lead 1 ( RA to LA ), lead 2 (RA to LL) and lead 3 ( LA to LL) are bipolar and aVL, aVR and aVF are unipolar using same electrodes changing how connected. (which is positive).
- V1-V6 unipolar.
what are the 12 leads? differentiate between the 2 different planes of views.
- 4 electrodes on limbs provide L1, L2, L3 (limb leads), aVR, aVL, aVF (augmented limb leads) and RL electrode for grounding.
- vertical plane.
- 6 on chest V1-V6 (pre-cordial leads)
- horizontal plane.
what causes positive and negative deflection change seen on ECG’s?
- positive deflection caused my the impulse travelling towards the positive electrode, size of deflection can vary depending on direct angle of approach.
eg : lead 2 from RA to LL - negative is when the impulse direction is away from the positive electrode.
eg: aVR
how long does atrial depolarisation last?
- 80 to 100ms
how long does it take for spread of impulse from atria to ventricle?
- 120 to 200ms from start of atrial to start of ventricular depolarisation.
how long is complete ventricular muscle depolarisation?
- 80 to 120 ms for QRS complex.
what are leads V1-V4 good for observing?
antero-septal view.
what are the lead V1 & V4 good for observing?
RV and septum.
