implantable cardioverter-defibrillators and programming





arrhythmia  不整脈;

biventricular  両室型の;       

bundle branch block  脚ブロック... 房室束脚の伝導障害のため, 心室末梢に興奮が伝導されない状態;

coronary sinus  冠状静脈洞;

implantable cardioverter-defibrillator   植込み型除細動器; 

implantation surgery  移植手術;      

infraclavicular  鎖骨下の;    

palpitation  動悸;     

right ventricular apex  右心室尖部;

superior vena cava  上大静脈;          

tiered-therapy  段階的療法 ... 症状に応じて強度を高くすることが出来る;

ventricular fibrillation (VF)  心室細動;        

ventricular tachycardia (VT)  心室性頻脈 ... 心室内に起因し, 房室運動不調を伴う


ICD Pulse Generators and Leads



Implantable cardioverter-defibrillators (ICDs) are electronic devices that are implanted beneath the skin of the chest of the patient without major surgery to treat life-threatening arrhythmias.



ICDs can detect and stop ventricular arrhythmias and restore a normal heartbeat for patients to prevent sudden death.


To date, ICDs are very light (about 60 grams) and have multiprogrammable modes and advanced detection algorithms.  They can also pace for antitachycardia and antibradycardia (including dual-chambers), deliver biphasic shocks at strengths of less than 1 to 42 J, and record activities of the heart during arrhythmic episodes.



Since pulse generators are so small as to implant in the infraclavicular area and leads are placed transvenously in the cardial chambers, the implantation surgery has been very simplified.



ICDs can deliver shocks to stop atrial fibrillation, as well as ventricular tachycardia and ventricular fibrillation.



Biventricular ICDs can be used for patients who have advanced to class III or IV of heart failure and a bundle branch block.



Class III of heart failure ... Marked limitation of physical activity. Comfortable at rest. Less than ordinary activity causes fatigue, palpitation, or dyspnea.



Class IV of heart failure ... Unable to carry on any physical activity without discomfort. Symptoms of heart failure at rest. If any physical activity is undertaken, discomfort increases.


ICDs having a single lead that contains a pacing-sensing electrode and two defibrillating coils can be used.



If the single-lead type ICDs cannot adequately stop defibrillation, a subcutaneous patch electrode or subcutaneous array can be used. 



ICDs having a pulse generator operates as an electrode and a lead that is placed at the right ventricular apex and that has a proximal pacing-sensing electrode and a distal defibrillating coil electrode can be also used.



In ICDs, a chest wall patch electrode and defibrillating electrodes in the right ventricular apex, superior vena cava, or coronary sinus can be used in combinations.



For a biventricular ICD, a lead is inserted into a branch of the coronary sinus to pace left ventricle.


Programming of ICDs



To prevent patients from receiving inappropriate shocks and thus negative outcome, ICDs should be appropriately programmed.



When ICDs are implanted, the energy necessary to stop defibrillation is determined.



If the patient has episodes of ventricular tachycardia, antitachycardia pacing should be programmed to stop this symptom.



Tiered-therapy type ICDs can use two ventricular tachycardia zones and one ventricular fibrillation zone to individually treat patients with ventricular arrhythmias that have different heartbeat rates.



The defibrillation threshold and sequences of antitachycardia pacing and low-or high-energy shocks can be programmed for each of the two ventricular tachycardia zones.



The ventricular fibrillation zone is a high-heartbeat rate zone in which high-energy shocks are delivered.



When ICDs are properly programed, patient discomfort can be minimized, the chance of syncope with an arrhythmia episode can be reduced, the battery life of the pulse generator can be prolonged, and inappropriate shocks can be prevented.