Re-entry and bundle branch blocks

Question 1

re-entry circuits

Answer 1

electrical impulse originating high in the heart finds an alternate route to return to the electrical conducting pathway higher up
can create a closed loop

Question 2

Atrio-ventricular re-entry circuits

Answer 2

impulse follows an alternate route from the atria to the ventricles or vice versa via myocellular transmission

Question 3

atrio-ventricular nodal re-entry circuits

Answer 3

within the AV node, two pathways exist
conditions occur that an impulse transiting one path, meets the other path in a repolarised state, a circuit occurs creating a very dangerous tachycardia

Question 4

atrio-ventricular re-entry tachycardias

Answer 4

aim is to change the frequency of the circuit so that the self-sustaining impulse meets a refractory part of the circuit, stopping it
e.g. cardioversion or drugs

Question 5

bundle branch blocks and hemiblocks

Answer 5

left bundle branch subdivides further in and anterior and posterior fasicle
a BBB is a block in the normal conduction in one of the bundle branches
if it happens on the left side after the split in the fascicles it is called a hemiblock

Question 6

Left BBB

Answer 6

the normal direction of septal depolarisation is reversed, becomes right to left, as the impulse spreads first to the RVV via the right bundle branch and then to the LV via the septum
extends to QRS duration

Question 7

causes of LBBB

Answer 7

aortic stenosis, isachaemic heart disease, hypertension, dilated cardiomyopathy, anterior MI, primary degenerative disease of the conducting system, hyperkalaemia, digoxin toxicity

Question 8

right bundle branch blocks

Answer 8

activation of the right ventricle is delayed as depolarisation has to spread across the septum from the left ventricle

Question 9

causes of RBBB

Answer 9

right ventricular hypertrophy, pulmonary embolus, iscahemic heart disease, rheumatic heart disease, myocarditis, degenerative disease of the conduction system, congenital heart disease

Question 10

hemiblock

Answer 10

occurs when one or other of the left fasicles is blocked

Question 11

interventricular conduction delay (IVCD)

Answer 11

exists when a wide QRS occurs following a normal SA initiated P wave but without clear criteria for RBBB or LBBB