Dual chamber ICD

FIGURE I5.I Schematic representation of a dual-chamber ICD. The generator is implanted in the pectoral region. The defibrillation lead (lower) is in the rightventricle, where it is fixed by a helix at the distal (far) end of the lead. The atrial lead (upper) is secured by flexible tines in the right atrial appendage. (Reproduced with permission of Medtronic, Inc.)... 

In many ICD systems, pacing and sensing are hmited to the right ventricle (single-chamber ICDs), and usually, only a single lead is required. More often, a pace-sense lead is also inserted via the same transvenous route and is fixed in the right atrium (dual-chamber ICD). The right atrial lead provides... 

Discrimination can be pattern based, morphology based, or a combination of the two approaches. In pattern-based discrimination, specific features of the time sequence of events are used to classify the rhythm as SVT. The patterns indicative of SVT include timing irregularity (unless all R-R intervals are shorter than a fixed cutoff), gradual acceleration of the R-R intervals, or, in dual-chamber ICDs, certain specific relationships between the timing of atrial and ventricular events. 

Sweeney MO, Ellenbogen KA, Casavant D, Betzold R, Sheldon T, Tang F, Mueller M, Lingle J. Multicenter, prospective, randomized safety and efficacy study of a new atrial-based managed ventricular pacing mode (MVP) in dual chamber ICDs. J Cardiovasc Electrophysiol 2005 16 811-7. 

ICDs come in both ventricular and dual chamber varieties. Dual chamber ICDs also afford pacemaker function in the atrium, and may, depending on the brand, have the ability to treat paroxysms of atrial tachyarrhythmias with rapid pacing and cardioversion therapies. 

The right atrial lead of a dual chamber ICD. limitations. 

Sensing in the atria for dual chamber ICD models utilizes the same methodology as that in the ventricles in the current generation of devices. 

As such, these discriminators can be considered for helping to differentiate sinus tachycardia (or any other SVT for that matter) from VT. This is particularly relevant in single chamber ICDs (dual chamber ICDs may not have such features available). However, the phenomenon of BBA during SVT can "fool" such discriminators. 

Atrial tachycardia (AT) is a rapid ectopic rhythm originating in one of the atria. The onset tends to be sudden. Its rate is usually found between about 130-240 b.p.m., and the rhythm may conduct in a 1 1 fashion to the ventricles. Thus, the rapidly conducted varieties may likely enter the detection zone(s) of the ICD. The atrial electrogram (AEGM) P wave morphology for a dual chamber ICD may show a noticeable change with the onset tachycardia, while the VEGM should remain the same absent BBA. 

A sudden onset function will not likely be of much use for the ICD to discriminate AT from VT since both can initiate in this fashion. A ventricular morphology or width discriminator may help, again in the absence of BBA. Not all ATs conduct each beat to the ventricles, so this information ( P waves > R waves) in a dual chamber ICD event recording may allow the interpreter to help rule in the diagnosis of SVT. It should be noted that dual tachycardias, i.e. SVT and VT, can coexist in which the number of registered P waves is still greater then the number of registered R waves. 

During VT the atria may act independently or not be activated retro-gradely in a 1 1 fashion. Absent a fast concurrent SVT, the number of detected R waves is greater than the number of P waves in a dual chamber ICD. When this occurs it is one of the easier rhythms for the EGM interpreter and ICD to recognize as truly being VT. 

A 52-year-old male with a history of paroxysmal AF refractory to anti-arrhythmic medicines and a dual chamber ICD implanted for VT presents to the ER because he had multiple shocks within a very short period of time. The ICD is programmed as a two-zone device VT zone 160-200 b.p.m., 26 J, then all 31 J shocks VF zone > 200 b.p.m., all 31 J shocks. There is a stability discriminator active in the VT zone. You evaluate the ICD and obtain the following EGMs just prior to one of the shocks. 

A 71-year-old male with a dual chamber ICD for primary VF arrest presents due to multiple shocks from his device. It is programmed as a single zone device with an initial 24 J followed by all 30 J shocks for rates > 188 b.p.m. You obtain the AEGM and VEGM surrounding one shock representative of all episodes. 

A 75-year-old male with chronic AF/flutter and medically refractory Class IV CHF (EF 8%) with LBBB receives a dual chamber ICD with left ventricular and right ventricular leads plugged, respectively, into the atrial and ventricular ports of the ICD. It is programmed DVIR 75 p.p.m. with an AV interval of 10 ms. On the day following implant the ICD nurse evaluates pacing thresholds. 

Both leads can deliver pacing due to the "D" in the DVIR mode. Only the right ventricular lead can sense given the "V" in the second position. Thus, biventricular pacing is effectively accomplished with the short AV interval, the risk of double counting is eliminated as there is no sensing from the LV lead, and the cost of the standard dual chamber ICD is significantly lowered from that of a traditional biventricular heart failure device. 

An 18-year-old male with hypertrophic cardiomyopathy receives a dual chamber ICD for prevention of SCD. On the day following implant an interrogation is performed and reveals a "non-sustained tachycardia" recorded in the logbook from the prior day. 

A 65-year-old female with a history of VT and paroxysmal AF (PAF) receives a dual chamber ICD that has a morphology discriminator programmed on in a VT zone. An example of the atrial and ventricular EGMs during sinus rhythm is obtained below. 

A 71 -year-old male with a dual chamber ICD implanted for VT 3 years ago is admitted following multiple shocks without warning. You interrogate the ICD and note multiple shock episodes and diverted/non-sustained episodes similar in appearance to the "rhythm" below (AEGM, VEGM, and shock EGM from top to bottom). The atrial lead impedance is 243 Q (631 Q at implant) and the ventricular lead impedance is 560 Q (700 Q at implant). You are able to reproduce the "rhythm" by having the patient cough and move the left arm. 

A 47-year-old female has a dual chamber ICD with atrial antitachyarrhythmia therapies programmed on. 

An 85-year-old male with a dual chamber ICD placed 4 years ago for VT is admitted for pleuritic chest pain. He also states that he has been having an "electrical" sensation in his chest for the past 2 weeks. A 12-lead ECG demonstrates changes consistent with pericarditis. Evaluation of the ICD up to this point in time has been unremarkable. ICD interrogation now shows the following lead impedances and real-time EGMs. There is no atrial pacing capture or output seen, even at maximum output. 

Prior to closing the pocket of a newly implanted dual chamber ICD interrogation of the system is performed with a sterile wand. 

Five months after undergoing piacement of a dual chamber ICD for inducible VT a 43-year-old female is admitted after receiving multiple shocks without warning. The weekly average lead impedances, as measured by the device, and a non-sustained "tachycardia" episode, recorded by the ICD, are seen below. 

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