Flashcards in Arrhythmias: Mechanisms and Diagnosis Deck (33):
What are possible causes of prolonged QTc intervals? (6)
hypocalcemia, hypmagnesemia, hypokalemia
acute myocardial ischemia/infarction
congenital (inherited channelopathies)
increased intracranial pressure
What is the significance of leads I and II behind positive regarding QRS axis.
positive I puts axis in eastern hemisphere
positive II puts axis in southern hemisphere
optimal is south east corner
Differentiate the electrical evidence for ischemia v. injury.
ST elevation can mean acute injury or infarction
ST depression can mean ischemia
chronic infarct can be indicated by pathological Q waves
What are characteristic qualities of a normal sinus rhythm?
normal sequence of conduction, originating in the sinus node and proceeding to the ventricles via the AV node and His-Purkinje system
Describe two general ways by which arrhythmias can be generated.
abnormal automacity (includes ectopic pacemaker)
triggered activity (afterpolarizations)
or conduction block/reentry (altered conduction)
1. What is the key feature of arrhythmia generated by altered automaticity (on EKG).
gradual onset and termination of arrhythmia
in contrast with arrhythmias that are generated by reentrant or triggered patterns (abrupt initiation and cessation)
2. Compare the two major underlying mechanisms for triggered arrhythmias.
early after depolarization (phase ⅔)
delayed after depolarization (phase 4)
Discuss factors that increase automaticity.
catecholamines, other sympathomimetics (cocaine, phenylephrine)
Discuss factors that decrease automaticity.
increased vagal tone
Ca++ channel blockade
2. Name two types of arrhythmias that are associated with triggered activity.
torsades de points (polymorphic ventricular tachycardia associated with EAD)
ventricular tachycardia due to digoxin toxicity, catecholamine excess or sometimes ischemia (associated with DAD)
2. What are EAD? When does this phenomenon frequently happen, predisposing conditions.
EADs occur as a result of abnormal prolongation of action potential, resulting in a secondary depolarization phase prior to full depolarization (vulnerable purkije or M cells)
acquired long QT syndrome (drugs, electrolyte abnormalities, or ischmia) or congenital long QT syndrome (ion channelopathies)
2. What is a DAD?
DAD occur as a result of increased Ca2+ load in the cytosol and sarcoplasmic reticulum, often due to glycoside intoxication, ischmia, excessive catecholamines and other cardiac pathologies
AP duration is an important determinant of DAD formation, longer APs are associated with greater trans-sarcolemmal Ca2+
3. What characteristics are necessary or reentrant arrhythmias?
at least two pathways of depolarization with different conduction speeds
conduction time around one pathway must exceed the duration of the longest refractory period within the circuit to maintain an excitable gap
Name 5 types of reentrant rhythms.
AV nodal reentrant tachycardia AVNRT
AV reentrant tachycardia AVRT (orthodromic and antidromic)
What is the mechanism of a delta wave?
ventricular pre-excitation AVRT in the setting of a right-sided accessory pathway
What are recognizable characteristics of a reentry pattern on an EKG?
abrupt onset and termination
Pwave of the first beat of the arrhythmia is different when compared to the remaining beats of the arrhythmia (if Pwave is present at all
4. What are the characteristics and mechanism of sinus bradycardia.
slowed HR with normal wave morphology
caused by depressed intrinsic automaticity (aging or disease), medications (beta blockers or CCB) and metabolic causes as well as seen in highly trained athletes or pain or fear (vasovagal syncope)
note sinus bradycardia can be "taken over" by escape rhythms
4. What are the characteristics and mechanism of junctional rhythm.
lake a preceding P wave
QRS wave is typically narrow because beat still uses His-Purkinje system
slower rate 60-40 bpm
caused by inherent automaticity within the AV node
4. What are the characteristics and mechanism of idioventricular rhythm. (ventricular escape)
lacking P wave
widened QRS, does not propagate through His-Purkinje
very slow rate 20-40 bpm
caused by inherent automaticity or the myocardium
4. What are the characteristics and mechanism of atrial and ventricular premature contractions.
APC: early than expected P-wave, usually with abnormal shape, premature P wave not followed by QRS complex is termed a blocked APC
caused by electrical impulse that does not arise from SA node, resulting in abnormal conduction throughout the atria
PVC: not preceded by a P wave, and a widened QRS complex
caused by an ectopic ventricular focus fires an action potential
4. What are the characteristics and mechanism of sinus tachycardia.
fixed characteristic relationship between P waves and QRS complexes
narrow QRS complex unless other disease
caused by increased sympathetic or decreased vagal tone, an appropriate response to exercise or resulting from fever, anxiety, hypoxemia, hyperthyroidism, hypovolemia and anemia
4. What are the characteristics and mechanism of atrial tachycardia.
P wave precedes the QRS complex
abnormal P wave morphology due to depolarization from an abnormal site
caused by automaticity of an atrial focus or reentry
can be paroxysm (limited duration) or persist and is commonly observed in 24 recording of otherwise healthy people
4. What are the characteristics and mechanism of atrial flutter.
biphasic "saw tooth" flutter waves at a rate of 300 bpm, which consistent morphology (2:1, 3:1, 4:1 results in 150,100 or 75 bpm ventricular rate)
caused by large reentrant circuit in the wall of the right atrium (cavotricuspid isthmus)
note with 2:1 AV block, flutter waves can be brought out with adenosine
4. What are the characteristics and mechanism of atrial fibrillation.
numerous wavelets vary in amplitude and morphology (lack of coordinated atrial contraction)
irregularly irregular ventricular response, absent p wave
can lead to hemodynamic compromise, systemic embolization (stroke) and symptoms
4. What are the characteristics and mechanism of AV reentrant tachycardia.
PR interval is short
QRS has a slurred upstroke (delta wave) and is widened
caused by reentry
note commonly following myocardial infarction, caused by a bypass tract that spans the AV groove and connects atrial and ventricular tissue
4. What are the characteristics and mechanism of AV nodal reentrant tachycardia AVRT.
regular tachycardia with normal width QRS complexes
retrograde P wave and are typically inscribed at the same time of the QRS wave, or are inverted at the end of QRS complex in leads II, III and aVF
requires transient block in the fast pathway and relatively slow conduction through the other pathway
4. What are the characteristics and mechanism of torsades de points.
form of polymorphic VT presenting as varying amplitudes of QRS
can be caused by early after depolarization, esp with prolonged ST interval (drugs that can cause: erythromycin, phenothiazines, haloperidol and methadone)
4. What are the characteristics and mechanism of ventricular tachycardia.
a series of three or more PVCs (sustained lasts more than 30s), usually widened QRS (can be confused with supra ventricular tachy with aberrant ventricular conduction)
monomorphic VT: structural defect supports reentry
polymorphic VT: multiple ectopic foci or continually changing reentry circuit (ie. torsades des pointes)
caused by structural heart disease: myocardial ischmia, infarction, heat failure, ventricular hypertrophy, primary electrical disease or congenital cardiac abnormalities
4. What are the characteristics and mechanism of ventricular fibrillation.
chaotic, irregular appearance without discrete ARS waveforms
often initiated by VT, which degenerates, common cause of death post MI
5. List the differential diagnosis of a narrow QRS complex tachycardia.
6. Describe general underlying causes of inherited arrhythmia syndromes.
. ion channelopathies- long QT syndrome?
7. Discuss the tools used to diagnose arrhythmias.
holter monitor, event monitor or (implantable) loop recorder