What is the If chanel?
present in SA and AV nodes, pacemaker current; Na+/K+ channel
On the pacemaker node phase 0 is marked by the influx of what ion?
What inhibitors block the ca2+ current?
calcium channel inhibitors nifedipine verapamil
What is the effect of Ach released from the vagus nerve on the SA and AV node?
Decrease Rate of Depolarization (If activity) Decrease max diastolic potential (incrase Ik activity) Increase threshold (decrease ICa activity) Ach decrease If in SA node, reduces steepness of phase 4. As well Ach opens GIRK channels, increasing K+ conductance making the diastolic potential more negative; main effect is to decrease I ca making threshold more positive and also making it more difficult for once cell to depolarize neighbor
What is teh effect of norepinenphrine on SA and AV nodes?
increase If Increase Ca steepness increase Ca2+ influx
What is teh effect of body temp on SA node firing?
increase increases rate
What does hyperkalemia do to heart rythm?
fast inward current; reduce rate and amplitude of AP and slows conduction, tall T wave peaks
What does hypokalemia do to heart beat?
can cause AV block, by slowing repolariation and prolongation of AP duration flatten T wave
What do beta blokers do?
prevent calcium entry into cell; decrease HR, conduction velocity, strength of contration tx many cVS conditions
What do calcium channel blockers do?
decrease entry of calcium and delay of depolarization of nodes
How do you measure PR interval?
onset of P to onset of QRS
How do you measure QRS interval?
beginning to end of qRS
How do you measure QT interval?
onset QRSto end of T wave
How do you measure QT corrected?
measured QT/square of RR interval
What is the normal mean QRS axis?
normal -30 degrees to positive 90 degrees
Abnormalities of the P wave are best seen in what leads?
II and V1; looking at atrial contraction
What do you see on an EKG with LVH?
increase amplitude direted to the left, seeen in V6, increased amplitudeand can cause ST-segment depression and T wave inversion
What do you see in RVH on an EKG?
Shift teh QRS vector the the right; usually seen in an increase in S, q or decrease R in leav V1,andn increase in S in lead V6
What do you see in an EKG in RBBB?
V1 you see an R' after the S peak and an inverted T wave and in v1 you see a pronounced S wave
What do you see in an EKG of someone with LBBB?
notched S wave in V1, or notched R wave in V6 with inverted T wave
What are signs of reperfusion injury?
necrosis with contraction bands due to influx of calcium
What are the histological changs in MI's between the 12 and 24 hour mark, startinga s early as 4 hours?
When do arrythmias occur after MI?
early in course of MI
When does myocardial rupture occur after MI?
3-7 days after MI