IBHRE Review Exam: Key Concepts and Definitions for Cardiac Pacing and Arrhythmias, Exams of Advanced Education

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AV Node Reentry Tachycardia (AVNRT) - ✔✔✔ - - accounts for ~60% of arrhythmias presenting as SVT or paroxysmal atrial tachycardia (PAT)

• affects all age groups and genders equally
• no correlation with heart disease
• heart rate 150-250 bpm, palpitations, light-headedness, near-syncope, narrow QRS complex rheobase - ✔✔✔ - lowest point on a strength duration curve at an infinitely long pulse duration; for cardiac pacing, the rheobase is usually reached between 1-2ms chronaxie time - ✔✔✔ - pulse width at twice the rheobase value approximates most efficient stimulation pulse duration action potential - ✔✔✔ - the cellular characteristics of depolarization and repolarization 5 phases (0-4) phase 0 - ✔✔✔ - depolarization, rapid Na+ channels open, resting potential (-90mV) to ~0mV phase 1 - ✔✔✔ - early repolarization; peak of depolarization phase 2 - ✔✔✔ - the "plateau phase", mediated by slow Ca2+ channels, disrupts and delays the repolarization started in phase 1 and prolongs refractory phase 3 - ✔✔✔ - end of repolarization

phase 4 - ✔✔✔ - resting phase, leaking of K+ and Na+ silicone rubber insulation - ✔✔✔ - pros:

• can be easily repaired
• flexible
• proven performance history
• easy to produce cons:
• high friction coefficient
• absorbs lipids
• more thrombogenic & fibrotic
• cuts & tears easily
• large diameter (comparatively) polyurethane 80A (pellethane) - ✔✔✔ - pros:
• relatively nonthrombogenic
• thinner walls, flexible
• tougher, abrasion resistant
• resists cutting
• low friction coefficient cons:

• adverse history
• longevity <7 years
• not repairable
• very process-dependent recalled in 1995 by the FDA for inner insulation failure due to metal ion oxidation (MIO) polyurethane 55D (pellethane) - ✔✔✔ - pros:
• proven history
• longevity >12 years
• easy to process
• very tear-resistant and tough
• thinner walls
• abrasion resistant cons:
• less flexible
• not repairable expanded polytetrafluoroethylene (ePTFE) - ✔✔✔ - Goretex-type material that has been shown to improve the ease of extraction due to reducing the degree of fibrous ingrowth, especially on shocking coils pros:
• electrically inert and does not effect DFTs

• stable biomaterial/ chemically inert
• high tear strength
• low friction coefficient
• small lead diameter
• less fibrotic cons:
• stiff when >0.003"
• more prone to creep
• difficult to manufacture w/o pinholes environmental stress cracking (ESC) - ✔✔✔ - cracks or crazing that occurs in polyurethane in response to certain chemicals and external stresses oxidation occurs secondary to cellular adhesion metal ion oxidation (MIO) - ✔✔✔ - a polyurethane degradation whereby moisture & metal ions act as a catalyst to accelerate degradation metal ion oxidation pacemaker syndrome - ✔✔✔ - any combination of the variety of symptoms and signs occurring with ventricular pacing that are relieved with restoration of AV synchrony causes:
• loss of AV synchrony
• sustained retrograde conduction (PMT)

• a single ventricular rate when modulation is required for exercise diagnosis:
• fluctuation of peripheral BP
• cannon "A" wave in neck fallback - ✔✔✔ - upper rate behavior

1. Decouples atrial and ventricular events at the upper rate limit.
2. The ventricular inhibited pacing rate then gradually decrements to a programmed lower or "fallback" rate over a programmed duration.
3. When the fallback rate is reached, atrial synchrony is resumed. rate smoothing - ✔✔✔ - upper rate behavior
4. Eliminates large cycle to cycle variations by preventing the paced rate from changing more than a certain percentage (3%, 6%, 12%, etc.) from one paced V-V interval to the next.
5. Eliminates large fluctuations in rate during fixed ratio or pseudo-Wenckebach block. *only found in BSCI devices Brugada Syndrome - ✔✔✔ - clinically:
6. RBBB
7. ST segment elevation in V1 to V
8. sudden death
9. structurally normal heart

