Heart Block Flashcards
define heart block?
Atrioventricular (AV) block is a cardiac electrical disorder defined as impaired (delayed or absent) conduction from the atria to the ventricles.
severity of conduction abnormality is described in degrees-> first degree, second degree, type 1 ( Wenkebach or Mobitz I ) or type II ( Mobitz II), and third degree ( complete ) AV block
what are the three types of heart block?
1st degree AV
2nd Degree AV block
- Mobitz type 1 ( Wenckebach)
- Mobitz type 2
3rd degree ( complete Heart block)
what is 1st degree heart block?
prolonged conduction through the AV node
what is type 1 degree AV block?
prolonged conduction through the AV node
what is type 1 second degree AV block?
Mobitz type 1 ( Wenckebach): progressive prolongation of AV node conduction culminating in one atrial impulse failing to be conducted through the AV node
what is type 2 second degree heart block?
intermittent or regular failure of conduction through the AV node. Also defined by number of normal conductions per failed or abnormal one ( eg 2:1 or 3:1)
what is third degree heart block?
no relationship between atrial and ventricular contraction. Failure of conduction through the AV node leads to ventricular contraction generated by focus of depolarisation within the ventricle
summarise the epidemiology of heart block?
250,000 pacemakers are implanted every year and they are mostly for heart block
what are the risk factors of heart block?
MI or ischaemic heart disease (MOST COMMON)- right coronary artery
Infection (e.g. rheumatic fever, infective endocarditis)
Drugs (e.g. digoxin)
Metabolic (e.g. hyperkalaemia)
Infiltration of conducting system (e.g. sarcoidosis)
Degeneration of the conducting system
what are the presenting symptoms of heart block?
1st Degree - asymptomatic
2nd Degree - usually asymptomatic
Mobitz Type II and 3rd Degree - may cause Stokes-Adams Attacks(syncope caused by ventricular asystole)
- May also cause dizziness, palpitations, chest pain, fainting, fatigue and heart failure
what are stroke Adams attack?
syncope caused by ventricular asystole
what are the signs of heart block on physical examination?
often normal
COMPLETE HEART BLOCK:
- slow large volume pulse- less than 40bpm
- JVP may show canon waves
MOBITZ TYPE 2 AND 3rd DEGREE HEART BLOCK
- signs of reduced cardiac ouput ( hypotension, heart failure)
what are canon waves in heart block?
Cannon A Waves: waves seen occasionally in the jugular vein of humans with certain cardiac arrhythmias. This occurs when the atria and ventricles contract simultaneously the blood will be pushed against the AV valve, and a very large pressure wave runs up the vein.
what are the investigations for heart block?
12 lead ECG- GOLD STANDARD
Serum troponin – may be elevated
Serum K+/ Ca2+/ pH - may be very high or low
Serum digitalis – may be normal to elevated
outline the management for heart block?
- Chronic block: permanent pacemakers (PPM)in 3rddegree heart block is recommended, advanced Mobitz type II and symptomatic Mobitz Type I
- Acuteblock: if associated with clinical deterioration, give IV atropineand consider temporary pacemaker (this would be external) then put a pacemaker the next day
what are the complications of heart block?
- Asystole
- Cardiac arrest
- Heart failure
- Complications of pacemaker insertion-> bleeding, infection, vascular trauma, pneumothorax, cardiac tamponade, lead dislodgement, and pocket haematoma development. The risk of MI, stroke, and death is <1%.
outline the prognosis for heart block?
Mobitz type II and 3rddegree block usually indicate a underlying serious heart condition
what investigations would you consider for heart block and what you see on the investigations?
CXR
- cardiac enlargement
- pulmonary oedema
Transthroacic Echocardiogram
- may show ventricular dysfunction or hypertrophy, valvular disease, wall-motion abnormalities
describe the ECG for first degree heart block?
fixed prolonged PR interval ( more tha 0.2 seconds)
describe the ECG in Mobitz type 1 ( Wenckebach) heart block?
progressively prolonged PR interval , culminating in a P wave that is NOT followed by a QRS complex
pattern then begins again
describe the ECG in Mobitz type II heart block?
intermittently a P wave that is not followed by a QRS
May be a regular pattern of P waves not followed by
Describe the ECG in complete heart block?
no relationship between P waves and QRS complexes
If QRS is initiated in
- Bundle of His- narrow complex
- More distally - wide complex and slow rate ( roughly 30bpm)
