Ventricular tachycardia implantable cardioverter-defibrillator

Implantable cardioverter-defibrillator (ICD) A device implanted into the heart transvenously with a generator implanted subcutaneously in the pectoral area that provides internal electrical cardioversion of ventricular tachycardia or defibriUation of ventricular fibrillation. 

Abstract Two thirds of the nearly half a million deaths per year in the United States due to sudden cardiac death (SCD) is attributed to coronary artery disease (CAD) and most commonly results from untreated ventricular tachyarrhythmias. Patients with ischemic cardiomyopathy and left ventricular dysfunction are at highest risk for SCD, but this still defines only a small subset of patients who will suffer SCD. Multiple lines of evidence now support the superiority of implantable cardioverter defibrillator (ICD) therapy over antiarrhythmic therapy for both primary and secondary prevention of SCD in advanced ischemic heart disease. Optimization of ICD therapy in advanced ischemic cardiomyopathy includes preventing right ventricular pacing as well as the use of highly effective anti-tachycardia pacing to reduce the number of shocks. While expensive, ICD therapy has been shown to compare favorably to the accepted standard of hemodialysis in cost effectiveness analyses. 

Low doses (100-200 mg/d) of amiodarone are effective in maintaining normal sinus rhythm in patients with atrial fibrillation. The drug is effective in the prevention of recurrent ventricular tachycardia. It is not associated with an increase in mortality in patients with coronary artery disease or heart failure. In many centers, the implanted cardioverter-defibrillator (ICD) has succeeded drug therapy as the primary treatment modality for ventricular tachycardia, but amiodarone may be used for ventricular tachycardia as adjuvant therapy to decrease the frequency of uncomfortable cardioverter-defibrillator discharges. The drug increases the pacing and defibrillation threshold and these devices require retesting after a maintenance dose has been achieved. 

Some of the beneficial effects of fish oils after acute myocardial infarction have been attributed to an antidysr-hythmic effect on the heart (5). However, the results of a randomized trial in 200 patients with implantable cardioverter defibrillators are at variance with this the rate of cardioversion was higher in those taking fish oils 1.8 g/day than in a control group who took olive oil (6). The lack of benefit and the suggestion that fish oil supplementation may increase the risk of ventricular tachycardia or ventricular fibrillation in some patients with implantable cardioverter defibrillators can reasonably be interpreted as evidence that the routine use of fish oil supplementation in patients with implantable cardioverter defibrillators and recurrent ventricular dysrhythmias should be avoided. 

In a 62-year-old man with dilated cardiomyopathy and an implantable cardioverter defibrillator for ventricular tachycardia, microvolt T wave alternans differed when amiodarone was added (55). The onset heart rate with T wave alternans was lower and the alternans voltage higher with amiodarone than without it. 

In 154 patients with implantable cardioverter-defibrillators randomly assigned to dofetilide or placebo, there were pause-dependent runs of polymorphic ventricular tachycardia in 15 of the 87 patients who received dofetilide and in only five of the 87 who received placebo (57). There were five early events (at less than 3 days of therapy), all torsade de pointes in patients taking dofetilide. There were 15 late events, 10 with dofetilide and five with placebo. The median time to a late event was 22 (range 6-107) days for dofetilide and 99 (34—207) days for placebo. 

Mazur A, Anderson ME, Bonney S, Roden DM. Pause-dependent polymorphic ventricular tachycardia during long-term treatment with dofetilide a placebo-controlled, implantable cardioverter-defibrillator-based evaluation. J Am Coll Cardiol 2001 37(4) 1100-5. 

On the other hand, the medical condition where the heart beats too fast is known as tachycardia. If untreated, tliis condition may lead to ventricular fibrillation, that is, a condition in which the heart stops beating and shakes uncontrollably and is usually fatal. In 1980, a special device was developed and implanted in patients. It could sense the condition and provide a shock that would stop the fibrillation and restore the normal sinus rhythm via an electrode sutured onto the heart. The device was first powered by a lithium/vanadium pentoxide system later it was replaced by a system using a cathode material of silver vanadium oxide (SVO or Ag2V40ii). This is the actual system used in modem ICDs (implantable cardioverter/defibrillator). Another material used is the lithium/manganese dioxide system. Also, a new system using a sandwich cathode design with an inner cathode material of carbon monofluoride and an external cathode layer of silver vanadium oxide is in wide use. 

FIGURE 17-16. Example of an approach to the management of survivors of cardiac arrest (resuscitated VT/VF). Reversible causes of cardiac arrest (e.g., electrolyte abnormalities, acute phase of Ml) should be treated with specific therapy. AADs = antiarrhythmic drugs BBs = /i-blockers EPS = invasive electrophysio-logic studies ICD = implantable cardioverter-defibrillator VT/VF = ventricular tachycardia/ventricular fibrillation Ml = myocardial infarction. 

