Cardiovascular medicine, lecture I Flashcards
■ Systolic dysfunction – broadly refers to?
■ Diastolic dysfunction – broadly refers to?
■ Systolic dysfunction – pump failure
■ Diastolic dysfunction – filling failure
Forward failure broadly = ?
Backward failure broadly = ?
Forward failure = reduced cardiac output
Backward failure = congestion
Blood composition
■ Plasma 55%
■ ‘Buffy coat’ 4%
■ RBC 41%
Changes will have an effect on cardiac function.
How does the cardiac output from the left heart (systemic circulation) differ from the right heart (pulmonic circulation)?
Left CO is a bit more than right.
– 1-2% more blood is shunted from left cardiac output volume via bronchial circulation (returning to LA).
+ Small fraction of coronary circulation via
thebesian veins (cardiac veins).
The aorta divides into the…
Cranially into truncus brachiocephalicus,
a. subclavia sinistra & dextra, common carotid arteries etc. etc.
Caudally into the aorta decendens etc…. aa.iliaca.
The arterial system is mostly arranged “in parallel,” meaning that blood flows from the heart into separate arterial branches that independently supply different organs. This allows each organ to receive freshly oxygenated blood directly from the heart without being affected by other organs’ metabolic needs.
However, there are two major exceptions where circulation is arranged “in series” rather than in parallel:
splanchnic - Instead of returning directly to the heart, this blood is collected by the portal vein and directed to the liver.
& renal circulation - two-capillary-bed system is called a portal system (specifically, the renal portal system), allowing for filtration in the glomerulus and reabsorption/secretion in the tubules.
Describe the pulmonary circulation.
Right heart circulation: starting from the main pulmonary artery, truncus pulmonalis to left and right pulmonary arteries… pulmonary capillaries - pulmonary veins… returning to the left atrium.
Describe the events that occur during one cardiac cycle. (4+)
- LV contraction
■ Pressure generation - Blood flowing to aorta
■ Aortic elasticity - Ventricular relaxation
■ Systemic blood distribution and diffusion into capillaries
■ Collection to venous system
■ Vena cava -> RA
■ RA -> RV - RV contraction
■ Blood flows to pulmonary circulation
■ Oxygenated blood -> LA
Resistance arteries are
the smallest arteries and arterioles.
Branching arteries reduce BP pulsation (“pressure
reservoirs”).
Capillaries and small venules are exchange vessels.
Exchange vessels are
capillaries and small venules.
Then, veins are highly distensible, capacitance vessels (volume reservoir).
Smallest arteries and arterioles = resistance arteries
Volume reservoir is made up of
veins which are highly distensible, capacitance vessels (volume reservoir).
Percentage of blood volume in veins and arteries?
Blood volume: 70% in veins, 17% in arteries
What occurs in case of reduced cardiac output or blood volume loss?
venous contraction
Forward failure aka reduced
cardiac output presents with
Weakness, fainting, low blood
pressure, pale mucous
membranes
Backward failure aka
congestion presents with
*Left sided: pulmonary edema that can cause dyspnea, cough
*Right sided: ascites, pleural effusion, tachypnea
Anulus fibrosus is
the skeleton of the heart and acts as electrical insulation between atria and ventricles.
Desmosomes are
critical adhesion structures in cardiomyocytes.
Sarcomeres are
the basic contractile unit of muscle fiber. Each sarcomere is composed of two main protein filaments—actin and myosin.
■ Myocyte packed with myofibrils
■ Myofibril consists of sarcomeres
■ Sarcomere = basic contractile unit
Describe the mechanism of contraction of cardiac myocytes.
■ Shortening of sarcomeres, Ca++ initiates shortening
■ Released Ca²⁺ binds to troponin, causing a conformational change on the actin filament, exposing myosin-binding sites.
■ ATP energizes myosin head so it can bind actin and shorten the sarcomere. Contraction is linked to O2 supply.
■ Ca²⁺ is pumped back into the sarcoplasmic reticulum and K+ efflux occurs for repolarization.