abnormally high incidence of sudden cardiac death in young men from SE Asia (Philippines, Japan, Laos, etc.) due to genetic transmission - autosomic dominant, SCN5A, which encodes for the cardiac sodium channel - phase 2 of the action potential drugs with hepatic elimination - ✔✔✔ - quinidine procainamide lidocaine mexiletine flecainide encainide propafenone moricizine amiodarone verapamil diltiazem drugs with renal elimination - ✔✔✔ - disopyramide tocainide bretylium sotalol digoxin drugs that increase the digoxin level - ✔✔✔ - quinidine flecainide amiodarone

propafenone verapamil total atrial refractory period (TARP) - ✔✔✔ - sum of paced AV delay (PV delay) and atrial refractory period (PVARP) if rate responsive PVARP is ON use the shortest in calculations = pacemaker's 2:1 block point Wenckebach window - ✔✔✔ - max tracking rate (MTR) to TARP if MTR = TARP; no Wenckebach window - only 2:1 blocking rate battery longevity calculation - ✔✔✔ - 114 x A hr (battery capacity) / μA (battery current drain) = Longevity (years) Ashman's Syndrome - ✔✔✔ - a predisposition to ectopy and aberration when a longer R-R interval precedes a shorter one - wide QRS complex mistaken for PVC the bundle branches reset their repolarization time for the longer period and are caught off guard by the shorter cycle length, often causes aberration through the bundle that hasn't repolarized Chagas Disease - ✔✔✔ - - most prevalent in Central and South America, spread by vector (insect, hematophagous assassin bug)

• results in acute infection of the heart, damaging myocardium
• progressive, chronic heart disease - infected myocardium is replaced by scar tissue, resulting in thinning walls of the heart
• Class IIa indication for ICD placement crosstalk - ✔✔✔ - inappropriate detection of a pacemaker-generated event in one channel by the sensing amplifier of the other channel that causes inhibition of the second channel's output causes:

1. atrial output is high (>5.0V)
2. ventricular sensitivity is high (<1.0mV)
3. insulation breach between the 2 leads, resulting in energy transferring from one lead to another at atrial output presentation:
4. AV Delay intervals 100-120ms
5. high atrial output/ low impedances, or high ventricular sensitivity
6. atrial outputs in the absence of ventricular output, coinciding with rates faster than programmed w/o rate response on antitachycardia pacing (ATP) - ✔✔✔ - - introduction of a sequence of pacing impulses, faster than the tachycardia rate, in an attempt to terminate the arrhythmia

• most effective for VTs <200 bpm
• can result in:
  1. no effect
  2. acceleration of tachycardia

3. termination of arrhythmia

• burst/ramp/scan Torsades de Pointes - ✔✔✔ - - ventricular tachycardia that is irregular, polymorphic, and often exhibits a "streamer" effect as the QRS complex transitions from positive to negative and back again
• difference between polymorphic VT and this is the presence of a prolonged QT interval in the underlying rhythm causes:
• hypokalemia & hypomagnesemia (malnourished or chronic alcoholics)
• long QT syndrome (of any cause)
• class Ia antiarrhythmics
• hypoxia
• HF
• LV hypertrophy
• females Class IA antiarrhythmics - ✔✔✔ - quinidine, procainimide, disopyramide Class IC antiarrhythmics - ✔✔✔ - encainimide, flecainide Class III antiarrhythmics - ✔✔✔ - sotalol, amiodarone

hypokalemia & hypomagnesemia - ✔✔✔ - cause a delay in phase 3 of the action potential and forms the substrate for emergence of the dysrhythmia; patients with cirrhosis or hypothyroidism are particularly affected Wedensky effect - ✔✔✔ - - a prolonged lower threshold of excitability induced by strong stimulus, loss of capture at a lower voltage than you recapture

• under certain conditions, one impulse could trigger a second impulse without invoking vulnerability or supernormality open loop sensor - ✔✔✔ - this type typically does not respond to a specific physiologic function, i.e. piezoelectric crystal and accelerometer partially ___-loop sensors include temperature and respiration sensors closed loop sensor - ✔✔✔ - this type of sensor responds to physiologic change; causes a rate increase or decrease according to bodily needs; measures the effect and modifies its output (rate modulation) as required, i.e. stimulus to T wave (QT sensors), dP/dT of RV contraction sensors, pre-ejection interval (PEI) sensors, and oxygen saturation sensors piezoelectric crystal - ✔✔✔ - bonded to the inside of the IPG and is highly sensitive to activity associated with walking (heel strike rate) - NOT a physiologic sensor frequency ~10Hz, resonant frequency of the human body - max. sensitive to up and down motion accelerometer - ✔✔✔ - a piezoelectric crystal attached to the circuit board within the device can

