practical cardiovascular physiology Flashcards
electrocardiogram (ECG): demonstrate ability to perform an ECG and recognise normal ranges
normal duration of P wave
80ms
normal duration of R wave (QRS complex)
80-120ms
normal duration of T wave
160 ms
normal duration of of PR segment
50-120ms
normal duration of ST interval
320ms
normal duration of QT interval
350-450ms
horizontal: how many seconds does 5mm (5 squares) on an ECG correspond to
0.2 seconds
vertical: how many mV dows 5mm (5 squares) on an ECG correspond to
0.5mV
what does an upward deflection denote
wave of depolarisation towards cathode (+) or repolarisation away from cathode (+)
what does a downward deflection denote
wave of depolarisation towards anode (-) or repolarisation away from anode (-)
what is the gradient equal to
velocity of action potential
what is the width equal to
duration of event
what happens during P wave
SAN autorhythmic myocytes depolarise, causing P-wave and atrial depolarisation, with wave moving across from right to left ventricle via internodal fibres, and slightly towards cathode
what happens in the PR segment
AVN depolarises in PR segment and is isoelectric as delayed impulse allowing for ventricular filling
what happens during Q wave: isoelectric section
isoelectric as bundle of His rapidly conducts wave of depolarisation down septum
what happens during Q wave
septum depolarises away from cathode
what happens during R wave
ventricular depolarisation due to Purkinje fibres, with wave spreading towards cathode
what happens during S wave
Purkinje fibres carry wave up myocardium for late ventricular depolarisation, moving away from cathode
what happens during ST segment
depolarised ventricles produce an isoelectric ECG
what happens during T wave
ventricular repolarisation moving towards cathode
what happens during the U wave (may not be obeserved as small size)
Purkinje fibre repolarisation towards cathode
what are electrodes
conductive material in contact with skin
what do cables/wires attach to
electrodes
why is conductive gel put on electrode and arm before ECG
human body not particularly good at conducting
where are the 4 limb leads placed
right arm, left arm, left leg, right leg
what are the chest leads
V1-V6
where is V1 placed
4th intercostal, right sternal border
where is V2 placed
4th intercostal, left sternal border
where is V3 placed
in-between V2 and V4 (on top of 5th rib)
where is V4 placed
5th intercostal, mid-clavicular line
where is V5 placed
5th intercostal, anterior axillary line (usually halfway between V4 and V6)
where is V6 placed
5th intercostal, mid-axillary line
what is the speed an ECG runs at
25mm/sec
what is Einthoven’s triangle
imaginary formation of three limb leads in triangle, formed by arms and legs, forming inverted equilateral triangle with heart at centre, producing zero potential when voltages summed
what is limb lead I from
right arm to left arm
what is limb lead II from
right arm to left leg - normal ECG lead
what is limb lead III from
left arm to left leg
what plane does Einthoven’s triangle use to measure movement of electricity away from heart
coronal
why are limb leads I, II and III bipolar
have physical anodes and cathodes
in bipolar leads, what is a net deflection equal to
sum of net deflections in other 2 leads
what are the unipolar leads (and midpoint of which limb leads)
aVF (limb lead I), aVL (limb lead II), aVR (limb lead III)
what do unipolar leads measure potential difference between
null point with relative 0 potential at centre of triangle (midpoint between two limb electrodes)
what do precordial leads use as cathodes and measure
chest leads, so measure electrical activity flowing from heart towards chest leads
what 3 cardiac arteries are involved with ECG and what heart position do they correlate to
left circumflex (LCx) - lateral, right coronary (RCA) - inferior or anterior, left anterior descending (LAD) - septal
lead I: heart region, artery, cathode, anode
lateral, LCx, left arm, right arm
lead II: heart region, artery, cathode, anode
inferior, RCA, left leg, right arm
lead III: heart region, artery, cathode, anode
inferior, RCA, left leg, left arm
aVR: heart region, artery, cathode, anode
n/a, n/a, right arm, halfway between leg arm and left leg
aVL: heart region, artery, cathode, anode
lateral, LCx, left arm, halfway between right arm and left leg
aVF: heart region, artery, cathode, anode
inferior, RCA, left leg, halfway between right arm and left arm
V1: heart region, artery, cathode, anode
septal, LAD, V1, heart
V2: heart region, artery, cathode, anode
septal, LAD, V2, heart
V3: heart region, artery, cathode, anode
anterior, RCA, V3, heart
V4: heart region, artery, cathode, anode
anterior, RCA, V4, heart
V5: heart region, artery, cathode, anode
lateral, LCx, V5, heart
V6: heart region, artery, cathode, anode
lateral, LCx, V6, heart
what is the axis of a wave or complex
direction wave of depolarisation is moving in on coronal plane (not using precordial leads)
what is the normal cardiac axis
-30 to +120
lead I axis
0
lead II axis
60
lead III axis
120
aVL axis
-30
aVF axis
90
aVR axis
-150
diagram of leads and axis
benjis
how do you calculate the axis
select 2 leads at 90 degrees, work out net QRS depolarisation on each lead, form triangle by drawing x mm along numerical lead, and y mm perpendicular from lead, take theta as tan^-1 ( augmented lead net depolarisation (y)/numerical lead net depolarisation (x)); cardiac axis = numerical lead axis - theta
axis and corresponding ECG
benjis
systematic approach to interpretation
correct recording → signal quality and leads → voltage and paper speed → patient background (CVS/resp disease as axis moves on COPD) → heart rate (300/no. big squares) → durations of P, PR, QRS, ST, QT, T → QRS axis
features of sinus rhythm
Ps followed by QRS 1:1; regular rate and normal; otherwise unremarkable
features of sinus bradychardia
Ps followed by QRS 1:1; regular rate and slow; can be healthy/medication/vagal stimulation
features of sinus tachycardia
Ps followed by QRS 1:1; regular rate and fast; often physiological or decreased venous return
features of sinus arrhythmia
Ps followed by QRS 1:1; irregular rate and normal-ish rate; R-R varies with breathing
features of atrial fibrillation
oscillating baseline so asynchronous atria contraction; irregular and slow rhythm; turbulent flow pattern increases clot risk
features of atrial flutter
regular saw-tooth pattern in baseline on II, III, aVF; atrial:ventricular beats 2:1, 3:1 or higher; not visible in all leads as some flutters hidden in QRS complex
features of 1st degree heart block
prolonged PR due to slower AV conduction; regular rhythm of P:QRS; mostly benign
features of 2nd degree heart block (Mobitz 1)
increasing PR until missed QRS; regularly irregular due to diseased AVN; Wenckebach
feaures of 2nd degree heart block (Mobitz 2)
no PR elongation and some QRS complexes missed; regularly ireregular with fixed ratio of successes to failures (e.g. 2:1); can rapidly deteriorate to 3rd degree
features of 3rd degree heart block
regular P waves and QRS complexes but no relationship; AVN/myocardium can be auto-rhythmic; non-sinus with backup pacemakers; P waves regular and fast, QRS regular and slow
features of ventricular tachycardia
P waves hidden in dissociated atrial rhythms; ventricles beating rapidly and very hard; rate regular and fast; risk of deterioration to ventricular fibrillation; shockable rhythm; all vectors look the same
features of ventricular fibrillation
heart rate irregular and >250bpm; no output; shockable; vectors will change and don’t all look the same
features of ST elevation
P waves visible and followed by QRS; regular normal rate; ST-segment elevated >2mm above isoelectric; caused by infarction
features of ST depression
P waves visible and followed by QRS; regular normal rate; ST-segment depessed >2mm below isoelectric; caused by ischaemia
