Non AI Lecture 20 electrophysiology

Explain the flow of the electrical system of the heart

SA node, atria, AV node, bundle of his, bundle branches, purkinje fibers

Myofibrils within cardiac cells contain

contractile machinery

The mitochondria in cardiac cells are important due to the

continuous ATP demand

Stores the calcium necessary for contraction

Sarcoplasmic reticulum

Inward extensions of the cell membrane whose lumen communicates with extracellular fluid. They carry membrane depolarization into the cell and position calcium entry close to the SR

T-tubes

________ are a unique feature of cardiac cells that all for faster transmission of action potentials

Intercalated discs

Cardiac cells have a large number of mitochondria due to needing a higher amount of _____ in comparison to skeletal cells

ATP

T-tubules of cardiac cells allows for readier access to ____

ions

What are the two types of cardiac cells

conduction, contraction

conduction cells correlate with the pacemakers of the heart which are the

SA and AV nodes

Contratcion cells correlate with the cardiac muscles such as the

atria and ventricles

Gap junctions allow for adjacent cadiac myocytes communicate in what two ways

chemically, electrically

Calcium enters the myocardial cell after electrical excitation increasing membrane permeability to calcium. Once it enters it diffuses towards the myofibrils and bids with what protein complex

Troponin

Troponin is a protein complex that plays a key role in ______. It also acts a a biomarker to help diagnose _______

muscle contraction; heart damage

______ refers to a system of electric impulses generated in the heart to cause the heart to contract

cardiac conduction

Explain the steps of cardiac conduction

SA node generates an electrical impulse, atria contracts, impulse travels to AV node where there is a small delay for ventricular filling, conduction then moves bundle of his- R/L bundle branches, then reaches purkinje fibers and causes ventricular contraction

What establishes normal sinus rhythm

SA node

What is the purpose of the delay at the AV node

completion of atrial activation/contractions and ventricular filling

During the refractory period the base of the heart ________. This also give time for the atria/ventricles to recover which prevents _______

depolarizes, quivering

What can impact the speed of AV node conduction

parasympathetic/sympathtic (ANS)

Purkinje fibers relay waves to the septum allowing for

depolarization

The pacemaker hierarchy states that the fast pace-making rate wins, what is the order of structures/rate

SA nodes (60-100), AV (40-60), Purkinje (20-40)

What are the three main ions associated with pacemaker physiology

Na, Ca, K

What is the order of phases in a cardiac conduction cell

spontaneous depolarization (4), depolarization (0), repolarization (3)

explain the events that occur in a cardiac conduction cell (ions)

slow, spontaneous depolarization driven by Na/Ca influx, threshold met around -40mv rapid Ca channels open, around +30mv Ca channels close and K efflux channels open returning to resting (-65mv)

explain the physiologic events that occur in a cardiac conduction cell

spontaneous depolarization speed associated with HR, determines the pacing rhythm (fast-symp, slow-parasymp), depolarization spreads through atria and initiates contraction, repolarization ends the nodal action and resets for the next cycle

What is the order of phases in a cardiac contraction cell

rapid depolarization (0), early repolarization (1), plateau (2), repolarization (3), resting phase (4)

explain the events that occur in a cardiac contraction cell (ions)

purkinje fibers deliver impulses causing fast Na channels to open, Na channels deactivate and short period of fast K efflux, Ca+ influx and K efflux balance out, Ca channels close and K efflux dominates returning to resting potential, -90mv (resting), maintained by sodium/potassium pumps and K leak channels

explain the physiologic events that occur in a cardiac contraction cell

ventricular muscle depolarizes and initiates contraction, transition between depolarization and plateau, maintains prolonged depolarization allowing for sustained contraction, ventricles relax (diastole begins), ventricles ready for next impulse

What is significant about conduction cells membrane potential

Unstable

Which phases do not occur in a conduction cell

early repolarization and plateau (1&2)

Unlike skeletal muscle or contraction cells, conduction cells are never truly what

at rest

Myocytes are strongly negative, which ion helps them maintain this voltage

Potassium (K+)

The plateau prolongs the _____________ supporting contraction and extending the period during which the tissue cannot be readily re-excited

ventricular action potential

effective refractory period = ______
relative refractory period = ______

No AP; AP if stimulus is strong enough

Explain the steps of excitation-contraction coupling in cardiomyocytes

AP generated, Ca enters (plateau), Ca induced Ca release via SR, Ca binds troponin, actin and myosin interact, contraction

Explain sympathetic autoregulation

sympathetic system releases NE, inc cAMP, inc Ca & Na, move AP threshold toward Vm (Ca) and inc phase 4 depolarization rate (Na) = inc HR and inc rate of conduction AV

Explain parasympathetic autoregulation

parasympathetic release ACh, dec cAMP + inc muscarinic K+ activity, dec Na dec Ca and inc K efflux, dec depolarization rate (Na), move AP away from Vm, shift Vm more negative (K+) = dec HR and dec rate of conduction AV

An effect/change in heart rate

chronotropy

an effect/change in the contractility

Inotropy

Which adrenergic receptor increases contractility (chronotropy)

Beta-1

What action is associated with a P wave on an ECG

atrial depolarization

What action is associated with the PR interval on an ECG

time from the onset of atrial activation to onset of ventricular activation

What event/action is associated with the QRS complex

sum of all ventricular depolarization

What event is associated with the ST interval

Ventricular myocardium depolarization

What event is associated with the QT interval

“electrical systole” of the ventricles, varies inversely with HR (total duration of ventricular electrical activity in the heart)

a P wave is what electrical and mechanical event

atrial depolarization; atrial contraction

The QRS complex is what electrical and mechanical event

ventricular depolarization; ventricular contraction

a T wave is what electrical and mechanical event

ventricular repolarization; ventricular relaxation

What does the PR interval represent

atrial to ventricular activated timing

What does the QT interval represent

time from ventricular depolarization to repolarization

The RR interval (peak to peak) indicates

time btwn beats, aka HR

an inconsistent RR interval indicates what

an irregular rhythm

What does a QRS interval that is too long indicate

conduction block in the ventricle

What does a PR interval that is too long indicate

AV node delay

What does a PR interval that is too short indicate

ventricles excited too soon

The QT interval can be influenced by changes in serum

Ca or K

ST depression or elevation is a shift that suggest what

ischemia

What are two common causes of dysrhythmias

abnormal rate of impulse generation, abnormal impulse conduction

What electrolyte abnormality is depicted by tall peaked T waves on and ECG

Hyperkalemia

What electrolyte abnormality is depicted by flatten P wave and widened QRS

Severe hyperkalemia

What electrolyte abnormality is depicted by ST depression, flattened T wave, and prominent U wave

Hypokalemia

What electrolyte abnormality is depicted by shortened QT interval

Hypercalcemia

What electrolyte abnormality is depicted by prolonged QT interval

Hypocalcemia