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** Venous thrombosis (vena cava superior syndrome, deep vein thrombosis, lung embolism) | ** Venous thrombosis (vena cava superior syndrome, deep vein thrombosis, lung embolism) | ||
==ICD== | ==Implantable cardioverter defibrillators (ICD)== | ||
* | An ICD is a device that monitors heart rhythms. If it senses dangerous rhythms, it delivers shocks or anti-tachypacing (ATP) therapy. Many ICDs record the heart's electrical patterns when there is an abnormal heartbeat. | ||
[[File:temp.jpg|thumb|none|VB ECG shock strook]] | |||
[[File:temp.jpg|thumb|none|Plaatje ICD met lead, pulse generator, header, insulation, etc]] | |||
Nowadays, transvenous ICDs can also deliver pacing therapy if necessary. If a patient does not have an indication for pace-therapy, the pacemaker in the ICD is programmed at ''VVI 40 bpm'' (see above pacemaker programming). | |||
===Patients=== | |||
Many ICD trials have been performed to establish the ICD indications, particularly in ischemic and dilated cardiomyopathy. Indications for ICD therapy can be divided into secondary and primary prevention. Basically, the indications are expanding from secondary to primary prevention, depending on the underlying heart disease. | |||
[[Link to ICD indications]] | |||
[[Link to ICD trials]] | |||
===Secondary prevention=== | |||
Secondary prevention is therapy for patients who have already suffered a cardiac arrest or syncopal/hypotensive ventricular tachycardia. All patients who are resuscitated from VT/VF or who experienced spontaneous hemodynamic non-tolerated sustained VT ''in the absence of a reversible cause'' (e.g. acute myocardial infarction or electrolyte disturbances) have an indication for ICD therapy, regardless of the type of underlying heart disease. | |||
===Primary prevention=== | |||
Primary prevention is therapy that is given in order to prevent sudden death in patients who have not yet suffered a life-threatening sustained ventricular arrhythmia, but who are at high risk of such an arrhythmia. ICD therapy is effective in patients with a low left ventricular ejection fraction (LVEF) ≤30% more than one month after myocardial infarction that never had shown any ventricular arrhythmia (MADITT II trial). Additionally ICD therapy appeared to be effective in patients with ischemic or dilated cardiomyopathy and a LVEF of ≤35% and congestive heart failure NYHA class II or III. | |||
Patients do not meet the evidence based ICD implantation criteria if they have (1) a myocardial infarction within 40 days before ICD implantation; (2) newly diagnosed heart failure at the time of ICD implantation without prior therapy; (3) NYHA class IV symptoms of congestive heart failure. | |||
===Implantation=== | |||
ICDs are implanted under local anaesthesia in a sterile operating room or catheterization laboratory. Transvenous ICD implantation starts, like pacemaker implantation, with inserting the ICD leads in the left or right cephalic vein. Fluoroscopy is used to ensure the appropriate location in the atrium or ventricle. Leads are often positioned in the auricle of the right atrium and/or the right ventricular apex. | |||
After implantation, defibrillation testing is done by inducing VT/VF to test the ICD system and determine the defibrillation threshold. | |||
Device measurements | |||
Also device measurements will be done during and after ICD implantation. These are indicators of device and lead functioning and are comparable to the measurements in pacemaker systems (see above). Heart signal, sensing and pacing thresholds and lead impedance will be measured implantation: | |||
* '''Heart signal:''' Real time intracardial electrocardiograms are measured. During follow up, sudden and significant decrease or disappearance of amplitudes and/or slew rates for P and/or R waves can be a sign of lead- or device problems and are further investigated. | |||
* '''Sensing and pacing thresholds:''' During ICD implantation baseline sensing and pacing thresholds are measured. During follow-up the sensing and pacing thresholds will be compared to the chronic baseline. Significant increases or decreases may be indicative for lead- or device problems and are further investigated. | |||
* '''Lead impedance:''' During ICD implantation baseline lead impedance is measured. During follow-up lead impedance is compared to the chronic baseline. Decreases of pacing impedances may be indicative of insulation failure. Sudden and significant increases in pacing impedance may be indicative of conduction fracture. | |||
* '''Battery status:''' Battery status is determined during implantation and every follow up visit. | |||
===Programming=== | |||
In order for and ICD to deliver therapy for specific tachyarrhythmias, it needs a reliable method to sort out arrhythmias, group them by categories (e.g. supraventricular tachycardia (SVT) and ventricular tachycardia (VT)) and make a determination as to when therapy delivery is mandated. Different ICD variables can be programmed in different ICDs, depending on the ICD manufacturer. Mainly, these ICD variables can be programmed: | |||
===Arrhythmia detection zones=== | |||
The ICD diagnoses rhythm disorders by counting intervals on the intracardiac electrogram. This is a rate-based detection scheme that can be adjusted to meet the individual patient’s needs by programming. The ICD counts the current interval as one value and then average of the current interval and the preceding intervals. If these intervals fall into the same category, the event is binned in that category. If both events are tachycardia of fibrillation, but not in the same category, the interval is binned in the higher category. | |||
