Arrhythmias Flashcards
What are the native pacemaker cells and where are they located in the heart?
SA node (junction of the RA and SVC) + AV node (RA septal wall anterior to the coronary sinus)
Describe how an action potential occurs for a cardiac pacemaker cell.
Phase 4: slow Na and Ca influx (via leak and L and T-type Ca channels) -> Phase 0: threshold voltage reached causing rapid Ca influx (via L-type Ca channel) while K permeability decreases -> Phase 3: Peak voltage reached, Ca channels close and permeability to K is restored (K efflux)
Describe how an action potential occurs for a myocyte (not a pacemaker cell).
Phase 0: Reaching threshold opens Na-channels (rapid Na influx) -> Phase 1: peak voltage reached, Na channels close and K permeability increases (K-efflux) -> Phase 2: Plateau phase (K+ efflux and Ca influx via slow Ca channels) -> Phase 3: rapid depolarization (from slow Ca channels closing leading to rapid K efflux)
How do myocytes propagate the action potential?
Via gap junctions between cells
What is the pathway for normal heart conduction?
SA node -> internodal pathway (anterior/middle/posterior) -> AV node -> left and right bundle branches -> His-Purkinje fibers
How does the electrical pathway go from the RA to the LA?
Via Bachmann’s Bundle
What portion of heart conduction has the fastest conduction?
The His-Purkinje system has 50x the amount of Na channels (compared to the AV node) and generates the fastest conduction velocities to allow for nearly simultaneous and organized ventricular contraction
What supplies the parasympathetic innervation to the heart?
The vagus nerve (CN X) via M2 muscarinic receptors (stimulated by acetylcholine)
What supplies the sympathetic innervation to the heart?
T1-T4 sympathetic chain via beta1 receptors (stimulated by catecholamines)
What is the most common dysrhythmia associated with acute MI?
Sinus tachycardia
What is the second most common dysrhythmia associated with acute MI?
PACs
Do you see a compensatory pause with PACs? PVCs?
You see it with PVCs but not with PACs
How does typical atrioventricular nodal reentry tachycardia work?
90-95% of AVNRTs; Forward conduction along slow pathway through the AV node followed by retrograde conduction along fast accessory pathway (causes a reentrant loop)
How does atypical AVNRT work?
5-10% of AVNRTs; forward conduction occurs down the fast pathway and retrograde conduction up the slow pathway (opposite of typical AVNRT)
How can you tell if it is AVNRT via ECG?
The rate is 160-180 bpm + most cases, the p wave is hidden in the QRS complex but sometimes you will have a pseudo-R in V1 or a pseudoS in V2 (retrograde depolarization)
What is the treatment for hemodynamically stable AVNRT? Unstable? Recurrent?
Stable: vagal maneuvers, adenosine, CCBs or beta blockers; Unstable: CDV; Recurrent: digoxin, CCBs, beta-blockers, or ablation
What is an atrioventricular reentrant tachycardia (AVRT)?
Reentrant loop that involves the AV node as one leg and an accessory pathway as the other leg
How is AVNRT different from AVRT?
AVRT has one leg of the loop that is outside of the AV node (while AVNRT is all within the node)
What are the ECG findings of antidromic AVRT?
Shortened PR interval + delta wave + QRS > 0.12 sec
What is orthodromic AVRT?
AVRT where the antegrade limb from the atria to the ventricle is via the AV node and the retrograde limb is via an accessory bundle; 95% of AVRTs (most common form)
What does the ECG look like for orthodromic AVRT?
QRS is normal (since antegrade limb is via the AV node) + p wave follows the QRS and is retrograde (inverse); rate is 150-250 bpm
What is antidromic AVRT?
AVRT where the antegrade limb from the atria to the ventricle is via an accessory pathway and the retrograde limb is via the AV node; 5% of AVRTs
What are the ECG findings of antidromic AVRT?
QRS > 0.12 sec (since antegrade is via accessory pathway) + p-wave before QRS + delta wave; rate is 150-250 bpm; sometimes confused for VT since QRS is wide
What is Wolff-Parkinson-White (WPW) Syndrome?
An AVRT where the accessory pathway is via the Bundle of Kent
What medication should you avoid in WPW syndrome?
AV-nodal blockers (adenosine, CCBs, beta blockers) as they will decrease conduction through the AV node and allow the accessory pathway to propagate signals leading to potential Vfib
What is the treatment for orthodromic AVRT?
Adenosine, CCBs, beta blockers, vagal maneuvers, or ablation
What is the treatment for antidromic AVRT?
Amiodarone, procainamide, propafenone, sotalol, flecainide, or ablation
What is atrial flutter?
A large re-entrant circuit contained within the RA with variable passes through the AV node
What is the normal rate of atrial flutter?
Usually organized at around 250-350 bpm with varying degrees of AV block (classically 2:1 leading to a rate of 150 bpm)
What are common causes of atrial flutter?
Secondary to triggering events (i.e. pulmonary disease, MI, EtOH or s/p cardiac surgery or thryotoxicosis)
What is the treatment for atrial flutter?
Vagal maneuvers, amiodarone, CCB, beta blockers, procainamine, synchronized CDV, or ablation
What is multifocal atrial tachycardia?
Multiple ectopic atrial pacemakers, HR 100-180 bpm; usually triggered by underlying pulmonary exacerbation
What are the ECG findings for multifocal atrial tachycardia?
> 3 p wave morphologies with variable PR intervals; HR 100-180 bpm
What is the treatment for multifocal atrial tachycardia?
Treat underlying pulmonary condition or decompensation; MgSO4, CCBs, beta-blockers (but worry about bronchospasm)
What is the difference between atrial fibrillation and atrial flutter?
Afib is when multiple areas in the atrium depolarize in an unorganized manner
What are the sub-categories of atrial fibrillation?
Paroxysmal (2-7 days), persistent (>7 days), long-standing persistent (>12 months), permanent
What is the definition of VT?
> 3 PVCs in succession with HR > 100 bpm; sustained = >30 sec and non-sustained = <30 sec
What are the ECG findings for monomorphic VT?
QRS > 0.12 sec + AV dissocation (ventricular rhythm is faster than atrial rhythm so p wave is hidden in QRS) + same QRS morphology
What is the treatment for monomorphic VT?
Acute stable: lidocaine, amio, procainamide; Acute unstable: synchronized CDV; Chronic: amio, beta-blocker, ICD placement
What are examples of polymorphic VT?
Torsade de pointes, Brugada syndrome, Short QT syndrome, V fib
What is torsades de pointes?
Polymorphic VT usually 2/2 prolonged QT syndrome devolving into VT due to QT prolonging agents
What is the treatment for torsades?
Amio, magnesium, mixelitine
What is Brugada syndrome?
A channelopathy condition where an ectopic beat can lead to polymorphic VT
What is the triad of Brugada syndrome?
RBBB during sinus rhythm with ST elevations, VF and sudden death
What is Short QT Syndrome?
Inherited channelopathy (loss of inward Ca current + gain of functional outward K current) -> increased risk of polymorphic VT; QTc < 360sec
What is ventricular fibrillation?
Form of polymorphic VT with rapid, irregular ventricular arrhythmia + variable QRS cycle length and morphology
What is the treatment of bradycardia if secondary to CCB or beta blocker toxicity?
Glucagon
