Cardiac Electrophysiology Flashcards
What is the most common mechanism involved in clinically important cardiac
arrhythmias?
Triggered activity
Abnormal automaticity
Reentry
Early afterdepolarizations
Parasystole
Reentry is the most common mechanism underlying cardiac tachyarrhythmias, including
AVNRT, atrial flutter, AVRT with an accessory pathway, and VT in a diseased heart.
Torsades de pointes is characterized by all of the following except:
Results from triggered activity (early afterdepolarizations) that occurs during phase 2 or 3 of the cardiac action potential
Prolonged QT interval
Exacerbation by bradycardia with short-long coupling intervals
Polymorphic VT
Often provoked during amiodarone administration
Torsades de pointes is characterized by prolonged QT intervals, exacerbation by bradycardia, short-long couple intervals, “salvos” of nonsustained polymorphic VT before degeneration into a sustained ventricular arrhythmia, and polymorphic VT with characteristic “twisting around the axis” morphology. Although amiodarone often prolongs the QT interval, it rarely causes torsades de pointes.
Which one of the following currents is responsible for maintaining stable resting membrane potential in the atrial and ventricular cells?
a. If b. INa c. IKl d. IK e. ICa
IK1 (inward rectifier) is crucial for maintaining the resting potential near
The IKATP is a potassium channel that is inhibited by physiologic intracellular concentrations of ATP. How is this channel activated?
A consequence of If activation that enhances pacemaker activity
Physical opening of the channel pore by the N-terminal portion of the
channel
Chemical ligand binding in response to depletion of ATP from ischemia
Conformational changes in channel structure
The channel is only inhibitory and is not activated
The IKATP potassium channel is inactivated by chemical ligand binding in response to ischemia and depletion of ATP. Ventricular myocytes have high densities of these chan- nels and their activation accounts for the ST elevation on the ECG seen during a MI.
The sinus node is predominantly characterized by depolarization in which phase of the action potential?
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
The sinus node is predominantly characterized by its phase 4 depolarization, which accounts for the pacemaker activities. There are few sodium channels and the upstroke is primarily mediated by ICa,L. There is no discernible phase 1. The lack of IK1, which is active in phase 3, accounts for the relative depolarized state of the tissue.
Which one of the following antiarrhythmic agents does not prolong the QT interval?
a. Quinidine
b. Lidocaine
c. Sotalol
d. Procainamide e. Ibutilide
- Answer b.
Lidocaine is a weak sodium channel blocker and does not have significant potassium channel blockade. It does not prolong the QT and it is the one antiarrhythmic that may actually shorten it.
Which one of the following antiarrhythmic agents has the least effect on slowing conduction through the AV node?
Calcium channel blockers
Beta blockers
Amiodarone
Lidocaine
Sotalol
Lidocaine is a rather specific sodium channel blocker. The AV node conduction is mediated by ICa,L. The AV node is similar to the sinoatrial node in its lack of INa. Lidocaine does not have a significant effect on AV nodal conduction.
Which of the following antiarrhythmic agents may promote AF?
a. Adenosine b. Quinidine c. Propafenone d. Amiodarone e. Atenolol
Adenosine activates the IK,Achchannel in atrial tissue. Activation of the IK,Achchannel shortens the action potential duration, thereby shortening the refractoriness of the atrial tissue and promoting the induction of AF.
Which one of the following antiarrhythmic agents is least likely to cause torsades de pointes?
Quinidine
Procainamide
Flecainide
Ibutilide
Sotalol
Of the answer choices given, class 1A agents (quinidine and procainamide) and class 3 agents (ibutilide and sotalol) have a significant potassium channel blocking effect, there- fore prolonging the QT interval and potentially causing torsades de pointes. Flecainide (a class 1C agent) is a fairly specific sodium channel blocker without a significant potas- sium channel blocking effect. Prolongation of the QT interval is not associated with flecainide.
All of the following statements regarding the AV node are true except:
Conduction through the node displays decremental behavior
It is positioned in the subendocardium at the base of the triangle of Koch
It is composed of nodal cells and transitional cells
It is a right atrial structure
The AV node is positioned in the low RA at the apex, rather than the base, of the tri- angle of Koch. The triangle of Koch is comprised of the ostium of the CS, tendon of Todaro, and septal attachment of the tricuspid valve leaflet. The region within the tri- angle is comprised of nodal and transitional cells.
In which of the following tissues is the upstroke of the action potential generated by ingoing calcium currents?
a. Atrial
b. AV node
c. His-Purkinje
d. Ventricular
Both the AV and sinoatrial nodal cells lack INa. Conduction is mediated in these tissues by ICa,L.
Conduction velocity is most rapid in which tissue?
a. Atrial
b. AV node
c. His-Purkinje
d. Ventricular
The conduction velocity is the most rapid in the His-Purkinje tissue.
Repolarization of the myocardial cells is determined mostly by which current?
Outgoing sodium
Ingoing calcium
Outgoing potassium
Ingoing chloride
Ingoing sodium
The outgoing potassium current is the principal determinant of repolarization of myocardial cells.
