Atrioventricular block Flashcards
what is atrioventricular block
often referred to as ‘heart block’
involves the partial or complete interuption of impulse transmission from the atria to the ventricles
common causes of AV block
idiopathic fibrosis and sclerosis of the conduction system
what investigations should be done
ECG: to help determine the subtype of AV block
lab investigations: FBCs, U&Es, TSH, troponin: to rule out inderlying causes
echo: to rule out structural heart disease
first degree AV block is when
there is consistant prolongation of the PR interval (>0.2 seconds) due to delayed conduction via the AV node
there is no dropped QRS complexes
common and may be an incidental finding
causes of first degree heart block
- enhanced vagal tone, aften seen in atheletes and non-pathological
- post myocardial infarction
- lyme disease
- systemic lupus erythematosus
- congenital
- myocarditis
- electrolyte derangements
- drugs: particularly AV blocking drugs such as beta blockers, rate limiting calcium-channel blockers, digoxin and magnesium
- thyroid dysfunction
typical ECG findings of first degree heart block
regular rhythm
P wave: every p wave is present and followed by a QRS complex
PR interval: prolonged >0.2 seconds
QRS complex: normal morpholohy and duration <0.12 seconds
clinical features of first degree heart block
patients are usually asymptomatic
clinical examination is usually unremarkable
management of first degree block
any AV blocking drugs should be ceased
no intervention is usually required if the patient is asymptomatic
if the patient is symptomatic, a pacemaker may be considered
complications of first degree heart block
does not usually progress to higher degree AV blocks
those with first degree AV block may be at risk for atrial fibrillation
what is second degree AV block type 1
progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped
other naames for second degree AV block type 1
mobiitz type 1 AV block or wenckebach phenomenon
aetiology of second degree AV block type 1
increased vagal tone: often seen in athletes, not pathological
drugs: beta blockers, calcium chennel blockers, dioxin, amiodarone
infrior myocardial infarction
myocarditis
cardiac surgery (mitral valve repair, tetrology of fallot repair)
second degree AV block type 1 ECG findings
irregular rhythm
P wave: every p wave is present, but not all are followed by a QRS complex
PR interval: progressively lengthens before a QRS complex is dropped
QRS complex: normal morphology and duration (<0.12 seconds), but are repeatedly dropped
clinical features of second degree AV block type 1
patients are usually asymptomatic, but some can develop symptomatic bradycardia and present with symptoms such as pre-syncope and syncope
O/E: irregular pulse and bradycardia
management of second degree AV block type 1
AV blocking drugs should be stopped
usually benign and rarely causes haemodynamic compromise
usually, no intervantion is required if the patient is asymptomatic
if the patient is symptomatic a pacemaker may be considered
complications of second degree AV block type 1
the patient may become haemodynaamically compromised but this is rare
what is second degree AV block type 2
also called Mobitz type 2 AV block
consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction
dropping of QRS complexes usually follows a repeating cycle
when is mobitz type 2 block pathological
always, with the block typically occuring at the bundle of His or the bundle branches
causes of second degree AV block type 2
- myocardial infarction
- idiopathic fibrosis of the conducting system
- cardiac surgery
- inflammatory conditions (rhuematic fever, myocarditis, lyme disease
- autoimmune (SLE, systemic sclerosis)
- infiltrative myocardial disease (amyloidosis, haemochromotosis, sarcoidosis)
- hyperkalaemia
- drugs eg. beta blockers, calcium channel blockers, digoxin, amiodarone)
- thyroid dysfunction
ECG findings of second degree type 2 heart block
rhythm: irregular, may be regularly irregular
p wave: present but there are more p waves than QRS complexes
PR interval: consistant normal PR interval duration with intermittantly dropped QRS complexes
QRS complex: normal (<0.12 seconds) or borad (>0.12 seconds)
the QRS complex will be broad if the conduction failure is located distal to the bundle of His
clinical features of mobitz type 2 heart block
palpitations
pre-syncope
syncope
O/E: may detect a regularly irregular pulse, where there is a pattern of how many atrial depolarisation (p waves) lead to ventricular depolarisation (QRS waves) such as 3:1 block
management of mobitz type 2 heart block
due to risk of progression to complete heart block, patients should be places on a cardiac monitor as soon as possible
underlying cause should be investigated
temporary pacing or isoprenaline may be required is the patient is haemodynamically compromised due to bradycardia
a permanenet pacemaker is usually inserted if there are no reversible causes identified
complications of mobitz type 2 heart block
patients are at risk of progressing to complete ysmptomatic AV block, in which the escape rhythm is likely to be ventricular and thus too slow to maintain adequate systemic perfusion
patients are also at risk of developing asystole
what is third degree (complete) AV block
there is no electrical communication between the atria and ventricles due to complete failure of conduction
presence of p waves and QRS complexes that have no association with each other due to the atria and the ventricles perfoming independantly
