Arrhythmia
Diagnosis Following an ICD Shock: Reply
Roy
M. John, MD PhD
Address for correspondence: Roy M. John, MD, PhD, Section of
Cardiology, Lahey Clinic Medical Center, 41 Mall Road,
Burlington, MA 01805.
Email: roy.m.john@lahey.org
Dr. Levine's comments1 are greatly
appreciated. Most modern ICDs have arrhythmia discrimination algorithms
that have variable success in withholding inappropriate therapy. It
must be borne in mind that enhancing specificity for ventricular
arrhythmia detection can entail a
loss of
sensitivity. Accordingly, all algorithms necessarily err on the side of
safety and will withhold therapy for only brief period of time. A
persistent high rate will eventually be treated as a ventricular
arrhythmia and can result in unnecessary and repetetive shocks. Hence
the importance of aggressive management of supraventricular arrhythmias
in these patients cannot be overemphasized.
The patient presented in the case study2 had an older generation single chamber ICD.
Although, the provocation of ventricular tachycardia by
anti-tachycardia pacing led to an ICD shock and termination of the
atrial arrhythmia in this particular instance, atrial arrhythmias are
often not terminated by ICD shocks delivered between an RV lead and the
generator can. Further therapies with repeated induction of VT could
have resulted. In patients with severe LV dysfunction or ischemia, such
arrhythmias have a potential for progression to intractable ventricular
fibrillation and death.
The modern dual chamber detection algorithms have significantly
improved
specificity for ventricular arrhythmia detection. I am in total
agreement
with Dr. Levine regarding the programming of monitoring zones in the
early
post implant period. When done correctly, such programming can provide
a
great deal of information on arrhythmia characteristics and accuracy of
discrimination algorithms.
References
1.
Paul A. Levine. Arrhythmia Diagnosis Following an ICD Shock:
Comment. Indian Pacing and Electrophysiology
Journal; 2002;2(1):6. [Free full
text]
2. Roy
M. John. Arrhythmia Diagnosis Following an ICD Shock.. Indian Pacing and Electrophysiology Journal; 2001;1(1):5. [Free full text]
