Cardiovascular Physiology and Electrophysiology Review

Comprehensive vocabulary flashcards covering cardiac anatomy, excitation-contraction coupling, electrophysiology, arrhythmias, cardiac cycle mechanics, pressure-volume loops, hemodynamic monitoring, and congenital defects.

In-Series Ventricular Arrangement

The anatomical organization where the right and left ventricles pump sequentially, requiring their average stroke volumes and outputs to match despite generating vastly different pressures.

Wall Stress Equation

The relationship defined by $\sigma = \frac{P \cdot r}{2h}$, where wall stress ($\sigma$) increases with chamber pressure ($P$) and radius ($r$), but decreases with greater wall thickness ($h$).

Concentric Hypertrophy

Cardiac remodeling pattern driven by chronic pressure overload, characterized by sarcomeres assembling in parallel to increase wall thickness ($h$).

Eccentric Hypertrophy

Cardiac remodeling pattern driven by chronic volume overload, characterized by sarcomeres assembling in series to increase ventricular chamber radius ($r$).

Right vs. Left Ventricular Dimensions

Normal structural differences where the RV wall thickness is $3\text{--}5\,\text{mm}$ with pressures around $25/4\,\text{mmHg}$, while the LV is $8\text{--}11\,\text{mm}$ ($\sim 3\times$ thicker) with pressures around $120/8\,\text{mmHg}$ ($\sim 5\times$ higher pressure).

Pericardium

A stiff fibrous and serous sac containing $15\text{--}50\,\text{mL}$ of fluid that restricts acute ventricular distension, mediates ventricular interdependence, and can cause tamponade upon rapid accumulation of $100\text{--}200\,\text{mL}$ of blood.

Cardiac Fibrous Skeleton

Dense connective tissue providing a mechanical anchor for the valves and myocardium, while functioning as an electrical insulator that confines atrial-to-ventricular conduction strictly to the AV node and bundle of His.

Semilunar Valves

Heart valves (aortic and pulmonary) composed of 3 cusps without chordae tendineae that close passively at the end of systole.

Atrioventricular (AV) Valves

Passive cardiac valves (mitral with 2 leaflets, tricuspid with 3) attached to chordae tendineae and papillary muscles that close at the start of systole.

Mitral Valve Apparatus

The multi-component functional unit consisting of the annulus, leaflets, chordae tendineae, papillary muscles, and ventricular wall.

Coronary Ostia

The entry points of the coronary arteries situated within the right and left aortic sinuses (of Valsalva), directly superior to the aortic valve cusps.

Heart Sounds (S1, S2, S3, S4)

Acoustic milestones: $S_1$ marks mitral and tricuspid closure; $S_2$ marks aortic and pulmonary closure; $S_3$ represents rapid ventricular filling in young or failing hearts; $S_4$ represents atrial kick into a stiff ventricle.

Intercalated Discs

Microscopic junctions containing gap junctions for electrical coupling and desmosomes/fascia adherens for mechanical coupling, binding cardiomyocytes into a functional syncytium.

Myocardial Wringing / Twist

The helical fiber arrangement shifting from left-handed in the epicardium to right-handed in the endocardium, inducing opposite rotational movement between apex and base during systole and facilitating untwisting for early diastolic filling.

Coronary Vascular Territories

Specific blood supply distributions corresponding to ECG leads: LAD supplies the anterior wall and septum ($V_1\text{--}V_4$); Circumflex supplies the lateral wall ($I$, $\text{aVL}$, $V_5\text{--}V_6$); RCA supplies the inferior wall ($II$, $III$, $\text{aVF}$).

Coronary Dominance

Anatomical classification based on which coronary artery branches into the posterior descending artery: Right-dominant ($\sim 85\%$), Left-dominant ($\sim 8\%$), or Co-dominant ($\sim 7\%$).

Nodal Blood Supply

The arterial branches nourishing the pacemakers: the SA node is supplied by the RCA in $\sim 60\%$ and LCx in $\sim 40\%$; the AV node is supplied by the RCA in $\sim 90\%$ of individuals.

Diastolic Coronary Perfusion

The mechanism whereby the LV myocardium is perfused primarily during diastole, since systolic contraction compresses intramural vessels; elevated heart rates shorten diastole and endanger subendocardial perfusion.

Calcium-Induced Calcium Release (CICR)

The process in excitation-contraction coupling where trigger $\text{Ca}^{2+}$ entering through L-type channels opens sarcoplasmic reticulum RyR2 channels, releasing approximately $10\times$ more calcium into the cytosol.

