Chapter 2 Flashcards
P wave is caused by…
the SA node (located at the top of the right atrium) initiating atrial depolarisation
P wave amplitude…
< 0.25mV (2.5 small squares)
P wave duration…
< 0.12s (3 small squares)
P wave is positive in…
I and II
Inverted p wave in I may suggest…
arm electrodes are placed wrong, dextrocardia or abnormal atrial rhythm
P wave is inverted in…
aVR
P wave in V1 can be…
biphasic
PR interval =
The time between onset of atrial depolarisation and onset of ventricular depolarisation as the electrical impulse is conducted through the AV node, the bundle of His, bundle branches and Purkinje fibres
Duration of PR interval =
0.12 – 0.20s (3-5 small squares)
QRS complex =
Ventricular depolarisation
QRS duration =
< 0.10s (2.5 small squares)
Delays in ventricular depolarisation e.g. bundle branch block =
wide QRS (>0.12s, 3 small squares)
The left side of the septum depolarises first and then the impulse travels towards the right…
Lead V1 lies immediately to the right of the septum = an initial small positive deflection (R wave) is caused as the depolarisation wave travels towards this lead
When the wave of depolarisation travels away from the recording electrode…
the first deflection is negative = small Q wave
normal Q waves =
<2 small squares deep, <1 small square wide and <25% of the amplitude of the R wave
are often present in lateral leads (I, aVL, V5, V6)
Precordial lead QRS morphology changes depending on whether the depolarisation forces are moving towards or away from a lead:
V1 = small positive (R) wave followed by large negative deflection (S wave)
R wave increases in amplitude from V1-V6 (usually <27mm in V5-V6)
S wave depth decreases from V1-V6 (V1 = <30mm, often absent in V5-V6)
QRS complex changes from being predominantly negative in V1 to being predominantly positive in V6 (the transition zone lies between V3 and V4)
ST segment =
Period between end of ventricular depolarisation and the begging of repolarisation
ST segment in V1-V3 =
rapidly ascending S wave merges with T wave (high-take off)
Non-pathological ST elevation can be associated with…
benign early repolarisation (common in young men, athletes and black people)
T waves =
Ventricular repolarisation
T waves are…
Asymmetrical - first half more gradual slope than the second half
Inverted in aVR, sometimes in III and V1 (occasionally in V2 as well as V1 – isolated V2 inversion is abnormal)
If symmetrical and inverted suggests myocardial ischemia
Tall T waves?
?acute myocardial ischemia or hyperkalaemia
QT interval is…
Total time taken for depolarisation and repolarisation of the ventricles
QT interval duration =
0.35-0.45s
U waves =
Small deflection that follows the T wave
Generally upright (except in aVR)
Most prominent in V2-V4
Results from repolarisation of mid-myocardial cells (those between the endocardium and epicardium) and His-Purkinje system
seen in athletes, hypokalaemia and hypercalcemia
