Cardiac Flashcards
Action potentials with plateau phases
Found in atrial and ventricular muscle cells
Biphasic action potentials
Arising in the SA and AV node
Inotropy
CA impacting squeeze of the heart
Chronotropy
HR
Dromotropy
Speed to the AP down the pathway
Lusitropy
Relaxation of the heart (diastolic heart failure)
Cardiac conduction pathway
- Sa node
- Intermodal tracts (controversial)
- AV node
- AV bundle of HIS
- Bundle branches
- Purkinje fibers
- Ventricular muscle
Spontaneous depolarization
- Potassium efflux progressively slowing
- Sodium influx progressively increasing
- Calcium influx
Resting membrane potential of ventricular cell
All striated muscle
-90 mV
Resting membrane potential of SA node
-70 mV
SA node rate with no influences
108-115
Calcium influence of K channel
Hypocalcemia- duration of plateau is prolonged
Hypercalcemia- duration of plateau is shortened
PR interval
Beginning of P wave to beginning of QRS
Normal 0.12-0.2 seconds
QRS interval
Normally 0.12 or less
HR method
From R-R
- Divide 1500 by number of mm between 2 consecutive R waves
- Count R waves occurring in 6 seconds and multiply by 10
Each mm on EKG strip
40 ms (0.04 seconds)
1st degree heart block
PR greater than 0.2 and is constant
2nd degree AV block type 1
Wenckebach
Mobitz I
Progressive PR increase until QRS beat is dropped
Progressive shortening of R-R
2nd degree AV block
Mobitz II
Sudden appearance of nonconducted P wave
PR and RR intervals constant
3rd Degree heart block
Complete heart block
Independent atrial and ventricular activity
No relationship between P and QRS
Bain bridge reflex
Increase in HR during inspiration due to right atrium stretch
Thoracic pressure falls—>inferior vena cava widens—>venous BP falls—>increased venous return to RA—>right atrium stretch
Subendocradial ischemia and injury
ST segment depression greater than 1mm
Transmural ischemia
Inverted T waves
ST segments elevation greater than 1 mm
QRS complex
Comes from ventricular depolarization (phase 0)
T wave
Comes from ventricular repolarization (phase 3)
QT interval
From duration of plateau phase (phase 2)
Shortened=hypercalcemia
Prolonged=hypocalcemia
U waves
Come from hypokalemia
Wolff Parkinson’s white syndrome
Less than 100 beats/min
Accessory track called bundle of Kent
P wave normal, short PR interval, delta wave leading into QRS
Avoid dig and verapamil- increases conduction through accessory tract
V1-V2
Posterior
Left circumflex
II, III, aVF
Inferior wall
RCA
I, aVL, V1-4
Septum, anterior wall
LAD
I, aVL, V5-6
Lateral wall
Left circumflex
Best lads for ST segment depression or elevation
V3-5, III, aVF
Lead for assessment of narrow QRS rhythms
Lead II
Ohms law
Q=change P/R
Q= flow rate
P=pressure
R=resistance
MAP
[(CO x SVR)/80] + CVP
SV
EDV-ESV
CO/HR
60-90mL
EF
SV/EDV
(EDV-ESV)/EDV
Adrenal gland pneumonic
GFR—> ACT
Glomerulosa—>Aldosterone (salt)
Fasciculaa—>Mineralacorticoids (sugar)
Reticularis—> Androgen (testosterone) (sex)
CO
HR x SV
Stroke volume determined by interplay
Preload
Afterload
Contractility
Preload determined by
Intravascular volume
Venous tone
Ventricular compliance
Atrial kick % of contraction
25-30%
SI
SV/BSA
40-60 mL/m2
SVR
(80)(MAP-CVP)/CO
900-1500 dynes.sec.cm-5
PVR
(80)(PAP-PCWP)/CO
50-150 dynes.sec.cm-5