Cardiac Dyad

The specialized junctional space where the T-tubule meets the sarcoplasmic reticulum, placing L-type calcium channels and RyR2 receptors approximately $12\,\text{nm}$ apart to generate local calcium sparks.

RyR2 Receptor

The cardiac sarcoplasmic reticulum ryanodine receptor that requires extracellular trigger $\text{Ca}^{2+}$ across a $12\,\text{nm}$ gap and resists calcium shut-off, differing from the mechanically linked skeletal RyR1.

Phospholamban

A regulatory protein that acts as an inhibitory brake on SERCA's reuptake of $\text{Ca}^{2+}$ into the sarcoplasmic reticulum during myocyte relaxation.

Treppe (Cardiac Staircase)

The intrinsic myocardial property wherein an increased heart rate shortens the time available to clear cytosolic $\text{Ca}^{2+}$, progressively loading the SR and producing stronger successive contractions.

Digoxin Mechanism

Inhibition of the $\text{Na}^+/\text{K}^+$ pump, causing intracellular $\text{Na}^+$ accumulation, diminished NCX-mediated $\text{Ca}^{2+}$ extrusion, higher sarcoplasmic reticulum calcium storage, and augmented inotropy.

Resting Membrane Potential

The electrical baseline of a resting working cardiomyocyte at approximately $-90\,\text{mV}$, maintained near the $\text{K}^+$ equilibrium potential by selective resting potassium permeability.

Phase 0 (Upstroke)

The initial rapid depolarization of the cardiac action potential up to approximately $+20\text{--}30\,\text{mV}$, driven by fast voltage-gated $\text{Na}^+$ influx that dictates conduction velocity.

Phase 2 (Plateau Phase)

The prolonged $\sim 200\,\text{ms}$ phase of the cardiac action potential maintained by balanced inward L-type $\text{Ca}^{2+}$ currents and outward $\text{K}^+$ currents, ensuring an extended refractory period.

Absolute Refractory Period

The interval during the cardiac action potential when voltage-gated $\text{Na}^+$ channels remain inactivated, rendering the cell entirely unexcitable to any stimulus.

Funny Current ($I_f$)

A hyperpolarization-activated, non-selective inward cation current carrying $\text{Na}^+$ that drives phase 4 spontaneous diastolic depolarization in pacemaker tissue.

Pacemaker Hierarchy

The intrinsic gradient of cardiac automaticity governed by overdrive suppression, where the fastest pacemaker (SA node) sets the rhythm, backed up by the AV junction, and followed by the His-Purkinje system.

Vagal Effect on the SA Node

Parasympathetic slowing mediated by acetylcholine on $M_2$ receptors, which opens a $\text{K}^+$ channel to hyperpolarize the membrane and lowers cAMP to flatten the phase 4 drift slope.

PR Interval

The ECG segment lasting $120\text{--}200\,\text{ms}$ that represents AV nodal delay; it appears isoelectric because the nodal tissue mass is too small to register a deflection.

QRS Complex

The ECG waveform reflecting ventricular depolarization, typically narrow (less than $120\,\text{ms}$ or $0.12\,\text{s}$) due to rapid conduction throughout the Purkinje network.

First-Degree AV Block

A conduction disturbance characterized by a prolonged PR interval ($> 0.20\,\text{s}$) with every P wave followed by a QRS complex ($1:1$ conduction) due to delay in the AV node.

Mobitz Type I (Wenckebach)

A second-degree AV block marked by progressive prolongation of the PR interval until a single ventricular beat is dropped, typically occurring at the AV node and often vagally mediated.

Mobitz Type II Block

A dangerous second-degree infranodal block characterized by a constant PR interval accompanied by sudden, non-conducted P waves, frequently presenting with wide QRS complexes.

Third-Degree (Complete) AV Block

A complete dissociation between atria and ventricles where independent, faster regular P waves and slower regular escape QRS complexes occur with variable PR intervals.

Bundle Branch Block

An intraventricular conduction abnormality characterized by a normal PR interval and a widened QRS complex exceeding $0.12\,\text{s}$ caused by sequential, slow cell-to-cell ventricular depolarization.

R-on-T Phenomenon

An arrhythmogenic event where a premature ventricular contraction strikes the peak of the preceding T wave during the vulnerable period, inducing re-entry and triggering polymorphic VT or VF.

Atrial Flutter

A supraventricular arrhythmia characterized by an atrial rate exceeding $250/\text{min}$ with no flat isoelectric baseline, where the AV node limits ventricular transmission above approximately $200/\text{min}$.