Coronary artery blood flow occurs at what point of the cardiac cycle?
Diastole
■ Most blood returns via coronary
sinus to right atrium.
■ A proportion of drainage via
thebesian veins.
What is sinus of Valsalva?
The sinus of Valsalva refers to the three pouch-like dilations located just above the aortic valve in the ascending aorta.
These sinuses are important because they help direct blood flow into the coronary arteries, which originate from them.
Concentric hypertrophy vs eccentric hypertrophy
Concentric thickens inward due to pressure overload.
Eccentric thickens outward due to volume overload.
Sarcomeres added in parallel indicates?
Sarcomeres added in series indicates?
in parallel - concentric hypertrophy
in series - eccentric hypertrophy
What does Starling’s law of the heart tell us?
The more the ventricular muscle fibers are stretched during diastole (due to increased venous return), the stronger the subsequent contraction.
However, if the heart is overstretched (as in heart failure), the contractile force declines, leading to reduced cardiac output.
Describe the cardiac conduction system. (5)
sinus node / sinoatrial node / SA node (right atrium)
atrioventricular node / AV node
bundle of His
bundle branches
purkinje fibers
The P wave represents
sinus node activation aka atrial depolarization which will lead to atrial contraction
The PR interval represents
atrioventricular node delay (to allow the atria to empty into the ventricles)
The QRS bundle represents
ventricular depolarization (Bundle of His, Bundle Branches, Purkinje Fibers) resulting in ventricular contraction.
The T wave represents
ventricular repolarization
The ST segment represents
The ST segment represents the period between ventricular depolarization and repolarization (the plateau phase).
At the end of diastole all cardiac
chambers are
relaxed.
(for a brief moment)
Ventricular volume at the end of
diastole is termed?
Ventricular pressure at the end of
diastole?
end diastolic volume
(EDV)
end diastolic pressure
(EDP)
Atrial systole is 20% of ventricular filling.
What does this mean?
At the start of atrial systole, the ventricles are normally filled with approximately 70–80 percent of their capacity due to inflow during diastole.
Atrial contraction, also referred to as the “atrial kick,” contributes the remaining 20–30 percent of filling.
S1 heart sounds represents
Closure of the atrioventricular valves after the sharp rise of ventricular pressure reaches the threshold required.
For a brief moment, we have - isovolumetric contraction when the volume does not change at all.
What causes the aortic valve to open?
When the left ventricular pressure overtakes the aortic valve pressure.
Ventricular ejection involves:
■ Rapid ejection phase
■ Reduced ejection phase
Contraction ceases at second half of ejection.
What is the dicrotic notch?
The dicrotic notch which is a drop on the down slope shows systole termination and depicts the aortic valve closure and successive backward flow.
The position of the dicrotic notch throughout the cardiac activity differs as per the duration of aortic closure.
S2 heart sound represents
Closure of semilunar valves (aortic and pulmonary)
all heart valves are closed during
Isovolumetric relaxation
If EDP is high,
S3 can be heard.
Diastasis is
the period between rapid filling
and atrial kick.
second phase of
ventricular filling refers to
Atrial systole
If ventricles are stiff, S4 can be heard.
Cause remember that 80% of the systolic volume fills due to inflow during diastole. The rest comes with atrial contraction.
What is the pressure-volume loop?
Pressure-volume loops are graphs showing the changing relationship between left ventricular pressure and volume during a cardiac cycle.
They provide useful information such as stroke volume or end-diastolic volume, as well as systolic, diastolic, and pulse pressure.
Describe cardiac chamber pressures.
Right Atrium (RA) → 2–8 mmHg
* Lowest pressure since it receives blood from the body (via the superior and inferior vena cava).
Right Ventricle (RV) → 15–30 mmHg (systolic) / 2–8 mmHg (diastolic)
* Systolic pressure (15–30 mmHg): When the ventricle contracts.
* Diastolic pressure (2–8 mmHg): When it relaxes and fills.