The arrhythmia detection zone is the category in which a predefined therapy will be given: | |||
* '''Monitor zone (e.g. 160-180 bpm):''' All events in this zone will be recorded in the ICD and can be seen during follow up visits, however no therapy is given. | |||
* '''Fast VT zone (e.g. 180-240 bpm):''' All events in this zone will be recorded in the ICD and can be seen during follow up visits. Therapy is given or not if the arrhythmia satisfies several criteria, which are programmed as well, such as SVT/VT discriminators. | |||
* '''VF zone (e.g. >240 bpm):''' All events in this zone will be recorded in the ICD and can be seen during follow up visits and therapy is given immediately. | |||
{| class="wikitable" border="1" | |||
|- | |||
! SVT discriminators: | |||
|- | |||
| | |||
# waveform morphology (broad vs. small complex or comparison of morphology with template of normal QRS wave) | |||
# onset of arrhytmia (sudden vs. slowly) | |||
# stability of arrhythmia (regular vs. irregular) | |||
# relationship between P- and R-waves (atrial lead required) | |||
|} | |||
===Numbers of intervals to detect / Time to detect=== | |||
The ICD diagnoses an arrhythmia when a sufficient (and programmable) number of events in an event sequence are binned. This is usually stated in an “X out of Y” pattern, such as 12 out of 16 intervals. | |||
===Therapy=== | |||
* '''ATP:''' ATP refers to the use of pacing stimulation techniques for termination of monomorphic ventricular tachyarrhythmias. Such techniques offer the potential for painless termination of VTs. | |||
* '''Shock:''' High voltage shocks are given to restore VT/VF into sinus rhythm. | |||
Different detection schemes and therapies can be programmed for different categories. For example, ATP may be appropriate treatment for slow VTs and shock therapy is an appropriate treatment for VF. After therapy is deliverd, the ICD monitors the next intervals to redetect sinus rate (which means the therapy worked) or redetect the arrhythmia (which results in resumed therapy). | |||
===Follow up=== | |||
Like pacemaker implantation, the first 6-8 weeks after transvenous ICD implantation, patients are advised not to over-stretch their arm on the same side as the ICD (such as golf, swimming etc.) to allow time for the lead to mature. | |||
Control visits for ICD are usually every 6 months. During this visit several electrical parameters are measured: battery status, sensing and pacing thresholds and impedance of all leads (see above). | |||
===Complications=== | |||
Also in ICDs problems of undersensing, oversensing, non-capture, changes in impedance, operative failures and long-term complications can occur (see above at pacemaker complications). | |||
Additionally, a major complication in some patients with ICDs is the occurrence of inappropriate shocks. An inappropriate shock is shock therapy for anything else but ventricular fibrillation or ventricular tachycardia. This can be due to, for example, supraventricular tachycardia with fast ventricle response (including sinus tachycardia and atrial fibrillation), T-wave oversensing, detection of physiological- or other non-cardiac activity and lead- or device failure. | |||
===Cardiac resynchronisation therapy (CRT)=== | |||
CRT-pacemaker (CRT-P) is a biventricular pacemaker with leads in both ventricles to ensure synchronized contraction. A CRT-defibrillator (CRT-D) is an ICD with biventricular pacing option. | |||
In appears that atrio-ventricular and intraventricular conduction delays further aggrevates left ventricular (LV) dysfunction in patients with underlying cardiomyopathies. Notably, left bundle branch block (LBBB) alters the sequence of LV contraction, causing wall segments to contract early or late. Dyssynchrony seems to represent a pathophysiological process that directly depresses ventricular function, causing LV remodelling and congestive heart failure and as a consequence causes a higher risk of morbidity and mortality. Atrio-biventricular pacing (CRT) for patients with symptomatic heart failure and intra- or interventricular conduction disturbances has proved beneficial. | |||
===Patients=== | |||
CRT-P or CRT-D appears to be effective in patients with NYHA function class ''III/IV'' for congestive heart failure, LVEF ≤35%, QRS width ≥ ''120 ms'' (especially LBBB) who are on optimal medical therapy. Patients with NYHA function class IV should be ambulatory (no admissions for heart failure during the last month and a reasonable expectation of survival > 6 months). | |||
[[Link to CRT indications]] | |||
Also patients with NYHA function class II, LVEF ≤35%, QRS width ≥ ''150 ms'' (especially LBBB) who are on optimal medical therapy are appropriate patients for CRT-D therapy. | |||
===Implantation=== | |||
CRT-P or CRT-D implantion requires implantation of three transvenous leads: | |||
* Right atrial lead | |||
* Right ventricular lead | |||
* Left ventricular lead (positioned in the coronary sinus) | |||
[[File:temp.jpg|thumb|none|Plaatje CRT positie]] | |||
===Programming, follow up and complications=== | |||
Programming should specifically aim at ensuring atrial-synchronous permanent biventricular pacing, by performing AV-interval optimization (echocardiography guided or using invasive haemodynamic measurments) and performing ventricular-ventricle (VV) interval optimization. Further programming, follow up and complications are similar to pacemakers and ICDs (see above). | |||
==References== | |||
- Vardas et al. Guidelines for cardiac pacing and cardiac resynchronization therapy. Europace 2007 | |||
- Epstein et al. Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities. Heart Rhythm 2008 | |||