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List the Conduction pathway through tthe heart
SA node -- AV node -- Bundle of His -- Purkinje Fibers -- Ventricular muscle
What does the Pwave on the ECG symbolize in terms of the conduction pathway through the heart?
QRS?
T wave?
P wave = Atrial depolarization
QRS = Ventricular depolarization (and atrial repolarization)
Twave = Ventricular repolarization
What is the resting potential of the cardiac ventricular cell?
what is the resting potential of the SA or AV nodal cell
-90 mV

-70 mV
During phase 0, rapoid depolarization of the ventircular cell, what ion is invoved?
Na diffuses into the cell
Liost the phases of venticular cell action potential and th eassociated ionic movements in and out of the cell
  • Phase 0 depolarization: Na+ moves in
  • Phase 1 Brief Repolarization: Cl in and K out
  • Phase 2 Plateau: Ca moves in
  • Phase 3 Repolarization: K moves out
  • Phase 4 Diastole: Na/K pump work to resore levels
What phase of the SA node action potential is affected by sympathetic and parasympatthetic stimulation?
Phase 4
parasympathetic stimulation lengthens phase 4, so it takes longer to get to threshold = decreased HR (acetycholine stimulated the muscarinic recepotr on the SA node/vagus nerve)
Sympathetic stimulation makes phase 4 shorter, so the HR is increased  (cardioacceleratior fibers/Beta1 receptors)
on waht phase of the nodal action potential does digitalis work to slow heart rate
Phase 4
on what phase of the nodal actionpotential do calcium channel blockers work to slow heart rate?
Phase 4
on what phase of the cardiac ventricular action potential do calcium channel blockers work? what phase of the nodal action potential?
Phase 2
Phase 4 -- HR is always controlled by phase 4 in the nodes*
On what phase ofht eactionpotential does lidocaine or phenytoin work to control ventricular dysrythmias?
Phase 4: they stabilize phase 4 to avoid depolarization
What ion is mainly responsible for maintaining the resting potential (-90mV) of the cardaic ventricular cell?
Potassium: there are "leaky" K channels
they allow K to movein and out to maintain negative charge inside (protiens) and postitive outside (Na and Ca)
What ion gate is shut during the absolute refractory period of the cardiac cell?
the Na gate --is is closed and in an inactive state, so another action potetnial cannot be fired, no matter how strong the stimulus is (this is Phase 2 Plateau phase).  Ca channel is open and Ca is entering the cell at this time
What ion goes into the cell during phase 2 and what does this cause?
Ca - 2 things happen:
  • Causes contraction
  • second messenger-- signals to K channels to get ready for phase 3
What happens to the duration of the plateau (Phase 2) with Hypocalcemia or hypocacemia)
Ca controls the opening of the K channel (allowing for repolarization and phase 3 to begin)
  • Hypocalcemia will prolong the plateau of the action potential becuase it will take longer for Ca to accumulate and stimulate the K channel
  • Hypercalcemia will shorten the plateau b.c it will accumulate quicker.
What is the normal PR interval
0.12 - 0.2 seconds
What is the normal QRS interval?
0.12 seconds
What leads will show a rith BBB?
V1 and V6
What does the ECG look like is first degree hear block?
the PR interval is greater than 0.20 seconda nd is constant from beat to beat
What does the ECG look like in Second drgree AV block - Mobitz type I
Wenckebach has a progressive increase in PR interval until finally the QRS complex and a beat is dropped
What does the ECG loiok like in second-dgree AV block Mobitz type II?
PR intervals are constant, but there is the sudden appearance of a concunducted P wave and it is not followed by a QRS complex
What does the ECG look like in Thrid degree (complete) heart block?
there is independnet (dissociated) atrial (p) and ventricular (QRS) activity.  The p waves have no fixed relationship to the QRS complex
What happens to the HR during inspiration? why?