Strickberger SA, Hummel JD, Bartlett TG, et al. Amiodarone versus implantable cardioverter-defibrillator randomized trial in patients with nonischemic dilated cardiomyopathy and asymptomatic nonsustained ventricular tachycardia. AMIOVIRT. J Am Coll Cardiol 2003 41 1707-1712. 

FIGURE 18-4. Treatment algorithm for hypertrophic cardiomyopathy. ACEI = angiotensin-converting enzyme inhibitor NSVT = nonsustained ventricular tachycardia ICD = implantable cardioverter-defibrillator LV = left ventricular SCD = sudden cardiac death. 

The implantable cardioverter defibrillator (ICD) is a cardiac pacemaker. It can be used to pace one or both chambers on the right side of the heart It has an additional feature, though. ICDs can also impart powerful shocks to the heart if it is beating too fast (tachycardia) or goes into ventricular fibrillation. Either condition means that blood cannot be pumped very efficiently, if at all. A number of major clinical studies were done that identified various categories of heart patients who could benefit from the therapies delivered by devices like the ICD. 

Wathen MS, DeGroot PJ, Sweeney MO, Stark AJ, Ottemess MF, Adkisson WO, Canby RC, Khalighi K, Machado C, Rubenstein DS, Volosin KJ. Prospective randomized multicenter trial of empirical antitachycardia pacing versus shocks for spontaneous rapid ventricular tachycardia in patients with implantable cardioverter-defibrillators Pacing Fast Ventricular Tachycardia Reduces Shock Therapies (PainFREE Rx It) trial results. Circulation 2004 110 2591-6. 

Guerra JM, Wu J, Miller JM, Groh WJ. Increase in ventricular tachycardia frequency after biventricular implantable cardioverter defibrillator upgrade. J Cardiovasc Electrophysiol 2003 14 1245-7. 

CAD, coronary artery disease ICD, implantable cardioverter defibrillators MI, myocardial infarction Pts, patients SD, sudden death VF, ventricular fibrillation VT, ventricular tachycardia Yr, year EF, ejection fraction EP, electrophysiology SCD, sudden cardiac death. 

Bocker, D., et al.. Benefits of treatment with implantable cardioverter-defibrillators in patients with stable ventricular tachycardia without cardiac arrest. Br Heart J,... 

Even more severe than the diseases leading to cardiac pacemaker implantation is the sudden cardiac death (SCO). It is the most often reason for death in western industrial countries and accounts for 1200 deaths per day in the USA. SCD is caused by ventricular tachycardia or fibrillation and death occurs within minutes. The only possibility to overcome the tachycardia and to induce a regular heart beat is to delibrillate the heart. In these cases, instead of a normal cardiac pacemaker, a different implant has to be applied. Implantable cardioverter-defibrillators (ICD) have been developed in the 1980s and more than 25 000 devices have been implanted worldwide up to the mid... 

A potential case of an interaction between quinidine and flucloxacillin was demonstrated in a 63-year-old patient with recently diagnosed dilated cardiomyopathy who was admitted to the hospital with polymorphic ventricular tachycardia and ventricular fibrillation episodes induced by bradycardia. The patient was on a heart failure regimen of furosemide, spironolactone and perindopril, and was initiated on oral quinidine in the hospital for the prevention of ventricular arrhythmias. The patient s temporary pacemaker lead was removed and an implantable cardioverter-defibrillator was placed due to continued ventricular fibrillation. The next day, the patient became febrile. Culture of pacemaker lead tip and blood cultures were positive for S. aureus. Flucloxacillin and rifampin were initiated, but rifampin was discontinued due to the development of renal insufficiency and liver test abnormalities. These were normalised after rifampin was discontinued. The patient required continuous pacing to prevent ventricular tachycardia episodes, and quinidine was increased to 2800 mg per day (maximum daily dose). Quinidine plasma levels were subtherapeutic at 1.1 mg/L. The authors speculate that this interaction was due to quinidine being a substrate of Pgp and CYP3A4, and flucloxacillin s ability to induce these enzymes. While this may be a potential mechanism, the authors do not comment on how long the patient received rifampin. Rifampin is also a CYP3A4 inducer and could have been parf of fhe reason for fhe decrease in quinidine level [46 ]. 

Implantable cardioverter-defibrillator (ICD) if recurrent ventricular tachycardia. 

Patients with hemodynamically significant ventricular tachycardia or ventricular fibrillation not associated with an acute Ml who are resuscitated successfully (electrical cardioversion, pressors, amiodarone) are at high risk for death and should receive implantation of an internal cardioverter-defibrillator. 

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