Tachycardias Flashcards
3 basic mechanisms causing tachyarrhythmias
- enhanced automaticity
- triggered arrhythmias
- re-entry
basic mechanism causing tachyarrhythmias: enhanced automaticity
*refers to an increased rate of generating action potentials, either by the normal pacemaker tissue or abnormal tissue within the myocardium
*automaticity is a normal feature of sinus node, AV node, infra-nodal conduction system
*automaticity generally arises from the SA (sinus) node, but can arise from other areas, including atria, AV node, or ventricles → enhanced automaticity
*the fastest pacemaker will drive the heart
basic mechanism causing tachyarrhythmias: triggered arrhythmias / triggered automaticity
*when a normal action potential induces a spontaneous abnormal action potential immediately after it (an “afterdepolarization”), which cause extra beats
*stimulations that occur in a critical period of the cardiac cycle
*early afterdepolarization (arises from the plateau)
*late afterdepolarization (arises from the resting potential)
basic mechanism causing tachyarrhythmias: reentry
*refers to continuous propagation of an electrical impulse traveling a circuitous pass, resulting in reactivation of the original site that generated the electrical impulse → continuing the cycle in a loop → tachycardia
*usually starts with a PREMATURE BEAT resulting in unidirectional block
*substrates:
-normal heart: AV nodal reentry, accessory pathway
-diseased heart: ventricular tachycardia post-MI
*fibrillation: probably due to multiple reentrant wavelets causing a very rapid rate
premature atrial beats (APBs)
*extra beats arising from ectopic foci in atria instead of SA node
*premature contraction of the atria → early NARROW QRS, always preceded by a p-wave
*very common, can occur with a normal heart (especially with stimulants) or virtually any type of organic heart disease
premature ventricular beats
*ectopic beats arising from ventricle instead of SA node
*premature contraction of the ventricles → early WIDE QRS (with no preceding P wave), followed by a compensatory pause
*common (increases with aging); +/- palpitations
*can occur with normal hearts (benign), serious organic heart disease (e.g. MI), certain medications (e.g. caffeine, sympathetic stimulants) or electrolyte disturbances
*NO DATA THAT TREATMENT PROLONGS LIFE
tachycardia - defined
*HR > 100 beats per minute
*divided into narrow complex vs. wide complex tachycardias
narrow-complex tachycardia - defined
QRS < 120 ms (narrow; < 3 small boxes)
HR > 100 bpm (tachycardia)
note: can be regular or irregular
wide-complex tachycardia - defined
QRS > 120 ms (wide; > 3 small boxes)
HR > 100 bpm (tachycardia)
note: can be regular or irregular
narrow-complex tachycardias (first aid)
*narrow QRS complex < 120 ms (< 3 small boxes)
*rapid ventricular activation via normal conduction system
*tachycardia originates within or above AV node (supraventricular arrhythmias)
wide-complex tachycardias (first aid)
*wide QRS complex > 120 ms
*slow ventricular activation outside normal ventricular conduction pathway
*tachycardia originates below AV node (ventricular arrhythmia)
paroxysmal supraventricular tachycardia (SVT)
*a type of REGULAR, NARROW-complex tachycardia
*typically does not have discernible p-waves
*most often due to a reentrant tract between the atrium and ventricle, usually in AV node
*rate 140-280 bpm, constant
*sudden onset and offset (paroxysmal)
*several types, with most common being:
1. AV node re-entrant tachycardia (AVNRT)
2. orthodromic reciprocating tachycardia (ORT)
3. atrial tachycardia (AT)
paroxysmal supraventricular tachycardia (SVT) - treatment
*ADENOSINE almost always works to terminate the reentry rhythm by slowing AV node conduction
*other tx: vagal maneuver; electrical cardioversion if hemodynamically unstable
*definitive treatment is catheter ablation of the reentry tract
examples of REGULAR narrow-complex tachycardia
- sinus tachycardia
- supraventricular tachycardia (SVT)
recall: narrow-complex tachycardia is defined by QRS < 120 ms (< 3 small boxes) and HR > 100
examples of irregular narrow-complex tachycardia
- atrial fibrillation
- variable conduction (atrial flutter, multifocal atrial tachycardia)
note - irregular means that the R-R intervals are not consistently the same length
recall: narrow-complex tachycardia is defined by QRS < 120 ms (< 3 small boxes) and HR > 100
atrial fibrillation (AF) - EKG rhythm
*irregularly irregular rate and rhythm with NO DISCRETE P WAVES
*irregular, narrow-complex tachycardia
atrial flutter - EKG rhythm
*rapid succession of identical, consecutive atrial depolarization waves causing a “sawtooth” appearance of P waves
*irregular, narrow-complex tachycardia
sustained ventricular tachycardia - EKG findings
*sustained rapid rhythm with WIDE QRS complex (>120ms or > 3 small blocks)
*wide complex tachycardia
*can be MONOMORPHIC (beats look the same) or POLYMORPHIC
*usually life-threatening
-most often the initial rhythm during a cardiac arrest
Torsades de Pointes - EKG findings
*polymorphic ventricular tachycardia with prolonged QT interval
*MARKED QT PROLONGATION
*polymorphic nature
*pause-dependence
Wolff-Parkinson-White syndrome (WPW)
*most common type of ventricular preexcitation syndrome
*abnormal FAST ACCESSORY PATHWAY from atria to ventricle bypasses rate-slowing AV node → ventricles partially depolarize earlier → CHARACTERISTIC DELTA WAVE with widened QRS complex & short PR interval
ventricular fibrillation
*disorganized rhythm with no identifiable waves
*final common pathway of the wide-complex tachycardias
*tx: fatal without immediate CPR and defibrillation