1. rapid response to onset of exercise
2. functionally simple
3. compatible with any pacing lead

No direct relationship between detected levels of activity and metabolic demand, susceptible to environmental noise upper limit of vulnerability (ULV) - ✔✔✔ - weakest shock strength at or above which VF is not induced when the shock is delivered at any time during the vulnerable period (T wave) ULV~DFT strongest shock that induces V, lower limit of invulnerability (minimum shock strength) anodal stimulation - ✔✔✔ - during "common ring" pacing configuration of Bi-V pacing devices, the anodal electrode of the RV lead is used as the anodal electrode of the LV/CS lead - results in third site of pacing within the ventricles: LV tip, RV tip, and RV prox. ring COMPANION - ✔✔✔ - Comparison Of Medical therapy, Pacing and defibrillation In chronic heart failure NEJM, 2004 20% risk reduction for the primary endpoint by CRT/CRT-ICD v. OPT; total mortality and hospitalization (p<0.01) LVEF <= 35%, QRS >=120ms and PR > 150ms SCD-HeFT - ✔✔✔ - Sudden cardiac death in heart failure trial NEJM, 2005

heart failure class II or III, CAD, or DCM + LVEF<35% 23% decreased risk of death for ICD therapy (v. placebo v. amiodarone - no difference) MADIT I - ✔✔✔ - Multicenter Automatic Defibrillator Implant Trial 1996 ICD patients reduced risk of all-cause mortality by 54% compared to patients on conventional drug therapy (amiodarone) LVEF <= 35%, MI >3 weeks, and inducible non-suppressible VT on EP testing w/ procainamide (primary prevention in high-risk patients) MADIT II - ✔✔✔ - Multicenter Automatic Defibrillator Implant Trial Circulation, 2001 (2003?) evaluate survival benefit of prophylactic ICD in patients with prior MI (>4 weeks) and LVEF <=30% ICDs significantly reduced the absolute risk of death by 31% compared to drug therapy alone - stopped early AVID - ✔✔✔ - Antiarrhythmics Versus Implantable Defibrillators

Circulation, 1999 stopped early because of significant reductions in mortality and arrhythmic death ICD > amiodarone in all-cause and arrhythmic death for LVEF <35% MUSTT - ✔✔✔ - Multicenter Unsustained Tachycardia Trial NEJM, 2000 inducible ventricular arrhythmias to no antiarrhythmic therapy or EP guided therapy (no AA therapy, EPS w/ ICD, EPS w/o ICD) ICDs reduced the risk of sudden death, and antiarrhythmic drug therapy was not included CASH - ✔✔✔ - Cardiac Arrest Study - Hamburg Am J of Cardiol, 1993 ICDs, amiodarone, or metoprolol LVEF <45% 39% reduction in all-cause mortality for ICD therapy, metoprolol = amiodarone

CIDS - ✔✔✔ - Canadian Implantable Defibrillator Study Am Heart Journal treatment of VT/VF w/ ICD or amiodarone risk reduction 29.7% total mortality, 31.4% arrhythmic death five determinants of myocardial performance - ✔✔✔ - 1. heart rate

2. conduction velocity
3. preload
4. afterload
5. contractility Frank-Starling Law - ✔✔✔ - - mechanism of compensation in CHF

• ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return
• the more the ventricle is filled w/ blood during diastole (end-diastolic volume), the greater the volume of ejected blood will be during the resulting systolic contraction (stroke volume)
• however, results in symptoms such as dyspnea to maintain cardiac output Class I ICD indication - ✔✔✔ - cardiac arrest secondary to VT/VF in absence of reversible cause structural heart disease & sustained VT syncope of unknown origin & clinically relevant VT/VF at EPS

