Flashcards in EKG Deck (45):
What occurs in phase 0 of cardiac action potential?
phase 0 = depolarization
- Na+ channels open and there is a rapid influx of Na+
- Na+ channels are rapid opening and rapid closing
- resting membrane potential is -90mV
- Ca2+ channels are also opened, but slower at opening and closing than Na+
What is the cardiac cell muscle permeable to during rest?
K+ ions only
What occurs in phase 1 of cardiac action potential
phase 1 = repolarization begins
- some K+ channels remain open while others are closed resulting in outflow of K+
- Ca2+ channels still open
Why does cardiac m have a prolonged AP in comparison to skeletal m?
Ca2+ channels open slower and have an extended opening
What occurs in phase 2 of cardiac action potential?
phase 2 = plateau
- outward flow of K+ is balanced by inward flow of CA2+
- delayed resting membrane potential
What occurs in phase 3 of cardiac action potential?
phase 3 = completion of repolarization
- closure of Ca2+ channels accompanied by opening of additional K+ channels, causing rapid outflow of K+
- negative resting membrane potential is restored
What occurs in phase 4 of cardiac action potential?
phase 4 = resting phase
- Na+ and Ca2+ are actively pumped out of the cell and K+ is pumped into the cell
Why is intrinsic atrial rhythm more rapid than intrinsic ventricular rhythm?
the refractory period of atrial cells is significantly shorter than that of the ventricular cells
What are the standard limb leads?
I = diff btwn L arm and R arm
II = diff btwn L leg and R arm
III = diff brown L leg and L arm
- bipolar leads
What are the augmented limb leads?
aVR, aVL, and aVF
- unipolar leads
Where are the precordial leads?
V1 = 2nd ICS, to R of sternum
V2 = 2nd ICS, to L of sternum
V3 = midway between V2 and V4
V4 = 5th ICS, L midclavicular line
V5 = 5th ICS, L anterior axillary line
V6 = 5th ICS, L mid axillary line
What are the "big box" intervals for HR?
300, 150, 100, 75, 60, 50, 42
What is the conduction of normal nerve impulse?
SA node --> AV node --> Bundle of his --> BB --> Purkinje --> depolarization of myocardial cells
What is a normal PR interval and QRS?
Arrhythmia related to discharge from atrial foci; characterized by waves of different shapes
Arrythmia with no clear p wave, quivering baseline; occasional impulse gets through to stimulated ventricles; determine rate with 3 second marks
originates in ventricular ectopic foci; giant ventricular complex after the pause; 20-40 bpm
What are the HRs for paroxysmal tachy, flutter, and fibrillation?
Paroxysmal = 150-250
flutter = 250--350
fibrillation = 350-450
What does paroxysmal tachy look like for atrial? jxn'l? ventricular?
Atrial = P waves look different
jxn'l = inverted or no p-wave
ventricular = rapid PVC's
What does flutter look like for atrial? ventricular?
atrial = saw-tooth appearance
ventricular = smooth wave appearance
What does fibrillation look like for atrial? ventricular?
atrial = no p waves, irregular baseline, QRS irregular
ventricular = "bag of worms", no repetition is recognizable
What's 1* AV block criteria?
PR interval > 5 boxes (.2s)
What's 2* AV block, Mobitz 1, criteria?
PR interval becomes gradually longer cycle to cycle
What's 2* AV block, mobitz 2, criteria?
QRS dropped without lengthening PR interval
What's 3* AV block criteria?
No associated P wave and QRS complex; going to their own beat
What are the criteria for axis?
Normal: I = +, aVF = +
LAD: I = +, aVF = -
RAD: I = -, aVF = +
Extreme RAD: I = -, aVF = -
- impulse goes toward hypertrophy and away from infarct
What are the criteria for atrial hypertrophy?
Diphasic p wave
initial portion larger = RAH
terminal portion larger = LAH
What symptoms would you see with hypertrophy upon examination?
increased PMI and BP
What are the criteria for ventricular hypertrophy
RVH = S persists in V5 and V6
LVH = S1 + R5 > 35mm
What are the criteria for ischemia?
- Jpoint > 1mm below baseline
- inverted T wave
What are the criteria for injury?
- ST elevated > 4mm
- big tombstones = acute infarction
What are the criteria for infarct?
significant Q waves
- width > 1mm
- amplitude ⅓ of QRS
(not significant in aVR and V1
What chest leads indicate anterior infarct?
What chest leads indicate lateral infarct?
What chest leads indicate inferior infarct?
II, III, aVF
Symptoms of bradycardia?
- sx of hemodynamic compromise
symptoms of SVT?
Pts perceive a racing heart; also have sx of hemodynamic compromise
What is afib often associated with clinically?
embolic cardiac events
symtoms of V-tach?
-pt may be asymptomatic if it is a brief run
- if sustained, pt may be asymptomatic, symptomatic, or unconscious and pulseless
symptoms of V-fib?
immediate loss of consciousness and loss of circulation
what conditions refer the myocardium vulnerable to v fib?
2. myocardial ischemia or infarction
3. dilation of the heart
5. electric shock
Posterior infarction: larg R with ST depression in V1 and V2; what artery is compromised?
R coronary artery
Lateral infarction: Qs in lateral leads I and aVL; what artery is compromised?
Lateral circumflex coronary artery
Inferior infarction: Q's in inferior leads II, III, and aVF; what artery is compromised?
R or L coronary artery