Pulmonary Artery (PA) → 15–30 mmHg (systolic) / 4–12 mmHg (diastolic)
* Similar to RV but slightly higher diastolic pressure due to pulmonary vascular resistance.
Left Atrium (LA) → 2–12 mmHg
* Slightly higher pressure than RA to push blood into the left ventricle.
Left Ventricle (LV) → 100–140 mmHg (systolic) / 3–12 mmHg (diastolic)
* Systolic pressure (100–140 mmHg): When it contracts.
* Diastolic pressure (3–12 mmHg): When it relaxes.
Aorta → 100–140 mmHg (systolic) / 60–90 mmHg (diastolic)
* Pressure is highest in the systemic circulation.
* Diastolic pressure is maintained by the elastic recoil of the aorta.
CO =
Cardiac output – volume of blood pumped in a minute.
(equation)
CO=HR * SV
Affected by characteristics of heart tissues (HR + contractility) and characteristics of vascular resistance (preload & afterload).
Regulation of the heart rate.
■ HR control mainly via autonomic NS
■ Sinus rate – controlled by symp- and parasymph- NS.
Normally parasymph predominates.
Parasympatholytic drugs increase HR significantly.
What do sympatholytics do?
Sympatholytics actually only reduce the HR slightly (e.g. beta blockers).
That’s why we favor atropine instead which is parasympatholytic and brings up the heart rate.
Fancy terms for increasing the following:
– Heart rate
– Strenght of contraction
– Conduction velocity
– Relaxation
– Heart rate (chronotropy)
– Strenght of contraction (inotropy)
– Conduction velocity (dromotropy)
– Relaxation (lusitropy)
Preload is
Filling of the heart prior to contraction (EDV)
Preload, afterload and inotropy have interdependent effects - changing any of these variables, changes the other two.
Frank-Starling law of the heart: increased venous return results in
increased force of contraction.
Frank-Starling law of the heart: increased venous return results in
increased force of contraction.
Preload, afterload and inotropy have interdependent effects - changing any of these variables, changes the other two.
Afterload is
the total resistance
to blood flow
out of the heart.
Preload, afterload and inotropy have interdependent effects - changing any of these variables, changes the other two.
Primary physiologic way of
increasing cardiac output is…
By increasing contractility by way of the effect of
noradrenaline or adrenaline.
Preload, afterload and inotropy have interdependent effects - changing any of these variables, changes the other two.
inotropy
Definition of heart failure.
HF = a complex clinical syndrome resulting from any structural or functional disorder impairing ventricular filling or ejection.
– Inability to meet metabolic needs; or meets only
with elevated filling pressures.
– Circulatory failure
– Myocardial failure: deficiency of myocardial contraction
– Insufficient cardiac filling
Heart failure - classification (2)
■ Congestive heart failure (CHF): “backward failure”
■ Reduced cardiac output: “forward failure”
Congestive heart failure (CHF): “backward failure” is characterized by (2)
– Left sided: pulmonary edema
– Right sided: jugular distension, pleural effusion, hepatic congestion, ascites, (peripheral edema)
Reduced cardiac output: “forward failure” is characterized by
Weakness, syncope, hypotension, poor perfusion
Main 4 compensatory mechanisms in a failing heart. (4)
Four levels of compensatory mechanisms:
– Reduction of parasympathetic tone
– Increase of sympathetic tone
– Water retention
– Cardiac remodeling
These are only effective short-term afterwhich decompensation occurs.
Basic steps of RAAS.
Renin-Angiotensin-Aldosterone system
- Kidneys detect low blood pressure or low sodium (or are activated sympathetically) and release renin from the juxataglomerular cells).
- Renin acts on angiotensinogen (produced by the liver) and converts it into angiotensin I.
- Angiotensin-Converting Enzyme (ACE) (mainly from the lungs) converts angiotensin I into angiotensin II.
- Angiotensin II is a powerful vasoconstrictor that raises blood pressure.
* It also stimulates Aldosterone Release (adrenal glands) which increases sodium and water retention.
* And stimulates ADH Release (from the posterior pituitary) which promotes water reabsorption in the kidneys.
