14. Clinical IV - Conducting System and the ECG Flashcards
PHASES in CARDIAC MYOCYTE (NON-PACEMAKER) ACTION POTENTIAL
4 - FLAT, STABLE RESTING POTENTIAL at -90 mv
0 - DEPOLARISATION due to Na+ INFLUX
1 - INITIAL REPOLARISATION as K+ channels open
2 - PLATEAU as Ca2+ channels open
3 - Rapid REPOLARISATION due to K+ efflux (ca2+ channels close)
4 - resting potential - K+ efflux
in ECG what does QT INTERVAL represent
LENGTH of VENTRICULAR DEPOLARISATION & REPOLARISATION
- relates to HEART RATE
slower heart rate -> longer QT interval
PHASE 0 - rapid DEPOLARISATION due to Na+ INFLUX, of CARDIAC MYOCYTES ACTION POTENTIALS is represented by which part on an ECG
QR INTERVAL
- rapid rising slope
RS INTERVAL (down slope) on ECG represents which PHASE of the CARDIAC MYOCYTE ACTION POTENTIAL
INITIAL REPOLARISATION
PHASE 2 PLATEAU is represented by which part on ECG
ST INTERPHASE
T WAVE REPRESENTS which PHASE of CARDIAC MYOCYTE ACTION POTENTIAL
PHASE 3 REPOLARISATION (K+ efflux)
PR SEGMENT on ECG represents…
DELAY at AV NODE
what does ABSOLUTE REFRACTORY PERIOD mean
CANNOT GENERATE NEW ACTION POTENTIAL in this period
- before Repolarisation phase 3
RELATIVE REFRACTORY PERIOD is when a stronger than before stimulus may generate a new action potential. what part of the ECG does it COINCIDE with
(stimulation here may cause life threatening arrhythmias)
T WAVE APEX
- during REPOLARISATION
CONDUCTION starts where (via PURKINJE FIBRES) and goes in what DIRECTION of heart layers
in ENDOCARDIUM
and spreads outwards TOWARDS EPICARDIUM
12 LEAD ECG uses how many ELECTRODES
(all 12 leads are Bipolar)
10 ELECTRODES
in an ECG RECORDING a 1 MM SQUARE corresponds to how much VOLTAGE and how much TIME if the PAPER SPEED is 50 mm/s
0.1 mV
0.02 seconds
(large 5 mm square is 0.5 mV and 0.1 seconds)
what are the 2 ANATOMICAL PLANES used for ECG LEADS
FRONTAL PLANE & HORIZONTAL PLANE
detecting electrical vectors travelling in frontal / horizontal plane
CHEST LEADS are placed in which PLANE
HORIZONTAL PLANE
what are the 2 ELECTRODES used in an ECG
EXPLORING ELECTRODE : + POSITIVE deflection/wave (upwards above baseline)
the electrical vector is directed TOWARDS it
REFERENCE ELECTRODE: - NEGATIVE deflection (downwards below baseline)
electrical vector is directed AWAY from Exploring Electrode
which ELECTRODE produces a POSITIVE WAVE
EXPLORING as the electrical vector is directed TOWARDS it
AVF LEAD is at what ANGLE of ELECTRICAL AXIS
90 DEGREES
- AVR LEAD is at what ANGLE of ELECTRICAL AXIS
(recommended that avR lead is inverted to -avR as this fills a gap in the coordinate system and thus facilitates interpretation of the ECG)
30 DEGREES
AVL LEAD is at what ANGLE of ELECTICAL AXIS
-30 DEGREES
there are 6 ELECTRODES and 6 LEADS across the CHEST WALL (horizontal plane).
