Dr. E. Cardiac Lecture Flashcards
right atrium: Systemic veins empty into R Atrium via:
- The superior vena cava (SVC)
- The inferior vena cava (IVC)
The Eustachian valve protects the lVC - Coronary veins empty into R Atrium via: The coronary sinus
The Thesibian valve protects the coronary sinus
- The inferior vena cava (IVC)
The valve of the inferior vena cava (Eustachian valve) lies at the junction of the inferior vena cava and right atrium.
..
What valve protects the IVC?
Eustachian valve
Coronary Veins empty into R atrium via
coronary sinus
What valve protects the coronary sinus?
Thesibian
The valve of the coronary sinus (Thebesian valve) is a semicircular fold of the lining membrane of the right atrium, at the orifice of the coronary sinus. It is situated at the base of the superior vena cava.
The valve may vary in size, or be completely absent.[1]
It may prevent the regurgitation of blood into the sinus during the contraction of the atrium.
Right VENTRICLE:
Propels blood to the pulmonary vessels via the pulmonary orifice: infundibulum (is the outflow portion of the right ventricle)
Communicates with R atrium via the tricuspid orifice: chord tendineae (heart strings, are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart)
Has several muscle bundles: trabeculae carneae-one of which carries the right branch of the AV bundle (bundle of his)
RV communicates with the RA via
triscuspid orfice
Left Atrium
Larger than R atrium
Superior and posterior to the other chambers
Receives pulmonary veins
-Reservoir for oxygenated blood
-Provides the “atrial kick” in LVEDV-important in certain conditions
Communicates with the left vetricle via the AV orifice-mitral valve
The LA receives pulm
veins
The LA communicates w/the LV via
av orifice mitral valve
The LA provides the “atrial kick” in LVEDV and this is important in what conditions?
Atrial kick is absent if there is loss of normal electrical conduction in the heart, such as during atrial fibrillation, atrial flutter, and complete heart block. Atrial kick is also different in character depending on the condition of the heart, such as stiff heart, which is found in patients with diastolic dysfunction
Left Ventricle
Receives oxygenated blood from the LA
Pumps blood to the body via the Aorta
Ventricular septum: R and L ventricles
Upper 1/3 of the septum is smooth
Lower 2/3 is muscular and covered with trabeculae carneae
2 large papillary muscles-chordae tendineae-cusps of the mitral valve
Ventricular septum: R and L ventricles
Upper 1/3 of the septum is smooth
Lower 2/3 is muscular and covered with trabeculae carneae
The greater portion of it is thick and muscular and constitutes the muscular ventricular septum.
Its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum (septum membranaceum)..
What are the 2 AV valves?
Tricuspid
Within the R AV orifice
3 leaflets-anterior, posterior, septal
Valve area: 7cm2, symptoms occur at area <½ of normal area
Which valve is in the RA AND LA ORIFICE respectively?
Tricuspid
Within the R AV orifice
3 leaflets-anterior, posterior, septal
Valve area: 7cm2, symptoms occur at area <½ of normal area
Describe the Tricuspid valve
Tricuspid
Within the R AV orifice
3 leaflets-anterior, posterior, septal
Valve area: 7cm2, symptoms occur at area <½ of normal area
Describe the Mitral Valve.
Tricuspid
Within the R AV orifice
3 leaflets-anterior, posterior, septal
Valve area: 7cm2, symptoms occur at area <½ of normal area
What are the 2 semilunar valves?
Aortic valve: Out flow tract of the aorta and the LV Has 3cusps Sinus of Valsalva Valve Area: 1-3cm2 area <1/2 or 1/3 symptomatic
Describe the aortic valve
Aortic valve: Out flow tract of the aorta and the LV Has 3cusps Sinus of Valsalva Valve Area: 1-3cm2 area <1/2 or 1/3 symptomatic
Describe the pulmonic vlave
Aortic valve: Out flow tract of the aorta and the LV Has 3cusps Sinus of Valsalva Valve Area: 1-3cm2 area <1/2 or 1/3 symptomatic
Describe the sinus of valsalva
n aortic sinus is one of the anatomic dilations of the ascending aorta, which occurs just above the aortic valve.