HR increases -- Bainbridge Reflex
Intrathoracic pressure fall,s o venous return increases, Right Atrium strectches and reflexively the heart ratre increases
What is a nonconducted atrial premature contraction?
This is when an atrial premature contraction occur so early that the ventricles are still in the absolute refractory period, so there is no QRS following it.
What ECG changes occur with Subendocardial Ischemia? Infarct?
St Segment deppression of greater than 1 mm occurs with both
What ECG changes occur with Transmural Ischemia? Infarct?
Ischemia: Inverted T waves
Infarct: ST segmaent elvation greater than 1 mm
what electrolyte disturbance can casue a shortened QT interval
Hypercalcemia (shortens phase 2 --platueau, so phase 3 repolarization happens faster)
What electrolyte disturbance causes peaked T waves?
Hyperkalemia
What elecrolyte disturbance causes U waves?
Hypokalemia
What does hypocalcemia do to the ECG
Prolonged QT interval
What leads in the ECG would show an Mi in the posterior and inferior walls?
what coronary arteries supply this area?
Leads II, III and aVF
RCA supplies this area
what leads would show an MI in the septum and anterior wall?  what coronary artery supplies this area
V2-V5
LAD supplies this area
An MIseen in leads I, aVL, V4-V6 is affecting what part of the heart? what coronary artery supplies this area?
Lateral wall
Left circumflex
What 2 factors determine MAP?
SVR and CO
What hormone is the most improtant for controlling vascular volume?
Aldosterone
What 2 factors determine CO?
HR and SV
What 3 factors determine Stroke volume?
preload, afterload, contractility
Describe concentric Hypertrophy of the left ventricle
Causes?
the wall thickens, but the chamber size remains the same
chronic, uncontrolled HTN, Chronic Aortic stenosis, coarctation of the aorta
what is Eccentric Hypertorphy of the left ventricle
Causes?
the wall dilate and the chamber is enlarges
chronic mitral insufficeincy
chronic aortic valve insufficiency
morbid obesity
What Law applies to ventricular hypertrophy?
Law of LaPlace T = P x r
On the Left Ventricular Pressure - volume Loop, when does diastolic filling occur?
Betwwen point A (mitral valve opening) and point B MItral vavle closing
If preload (end diastolic volume) is increased, how will this affect end systolic volume and stroke volume?
ESV will remain the same, so SV will increase b.c SV = EDV - ESV
What happens to the pressure volume loop in aortic stenosis?
the pressure of the LV increase, but the volumes remain the same, so the loop shifts upward (gets taller)
what happens to the pressure volume loop in IHSS?
Idopathis hypertrophic stenosis: smaller volume sna dlarger pressures (thin and tall loop)
on the Left venticle pressure-volume loop, what does point A symbolize?
B?
C?
D?
A = Mitral valve openig
B = Mitral valve closing
(B to C is Contraction)
C = Aortic Valvle opening
(C to D is Ejection)
D = aortic Valve closing
When there is an acute increase in preload, what hemodynamic changes occur?
End diastolic volume and pressure increases
Stroke volume increases (more blood is ejected)
Blood pressure increases
Hr an dSVR may reflexively decrease (baroreceptors)
If you give a patient Neo (increase their afterload), what happens ot SV, BP, and LV (End diastilic and end systolic volumes)?
SV decreases (due to increased SVR)
BP increases
EDV increases and ESV increases (more blood being returned to the heart, but it ismore difficult to pump it out bc of increased pressure)
If you give a pt Nipride, what happens to the SV, BP, and LV volumes (EDV and ESV)?
SV increases
BP decreases
EDV decreases
ESV decreases (less blood going back to the heart)
What are the 2 direct determinants of mean arterial blood pressure?
CO and SVR
Flow through the left circumflex artery ceases b/c of a thrombus, what area of the heart is affected and what leads best detect the resulting ischemia?
Lateral
aVL, V5 - V6
Nitric oxide stimulates the production of what second messenger?
Cyclic GMP
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