heart block

Question 1

definition of heart block

Answer 1

Impairment of the atrioventricular (AV) node impulse conduction, as represented by the interval between P wave and QRS complex.

Question 2

1st degree heart block

Answer 2

Prolonged conduction through the AV node.

Question 3

2nd degree heart block

Answer 3

Mobitz 1 (Wenckebach): progressive prolongation of AV node condiction, with 1 atrial impulse failing to be conducted through AV node - cycle

mobitz 2 - Intermittent or regular failure of conduction through AV node. Also definedby the number of normal conductions per failed or abnormal one (e.g. 2 : 1 or 3 : 1).

Question 4

3rd degree heart block

Answer 4

no relationship between atrial and ventricle contraction.

Failure of conduction through the AV node leads to a ventricular contraction generated by a focus of depolarization within the ventricle (ventricular escape)

Question 5

aetiology of heart block

Answer 5

inferior MI/IHD - most common

infection - rheumatic fever, infective endocarditis

drugs - digoxin, B-blockers, Ca channel antagonists

metabolic - hyperkalaemia, cholestatic jaundice, hypothermia

infiltration of conducting system - sarcoidosis, cardiac neoplasms, amyloidosis

degeneration of the conducting system

Question 6

aetiology of 1st and 2nd degree heart block

Answer 6

normal variant,

athletes,

sick sinus syndrome,

acute myocarditis

Question 7

aetiology of 3rd degree heart block

Answer 7

idiopathic (fibrosis),

congenital,

aortic valve calcification,

cardiac surgery/trauma,

infiltration (abscesses, granulomas, tumours, parasites).

Question 8

epidemiology of heart block

Answer 8

Majority of the 250 000 pacemakers implanted annually are for heartblock.

Question 9

sx of 1st degree heart block

Answer 9

asymptomatic

Question 10

sx of mobitz type 1

Answer 10

usually asymptomatic

Question 11

sx of mobitz 2 and 3rd degree heart block

Answer 11

May cause Stokes–Adams attacks (syncope caused by ventricular asystole),

dizziness,

palpitations,

chest pain

HF

Question 12

signs of heart block

Answer 12

often none

signs of cause

complete - slow. large vol pulse. JVP can show cannon waves

Mobitz type II and third-degree block: Signs of a reduced cardiac output (e.g. hypo-tension, heart failure).

Question 13

Ix for heart block

Answer 13

ECG - consider ambulatory Holter/24h

CXR - cardiac enlargement, pul oedema

blood - TFT, digoxin level, cardiac enzyme, trop

echo - wall motion abnormalities, aortic valve disease, vegetations

Question 14

ECG for 1st degree heart block

Answer 14

prolonged PR >0.2s

Question 15

ECG for Wenckebach heart block

Answer 15

Progressively prolonged PR interval, culminating in a P wave that is not followed by a QRS.

The pattern then begins again

Question 16

ECG for mobitz type 2

Answer 16

Intermittently a P wave is not followed by a QRS.

may be a regular pattern of P waves not followed by QRS (e.g. two P waves per QRS, indicating 2 :1 block)

Question 17

ECG for complete heart block

Answer 17

No relationship between P waves and QRS complexes.

If QRS initiated by focus in the bundle of His, the QRS is narrow.

QRS initiated more distally are wide and slow rate (30 beats/min)

Question 18

Mx of chronic heart block

Answer 18

Permanent pacemaker (PPM) insertion for third-degree heart block, advanced Mobitz type II and symptomatic Mobitz type I.

Question 19

Mx of acute heart blockm

Answer 19

(e.g. secondary to anterior MI):

If associated with clinical deterioration,

IV atropine and consider temporary (external) pacemaker.

Question 20

Mx of 1st degree heart block

Answer 20

observe closely because 40% develop higher levels - in which case CCB and B blockers should be stopped

Question 21

Mx of Mobitz

Answer 21

pacemaker because high risk of developing complete block

Question 22

Mx of complete heart block

Answer 22

Usually resolves within a few days.

Insert pacemaker (may not be necessary after inferior MI if narrow QRS, reasonably stable and pulse 40–50).

Question 23

complications of heart block

Answer 23

asystole

cardiac arrest

complications of pacemaker

3rd degree - As tissue distal to the AVN paces slowly, the patient becomes very bradycardic, and may develop haemodynamic compromise

Question 24

Px of heart block

Answer 24

Mobitz type II and third-degree block usually indicate serious underlying cardiac disease.

mobitz 2 - dangerous as may progress to complete heart block