what do V1 and V2 OBSERVE
VENTRICULAR SEPTUM (SEPTAL LEADS) normally
what do V3 and V4 across the chest wall observe
ANTERIOR WALL of LEFT VENTRICLE
(ANTERIOR LEADS)
what do V5 and V6 across the chest wall observe
LATERAL WALL of LEFT VENTRICLE
(LATERAL LEADS)
in ECG if the 1ST WAVE is NEGATIVE (below baseline) what wave is it
Q WAVE
what does it mean in an ECG if the 1ST WAVE is POSITIVE (above baseline)
NO Q WAVE
all POSITIVE WAVES in an ECG are which wave
R WAVE
any NEGATIVE WAVE AFTER a POSITIVE (R) WAVE is what wave
S WAVE
How do we represent LARGE and SMALL WAVES in ECG
LARGE - CAPITAL LETTERS
SMALL - lower case
in ECG what is the 1ST DEPOLARISATION
the ATRIA
in ECG what is the 2ND DEPOLARISATION of
INTERVENTRICULAR SEPTUM (via purkinje fibres)
- creates small + R wave in V1 and small - Q wave in V5
in ECG what is the 3RD DEPOLARISATION of
VENTRICULAR FREE WALL
- large + R wave in V5 (towards it)
- large - Q wave in V1
in ECG what is the 4TH DEPOLARISATION of
BASAL PART of VENTRICLES
- small - S wave in V5 (heading away from v5)
(V1 does not detect this vector)
what comes after the 4th DEPOLARISATION in ECG
REPOLARISATION
T WAVE is CONCORDANT / in the SAME DIRECTION as the QRS WAVE
why is this
(depolarisation is detected from endocardium to epicardium)
- the duration of the ACTION POTENTIAL is SHORTER in EPICARDIAL CELLS
therefore REPOLARISATION starts in EPICARDIUM towards endocardium
therefore REPOLARISE EARLIER
the direction of the vectors during depolarisation and repolarisation are opposite but so is the flux of ions therefore there is NO NET DIFFERENCE in the DIRECTION of the electrical vector
what is the NORMAL ELECTRICAL AXIS range in ECG
(reflects the average direction of ventricular depolarisation during ventricular contraction)
from -30 DEGREES to 90 DEGREES
(to the left and downwards)
what is it called if ELECTRICAL AXIS is MORE POSITIVE than 90 DEGREES
RIGHT AXIS DEVIATION
when does ELECTRICAL AXIS become LEFT AXIS DEVIATION
if MORE NEGATIVE than -30 DEGREES
SINOATRIAL NODE is SUPPLIED by which ARTERY
RIGHT CORONARY ARTERY (in 60% of people)
in 40% of people from Left Circumflex Arterty
ATRIOVENTRICULAR NODE is SUPPLIED by which ARTERY
RIGHT CORONARY ARTERY (90% people)
(left circumflex in 10% people)
RIGHT and LEFT BUNDLE BRANCHES are SUPPLIED by which ARTERY
LEFT ANTERIOR DESCENDING (LAD)
may have collaterals from right coronary artery and left circumflex
BUNDLE of HIS is SUPPLIED by which ARTERY
mainly from RIGHT CORONARY ARTERY
but contributions from septal branches of Left Anterior Descending
POSTERIOR FASCICLE activates the inferior and posterior wall
what is it SUPPLIED by
PROXIMALLY by RIGHT CORONARY ARTERY
and occasionally septal branches of Left Anterior Descending
DISTALLY by ANTERIOR and POSTERIOR SEPTAL BRANCHES
ANTERIOR FASCICLE activates the anterior wall
what is it SUPPLIED by
SEPTAL BRANCHES of LEFT ANTERIOR DESCENDING
(very sensitive to ischaemia)
RIGHT CORONARY ARTERY detected by which LEADS
II, III and AVF
V1, V3R - V6R
LEFT CIRCUMFLEX ARTERY observed by which LEADS
I, AVL, -AVR
V4 - V9
LEADS that observe INTERVENTRICULAR SEPTUM
V1 & V2
LEADS that observe INFERIOR WALL
II, III, AVF
LEADS that observe ANTERIOR WALL
V3 & V4
LEADS that observe ANTEROLATERAL WALL
V5 & V6
LEADS that observe LATERAL WALL
I, AVL, -AVR
why are the P and T WAVES SMOOTH but the QRS complex have SHARP SPIKES
- P and T WAVES generated by LOW FREQUENCY SIGNALS
- QRS complex has much HIGHER FREQUENCY SIGNALS
