Cardiac Monitoring

Cardiac skeleton

Fibrous CT supporting valves that acts as an insulating layer between atria and ventricles

Fibrous pericardium

Outermost layer of pericardium; anchors the heart to great vessels, diaphragm, and sternum and helps limit excessive cardiac distension

parietal layer of serous pericardium

Lines and is fused to the inner surface of the fibrous pericardium

visceral layer of serous pericardium

directly covers the heart, aka epicardium

pericardial cavity

space between the visceral and parietal layers of the serous pericardium; contains some fluid to reduce friction

endocardium

serous membrane that lines the inner surfaces of the heart and extends out to form valves. similar to endothelial cells lining blood vessels

tricuspid valve

Normal size: 4-6 cm-squared. 3 leaflets separating RA and RV

mitral valve

Normal size: 4-5 cm-squared. 2 leaflets separating LA and LV

atrioventricular valves

anchored by chordae tendinae to papillary muscles which prevent prolapse during systole. tricuspid and mitral

aortic valve

Normal size: 3-4 cm-squared. Prone to stenosis (<2cm-squared), calcification, bicuspid defect, and regurgitation

pulmonary valve

separates RV from pulmonary arteries

semilunar valves

composed of three half-moon shaped leaflets attached to a fibrous ring. aortic and pulmonary

normal pRA

0-8 mmHg

normal pRV

25 / 4 mmHg

normal pPA

15-25 / 8-15 mmHg. Mean = 10-20 mmHg

normal pLA

4-12 mmHg, generally equal to PCWP/PAWP and LVEDP

normal pLV

110-130 / 4-12 mmHg

normal blood pressure (aortic)

120 / 80 mmHg

SVC

receives 1/3 of venous return from the upper extremities

IVC

receives 2/3 of venous return from lower extremities

right heart blood flow

Coronary sinus drains most cardiac veins into RA with SVC & IVC. Low pressure system handling deoxygenated blood

pulmonary wedge pressure (PCWP/PAWP)

Estimate of left atrial pressure via Swan-Ganz catheter balloon inflation. Normal = 9-18 mmHg

cardiac cycle - systole

isovolumetric ventricular contraction, ventricular ejection

cardiac cycle - diastole

isovolumetric relaxation, ventricular filling, atrial systole

isovolumetric ventricular contraction

Ventricular depolarization; ventricular pressure increases and closes mitral and tricuspid valves

ventricular ejection

pLV > pAo, pRV > pPA; pulmonary and aortic valves open

isovolumetric relaxation

pLV < pAo, pRV < pPA; all valves close and ventricles are at their most empty

ventricular filling

Atrial pressures exceed ventricular pressures; tricuspid and mitral valves open. Ventricles fill 70%

atrial systole

Atrial kick supplies remaining 30% of blood to ventricles

venous pressure waveform

a - atrial contraction, c - tricuspid bulging w ventricular contraction, x - downward mvmt of tricuspid valve as papillary muscle contracts, v - passive atrial fill, y - atrial emptying through open tricuspid valve

arterial pressure waveform

Increase in systolic pressures as diastolic pressures decrease further away from the heart. Peripheral arteries are stiffer and less compliant.

cardiac conduction

SA node (RA), bachmann bundles (LA), internodal pathways, AV node (delay), bundle of his, R/L bundle branches, purkinje fibers (SBIABBP)

automaticity & electrical coupling

Spontaneous impulse generation; gap junctions in intercalated discs allow ions to pass rapidly for functional syncytium

sarcomere

basic functional contractile unit of cardiac muscle containing interdigitated actin and myosin

cardiomyocytes

Bundles of myofibrils composed of repeating sarcomeres

cardiac output (CO)

HR x SV. Amount of blood pumped by the heart each minute

stroke volume (SV)

EDV - ESV (fullest - emptiest). Amount of blood ejected by a ventricle each beat. 70 ml = average

chronotropy

HR. Typically set in SA node. Sympathetic increases, parasympathetic decreases

dromotropy

Conduction velocity (Ca2+ dependent). Delay in AV node. Sympathetic increases, parasympathetic decreases

Inotropy

Strength of contractility in ventricles (Ca2+ dependent). Sympathetic increases, parasympathetic has negligible effect

lusitropy

Relaxation in ventricles. Sympathetic speeds, parasympathetic has negligible effect

sympathetic cardiac modulation

Norepi + epi stimulate Beta-1 receptors to increase HR, AV conduction, contractility, and cardiac output. Receptors all over the heart - SA, AV, and ventricles

parasympathetic cardiac modulation

Acetylcholine stimulates M2 muscarinic receptors via the vagus nerve to decrease SA and AV conduction and decrease HR. Little effect on ventricular contractility.

atrial natriuretic peptide (ANP)

Release from atria stimulated by atrial strech/increased volume. Causes natriuresis, diuresis, and vasodilation to decrease blood volume and cardiac filling pressures.