All of the following statements regarding AV nodal cells are true except:
a. The resting membrane potential is typically
The resting membrane potential of AV nodal cells is
Vagal stimulation in each of the following tissue types changes the action poten- tial duration except in which cardiac structure?
AV node
His-Purkinje system
Ventricular myocardium
Atrial myocardium
Vagal stimulation has little effect on the ventricular myocardial action potential, whereas it increases the action potential in the AV node and reduces it in the atrial myocardium.
Early afterdepolarizations are favored by:
High potassium concentrations
Type III antiarrhythmic drugs
Fast underlying HR
Increased magnesium concentrations
Early afterdepolarizations are depolarizations that occur in phases 2 and 3 of the action potential. Conditions that prolong the action potential duration promote the development of early afterdepolarizations. They are facilitated by a low potassium level, low magnesium level, and class I or III antiarrhythmic drugs, and are typically pause-dependent.
The underlying arrhythmia mechanism most likely present in digitalis toxicity is:
Reentry
Delayed afterdepolarizations
Enhanced automaticity
Early afterdepolarizations
The mechanism that underlies the development of delayed afterdepolarizations is intracellular calcium overload. Digoxin increases intracellular calcium that can pro- mote delayed afterdepolarization-triggered activity. Delayed afterdepolarizations have also been implicated in ischemic reperfusion arrhythmias and ryanodine receptor dys- function.
Which of the following contain the normal A–H and H–V intervals?
40–80 msec, 35–60 msec
60–120 msec, 35–60 msec
60–120 msec, 25–50 msec
60–100 msec, 60–80 msec
60–120 msec, 35–60 msec
Patients with the Wolff-Parkinson-White syndrome typically show each of the following features except:
A wide QRS complex during normal sinus rhythm
A narrow complex SVT
A delta wave on the surface QRS
A long H–V interval on the His-bundle recording
The H–V interval in Wolff-Parkinson-White syndrome can be negative or very short with antidromic tachycardia because the ventricle is activated prematurely by the accessory pathway or normal in orthodromic tachycardia since conduction proceeds down the AV node to the ventricle and returns retrograde through an accessory pathway. The more typical form of Wolff-Parkinson-White syndrome is orthodromic and the QRS is narrow, even in tachycardia, unless functional bundle branch block occurs since the antegrade conduction proceeds through the AV node and His-Purkinje system.
Prerequisite conditions of the reentrant arrhythmia include all of the following except:
Two functionally distinct conducting pathways
An anatomical obstacle around which the impulse reenters
Unidirectional block in one pathway
Slow conduction via one pathway with return via the second
An anatomical obstacle is not necessary for reentrant arrhythmia. Recent studies have shown that reentry can occur in the absence of an obstacle as a consequence of con- duction and refractoriness in the atrial or ventricular tissue.
Antidromic reciprocating tachycardia in a patient with Wolff-Parkinson-White refers to:
AV conduction proceeding via the normal AV conduction system with return via the accessory pathway
AV conduction via the accessory pathway with return via the normal ven- triculoatrial conduction system
AVNRT with additional conduction via the accessory pathway
None of the above
In antidromic reciprocating tachycardia, conduction is “anti” the normal path through the AV node. Thus there is AV conduction via the accessory pathway with the return ventriculoatrial conduction via His-Purkinje system followed by the AV node.
The most common mechanism of arrhythmia in sustained VT is:
Sympathetically facilitated enhanced automaticity
Reentry involving ventricular myocardium
Triggered automaticity arising from early afterdepolarizations
Reflection of propagated impulses
The most common mechanism of arrhythmias in sustained VT is reentry involving ventricular myocardium, most often from scars due to underlying CAD.
A 54-year-old man is referred to you due to an enlarged cardiac silhouette dis- covered on routine chest X-ray as part of his employment physical exam. He reports no known past medical history. Although he denies symptoms of overt heart failure, he states that he tends to become short of breath with strenuous activity—a symptom that he felt was due to lack of exercise.
On physical examination he has a displaced apical impulse and a third heart sound. An ECG shows sinus rhythm with a LBBB. An echocardiogram discloses global LV dysfunction with an EF of 25% and mild functional mitral valve regurgi- tation. Coronary angiography is normal. A 24-hour Holter monitor shows 35,000 PVCs and 85 runs of nonsustained VT, 3 to 9 beats in duration.
What is the next appropriate test?
EP study
RV biopsy
Serum ferritin
Signal average ECG
No further testing is required; schedule the patient to receive an ICD
The patient has nonischemic cardiomyopathy and a search for potential secondary causes is warranted. Noninvasive testing, such as obtaining a serum ferritin to assess for hemochromatosis, should be performed prior to invasive studies, such as RV biopsy. In a minimally symptomatic patient, an EP study is not a first line test. Nonetheless, if the PVCs are monomorphic and other causes of cardiomyopathy are excluded, the patient may be considered for an EP study and attempted ablation of the focus. Prior to considering an ICD in this patient who has no other significant symptoms, medical therapy needs to be started and titrated to therapeutic doses.
