Rhythm Recognition Flashcards
What are the sites for defib pads
beneath the right clavicle
left mid-axillary line
What is the difference in voltage in myocardial cells and extracellular space?
90mV
What triggers depolarisation and contraction?
Ion shift
In normal sinus rhythm where does depolarisation begin?
the pacemaker cells (SA node)
What is the first wave in the ECG?
P wave
What does the P wave represent?
depolarisation spreading from the SA node through the atrial myocardium
What happens after the P wave
slow conduction through the AV node, followed by rapid conduction to the ventricular myocardium
What conducts through the ventricular myocardium?
Purkinje fibres
What carries Purkinje fibres?
Bundle of His
What does the QRS complex represent?
depolarisation of the ventricular myocardium
What does the segment between the P and QRS complex represent?
Isoelectric segment- delay in transmission in the AV node
What does the T wave represent?
recovery of the resting potential in the cells of the conducting system and ventricular myocardium
What is happening in bundle branch block?
One of the segments of the bundle of His is diseased or damaged and so conduction is carried much more rapidly through the other division and then more slowly through the ventricular myocardium
What happens to the QRS in bundle branch block?
broadened- because depolarisation of both ventricles takes longer
What is the 6 stage system to analyse an ECG?
- Is there electrical activity
- What is the QRS rate
- Is the QRS rhythm irregular/regular
- Is the QRS complex width normal?
- is atrial activity present
- is atrial activity related to ventricular activity
What is happening in VF?
All coordination of electrical activity is lost
- no effective ventricular contraction and no detectable cardiac output
What is PEA
There are complexes on the ECG that would be expected to produce a pulse but there isn’t one
What is a normal ventricular rate?
60-100
What represents one second on an ECG?
If calibrated to 25mms
5 large squares
How should you estimate ventricular rate?
Count the cardiac cycles in 30 large squares (6 seconds) and multiply it by 10
If the rhythm is irregular what needs to be decided?
- is it totally irregular
- is the basic rhythm regular with intermittent irregularity
- is there a recurring cyclical variation in the R-R intervals?
If the QRS complex of an ectopic is narrow where has it likely originated from?
The atria
What might broad complex ectopics represent?
Ventricular origin or ectopics with BBB
What is a premature beat?
Ectopic beats that occur early
What is an escape beat?
A beat that arises from the AV node of from the ventricular myocardium after a long pause
for example during sinus brady or after sinus arrest
this implies that the focus in the AV node or ventricle that generates this beat is acting as a back-up pacemaker because the function of the SA node is too slow or absent
What is complete AV block?
Escape rhythm in which the cells generating the ventricular rhythm are acting as a pacemaker because no atrial impulses are being transmitted to the ventricules
How many ectopics in quick succession need to occur to be classified as a tachyarrhythmia?
more than 3 in succession
What is bigeminy?
When ectopic beats are occuring alternately with sinus beats for a prolonged period?
What is the upper limit for the QRS?
3 small squares 0.12s
What does saw-tooth P waves suggest?
Atrial flutter
In sustained tachycardia where P waves cannot be seen what may be done?
Vagal stimulation (trainsiently increasing AV block) or adenosine
If retrograde activation of the atria is happening from the AV node what will you be able to see in P waves?
Inversion in II and aVF because atrial depolarisation is happening in the wrong direction
What are the causes of atrioventricular dissasociation?
- complete (third degree) AV block
- some examples of VT
If VF is present and the patient is conscious and has a pulse what should be done?
If it has been more than a few seconds, rhythm isn’t VF check again
What rhythms may resemble VF?
pVT , pre-excited AF
When can pre-excited AF occur?
In the presence of an accessory pathway connecting atrial and ventricular muscle in the WPW syndrome
What confirms the rhythm as VT?
the identification of P waves dissociated from the QRS during a broad complex tachycardia
In the presence of BBB what with a SVT produce?
A broad complex tachycardia
In which patients does TDP usually occur?
Patients with a prolonged Qt interval
What should be avoided in TDP?
Amiodarone
What is a bradyarrhythmia
ventricular rate less than 60
What can cause pathological bradycardia?
malfunction of the SA node or from partial/complete failure of atrioventricular conduction
What is first degree AV block?
PR interval >0.2 s and is a common finding
What does first degree AV block represent?
Delay in conduction through the AV junction
What are the causes of AV block?
physiological (Athletes)
fibrosis of the conducting system
structural heart disease
IHD
drugs
What is second degree AV block?
Some, not all P waves are conducted to ventricles
What are the types of second degree AV block?
- mobitz I
- mobitz II
- 2:1 and 3:1
What is Mobitz I AV block?
- PR interval shows progressive prolongation after each successive p wave until a P wave occurs without a QRS
What is mobitz II ?
Constant prolonged PR interval but some of the p waves are not conducted
these patients have an increased risk of complete AV block and asystole
What is complete heart block?
No relationship between P waves and QRS complexes
What is an agonal rhythm?
Occurs in dying patients
Slow, irregular, wide complexes often varying morphology
Doesn’t usually generate a pulse
What is atrial flutter often caused by?
Disease that affects the right heart
-COPD
-PE
-CHF
What does prolonged QT predispose to?
ventricular arrythmia
- tdp
- vf
Which is the best lead for measuring QT?
Lead III
What is the normal QTc?
- 0.43 in women
- 0.45 men
What does a QTc of >0.5 suggest
high risk of sudden cardiac death
what may cause a shortened QTc
- hypercalcaemia
- digoxin
What are some causes of prolonged QTc?
- hypokalaemia
- hypomagnesaemia
- hypocalcaemia
- hypothermia
- myocarditis