Transcript Cardiac Conduction

Cardiac Conduction
Autorhythmic: cardiac muscle cells
depolarize at regular intervals
 Cardiac Conduction system: cardiac cells
that are specialized to generate AP’s to
control contractions of the heart
 Pacemaker: the sinoatrial (SA) node,
found in the R atrium starts HB and
controls rate of contraction. AP’s from
node travel down walls of atrium

Cardiac Conduction
Atrioventricular (AV) node: found by the
AV valve, acts as a gateway carrying the
AP’s from the SA node to the ventricles
 AV bundle: a pathway for the AP’s from
the AV node to travel through the septum
as it splits into R and L branches toward
apex of heart
 Purkinje fibers: branches of the AV bundle
that travel from the apex upward

Cardiac Rhythm
Sinus rhythm: normal heartbeat 7080/min
 Nodal rhythm: caused by SA node damage
40-50/min, AV node still working but
ectopic focus working for SA node
 If both SA and AV nodes are damaged
then ectopic foci keep heart beating at 2040/min body lives but brain dies due to
lack of oxygen

Electrocardiogram
Electrocardiogram (ECG or EKG): a visual
record of the heart’s electrical activity
 Systole: contraction of a heart chamber
 Diastole: heart chamber relaxes and fills
with blood
 P wave: caused by the signal from the SA
node as it spreads through the atria
depolarizing the walls causing systole

Electrocardiogram
PQ segment: time it takes the signal to
travel from the SA to AV node,
 QRS complex: caused by the signal
traveling through the two ventricles,
 QRS interval: atria repolarization and
diastole
 ST segment: ventricular systole
 T wave: the repolarization of the ventricles
before diastole

Cardiac Output
Cardiac Output (CO): CO= HR x SV
normal CO =5250ml/min so all blood in
the body will pass through and return to
the heart in about a min
 Cardiac reserve: the difference of CO at
rest and max CO

Heart Rate
Pulse: the heart rate measured at an
artery
 Tachycardia: persistent heart rate at rest
above 100bpm
 Bradycardia: persistent heart rate at rest
below 60bpm

Stroke Volume
Preload: the stretch on the myocardium
before systole
 Contractility: how hard the myocardium
can contract for a certain preload
 Afterload: the blood pressure in the
vessels that resists the blood flow out of
heart
