Cardiophile MD Archive » ICD

Role of ICD in those with post myocardial infarction LV dysfunction

Johnson Francis — Sun, 01 Nov 2009 08:03:49 +0000

Previous MI has been documented in as many as 75% of SCA. SCD rates in those with previous MI is 4-6 times that in general population. High risk indicators are late VT/VF, LV dysfunction, frequent VPC and NSVT and inducible VT at EPS. ICD is recommended in VT/VF survivors with no reversible etiology. If there is inducible VT/VF, those with LVEF less than or equal to 40% need an ICD. The cut off LVEF is less than or equal to 35% those in symptomatic patients. The cut off is lower at LVEF of 30% or less regardless of any arrhythmic events or symptoms. ICD does reduce mortality significantly in those with post MI LV dysfunction.

Early ICD implantation was not shown to reduce mortality in previous studies, though recent studies, especially with risk stratification haves shown some promise. The earlier negative trial was DINAMIT.

Implantable defibrillator high voltage coils on X-ray chest PA view

Johnson Francis — Sun, 30 Aug 2009 16:27:02 +0000

Implantable defibrillator high voltage coils on X-ray chest PA view

Click on the image for a larger view

Implantable defibrillator (ICD) high voltage coils on X-ray chest PA view. The ICD generator is seen in the left infraclavicular region. Te lead is coursing through the left subclavian vein into the left brachiocephalic vein and hence into the superior vena cava. In this region the high voltage coil is seen. Another high voltage defibrillation coil is seen in the right ventricle. The ICD can is programmed as one electrode and the two high voltage coils as the other electrode. The addition of a coil in the superior vena cava reduces the defibrillation threshold compared to only a right ventricular coil. The position of the generator in the left infraclavicular region also reduces the threshold. If this position is not available, and the generator has to be implanted in the right infraclavicular region, defibrilation threshold will be high.

Implantable defibrillator high voltage coils on X-ray chest PA view - annotated

Congenital short QT syndrome

Johnson Francis — Mon, 26 Jan 2009 16:25:10 +0000

Congenital short QT syndrome is new inherited clinical syndrome which was described by Gussak et al in 2000. (Cardiology. 2000;94:99-102). A gene mutation causing short QT syndrome was first demonstrated by Brugada et al in January 2004. This mutation in HERG (KCNH2) gene was later called as SQT1 and was due to gain in function of Iks, the slow component of the delayed rectifier potassium current. Later on in the same year, SQT2 was described by Bellocq et al as a mutation in KCNQ1 (KvLQT1) which caused a gain in function of Ikr, the rapid component of delayed rectifier potassium current. SQT3 was identified by Priori et al as a mutation in KCNJ2 gene which causes a gain in function of Ik1 potassium current.

Short QT syndrome is characterized by consistently short QT intervals, usually below 300 msec, which does not lengthen with bradycardia. There is a propensity for sudden cardiac death and atrial fibrillation. Family history of sudden death may be forthcoming. Electrophysiologically short QT syndrome is characterized by short refractory periods and inducible VF (ventricular fibrillation) at EP (electrophysiological) study.

Shortening of QT interval can occur in tachycardia, hyperthermia and hypercalcemia. Digoxin can also shorten the QT interval. These should be excluded before considering a diagnosis of short QT syndrome.

Treatment options for short QT syndrome are limited. Some have reported lengthening of QT interval with quinidine. Most patients with short QT syndrome and a risk of sudden cardiac death get an ICD (implantable cardioverter defibrillator) implanted.

Beta blockers are quite effective in long QT syndrome type 1

Johnson Francis — Thu, 22 Jan 2009 16:12:14 +0000

Beta blockers have been once again shown to be quite effective in long QT syndrome type 1. Even though conventional teaching is that beta blockers are quite effective in long QT syndrome type 1, several instances of beta blocker failure have prompted clinicians to implant cardioverter defibrillators in this group of patients. A retrospective analysis by Vincent GM et al (Circulation. 2009;119:215-221) has shown that beta blocker non compliance and the use of QT prolonging drugs are responsible for most of the so called beta blocker failures. The study involved 216 genotyped long QT syndrome type 1 patients treated with beta blockers and a median follow up of 10 years. While 73% had cardiac events before beta blocker therapy, 75% were asymptomatic on beta blockers. 92% of those who suffered cardiac arrest / sudden death were non compliant, on QT prolonging drugs or both. The authors suggest that routine implantation of cardioverter defibrillators (ICD) may not be necessary in those with long QT syndrome type 1 as the efficacy of beta blockers have been documented once more.