There are generally three aortic sinuses: the left, the right and the posterior sinuses:
The left aortic sinus gives rise to the left coronary artery.
The right aortic sinus gives rise to the right coronary artery.
Usually, no vessels arise from the posterior aortic sinus, which is therefore known as the non-coronary sinus.
Each aortic sinus can also be referred to as the sinus of Valsalva, the sinus of Morgagni, the sinus of Mehta, the sinus of Otto, or Petit’s sinus.
Coronary circulation
Epicardial (the inner serous layer of the pericardium, lying directly upon the heart.)
Subendocardial
2 Epicardial Coronaries originate from the sinuses of Valsalva
Left Coronary Artery (LCA)
Right Coronary Artery (RCA)
LCA:
Short left main-ant. inf. & left. Bifurcates into the: LAD-diagonal branch, septal perforating branch-feeds the anterior of LV, and the interventricular groove (leads V3-V5) Circumflex-obtuse margin-feeds the posterior LV and part of RV (lead I)
*It typically runs for 10 to 25 mm and then bifurcates into the anterior interventricular artery (also called left anterior descending (LAD)) and the left circumflex artery (LCX). Sometimes an additional artery arises at the bifurcation of the left main artery, forming a trifurcation; this extra artery is called the intermediate artery.[1]
The part that is between the aorta and the bifurcation only is known as the left main artery (LM), while the term ‘LCA’ might refer to just the left main, or to the left main and all its eventual branches
RCA:
Branches into:
1. Sinus node artery- feeds SA node and RA Branch-feeds the RA
2. Av node artery-feeds AV node (in 90% of population)
3. Anterior RV Branches-feed the RV
4. PDA-feeds the posterior 1/3 of the interventicular septum
Leads II, III and aVf
The right coronary artery (RCA) is an artery originating above the right cusp of the aortic valve. It travels down the right atrioventricular groove, towards the crux of the heart. It branches into the posterior descending artery and the right marginal artery.
At the origin of the RCA is the conus artery.
In addition to supplying blood to the right ventricle (RV), the RCA supplies 25% to 35% of the left ventricle (LV).
In 85% of patients (Right Dominant), the RCA gives off the posterior descending artery (PDA). In the other 15% of cases (Left Dominant), the PDA is given off by the left circumflex artery. The PDA supplies the inferior wall, ventricular septum, and the posteromedial papillary muscle.
The RCA also supplies the SA nodal artery in 60% of patients. The other 40% of the time, the SA nodal artery is supplied by the left circumflex artery.
Which artery crosses the crux (junction between the atria and ventricles) to feed the posterior descending coronary branch
In 50% it is the RC
In 20% it is the LC
In 30% a balanced pattern exists
.
Coronary Artery Distribution
I. LCA Ant. descending branch R&L bundle branches Anterior and posterior papillary muscles of the mitral valve Anterolateral left ventricle II. Circ Lateral LV III. RCA SA & AV nodes RA RV Post. interventricular septum Interatrial septum
Coronary Physiology
5% of CO or 250ml/min perfusion
Flow is determined by:
Duration of diastole
CPP=Diastolic pressure-LVEDP
LCA: flow occurs mostly during diastole
RCA: flow occurs in both systole and diastole
Myocardial O2 consumption is high with cardiac venous sat. lowest in the body (30%) {The O2 saturation of blood returning from the coronary sinus to the right atrium has the lowest saturation of any body organ (30%).}
Coronary Physiology : Tufts
Coronary blood flow is directly dependent upon perfusion pressure and inversely proportional to the resistance of the coronary vessel.