LVEF <35%, CAD, 40 days post-MI, NYHA II or III LVEF <= 35%, non-ischemic DCM, NYHA II or III LVEF <30%, CAD, 40 days post-MI, NYHA I LVEF <40%, CAD, inducible VF or VT @ EPS Class IIa ICD Indications - ✔✔✔ - unexplained syncope, significant LV dysfunction, and non- ischemic DCM sustained VT & normal or near-normal LVEF HCM w/ 1+ risks for SCD ARVD w/ 1+ risks for SCD LQTS & syncope on beta-blockers, or VT/VF non-hospitalized patients awaiting transplantation Brugada syndrome and syncope or VT catachoaminergic PMVT, syncope, &/or sustained VT while on beta-blockers sarcoids, giant-cell myocarditis, and Chagas disease Class I CRT Indications - ✔✔✔ - systolic HF & LVEF <= 35%, NYHA II, III, or IV, w/ LBBB and QRS >= 150ms Class IIa CRT Indications - ✔✔✔ - LVEF <= 35%, QRS >=120ms, NYHA class II or III, or ambulatory IV, and AF LVEF <= 35%, NYHA functional class III or ambulatory class IV symptoms, and frequent dependence on ventricular pacing LVEF <= 35%, non-LBBB pattern w/ a QRS >= 150ms and NYHA class III or IV

Class IIb CRT Indications - ✔✔✔ - LVEF <= 35%, NYHA functional class I or II symptoms, who are receiving optimal recommended medical therapy undergoing implantation of a permanent pacemaker and/or ICD w/ anticipated frequent ventricular pacing NYHA class I symptoms with LVEF <30%, ischemic HF, sinus rhythm, and LBBB w/ a QRS >= 150ms NYHA Class I HF - ✔✔✔ - No limitation of physical activity. Ordinary physical activity does not cause undue fatigue, palpitation, or dyspnea NYHA Class II HF - ✔✔✔ - Mild Slight limitation of physical activity. Comfortable at rest, but ordinary physical activity results in fatigue, palpitation, or dyspnea. NYHA Class III HF - ✔✔✔ - Moderate Marked limitation of physical activity. Comfortable at rest, but less than ordinary activity causes fatigue, palpitation, or dyspnea. NYHA Class IV HF - ✔✔✔ - Unable to carry out any physical activity without discomfort. Symptoms of cardiac insufficiency at rest. If any physical activity is undertaken, discomfort is increased. Stokes Adams Syndrome - ✔✔✔ - An occasional temporary stoppage or extreme slowing of the pulse as a result of heart block, causing dizziness, fainting, and sometimes convulsions - heart block may last seconds, minutes, hours, days, and up to weeks Class I Pediatric Pacemaker Indications - ✔✔✔ - 1. Advanced second- or third-degree AVB associated with symptomatic bradycardia, ventricular dysfunction, or low cardiac output.

2. SND with correlation of symptoms during age-inappropriate brady.
3. Postoperative advanced second- or third-degree AVB that is not expected to resolve or that persists at least 7 days after cardiac surgery.
4. Congenital CHB with a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction.
5. Congenital third-degree AVB in the infant with a ventricular rate <55 bpm or with CHD and a ventricular rate less than 70 bpm. Class IIa Pediatric Pacemaker Indications - ✔✔✔ - 1. Congenital heart disease and sinus brady for the prevention of recurrent episodes of intra-atrial re-entrant tachy; SND may be intrinsic or secondary to antiarrhythmic treatment.
6. Congenital third-degree AVB beyond the first year of life with an avg. heart rate <50 bpm, abrupt pauses in ventricular rate that are 2 or 3 times the basic cycle length, or associated with symptoms due to chronotropic incompetence.
7. Sinus brady with complex congenital heart disease with a resting heart rate <40 bpm or pauses in ventricular rate >3 seconds.
8. CHD and impaired hemodynamics due to sinus brady or loss of AV synchrony.
9. Unexplained syncope in the patient with prior congenital heart block with residual fascicular block after a careful evaluation to exclude other causes of syncope. hyperkalemia - ✔✔✔ - normal: 3.5-5.0mEq/L

• increase stimulation thresholds or cause latency
• most common electrolyte abnormality to cause loss of capture in A or V
• may cause a wide paced complex, prolonged latency, a.k.a. 1st degree pacemaker exit block, which can progress to 2nd degree Wenckebach and eventually complete LOC
• atrium is more sensitive to its effects, impacting the amplitude & slew rate of the EGM, P-wave disappears on surface ECG

• oversensing of T-waves
• Far-R sensing of prolonged QRS hypokalemia - ✔✔✔ - normal: 3.5-5.0mEq/L
• can make one prone to Torsades de Pointes, R on T, and PATs