8. Rhythm recognition Flashcards
ECG electrodes should be placed over BONE/ MUSCLE
bone - to minimise artefact
in normal sinus rhythm, depolarisation begins in a group of specialised pacemaker cells called the ___ ___ node, located where?
SA node
close to the entry of the SVC in the right atrium
what is the p wave?
wave of depolarisation spreading from the SA node through the atrial myocardium
transmission of electrical impulse to the ventricles
1) firstly there is slow conduction through the __ __ node
2) then rapid conduction fo the ventricular myocardium by specialised conducting tissue called ___ ___
3) the ____ ___ ___ carries these fibres from the AV node and then divides into right and left bundle branches in the respective right and left ventricles
1) AV
2) purkinje fibres
3) bundle of his
what does the QRS complex represent
depolarisation of ventricular myocardium (<0.12s)
between the P and QRS there is a small isoelectric segment which largely represents what?
the delay in transmission through the AV node
what does the T wave represent?
ventricular repolarisation
standard paper calibration in ECGs? how many squares in 1 second?
25mm/s
5 large squares in a second (25 small squares)
estimating HR from ECG?
count number of R waves in30 large squares (6s) and multiple by 10
how to tell where an ectopic beat has originated from?
narrow QRS (<0.12): atrial muscle or AV node
broad QRS: ventricular muscle or supraventricular with BBB
some ventricular ectopic beats may be accompanied by a P wave occurring shortly after the QRS complex - what causes this?
retrograde conduction form the ventricles to the atria
T/F: complete AV block is an escape rhythm
true - the cells generating the ventricular rhythm are acting as a pacemaker because no atrial impulses are transmitted to the ventricles
if the QRS complex is less than 3 small squares in width, where does the rhythm originate from?
above the bifurcation of the bundle of His - may be the SA node, atria or AV node (but not the ventricular myocardium)
what is the term for when ectopic beats occur alternately with sinus beats for a sustained period?
bigeminy
typical rate in atrial flutter?
about 300/ min (usually seen best in inferior leads)
sinus P waves are UPRIGHT/ INVERTED in leads II and aVF
upright (if inverted, suggests retrograde activate of the AV node ie junctional rhythm or ventricular in origin)
1) shockable
2) non-shockable
cardiac arrest rhythms?
1) VF, pVT
2) asystole, PEA
T/F: if the pt is conscious or has a pulse, the rhythm is not VF
true
what two rhythm abnomalities may be mistaken for VF?
polymorphic VT
pre-excited AF
T/F: there is often little variation in heart rate during a single episode of VT
true
what is a capture beat in VT?
atrial activity may continue independently of ventricular activity. Occasionally, these atrial beats may be conducted to the ventricles causing capture beats or fusion beats- a single normal looking QRS complex during monomorphic VT
what is a fusion beat in VT?
a wave of depolarisation travels down from the AV node simultaneously with a wave of deploarisation travelling up from the ventricular focus producing the arrhythmia- hybrid QRS caused by fusion of the normal and monomorphic QRS complex
in the presence of bundle branch block, an SVT will produce a NARROW/ BROAD complex tachycardia
broad
but the safest approach is to regard all broad complex tachycardias as VT until proven otherwise
torsades de pointes is a type of _____ VT, which usually arises in patients with a prolonged ___ ___
polymorphic
QT interval (inherited syndromes/ antiarrhythmic drugs/ MI)
treatment of torsades de pointes?
IV magnesium and/ or potassium
removal of any predisposing drugs
may require overdrive pacing
name an antiarrhythmic drug that can prolong the QT interval
amiodarone
emergency treatment of most bradycardia is…
atropine and/ or cardiac pacing
occasionally isoprenaline or adrenaline
what is the PR interval and normal value
time between onset of p wave and start of the QRS complex
normally 0.12-0.2s
what is first degree AV block
when the PR is 0.2s
a common finding
causes of 1st degree AV block?
physiological e.g. athletes
fibrosis of the conducting system
IHD
structural heart disease
drugs
T/F: first degree AV block always requires immediate treatment
false - rarely causes symptoms or requires treatment
what is described here: when some, but not all, P waves are conducted to the ventricles resulting the absence of
two types of 2nd degree AV block?