Q ∞ Perfusion pressure / Vessel resistance
Coronary perfusion occurs in diastole hence diastolic pressure is more important than systolic pressure in determining coronary perfusion. Coronary vessels are divided into epicardial or conductance vessels (R1), pre capillary (R2) and microvascular vessels (R3). The epicardial vessels, the site most commonly affected by atherosclerosis, offer negligible resistance to coronary flow. Resistance to flow occurs in the pre capillary (R2), and microvascular (R3) vessels which are termed resistance vessels. The increase coronary blood flow in response to increase myocardial oxygen demand (MVO2) is achieved by the dilatation of these resistance vessels. Three factors play a key role in modifying vascular tone; the accumulation of local metabolites, endothelial factors and neural tone. The accumulation of adenosine during ischemia is an example of local metabolic factors. The most important endothelial substance mediating vasodilatation is nitric oxide (NO). Other important mediators are bradykinin, endothelium derived
1
hyperpolarizing factor and prostacyclin. On the other hand, endothelin-1 (ET-1) is a well known vasoconstricting substance. Angiotensin II and thromboxane A2 are other well known endothelium derived constricting factors. Alpha receptor adrenergic stimulation results in coronary vasoconstriction whereas beta 1 receptor stimulation leads to vasodilatation.
Coronary Autoregulation
CPP usually autoregulated at 50-120 mmHg
Pressure dependent changes
Myocardial oxygen demand alters autoregulation: O2 tenstion acting thru mediators, ie adenosine
Greatest dilation occurs in smallest vessels
LCA>RCA in autoregulation
*Tufts( Coronary vascular resistance can be reduced to 1/5th of baseline resistance leading to a five fold increase in the volume of perfusion in response to an increase in need. Coronary reserve is the term used to reflect the amount of increase in coronary perfusion to accommodate increased demand. Autoregulation, mediated by changes in the vascular tone of the resistance vessels, allows distal coronary perfusion to remain unaltered in the face of changes in proximal perfusion pressures. Impaired endothelial function disrupts autoregulation and may lead to ischemia. Diseases known to impair endothelial function include atherosclerosis, dyslipidemias, diabetes mellitus, hypertension, smoking (both passive and active) and hyperhomocysteinemia.
Cardiac Conduction system
Consists of: SA node Internodal tracts AV node AV bundle (bundle of His) Purkinje system
SA NODE
Mass of specialized cells Junction of SVC and RA 2 Cell types I. P cells (pacemaker cells) II. Transitional or intermediate cells- conduct impulses within and away from the node
*The SA node is richly innervated by parasympathetic nervous system fibers (CN X: vagus nerve) and by sympathetic nervous system fibers (T1-4, spinal nerves)
Internodal tract
Within the atria
Conduction pathways b/w the SA & AV
Also contain P cells and transitional cells
3 Major tracts:
1. Anterior (Buchmann’s bundle)-septum
2. Middle (Wenckebach’s tract)-SVC
3. Posterior (Thorel’s tract)-septum
AV NODE
Supplied by nerve endings including vagal ganglionic cells.
Causes a delay in the transmission of the action potential:
Size of cells: smaller
Resting memb. potential: more neg (-60
vs -50 for SA node).
Gap junctions: very few
Resistance to action potential: incr.
Rate of about 50bpm
*The atrioventricular node (abbreviated AV node) is a part of the electrical control system of the heart that coordinates the top of the heart. It electrically connects atrial and ventricular chambers.[
The blood supply of the AV node is via the AV nodal artery. The origin of this artery is most commonly (about 90% of hearts) a branch of the right coronary artery, with the remainder originating from the left circumflex artery.[5][6][7] This is associated with the dominance of the coronary artery circulation. In right-dominant individuals the blood supply is from the right coronary artery while in left dominant individuals it originates from the left circumflex artery.