All of the following clinical characteristics are associated with cardiogenic syn- cope and should prompt referral for an invasive EP study except:
Age
Answers a to d are all considered high risk characteristics for cardiogenic syncope. If any of these are present, the rate of spontaneous ventricular tachyarrhythmia or death is between 4% and 7% in 1 year. If 3 or more are present, this rate increases to 58% to 80%. Recurrent unexplained falls in an elderly patient should first be assessed with tilt table testing unless other high risk features are present.
A 38-year-old man underwent radiofrequency ablation in the RA for medically refractive symptomatic atrial tachycardia. He was dismissed on aspirin 325 mg/day. Six days following the procedure he developed left-sided persistent chest pain and mild dyspnea. His exam is notable only for tachycardia with a HR of 110 bpm. An ECG discloses sinus tachycardia. What is the next most appropriate test to request?
Echocardiogram
CT scan
Coronary angiography
Arterial blood gas, D-Dimer
Ventilation perfusion scan
The temporal presentation and symptoms of the patients are consistent with pulmonary embolism, complicating the EP study he had 6 days before. The next step is to assess for this complication with screening tests, such as an arterial blood gas and D-Dimer, fol- lowed by an imaging modality, such as a ventilation perfusion scan or CT scan. If the evaluation for a pulmonary embolus is negative, a next step is to consider pericarditis.
All the following are true about head-up tilt testing except:
The test should be performed at 60 to 80 degrees
Sensitivity and specificity of the test are approximately 80%
A vasodepressor response occurs most often in patients younger than 60
In patients without structural heart disease, it can provide a diagnosis in approximately 60% of them
A cardioinhibitory response tends to be infrequent in older patients
Vasodepressor response characterized by a profound drop in BP with minimal change in HR is more common in patients more than 60 years old. In contrast, cardioinhibitory response characterized by asystole and profound bradycardia that coincides with a decrease in BP, or a mixed-type event that is a combination of HR and BP reduction, is the initial event occurring more often in younger patients.
The arrhythmic substrate least likely to be definitely ruled out with a negative EP study is:
Sinus node dysfunction
Severe His-Purkinje disease
Accessory bypass tract
VT in a patient with ischemic cardiomyopathy
AVNRT
The sensitivity of EP testing for sinus node disease is
An active 78-year-old woman with recurrent syncope has an EP study. With atrial pacing at 150 bpm for 30 sec, a 7-sec atrial pause occurs when the pacing ceases. Her baseline examination and echocardiogram are all within normal limits. ECG shows sinus rhythm with first degree AV block. What is the next appropriate management step?
Implant a VVI single-chamber permanent pacemaker
Implant a dual-chamber ICD
Implant a DDDR dual-chamber rate responsive pacemaker
Implant an AAI single-chamber permanent pacemaker
Medical management with atropine
The patient has recurrent syncope with evidence of significant sinus node dysfunction. In this patient a pacemaker is indicated. The choices of therapy include an AAI versus a DDDR permanent pacemaker. AAI is indicated in a patient when AV conduction is completely normal. If there is evidence of dysfunction, such as this patient with first degree AV block, DDDR is the generally agreed upon treatment.
Programmed ventricular stimulation is an important tool in risk assessment in patients with CAD for which of the following patient subsets?
An EF of 30% to 35% and the presence of nonsustained VT
An EF of 35% to 40% and the presence of nonsustained VT
An EF of 30% to 35% and an abnormal signal averaged ECG
An EF of 35% to 40% and a history of cardiac arrest
MUSTT showed that patients with an EF
All of the following examples are considered positive responses to a drug in a patient with an expected cardiac channelopathy except:
A decreased QT interval with lidocaine in a patient suspected to have long QT3
An increased QT interval with epinephrine in a patient suspected to have
long QT1
Abnormal ST-T changes in leads V1–V2 with procainamide in a patient
suspected to have Brugada syndrome
AnincreasedQTintervalwithnotchedTwaveswithepinephrineinapatient
suspected to have long QT2
An increased QT interval with ajmaline in a patient suspected to have
long QT4
Answers a to d are all considered a positive response to pharmacologic stress in patients suspected to have a cardiac channelopathy. Ajmaline is a sodium channel blocking agent used in patients suspected to have Brugada syndrome.
Acute success rates for ablation of accessory pathways could be stated as:
50% to 70%
75%
85%
90% to 95%
Virtually 100%
Acute success rates for accessory pathway ablation in Wolff-Parkinson-White syndrome are approximately 90% to 95%. Right-sided pathways tend to have lower acute success rates in comparison to left-sided pathways.
The following findings are considered positive results during EP testing except:
A
An H–V interval from 55 to 99 msec is considered an intermediate result and requires either the presence of additional symptoms or other findings to direct therapy. An H–V interval
A patient has a loss of function mutation in KCNQ1. This patient is most likely to have events triggered by:
Swimming
Doorbells
The postpartum period
Sleeping
The vast majority of long QT cases are due to mutations in the KCNQ1 gene that encodes the slow component of the delayed rectifier potassium current (long QT1). During exercise these patients fail to shorten their QT. The gene-specific triggers of patients with long QT1 are exertion-related activities, in particular swimming. In long QT2 auditory stimuli and the postpartum period are important triggers. In long QT3 the most common trigger is sleep.
