CVS 1 Flashcards
Ventricle AP Phase 0
Rapid upstroke- fast Na channels open, inward Na flow
Ventricle AP Phase 1
Initial repolarization- K channels open, outward K flow
Ventricle AP Phase 2
Plateau- Ca channels open (L-type), inward Ca flow
Ventricle AP Phase 3
Rapid repolarization- K channels open more, massive outward K flow
Ventricle AP Phase 4
Resting membrane potential- high K permeability through leaky K channels
SA node AP Phase 0
Depolarization- inward Ca current
SA node AP Phase 3
Outward K current
SA node AP Phase 4
Slow depolarization- inward Na current
How does sympathetic stimulation affect SA node AP?
Increases rate of phase 4 depolarization & frequency of APs d/t increased permeability to Na & Ca
How does parasympathetic stimulation affect SA node AP
Decreases rate of phase 4 depolarization & hyperpolarizes the max diastolic potential to decrease frequency of APs d/t increased K permeability
_______ has stable RMP, while ____ has unstable RMP
Ventricular AP; SA node AP
Accounts for the pacemaker activity of the SA and AV nodes (automaticity)
Phase 4 depolarization (Na)
CCB effect on vascular smooth muscles (greatest to least)
Nifedipine > diltiazem > verapamil
CCB affect on Heart (greatest to least)
Verapamil > diltiazem > nifedipine
Verapamil = Ventricle
Adverse effects of CCB:
Flushing, dizziness, fatigue, constipation, headache, hypotension
Drug of choice for prevention of SVT
Digoxin
Reflects the time required for excitation to spread throughout cardiac tissues
Conduction velocity
Conduction velocity is fastest in ______; slowest in ______
Purkinje Fibers; AV node
Why is conduction velocity slowest in AV node?
Few gap junctions allowing time for ventricular filling
The ability of cardiac cells to initiate AP in response to inward depolarizing current
Excitability
Begins with upstroke of AP & ends after plateau;
NO AP can be initiated;
250 msec
Absolute refractory period
Slightly longer than ARP;
No AP can be generated
Effective refractory period
Period immediately after ARP;
AP can be elicited but more than usual inward current is required
Relative Refractory period
+ dromotropic effect
Increases conduction velocity through AV node, speeding conduction of AP from atria to ventricles and decreasing the PR interval
Sympathetic receptor on heart & parasympathetic receptor on heart
B1; muscarinic
S4 (atrial kick) is associated with?
A hypertrophic ventricle
‘a’ wave on venous pulse curve
Increase in atrial pressure caused by atrial systole
P-wave
Represents electric activation of the atria
7 phases of cardiac cycle
- Atrial systole;
- Isovolumetric ventricular contraction;
- Rapid ventricular ejection;
- Reduced ventricular ejection;
- Isovolumetric ventricular relaxation;
- Rapid ventricular filling;
- Reduced ventricular filling (diastasis)
What causes the fourth heart sound?
Filling of the ventricle by atrial systole
Closure of AV valve represents
First heart sound
Marks the end of both ventricular contraction and rapid ventricular ejection.
Represents repolarization of ventricles
Onset of T wave
Second heart sound is created by closure of?
Semilunar valves (aortic & pulmonic)
What happens when ventricular pressure becomes less than atrial pressure?
Mitral valve opens
Rapid blood flow from atria into ventricle cause? This is normal in ____ but is associated with _____
Third heart sound; children; CHF in adults
stroke volume=?
End-diastolic volume - end systolic volume (nl = 75 ml)
stroke index=?
Stroke volume / body surface area
MAP = ?
DBP + 1/3 pulse pressure
Pulse pressure = SBP- DBP
Contractility (and SV) increase with:
Catecholamines (increased activity of Ca pump in SR);
Increased intracellular Ca;
Decreased extracellular Na;
Digitalis (increased intracellular Na, resulting in increased Ca)
Contractility (and SV) decrease with:
B1 blockade;
Heart failure;
Acidosis;
Hypoxia/hypercapnia
Ejection fraction =
SV / end diastolic volume
Sympathetic stimulation via B1 receptor increases _________ current during the plateau of AP
Inward Ca
Period of highest O2 consumption in pressure-volume loop
B to C (Isovolumetric contraction)
What happens from C to D on pressure-volume loop
Ventricular ejection
D to A on pressure-volume loop
Isovolumetric relaxation
A to B on pressure-volume loop
Ventricular filling + atrial kick
Atrial kick accounts for ____% filling
20
Refers to an increase in ventricular end-diastolic volume (filling)
Increased preload
Preload (ventricular) increases with
Exercise;
Increased blood volume (pregnancy or over transfusion);
Excitement (sympathetic)
stroke volume is affected by?
Contractility, Afterload, Preload
Order of excitation of heart
SA node > internodal tracts > AV node > Bundle of His > Bundle branches > Purkinje fibers > Ventricular muscle
P-R interval
Conduction through AV node (<200 msec)
AV node is bypassed making PR interval < 0.12 sec and leads to early depolarization of ventricle.
Most commonly seen as?
Pre-excitation syndrome; Wolf-Parkinson-White syndrome
Cessation of P waves
Sinoatrial block
Occurs with inferior wall MI
2nd degree Type 1
Occurs with anterior wall MI
2nd degree Type 2
Complete AV block comes & goes;
Ventricles stop contracting for 5-30 sec b/c of overdrive suppression (used to atrial drive) then ventricle escape occurs with AV nodal or AV bundle rhythm (15-40 bmp)
Stokes-Adams Syndrome
Impulse is sometimes blocked and sometimes not in peripheral portions of Purkinje system resulting in abnormal QRS waves
Incomplete Intraventricular Block (electrical alternans)