Catheter Ablation for Ventricular Fibrillation

Johnson Francis — Thu, 23 Oct 2008 17:18:12 +0000

Thejus et al has written an editorial on catheter ablation for prevention of recurrent ventriular fibrillation in the current issue of Indian Pacing and Electrophysiology Journal (Thejus J et al. Indian Pacing Electrophysiol J. 2008; 8:238-241]. The current recommendation for treatment of recurrent ventricular fibrillation is the implantation of an ICD (Implantable Cardioverter Defibrillator). ICDs are costly and have a finite battery life, requiring replacement when the end of battery life is reached. The tolerance of ICD shocks are also not very good among patients, often leading to psychological problems due to fear of an impending shock. To overcome this problem, Haissaguerre et al pioneered the radiofrequency ablation of ventricular fibrillation and it has been taken up by several other investigators. Ventricular fibrillation is triggered by an ectopic impulse falling in the vulnerable period of the ventricular repolarisation and is maintained by multiple wavelets of reentry. Radiofrequency catheter ablation aims at controlling this trigger. Most of the cases of ventricular fibrillation are precipitated by ventricular premature complexes arising from the Purkinje system. Origin of the ventricular ectopic beat from the Purkinje system is identified by a Purkinje potential occurring just before the ectopic beat. It is a sharp spike of less than 10 msec in duration. Radiofrequency catheter ablation at this site causes the cessation of ventricular ectopic beats which trigger the ventricular fibrillation. The recurrence rate after successful ablation was only 9% over a mean follow up period of 22 months in cases of idiopathic ventricular fibrillation.

In another article in the same issue of the journal, Thoppil et al describe the successful treatment of post myocardial infarction electrical storm by targeting the Purkine potentials [Thoppil PS et al. Indian Pacing Electrophysiol J. 2008; 8: 298-303].

Fragmented QRS – a new predictor of prognosis in Brugada Syndrome

Johnson Francis — Tue, 21 Oct 2008 01:54:33 +0000

Multiple spikes within the QRS is known as fragmented QRS (f-QRS). Morita et al, from Okayama, Japan has found an association between f-QRS and ventricular fibrillation in Brugada Syndrome (Circulation. 2008;118:1697-1704). 115 patients were evaluated – 13 resuscitated from ventricular fibrillation, 28 with syncope and 74 asymptomatic. 43% of them had f-QRS. The highest occurrence was in the group with ventricular fibrillation (85%) while the lowest was in the asymptomatic individuals (34%; P<0.01). Those with f-QRS were more likely to have SCN5A mutations (33% in those with f-QRS vs 5% in those without f-QRS). In the group with ventricular fibrillation or syncope, only 6% without f-QRS had VF during follow up while 58% with f-QRS had recurrent syncope due to ventricular fibrillation (P<0.01). The authors go on to recommend implantation of an ICD (implantable cardioverter defibrillator) in Brugada Syndrome patients who experienced syncope without detected ventricular fibrillation, but have f-QRS as they are at increased risk for a subsequent arrhythmic event. In those with prior ventricular ventricular fibrillation, f-QRS indicates a risk of recurrent ventricular fibrillation including arrhythmic storm.

Useful practical markers which favor ICD implantation in those with LV dysfunction

Johnson Francis — Fri, 03 Oct 2008 11:22:02 +0000

QRS prolongation, QT prolongation and elevated BNP are good markers of SCD in persons with reduced left ventricular function. These markers can be considered while planning devices for those with left ventricular dysfunction.

ICD Follow Up

Johnson Francis — Fri, 03 Oct 2008 11:18:25 +0000

Goals:

Assess system integrity

Proper programming for better battery life

Basic steps:

Assess patient’s clinical status

Drug history has to checked

Inspection of the site of implantation

Chest radiography to document lead and device positions

ICD interrogation

Interrogation at the earliest after every device therapy (shock)

Whether a particular position of the body or activity triggered the shock

Charge time and battery life should be closely monitored

Criticism of MADIT Trials

Johnson Francis — Fri, 03 Oct 2008 11:16:20 +0000

Beta blocker use was more in the ICD arm than conventional therapy arm, which could have contributed to the better results in the ICD. This criticism was taken care of by MADIT II trial which showed that just the presence of a low ejection fraction following myocardial infarction was enough to implant a defibrillator. But some clinicians believe that this may not be true, considering the large number of patients requiring ICD implantation in this setting.

Potential problem of using amiodarone in ICD recipients

Johnson Francis — Fri, 03 Oct 2008 11:13:45 +0000

Amiodarone can raise the defibrillation threshold though it may not raise the pacing threshold

Amiodarone may slow the rate of spontaneous ventricular tachycardia below the detection threshold rate of the ICD

Role of amiodarone in ICD patients is to reduce the frequency of tachycardias requiring ICD discharge