Cardiac Action Potential

(phases)

[image]

Cardiac Action Potential

·         In the resting or polarized state, sodium is the primary extracellular ion, whereas potassium is the primary intracellular ion

·         during cellular stimulation, sodium or calcium crosses the cell membrane into the cell & potassium ions exit into the extracellular space – this exchange of ions creates a positively charged intracellular space & a negatively charged extracellular space that characterizes the period of depolarization

·         Repolarization: Part of the cardiac conduction cycle in which the cell returns to its resting state, a more negatively charged state

Phase 0

-         depolarization is initiated; positive ions influx into the cell, during this phase the atrial & ventricular myocytes rapidly depolarize as sodium moves into the cells through fast channels & calcium enters thought slow channels

Phase 1

early cellular repolarization begins during this phase as potassium exits the intracellular space

Phase 2

called the plateau phase b/c the rate of repolarization slows. Calcium ions enter the intracellular space

Phase 3

marks the completion of repolarization & return of the cell to its resting state

Phase 4

Baroreceptors

·         specialized nerve cells located in the aortic arch & in both right & left internal carotid arteries; they are sensitive to changes in BP

·         During significant elevations of BP these cells increase their rate of discharge transmitting impulses to the cerebral medulla which initiates parasympathetic activity & inhibits sympathetic response, lowering the heart rate & BP

·         Opposite is true during hypotension – results in less stimulation which prompts a decrease in parasympathetic inhibitory activity in the SA node allowing for enhanced sympathetic activity resulting in vasoconstriction & increase heart rate 

Frank-Starling Law

Ejection Fraction

Common Cardiovascular Symptoms

·         chest pain or discomfort, shortness of breath or dyspnea, peripheral edema, weight gain, abdominal distention due to enlarged spleen & liver or ascites, palpitations (tachycardia), vital fatigue, dizziness, syncope, or changes in level of consciousness 

pulse pressure

-the difference between the systolic & diastolic pressure

-it’s a reflection of stroke volume, ejection velocity, & systemic vascular resistance

-normally is 30-40 mm Hg

pulse deficit

- Dysrhythmias often results in this

- a difference between the apical pulse & the radial rate

- commonly occurs w/ atrial fibrillation, atrial flutter, premature ventricular contraction & varying degrees of heart block 

normal heart sounds

-          S₁ (first heart sound): tricuspid & mitral valve closure creates the first sound; “lub” 

-          S₂ (second heart sound): closure of the pulmonic & aortic valves produces the 2^nd sound referred to as the “dub” sound

S₃ (third heart sound)

occurs early in diastole during the period of rapid ventricular filling, heard immediately after S₂ sounds like “Lub-dub DUB”, representing as a normal finding in children & adults up to 35 or 40 yrs of age, in older adults it’s a sign of pathophysiology most commonly due to volume overload of one or both ventricles

 S₄ (gallop fourth heart sound)

occurs late in diastole, occurring just before S₁ & is generated during atrial contraction as blood forcefully enters a noncompliant ventricle; this resistance is due to ventricular hypertrophy caused by hypertension, CAD, cardiomyopathies, aortic stenosis, etc (“LUB lub-dub” is the sound)

opening snaps

abnormal diastolic sounds heard during opening of an AV valve which normally no sound would be produced when the valves open, it’s caused by high pressure in the left atrium that abruptly displaces or “snaps” open a rigid valve leaflet

systolic clicks

results from the opening of a rigid & calcified aortic or pulmonic valve during ventricular contraction, its caused by stenosis of one of the semilunar valves creating a short, high-pitched sound in early systole 

murmmurs

created by turbulent flow of blood, cause may be a critically narrowed valve, a malfunctioning valve that allows regurgitant blood flow, a congenital defect of the ventricular wall, a defect between the aorta & the pulmonary artery, or an increased flow of blood through a normal structure  

friction rub

cardiac biomarker enzymes

·         Myocardial cells that become necrotic from prolonged ischemia or trauma release specific enzymes:

- creatine kinase (CK)

- CK isoenzymes (CK-MB)

- proteins (myoglobin, troponins T, &  troponins I)

cholesterol levels

- normal level is less than 200 mg/dL

-          LDL (bad cholesterol) level is less than 160 mg/dL

-          HDL (good cholesterol) level range for men is 35-70 mg/dL; for women 35-85 mg/dL

triglycerides