Arrhythmia - possible consequence of ischaemic heart disease /CVD
Arrhythmia - possible consequence of ischaemic CVD
Arrythmia is a condition in which the heart beats
too fast (bradycardia), too slow (tachycardia),
too early (premature contraction)
or with an irregular rhythm (flutter or fibrillation).
This occurs when electrical signals to the heart that coordinate heart beats
stop functioning properly. Symptoms can sometimes be felt as palpitations (a feeling
that your heart has added or skipped a beat, or rapid pulsations), possibly including
dizziness and/or difficulty breathing.
The SA node
(a.k.a. sinus node) is the heart's primary natural pacemaker.
Normal heart rhythm of 60-100 beats per minute is controlled by the SA node,
a cluster of cells located in the right atrium. The specialized cells of the SA node generate regular
spontaneous "slow response" (i.e. slow depolarization) action
potentials through the muscle tissue of the atrial and ventricle chambers at a rate
of 100-110 action potentials ("beats") per minute. These are tempered by the autonomic
vagal nerve bringing the resting heart rate down to 60-80 "beats" per minute.
Normal
range is 60-100 "beats" per minute. A rate below 60 is termed sinus bradycardia,
and a rate above 100 is termed sinus tachycardia. "Slow response"
action potentials are carried into the cell primarily by relatively slow
Ca++ currents,
whereas most non
"The heartbeat". Action potentials
generated by the SA node spread through and depolarize the atrial tissue causing
atrial contraction, then the impulse travels via the Atrioventricular (AV) node
to the ventricles to elicit ventricular contraction.
Coronary Heart Disease (CHD) / Coronary Artery
Disease (CAD) can cause arrythmia. CHD/CAD reduces the blood
supply to the heart, which reduces the oxygen
supply to cardiac cells - lacking
oxygen ,
heart muscle cells can depolarize
Altered impulse formation.
Involves changes in rhythm that are caused by:
- Changes in the
spontaneous activity of heart's SA node pacemaker cells
- Abnormal generation
of action potentials at sites other than the SA node.
Other
pacemaker sites within the atria and ventricles (called ectopic foci )
can cause additional beats or take over from the SA node, which normally suppresses
these other pacemaker cells with its higher rate.
Altered conduction of
impulses
- AV block.
Impulses are not conducted from the atria to ventricles through the
AV node. Can be caused by excessive vagal action or drugs that reduce conduction
Eg. beta-blockers or calcium-channel blockers
- Abnormal conduction
pathways between atria and ventricles. Eg. accessory pathways.
How to treat
arrhythmia
