November 15 Flashcards
what does the rhythm describe?
the part of the heart that is controlling activation
why are P waves smaller than the QRS complex?
because the muscle mass of the atria is
What is the definition of the R wave?
the first upwards deflection - irrespective of whether or not there is a Q wave
what is the standard running rate of an ecg?
25 mm/s
what time period do a large and small square represent?
O.2 s and 0.04 s
Define the PR interval
the length of time between the beginning of the p wave and the beginning of the QRS complex
What does the PR interval represent
the time taken for depolarisation from the SA node to the AV node to the Bundle of His and then to the ventricles
What is the normal range of a PR interval
3-5 squares = 120-200ms
What does a lengthened PR interval suggest?
1st degree haert block. It is generally a benign finding that does not require any treatment, however it may be an indicator of higher degree AV block in the future and depending on the PR interval.
Name a medication that should not be given to someone with a lengthened PR interval.
Beta-Blockers
Give two causes for a shortened PR interval.
A short PR interval can be seen when the AV node delay is bypassed such as in Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome.
What does the breadth of the QRS complex represent?
length of time taken for the excitation to spread through the ventricles. a broad QRS complex implies a conduction abnormality
What is the normal length of time for a QRS complex?
The normal duration (interval) of the QRS complex is 0.08 and 0.10 seconds (80 and 100 ms). When the duration is between 0.10 and 0.12 seconds it is intermediate or slightly prolonged. A QRS duration of greater than 0.12 seconds is considered abnormal.
How is the QT interval defined?
The time from the beginning of the Q wave to the end of the T wave.
What should the maximum time be for a QT interval?
The QTc is considered prolonged if greater than 450 ms in males and 470 in females .
The normal QT interval is controversial and multiple normal durations have been reported. In general, the normal QT interval is less than 400-440 ms (0.4 to 0.44 seconds). Females have a longer QT interval than males. Also, lower heart rates result in a longer QT interval. A quick way to see if the QT interval is prolonged is to examine if the T wave ends past the half-way point between the R-R interval. If the T wave ends past the half-way point of the R-R interval, then it is prolonged.
What arrhythmia can occur is the QT is >450ms ?
VT
Name two causes for a lengthened QT interval.
Prolongation of the QT interval can occur from multiple medications, electrolyte abnormalities (hypocalcemia, hypomagnesemia and hypokalemia) and certain disease states (i.e. intracranial hemorrhage).
which lead(s) look at the right atrium?
VR
which lead(s) look at lateral side of the heart?
II, III and aVL
which lead(s) look at the inferior surface?
III and VF
which lead(s) look at the right ventricle?
V1 & V2
which lead(s) look at the septum and anterior wall of the Left Ventricle
V2, V3
which lead(s) look at the anterior and lateral walls of the Left Ventricle?
V5, V6
what are the important aspects of analysing the segments and intervals respectively?
segments - whether of not they are isoelectric
intervals - duration in ms
What pattern would you expect in leads I, II and II in
a) normal cardiac axis
b) right axis deviation
c) left axis deviation
a) ↑in I ↑in II & ↑in III - with the greatest depolarisation in II
b) ↓in I ↑in II & ↑in III - with depolarisation in III > II
c) ↑in I ↓in II & ↓in III
Give two explanations for RAD
- pulmonary disease (R ventricle has become hypertrophied and so puts greater effect on QRS)
- tall thin person
What is the most common cause for LV hypertrophy?
conduction defect
Describe first degree heart block
the PR interval > 220. The conduction does get through to the ventricles and completes but takes a long time to do so
Given four causes of first degree heart block
CAD, Rheumatic Carditis, Electrolyte Imbalance, Digoxin Toxicity
Describe a second degree heart block
conduction completely fails to pass the AV node and/or bundle of HIS
Name the main types of second degree heart block and describe the characteristics that would be seen on an ECG
1) Mobitz type I = Wencheback: would appear as PR getting longer and longer until there is a non-conducting p wave. Then returns to normal.
2) Mobitz II - constant PR but every now and then one is dropped. May proceed third Degree HB
3) Ratio of conducted to non-conducted
Describe the ECG changes that would be apparent in third degree heart block and explain why this occurs.
No relation between the P wave and the QRS complex. Indicative of normal atrial contraction (p wave) but this is not conducted (to stimulate QRS). Ventricles are only excited by escape mechanism.
3rd degree HB is more indicative of fibrosis than ischaemia
What is a ‘bundle branch block’ and how does it appear on an ECG
A bundle branch block is where there is a delay either through the left or right bundle branches which leads to a delay in depolarisation of the ventricular muscle.
This is seen on an ECG as a widened QRS Complex (>120ms)
What does RBBB suggest?
RBB can can indicate problems with the right side of the heart - but it can also be a normal variant - especially in athletes. (QRS should not be extended)
Can a LBBB be a normal variant?
No - it always suggests heart disease - especially in the LV. Usually indicative of Aortic Stenosis of Ischaemic Heart Disease.
How and where do you look for a RBBB on an ECG?
Best seen in V1 where there is a RSR(I)
How and where do you look for a LBBB on an ECG?
Best seen in V6 - notched top cf an ‘M’
What ECG changes would you expect in hyperkalaemia?
tented t waves, broad QRS complex and loss of P waves: can lead to a cardiac arrest rhytm
How can you establish the difference between a superventricular (sinus, atrial or junctional) vs ventricular rhythmn
Superventricular - depolarisation spreads in the normal way so normal QRS
Ventricular - abnormal conduction route - abnormal QRS
What are the characteristics of Atrial Tachycardia?
Loss of sinus rhythm (no P wave) and atria depolarise >150x/min
What are the characteristic features of Atrial Flutter?
Rate is .250/min: no flat baseline between p wave. “sawtooth”
What are the characteristic features of VT?
abnormal, wide QRS with no P waves
What do notched p waves imply?
Left Artrial Hypertrophy
What do tall R waves in V1 and V6 imply?
V1 - RVH, V6 - LVH
In which leads would you expect to see ST elevation with an
a) anterior infarct
b) inferior infarct
c) lateral infarct
d) posterior infarct
a) V3-V4 (but also V2-V5)
b) III, avF
c) I, avL and V5/6
d) R waves in V1
What do inverted T waves imply?
- may be normal - but may also be indicative of PE, Ischaemia or LVH/RVH
