heart beat and conductivity Flashcards
Heart and blood vessels
Heart = engine Blood vessels = pipes conveying blood Veins = towards the heart Arteries = away from the heart Capillaries = tiny vessels where arteries get in contact with veins and where exchange of gas/nutrients happens
Heart components - recap
Layers
Chambers
Valves
Other structures
Veins and arteries going in and out
Arteries supplying blood to the heart
Layers:
Endocardium, myocardium, epicardium, pericardium (with its three layers and the pericardial cavity)
Chambers: atria and ventricules
Valves: TV, PV, AV, MV
Other structures: Corda tendinae, papillary muscles, septum, sinoatrial node and atrioventricular node, Purkinje fibers and bundle of Hys
Veins and arteries going in and out - pulmonary veins, aorta artery, vena cava, pulmonary arteries
Arteries supplying blood to the heart – coronary artery and veins
Other: left and right azygous veins
Sinoatrial node
he sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is a group of cells located in the wall of the right atrium of the heart. These cells have the ability to spontaneously produce an electrical impulse (action potentia), that travels through the heart via the electrical conduction system causing it to contract. In a healthy heart, the SA node continuously produces action potential, setting the rhythm of the heart
Atrioventricular node
atrioventricular node ( AV node) a collection of cardiac fibers at the base of the interatrial septum that transmits the cardiac impulse initiated by the sinoatrial node
The Purkinje fibers
The Purkinje fibers (/ pɜːrˈkɪndʒi / pur-KIN-jee; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specialised conducting fibers composed of electrically excitable cell
Bundle of His
a collection of heart muscle cells specialized for electrical conduction. As part of the electrical conduction system of the heart, it transmits the electrical impulses from the atrioventricular node (located between the atria and the ventricles) to the point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinje fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval.
Apex of the heart
apex of the heart The tip of the left ventricle, opposite the base of the heart. The apex of the heart moves considerably with each heartbeat, and the point of maximal impulse (PMI) can be felt on the chest wall above the apex
Cardiac cycle – conduction system
The heart contracts when stimulated by an electrical wave that comes from specialised muscle cells spontaneously in the area of the heart known as the (1) sino-atrial node (SA Node) = pacemaker
SAN This node, which is not apparent to the naked eye, lies below the epicardium of the right atrial wall ventral to the cranial cava opening
Cardiac cycle – conduction system
This sequence is initiated as an electrical signal (action potential) and propagated from heart muscle cell to heart muscle cell
Wave spreads across the left and right atria atria depolarisation (contraction)
Wave reaches (2) atrio-ventricular node (AV node) (in the wall of the septum) and then travels along the (3) Bundle of His (made of Purkinje fibers) within the septum, then spreading out along the limbs of the bundle (4 and 5) causing ventricle depolarisation (contraction)
Bundle of His or AV bundle (with left and right limbs)
Purkinje fibers are specialised cardiac muscle cells
(Short delay between atria contraction and ventricle contraction)
Ventricle wave of contraction starts at the apex of the heart (bottom)
Spreads upwards through the myocardium pushing blood up towards the pulmonary artery and aorta exiting the heart (‘ventricular systole’)
Sinoatrial node (SAN) to atrioventricular node (AVN)
Atrial contraction (=depolarisation)
Atrioventricular node (AVN) to Bundle of His (Purkinje fibres)
Ventricular contraction!!! (= depolarisation)
What is the cardiac cycle?
The coordinated movement of the two pumps (left and right) that are a result of heart contraction and relaxation:
Left side receives clean blood (oxygenated) from the lungs and sends it to the tissues
Right side receives dirty blood (non oxygenated) from the tissues and sends it to the lungs
Made of two main parts: systole (contraction) and diastole (relaxation)
One cardiac cycle = one heart beat = one systole + one diastole = one PQRST on the ECG = one set of lub dub during auscultation
Timeline of the cardiac cycle
Ventricles filled with blood (during in diastole) pressure is low in ventricles
A-V valves closed
Full ventricles now contract (systole) maximum pressure
Pressure builds up in ventricles and opens the aortic valve and pulmonary valve Blood ejected through aorta and pulmonary arteries
Peak of the aortic and ventricular pressure = Systolic pressure (SAP)
Ventricles relax (diastole) lower pressure (diastolic pressure)
Opening of AV valves
SAN fires
Atrial contraction (atrial systole but part of the general diastole!)
80% of ventricles are full when atria contracts
Atria relaxes… AV valve close…. ventricles start to contract
And we start again!
S1
coincides with the AV valves closure (Tric and mitral), but it is not the valves themselves but vibration sounds from the valves and the walls due to blood hitting them
S2
coincides with the closure of aortic and pulmonary valves, and again is the backflow of blood into the ventricles when suddenly valves close what causes the real sound
S3
in large dogs and animals is the blood turbulence within the ventricles
S4
atria contraction, so the sound is the blood rushing towards ventricles. Important for atrial fibrillation diagnosis!!! Particularly in big dogs and big animals. The absence of this means there is AF
