its content.
ICD-Drug Interactions



ICD-Drug Interactions
Rationale for ICD Therapy
Efficacy of AA drug therapy for inducible
sustainable monomorphic VT [VT-S(m)] is low
ICD-Drug Interactions
ICD therapy for inducible VT-S(m) is
highly effective and superior to AA drug
therapy with amiodarone (MADIT,MUSTT
AVID trials)
ICD therapy for patients known to be at
high risk for VT/VF, and sudden cardiac
arrest, significantly reduced sudden death
and all cause mortality, compared with
optimal medical therapy(MADIT II +
ScDHeft Definite trails)






ICD System Configuration
ICD system consists of the generator and 1 or 2
leads; RV defibrillation lead and RA lead
Generator
lithium battery, capacitors, sensing algorhythms software,
sensing/pacing circuits
RV Lead
Close bipolar tip and ring electrodes, large surface area RV
and SVC shock coils
RA Lead
Standard close bipolar electrodes
ICD Evolution



ICD Implant
ICD System Configuration
RA Sensing and pacing via close bipolar
distal electrodes
RV- pacing/sensing via distal tip and ring
close bipolar electrodes
defibrilation shock delivered between RV
coil as cathode and proximal SVC coil and
active generator can tied together as anode
ICD Function
Pacing function:
Standard pacing mode algorhythms VVI,
VVIR, DDD, DDDR
also backup pacing during atrial
tachyarrhymias: VVI, VVIR, DDI, DDIR



ICD Function
Anti tachycardia modes
Sensing: rate cutoff ventricular rate above which
VT or VF episode is declared, and therapy
initiated
May program 1-3 zones with different rate boundaries
:slow VT zone, VT zone, VF zone
Therapy
Anti tachycardia pacing (ATP)
Cardioversion defibrilation
Can use combination of therapies in 2 lower rate (VT) zones
can only use cardioversion in highest rate (VF) zone
ICD System Function
Results of ATP
ATP optimally terminates VT
ATP may accelerate VT, causing
hemodynamic compromise
ICD System Function
Results of Cardioversion (ECV)
Low energy ECV usually terminates VT
Low energy ECV may accelerate VT or
convert it to VF
Effective back up high energy ECV is
critical to ICD function
DFT testing used to ensure effective back
up high energy ECV



ICD System Function
ICD Device Settings
ICD System Function
ATP terminating VT
ICD System Function
EVC Terminating VT



ICD System Function: ATP
accelerating VT; low energy shock
failing to convert VT
ICD System Function: DFT
Testing
ICD System Function: High DFT



Discrimination algorhythms to
differentiate SVT from VT
Single chamber devices
a. Regularity of R-R interval
b. Ventricular EGM morphology
c. Post burst pacing R-R interval regularity
d. Deceleration in R-R interval at onset
Dual chamber devices
a. Comparison of A and V rates
b. A and V relationship: fixed vs. changing
c. Chamber of acceleration
d. R-R interval stability
e. Slope of RR internal decrease
SVT-VT discrimination: Fixed A
V relationship indicates SVT
SVT-VT discrimination: Change
in A V relation indicates VT



3-75
3-76
SVT-VT Discrimination: Use of
ATP response
Resynchronization therapy &
rationale
AV conduction delays impairs efficiency of LV contractile
function
Intraventricular conduction delay causes sequential rather
than simultaneous LV wall contraction, impairing LV
systolic function
RV pacing induces intraventricular dyssynchrony of LV
Shortening AV delay with dual chamber pacing, and
shortening intraventricular delay with simultaneous septal
and lateral wall pacing, restores AV synchrony and septal
lateral LV synchrony
Indications for CRT
1) Class III or IV CHF
2) Prolonged AVN conduction time
PR>220ms
3) Intraventricular dyssynchrony
QRS>120ms
4) Need for continuous RV pacing in
setting of LV systolic dysfunction



Drug ICD interactions
Frequency of VT/VF Episodes
1) Increased frequency due to proarrhythmia
a) Class IA drugs cause LQTS and Torsades
b) Class III drugs (except amiodarone) prolong
repolarization, inhomogenously, causing
LQTS and Torsades
c) Class IA and IC drugs slow conduction,
widening excitable gap, and facilitating
induction of VT and or incessant VT
Proarrhythmia: IA drug causing
Torsades
Proarrhythmia: Facilitation of VT
induction



Proarrhythmia: Induction of
incessant VT
Proarrhythmia: IC drug causing
exercise induced polymorphic VT
Drug-ICD interactions:
Frequency of VT/VF episodes
1) Decrease frequency due to suppression of
VT induction
a) IA, IC and class III drugs suppress VT
induction by prolonging refractoriness and
preventing critically timed VES from
initiating reentry
b) Amiodanrone decreases frequency of VT/VF
particularly in VT storm
c) B-blockers decrease VT/VF frequency in VT
storm, associated with ischemia and excess
catecholamines



Drug ICD interactions
Effects of AADs pm induciblilty
of VT
Drug-ICD interactions:
Suppression of VT induction
Drug-ICD interactions:
Suppression of VT induction



Drug ICD interactions
Effects on VT/VF detection
1) AA drugs prolong VT CL (IA, IC, amiodanone) causing
sensing failure due to VT rate <rate cutoff
2) Class IC drugs can accelerate SVT causing inappropriate
VT sensing
3) AA drugs (Ca blockers B-blockers amiodanone) can slow
SVT ventricular rates preventing inappropriate ICD
discharges
4) AA drugs (IC and amiodanone) can reduce VT cycle
length stability, confusing SVT-VT discrimination
algorhythms and causing inappropriate classification as
SVT
5) AA drugs can alter electrogram (EGM) morphology
causing SVT to be classified as VT resulting in
inappropriate ICD shock
ICD Drug Interactions: Decreased
VT cycle length
ICD Drug Interactions: VT
slowing and altered morphology



ICD Drug Interactions:
Acceleration of VT
ICD Drug Interactions: Alteration
of EGM Morphology
AA Drugs slowing of AF
ventricular rates
diltiazem + metoprolol
BASELINE



Drug ICD interaction
Effects on therapy of VT/VF
1) Increase in DFT causing shock failure-
a) chronic amiodanone; IB, IC, and verapamil
2) AA drugs alter ability for pace termination of VT
a)
IA and IC drugs prolong VT CL by slowing conduction and
widening the excitable gap of the reentrant circuit, facilitating
pace termination
b)
IB drugs can sometimes shorten VT CL by increasing conduction
velocity with minimal effect on refractoriness, narrowing the
excitable gap, and inhibiting pace termination
c)
IA and IC drugs can sometimes excessively slow conduction and
widen the excitable gap, causing VT to become incessant
d)
IC drugs use dependence, often precipitate incessant VT under
conditions of elevated heart rates (increased catecholamines or
exercise)
Drug ICD Interaction
Effects on DFT
Effect of Drugs on VT Cycle
Length
Josephson 3
rd
edition Pg 635 fig 12-39



Effects of Drugs on Excitable Gap
Effects of IB Drug: Inhibition of
Pace Termination
Josephson 3
rd
Ed Pg 636 Fig 12-43