The flow of which 3 ions in and around the myocardial cells creates this electrical current?
Na+, K+ and Ca+
what do the 12 leads represent?
12 different viewpoints, each representing a different axis through the heart
normal P wave axis in adults vs kids (in degrees)
The normal P wave axis lies between 0 degrees to plus 70 degrees in adults (0 to plus 90 in children)
A wave of de-polarization moving toward a positive electrode will record what kind of wave?
a positive deflection (a P wave or QRS complex)
beats generating in the SA node should generate what kind of waves in lead II?
Beats originating in the SA node should generate an upright P wave Lead II
2 types of cardiac muscle cells
Contractile cells : which constitute the majority of the atrial and ventricular tissue. These cells are responsible for generating cardiac pressures.
Conducting cells.:Responsible for the spontaneous generation of electrical impulses (action potentials), and rapidly spreading the action potentials over the entire myocardium.
what is the normal pace of the SA node?
60-100 bpm - has the fasted firing rate
what is the SA nodes influence on other cardiac conducting cells?
normally overdrive suppresses other cells with intrinsic automaticity (the ability to spontaneously generate an action potential)
atrial cells, AV junction and ventricular conducting system
what are the atria internodal tracts
The action potential spreads from the SA node to the left and right atria via the atrial internodal tracts. Simultaneously, the action potential is conducted to the AV node
what does the AV node do- 2 fxns? what do increases in its conducting velocity do?
- slow conduction- insures that the ventricles have sufficient time to fill with blood before they are activated and contract.
- protects the ventricles from rapid atrial rates because of its slow conducting velocity and prolonged refractory period.
Increases =decrease ventricular filling and decrease stroke volume and cardiac output. (and vice versa)
what does the bundle of his connect?
connects the AV node to the 2 bundle branches.
what are included in the “AV junction”? what is the inherent firing rates of its cells?
AV node and the bundle of His
junctional pacemaker cells: 40 - 60 beats per minute.
what makes up the ventricular conducting system? what is its firing rate?
Right and left bundle branches and Purkinje system. Ventricular cells: 30 - 45 beats per minute.
what is an “ectopic pacemaker”?
Failure of the SA node to generate an impulse (sinus pause) will allow a lower pacemaker (atria, AV junction or ventricular) to escape overdrive suppression and become the heart’s pacemaker at its inherent firing rate;
AV junction 40 -60, ventricular 30-45.
what is “altered automaticity”? what 3 kinds of events increase this automaticity?
Pacemaker cells other than the SA node may also become the hearts pacemaker.
MI, increase sympathetic tone, hypokalemia.
escape or premature beats: what are they like if the originate above the bundle branches (unless…)? what if they originate in the ventricles?
originate above the bundle branches (atrium or A-V junction) are narrow complex
*unless there is an accompanying bundle branch block.
originating in the ventricles will be wide complex
wide vs narrow complex
narrow: QRS <0.12 seconds
wide: QRS equal to or >0.12 seconds
PJC- premature junctional (AV jxn) complexes: what will be the result?
captures the atria (retrograde) and the ventricles (antegrade).
The retrograde P wave may appear before, during, or after the QRS complex; if before, the PR interval is usually short (i.e., < 0.12 s)
inverse wave before the QRS = before jxn. (bundle of his) - at AV node
inverse after QRS = after jxn (bundle of his)
escape junctional beats: what are they? wide vs narrow?
a delayed beat originating not from the atrium but from an ectopic focus somewhere in the AV junction.
when the rate of depolarization of the SA node falls below the rate of the atrioventricular node.
narrow- above bifurcation, wide- below bifurcation
normal sinus rhythm: rate, rhythm, p wave positive in what lead, P:QRS ratio, PR interval, QRS complex length
- 60 - 100 beats per minute
- Regular (may vary some with respiration) - speed up a bit with inspiration
- P wave positive in lead 2
- 1 P wave before each QRS complex
- PR interval 0.12 - 0.20 seconds
- QRS complex less than 0.12 seconds
Sinus tachy: Dx
Same as sinus rhythm except rate between 100 - 160 at rest.
narrow complex tachycardia: QRS duration is < 0.12 seconds (narrow= super ventricular in origin)
sinus tachy: Txt
- Identify underlying cause, such as volume depletion, CHF or hyperthyroidism and treat appropriately.
- if hyperthyroidism: beta blockers or calcium channel blockers. (Verapamil or Diltiazem)
PSVT: paroxysmal super ventricular tachy
(aka wandering atrial pacemaker): what is it often caused by? Dx?
a reentry circuit w/in the AV node, precipitated by a PAC:
Regular narrow complex tachycardia between 150- 250 beats per minute.
Usually no P waves seen.
Txt GOAL for PSVT, then 3 step approach (each step done if the previous doesnt work)?
what about for unstable pts or pts refractory ot AV nodal blocking agents?
GOAL: blocking conduction through the AV node which terminates the re-entry circuit.
- vagal maneuvers which increase PSNS tone to the AV node.
- adenosine
- CCBs or beta blockers.
* unstable patients or patients refractory to AV nodal blocking agents: cardioversion
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