Contraction of myocytes (heart muscle cells) requires depolarization and repolarization of their cell membranes. Movement of ions across cell membranes causes these events. The cardiac conduction system (and AV node part of it) coordinates myocyte mechanical activity. A wave of excitation spreads out from the sinoatrial node through the atria along specialized conduction channels. This activates the AV node.[1] The atrioventricular node delays impulses by approximately 0.12s. This delay in the cardiac pulse is extremely important: It ensures that the atria have ejected their blood into the ventricles first before the ventricles contract.[9]
This also protects the ventricles from excessively fast rate response to atrial arrhythmias (see below).[10]
AV conduction during normal cardiac rhythm occurs through two different pathways:
the first “pathway” has a slow conduction velocity but shorter refractory period
the second “pathway” has a faster conduction velocity but longer refractory period.[11]
An important property that is unique to the AV node is decremental conduction,[12] in which the more frequently the node is stimulated the slower it conducts. This is the property of the AV node that prevents rapid conduction to the ventricle in cases of rapid atrial rhythms, such as atrial fibrillation or atrial flutter.
The AV node’s normal intrinsic firing rate without stimulation (such as that from the SA node) is 40-60 times/minute.[13]
AV bundle
Extends from the AV Node
Enters the posterior part of the ventricle
and Purkinje system.
Preferential channel for conduction from the atria to the ventricles
*The bundle of His is an important part of the electrical conduction system of the heart, as it transmits impulses from the atrioventricular node, located at the inferior end of the interatrial septum, to the ventricles of the heart. The intrinsic rate of the bundle of His is 20 or less beats per minute.[1] The bundle of His branches into the left and the right bundle branches, which run along the interventricular septum. The left bundle branch further divides into the left anterior and the left posterior fascicles. These bundles and fascicles give rise to thin filaments known as Purkinje fibers. These fibers distribute the impulse to the ventricular muscle. The ventricular conduction system comprises the bundle branches and the Purkinje network. It takes about 0.03–0.04 seconds for the impulse to travel from the bundle of His to the ventricular muscle.
purkinje system
2 systems: Left and Right 1. Left: Spreads under the endocardium Forms several fascicles-branch over the left ventricle 2. Right: Travels under the endocardium Base of the anterior papillary muscle
*During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from both the left and right bundle branch to the myocardium of the ventricles. This causes the muscle tissue of the ventricles to contract and generate force to eject blood out of the heart, either to the pulmonary circulation from the right ventricle or to the systemic circulation from the left ventricle.
Purkinje fibers also have the ability of firing at a rate of 15-40 beats per minute if upstream conduction or pacemaking ability is compromised. In contrast, the SA node in normal state can fire at 60-100 beats per minute. In short, they generate action potentials, but at a slower rate than sinoatrial node. This capability is normally suppressed. Thus, they serve as the last resort when other pacemakers fail. When a Purkinje fiber does fire, it is called a premature ventricular contraction or PVC, or in other situations can be a ventricular escape.
action potential
The cell at rest:
The resting cell is relatively permeable to potassium and much less to either sodium or calcium
Thus the resting membrane potential of the heart is most dependent on potassium
heart action potential
Five phases:
Phase 0-depolarization Fast Na+ channels
Phase I- repolarization Na+ influx ends
Phase II-plateau Slow Ca+ channels open allowing an influx of Ca+
Phase III-terminal repolarization Slow Ca+ channels are inactivated and efflux of K+ occurs
Phase IV-diastolic phase Na+ - K+ pump
Refractory Pds
Long lasting action potentials prevent premature excitation
Absolute: No response occurs during phase 0- middle of phase III
Relative: Middle of phase III to phase IV when a second stimulus will cause a weaker action potential than the first
cardiac nervous system
Sympathetic:
Arise from:
Stellate ganglion and caudal cervical fibers
Turn into:
The right dorsal medial and lateral cardiac nerves
They unite to form one large nerve that follows the course of the L main CA
They then branch along the ant. descending and circumflex arteries.
Cholinergic fibers-ventricle
