Week 8: Cardiology Flashcards
Purpose of His-Purkinje System and bundle branches
To coordinate contraction of left and right ventricles
Which vessels provide the major resistance in the vascular tree?
The arterioles.
They have smooth muscle that is subject to autonomic control. Because they are small and arranged in series, a small alteration to radius makes a large (^4) difference for resistance.
3 main epicardial arteries
Right coronary artery
Left main coronary artery, which divides into the left anterior descending artery and the left circumflex artery.
Three functions of pericardium
- Cardiac mechanics
- Lubrication with cardiac motion
- Barrier for limiting infections
3 main layers of heart
endocardium
myocardium
visceral pericardium - pericardial cavity - parietal pericardium
Composition of a sarcomere in cardiac muscle
thin filament (actin-troponin-tropomyosin) and thick filament (B myosin) with subtypes specific to cardiac muscle.
What is the mechanism of cardiac contraction at the cellular level?
calcium-induced calcium release (excitation-contraction coupling). This is unique to cardiac sarcomere.
What kind of valves are the aortic and pulmonary valves?
Semilunar
What two events delineate the beginning and end of systole?
AV valve closure and semilunar valve closure. I.e., S1-S2
Equation for cardiac output
CO = SV x HR
Equation for BP
BP = CO x SVR
Define stroke volume
The volume of blood ejected from the ventricle with each contraction
Define cardiac output
The volume of blood ejected from the ventricle per minute
Define vascular resistance
The resistance conferred by the vessels that must be overcome by ventricular contraction
What is the S1 sound?
Mitral valve and tricuspid valve closure
What is the S2 sound?
Pulmonary valve and aortic valve closure
S3 sound
An abnormal heart sound that, if present, occurs in diastole. Occurs when the ventricle is volume overloaded, whereby the rapid cessation of blood flow early in diastole (as the atrial and ventricular pressure equilibrate) results in an abnormal heart sound.
S4 Sound
An abnormal heart sound that, if present, occurs late in diastole. Occurs in pressure overloaded ventricle, whereby the extra pressure and volume conferred by atrial contraction into a stiff ventricle results in an abnormal heart sound.
What is a murmur?
Increased turbulent flow.
What are the three increased flow states that may be associated with a murmur?
- Increased flow through normal structures in the context of increased metabolic demand
- Turbulent flow through narrow orifices (narrowed valve, regurgitation, septal defect)
- Flow into a larger distal chamber (aortic aneurysm)
When does pulmonic stenosis cause a murmur
Systole
When does mitral stenosis cause a murmur
During diastole
How can anemia cause a murmur?
Increased flow through normal structures.
when would aortic regurgitation make a murmur?
During diastole
What pressure difference signals the aortic valve to open?
When the LV pressure exceeds the aortic pressure
what is the ejection fraction?
Used to assess systolic function.
= SV / LV end-diastolic volume
Three determinants of stroke volume?
Preload
Afterload
Contractility
Define preload
the ventricular wall tension developed at the end of diastole. Closely approximates LVEDV (left ventricular end diastolic volume)
Define afterload
the ventricular wall stress encountered during contraction (systole) that must be overcome in order to eject blood.
What does increasing preload do to stroke volume?
Increased stroke volume (start with a push)
What does increased afterload do to stroke volume?
Decreases stroke volume (need to push against resistance)
What does increased contractility do to stroke volume?
Increases stroke volume (squeeze harder and get more blood out).
What happens to the heart function during exercise?
- Increase CO to meet metabolic demands, with corresponding increases in HR and SV.
Preload, afterload, and contractility all increase and SV increases as a result. Increased preload overcome by increased contractility.
What does the law of laplace have to do with heart hypertrophy?
The law of laplace states that walls need to thicken (concentric hypertrophy) to compensate for increased pressure. This is what happens with the heart faces chronic increase in afterload
Why does eccentric hypertrophy of the heart occur?
In chronic volume overload states, the physiological response is to increase the cavity chamber size, thus accommodating increased volume without significant rise in pressure.
Concentric vs eccentric hypertrophy. What do they look like and when do they occur?
Concentric = thick; increased afterload response. eccentric = increased chamber size' increased preload response
3 major fetal shunts
1) Ductus venosus (bypass liver –> fetal heart)
2) Foramen oval shunts blood from RA to LA
3) Ductus arteriosis (shunt blood from pulmonary artery to aorta
Describe fetal circulation
Single circulation.
Oxygen comes to fetus via umbilical vein from placenta. Enters RA and access LA via foramen ovale.
Neonatal transitional circulation
No longer a single path.
R and L pumps are equal in pressure and circulation bypass is still possible through patent foramen ovale and ductus arteriosus.
Incidence of congenital heart disease
~3:1000
What CHDs present as cyanotic?
Tetralogy of Fallot Transposition of great arteries Truncus arteriosus Tricuspid abnormalities Total anomalous pulmonary venous return
What distinguished Eisenmenger syndrome from other forms of R to L shunting?
R to L shunting in Eisenmenger syndrome is caused by pulmonary hypertension due to chronic L to R shunting.
During what weeks of gestation does the heart develop?
The 3rd and 9th week of gestation
Describe formation of the embryonic heart tube
Cardiac precursor cells arise within splanchnic mesoderm at the cranial end.
Cells are arranged in an inverted U pattern and then aggregate into two endocardial tubes that lie side by side in the cardiogenic area of the embryo.
Embryo folds laterally, bringing the two tubes together at the midline.
Cephalocaudal folding brings the heart tube into the thorax and bulging into the future pericardial cavity (Day 21).
The heart tube is the inner lining of the mature heart - will form endocardium.
Outline the process of cardiac folding.
The heart tube is fixated at each end and so when it elongates, the middle dilations twist and fold to move the heart chambers into the correct anatomical position.
Name the dilations of the primitive heart
Bulbis cordis
Primitive ventricle
Primitive atria
Sinus venosus
What does the bulbus cordis become become?
Parts of RV and LV and aorta and pulmonary artery
What does the primitive ventricle become?
Parts of RV and LV
What does the primitive atrium become
Left and right auricles (the bumpy bits in the atria)
What does the sinus venosus become?
parts of the coronary sinus and RA
PICO
Patient
Intervention
Comparator
Outcome
For formulating a strong research question.