Mobitz I (Wenckebach)
Progressive prolongation of PR until a P wave occurs without a QRS complex
Mobitz II
Constant (often prolonged) PR interval in the conducted beats but some of the P waves are not followed by a QRS
which type 2 heart block has a higher risk of progression to complex AV block and asystole?
Mobitz II
what is 3rd degree AV block (CBH)
no relationship between P waves and QRS complexes - atrial and ventricular depolarisation arises independently from separate pacemakers
1) in complete heart block, if the site of the ‘pacemakers’ stimulating the ventricles if located in the AV node or proximal BoH, this will produce an intrinsic rate of ____
2) if located in the distal Purkinje fibres or ventricular myocardium will produce broad QRS complexes, often with a rate of ____
1) 40-50
2) 30-40 (more likely to stop abruptly resulting in asystole)
if the normal cardiac pacemaker cells (SA node) fails, the rhythm will be generated more distally and the rate will be FASTER/ SLOWER
slower
what is a junctional rhythm?
where the heartbeat originates from the AV node or His bundle
what will normally be slower - a ventricular escape rhythm or a junctional rhythm?
ventricular escape rhythm (because the ‘pacemaker’ cells are lower down)
what is an idioventricular rhythm?
a rhythm arising from the ventricular myocardium
what is an accelerated idioventricular rhythm?
occurs with a normal HR (usually faster than sinus but not quite VT) - often observed after successful thrombolysis or PCI ‘reperfusion arrhythmiaw
what is an agonal rhythm
occurs in dying patients - slow, irregular, wide ventricular complexes, often of varying morphology
when is a tachyarrhythmia described as supraventricular?
when it arises from tissue situated above the bifurcation of the bundle of His
T/F: sinus tachycardia is not an arrhythmia
true - it represents a response to some other physiological or pathological state e.g. exercise, anxiety, blood loss, fever etc
what is the commonest sustained arrhythmia encountered in clinical practice?
AF
common causes of AF?
hypertension, obesity, alcohol excess, structural heart disease
in atrial flutter, atrial flutter is seen as flutter waves at a rate of about _____, best seen in the ____ leads
300
inferior - ‘saw tooth’ pattern
atrial flutter usually arises in the right atrium, so is a recognised complication of diseases that affect the right heart including…
COPD
major PE
complex congenital heart disease
CCF
2 causes of a broad complex tachycardia
1) tachycardia arising in the ventricle below the bifurcation of the bundle of His
2) supraventricular tachycardia conducted aberrantly (right or left bundle branch block)
classic ECG feature in WPW? what is this caused by?
they have accessory pathways connecting atrial and ventricular myocardium
some conduction occurs through these pathways as well as through the AV node - resulting in pre-excitation
> > widens the QRS complex by delta waves
QT prolongation predisposes people to which arrhythmias in particular?
TdP
VF
what is the QT interval measured as?
start of the QRS complex to the end of the T wave
which lead usually allows the best measurement of the QT interval?
lead II
the QT interval is usually slightly SHORTER/ LONGER in the presence of bundle branch block
longer
the QT interval SHORTENS/ LENGTHENS as the heart rate increases
shortens
(the QTc corrects for this)
normal QTc in men and women?
up to 0.45s in women and 0.43s in men
a QTc of ___s or more indicates a high risk of cardiac arrest and sudden death
0.5s
causes of
1) shortened QT interval
2) prolonged QT interval
1) hypercalcaemia, digoxin treatment
2) hypokalaemia, hypomagnesaemia, hypocalcaemia, hypothermia, myocarditis, MI, drugs
6 stage system to analyse an ECG rhythm?
1) is there electrical activity
2) what is the QRS rate
3) QRS regular or irregular
4) QRS wide or narrow
5) if atrial activity present
6) is atrial activity related to ventricular activity- how so
look at pages 112-113 for rhythm strip recognition
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