ALS Lecture 12 - The Rhythm of the Heart DONE Flashcards
the electrical system of the heart (4)
sinus node, atrio-ventricular node, His-Purkinje system, cardiac myocytes
sinus node (2)
pacemaker, electrical impulses start here
atrio-ventricular node (2)
slows down atrial impulse, prevents very high atrial rates transmitted to ventricles
His-Purkinje system (2)
spreads electrical impulse rapidly, synchronously through left and right
cardiac myocytes (2)
conduct from H-P system, then contract
electrical pathway of heart (6 steps)
- impulse begins at SAN
- spread across atria, atria contract
- AVN stimulated, signal delayed
- impulse down bundle of His, goes left and right
- up Purkinje fibres in ventricles
- ventricles contract from base up
label the diagram of the electrical pathway of the heart (A)
done
what drives the rate of sinus node firing? (2)
sympathetic NS, parasympathetic NS
increased PNS activity does what?
bradycardia
decreased PNS activity does what?
tachycardia
examples of increased PNS activity (3)
sleep, fainting, fitness
examples of decreased PNS activity (4)
exercise, blood loss, heart failure, atropine
increased SNS activity does what?
tachycardia
decreased SNS activity does what?
bradycardia
examples of increased SNS activity (5)
exercise after 1st minute, fear, heart failure, adrenaline, salbutamol
examples of decreased SNS activity (3)
rest and sleep, beta-blockers, fainting
P wave
atrial depolarisation
PR interval
time for impulses to go from SAN to AVN
PR interval is between
start of P wave, start of QRS
PR segment
conduction from AVN, down bundle of His, up Purkinje fibres
QRS complex
ventricular depolarisation
ST segment
ventricles depolarised during plateau of action potential
T wave
ventricular repolarisation
QT interval
time between end of ventricular depolarisation and repolarisation
U wave
repolarisation of papillary muscles/Purkinje fibres
label the diagram of ECG (B)
done
normal PR interval
<200msec, <5 small squares
normal QRS complex
<110msec, <3 small squares
normal QT interval is ___ _____
rate dependent
normal QT interval
<460msec, <12 small squares
QTc
QT interval corrected for rate
QTc =
QT / square root of RR interval in seconds
QTc and QT are the same at
60bpm
on ECG, one small square =
40msec
on ECG, one large square =
200msec
one minute is how many large squares?
300
to get the heart rate in bpm we
divide 300 by number of large squares between each RR interval
if there are 4 large squares between the peaks of QR, what is the heart rate in bpm?
300/4 = 75bpm
in normal sinus rhythm, what is the ratio of P wave to QRS?
1:1, P wave in front of every QRS
look at the ECG showing normal sinus rhythm (C)
done
take a look at ECGpedia (D)
done
ectopic pacemaker
excitable cells cause premature heartbeat outside normal SA node function
ectopic pacemaker pathophysiology (3 steps)
- ectopic pacemaker initiates beat, premature contraction
- does not follow normal signal pathway
- can make heart refractory or incapable of normal function
types of ectopic pacemaker (3)
atrial, junctional, ventricular
bradycardia is a heart rate of
60bpm or less
a person may have resting bradycardia due to
good fitness
bradycardia questions after “are the QRS complexes regular?”
Q. if yes, is there a P-wave in front of each QRS complex with normal AV delay?
- if yes = sinus bradycardia
- if no = heart block
bradycardia questions after “are the QRS complexes irregular?”
Q. are there P waves?
- if no = slow AF
- if yes = look at relationship between P waves and QRS
look at sinus bradycardia ECG example (E)
done
in sinus bradycardia ECG (2)
wide impulse separation, normal impulses
what are QRS complexes like in sinus bradycardia?
regular
what are P waves like in sinus bradycardia? (2)
P wave before QRS, normal AV delay
look at first degree heart block ECG example (F)
done
in first degree heart block, the QRS complexes are
regular
in first degree heart block, P waves are
before each QRS
in first degree heart block PR interval is
prolonged
prolonged PR interval shows
delay in conduction from SAN -> AVN
2 types of second degree AV block
type 1 - Wenckebach
type 2 - Mobitz II
look at the second degree AV block type 1 (Wenckebach block) ECG example (G)
done
what are QRS complexes like in second degree AV block type 1 (Wenckebach block)?
irregular
describe complexes 1, 2 and 3 in second degree AV block type 1 (Wenckebach block)
complex 1 - P wave followed by QRS with normal PR interval
complex 2 - P wave with QRS but longer PR interval
complex 3 - PR interval very long, followed by P wave, no QRS
second degree AV block type 1 (Wenckebach block) heart block type
3:2, 3 P waves for every 2 QRS
look at the second degree AV block type 2 (Mobitz II block) ECG example (H)
done
what are QRS intervals like in second degree AV block type 2 (Mobitz II block)?
regular
second degree AV block type 2 (Mobitz II block) heart block type
2:1, 2 P waves for every QRS
look at third degree AV block (complete heart block) ECG (I)
done
what are QRS complexes like in third degree AV block (complete heart block)?
regular
what are P waves like in third degree AV block (complete heart block)?
P wave doesn’t precede QRS every time, not dependent on each other
look at the ECG example of sinus arrest (J)
done
sinus arrest is (3)
failure of sinus node to discharge, absence of depolarisation, ventricular asystole
look at ECG of brady-tachy syndrome (K)
done
Brady-Tachy syndrome
intermittent episodes of slow and fast rates from SA node or atria
sinus bradycardia treatment (4)
beta-blockers, calcium channel blockers, digoxin, conservative
heart block is caused by
slow/blocked conduction through AV node
heart block bradycardia treatment (2)
IV atropine, underlying cause
look at the ECG os left and right bundle branch block (L)
done
left bundle branch block (2)
assess LV function, bad prognostic
right bundle branch block (3)
benign, with lung disease, maybe right ventricle strain
tachycardia ECG questions after “are the QRS complexes regular and <120msec wide?”
if yes, supraventricular tachycardia, look for P wave, if <120bpm = sinus tachycardia, if >140bpm SVT
tachycardia ECG questions after “are the QRS complexes regular and >120msec wide?”
if yes assume VT
tachycardia ECG questions if the QRS complexes are irregular (2)
<120msec = AF >120msec = probs AF, VT if pts ill
if unsure whether it’s SVT or VT (2)
inject adenosine, adenosine blocks AV node so rate should slow if SVT
causes of sinus tachycardia (5)
hyperthyroidism, anxiety, heart failure, hypovolaemia, septicaemia
stable SVT treatment (3)
IV adenosine, no digoxin, may revert spontaneously
stable VT treatment (2)
IV amiodarone, electrical cardioversion, correct hypokalaemia
look at ECG of atrial tachycardia (SVT)
done
atrial flutter often degenerates to
atrial fibrillation
look at the ECGs of atrial flutter (M)
done
atrial flutter treatment (3)
anticoagulate, external electrocardioversion, electrophysiological ablasion
AF risk increases 4-fold after
stroke
in AF, ECG is
irregularly irregular
look at the ECGs of rapid ventricular response and controlled ventricular response rate (N)
done
atrial fibrillation treatment (3)
rhythm control, ventricular rate control, anti-thrombotic (NOT aspirin)
look at the ECG example of ventricular tachycardia (N)
done
look at ECG of ventricular fibrillation (O)
done
in ventricular fibrillation (4)
rate is 0, no QRS, no pattern, needs defibrillating
Torsades de Pointes treatment
magnesium
Torsades de Pointes is exacerbated by (2)
low K+, low Mg2+
Torsades de Pointes occurs in (2)
drugs, existing bradycardia