B-type natriuretic peptide (BNP)

Release from ventricular myocardium stimulated by ventricular wall stress and increased filling pressures. Causes natriuresis, diuresis, and vasodilation. Common biomarker of heart failure

Natriuretic peptides

Hormones released during cardiac distension to decrease blood volume, BP, preload, and vascular resistance. Opposes RAAS

concentric hypertrophy

Widespread thickening of myocardium and decrease of LV volume. Characterized by diastolic dysfunction. Compensation for increased SVR, untreated HTN, or aortic stenosis/coarctation

eccentric hypertrophy

Cardiomyocytes increase in length and myocardial wall dilates. Characterized by systolic dysfunction. Attempt to compensate for volume overload, valve prolapse

RCA major branches

acute marginals, posterior descending artery (PDA)

Perfused by RC

coronary dominance

Determines which coronary artery (R, L, or both) gives rise to the posterior descending artery (PDA). Set from birth, but collateralization can bypass blockages. R is most common

Law of Laplace

Tension = P x r / wall thickness. The larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure.

factors affecting myocardial oxygen consumption

Ventricular wall tension (Laplace/DCM), contractility, HR

Pascal’s principle

Pressure is transmitted undiminished in an enclosed static fluid. Pproximal = Pdistal. Eg. PCWP, PAWP

Poiseuille’s law

Flow = pi x pressure gradient x r^4 / 8 x viscosity x vessel length. Flow rate = pressure difference divided by viscous resistance.

% of CO perfusing the digestive system

21%

% of CO perfusing the liver

6%

% of CO perfusing the kidneys

20%

% of CO perfusing the brain

13%

% of CO perfusing SKM

15%

% of CO perfusing myocardium

3%

% of CO perfusing skin

9%

ejection fraction

SV / LVEDV x 100. Measure of how efficiently the blood is pumping out the volume it receives. Normal = 55-75%

systemic vascular resistance (SVR)

(MAP - CVP / CO) x 80. Normal = 900-1440 dynes x s x cm^-5

pulmonary vascular resistance (PVR)

(MPAP - LA / CO) x 80. Normal = 20-120 dynes x s x cm^-5

mean arterial pressure (MAP)

(1/3) systolic + (2/3) diastolic

Low BP

Firing rate of baroreceptors decreases, which stimulates sympathetic activity to increase HR, contractility, and vascular tone.

High BP

Firing rate of baroreceptors increases, stimulating parasympathetic activity and decreasing sympathetic activity to decrease HR and vascular tone

Carotid bodies

contain chemoreceptors that relay sensory information to the brain via the glossopharyngeal nerve (CN IX)

Aortic bodies

contain chemoreceptors that relay sensory info to the brain via the vagus nerve (CN X)

carotid sinus

contains baroreceptors that relay sensory info to the brain via the glossopharyngeal nerve (CN IX)

aortic arch

contains baroreceptors that relay sensory info to the brain via the vagus nerve (CN X)

3-5 mm

Average size of a large coronary artery

Areas perfused by RCA

RA, RV, SA & AV nodal arteries, inferior LV & posterior interventricular septum if R-dominant.

Conus artery

Usually the first branch of RCA, but sometimes arises straight from aorta

capillary fluid movement factors

hydrostatic pressure, colloid osmotic pressure, interstitial pressure

left main coronary artery branches

L anterior descending (LAD), ramus intermedius (20%), L circumflex

LAD branches

Diagonal branches (Dx) supply anterolateral LV, Septal perforators supply anterior interventricular septum

LCx branches

Obtuse marginals supply LA and lateral/posterolateral LV

threshold BP for hypertension

140/90 mmHg

arterial pressure monitoring sites

radial, femoral, dorsalis pedis, posterial tibial, brachial (in order of pref)

pulsus alternans

Alternation between strong and weak pulse pressure amplitudes while rhythm stays regular. Hallmark of severe LV dysfunction - needs a beat to recover Ca2+ stores

pulsus paradoxus

An exaggerated decrease (>10 mmHg) in systolic blood pressure during inspiration. Hallmark of cardiac tamponade, severe obstructive pulmonary disease

auscultation

Listening to heart sounds for abnormality via stethoscope. S1= AV valves closing (onset of systole) S2 = SL valves closing (onset of diastole)

systolic murmurs

Occur between S1 and S2. Aortic stenosis (wooshing), mitral regurgitation, VSD

diastolic murmurs

Occur between S2 and S1. Mitral stenosis (valve won’t open) , aortic regurgitation (valve won’t close).

cardiac stress tets

Detects specific areas of myocardial ischemia during increased workload.

non-ambulatory cardiac stress test

IV drugs (adenosine, dobutamine, and regadenoson) simulate exertion on the heart if patient is unable to use a treadmill

stress test contraindications

Active myocardial injury - positive troponins, ischemic EKG changes, acute coronary syndrome presentations

coronary angiography

Cardiac cath maps anatomy, grades severity of stenosis, quantifies blood flow, measures hemodynamics and pressures, and can be used for angioplasty, stents, or impella

Fractional flow reserve (FFR)

Measures pressure drops across a plaque to show how it behaves physiologically. >0.8 requires treatment