Isovolumetric Contraction

The early systolic phase following the QRS complex where LV pressure exceeds LA pressure to close the mitral valve ($S_1$) with all valves shut, creating the steepest rate of ventricular pressure rise at constant volume.

Isovolumetric Relaxation

The early diastolic phase following aortic valve closure ($S_2$) where all valves are closed, chamber volume stays at ESV ($\sim 50\,\text{mL}$), and LV pressure drops precipitously.

Jugular Venous Waves (a, c, v, x, y)

Right atrial pressure waveforms: 'a' represents atrial contraction, 'c' is tricuspid bulging, 'v' is atrial filling against a closed valve, 'x' is atrial relaxation, and 'y' is tricuspid opening.

Physiological S2 Splitting

The audible split where aortic closure ($A_2$) precedes pulmonary closure ($P_2$), which widens during inspiration as increased venous return prolongs right ventricular ejection.

End-Diastolic Pressure-Volume Relationship (EDPVR)

The passive filling curve of the relaxed ventricle defining preload; its nonlinear slope represents ventricular stiffness.

End-Systolic Pressure-Volume Relationship (ESPVR)

The maximal active boundary line of ventricular elastance whose slope represents end-systolic elastance ($E_{es}$), a load-independent index of contractility.

Preload

The mechanical stretch on the ventricular myocardium immediately prior to contraction, clinically quantified by end-diastolic volume (EDV).

Afterload

The resistance or load the ventricle must overcome to eject blood, representing aortic pressure or ejection wall stress; higher afterload increases ESV and narrows stroke volume.

Pressure-Volume Area (PVA)

The total mechanical energy bounded by the PV loop, combining external stroke work with potential elastic energy, which directly mirrors myocardial oxygen consumption.

Heart Failure with Preserved Ejection Fraction (HFpEF) PV Loop

A pressure-volume loop abnormality marked by an upward shift and steepening of the EDPVR with normal ESPVR, driving high filling pressures and pulmonary congestion despite a normal ejection fraction.

Cardiac Index

Cardiac output normalized for body surface area ($\text{CI} = \frac{\text{CO}}{\text{BSA}}$), having a standard resting range of $2.6\text{--}4.2\,\text{L/min/m}^2$.

Fick Equation

The physiological formula calculating cardiac output from oxygen consumption and arteriovenous oxygen difference: $\text{CO} = \frac{\dot{V}O_2}{C_aO_2 - C_vO_2}$.

Tanaka Formula

A regression formula used to estimate maximal heart rate based on age: $\text{HR}_{\max} = 208 - (0.7 \times \text{age})$, possessing a standard deviation of approximately $\pm 10\text{--}12\,\text{bpm}$.

Heart Rate Reserve (HRR)

The difference between maximal and resting heart rate ($\text{HRR} = \text{HR}_{\max} - \text{HR}_{\text{rest}}$), used in the Karvonen formula to calculate training target heart rates.

Chronotropic Incompetence

The inability of the heart rate to increase appropriately during exercise, substantially limiting physical work capacity even when stroke volume remains intact.

Ductus Venosus

A fetal vascular shunt that directs oxygen-rich blood from the umbilical vein into the IVC, bypassing the fetal liver, and subsequently obliterates into the ligamentum venosum.

Foramen Ovale

A cardiac shunt directing blood from the right to the left atrium in the fetus, which functionally shuts when LA pressure exceeds RA pressure at birth and fuses as the fossa ovalis.

Ductus Arteriosus

A fetal vessel connecting the pulmonary artery directly to the aorta; maintained patent by low oxygen and $\text{PGE}_2$, it constricts post-birth ($\sim 24\text{--}48\,\text{h}$) to form the ligamentum arteriosum.

Eisenmenger Syndrome

The development of severe pulmonary vascular remodeling secondary to a chronic left-to-right shunt, driving PVR above SVR and reversing blood flow into a cyanotic right-to-left shunt.

Tetralogy of Fallot

A cyanotic congenital defect consisting of four classic lesions: large ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta.

Transposition of the Great Arteries

A congenital condition where the aorta arises from the RV and the pulmonary artery from the LV in two parallel non-communicating circuits, requiring a mixing shunt and prostaglandin infusion to sustain life.

Coarctation of the Aorta

Congenital constriction of the aorta near the ductus arteriosus, resulting in upper extremity blood pressures exceeding lower extremity pressures, accompanied by diminished femoral pulses.

Bulbus Cordis

The primitive embryonic heart tube region that gives rise to the adult right ventricle.

Truncus Arteriosus

The embryonic heart tube segment that divides to form the adult aorta and pulmonary trunk.