Single chamber ICD

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... 

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. 

Some devices have the ability to record an additional signal between the can and a shocking coil, which can mimic a surface EGG lead. This can also aid the interpreter in the troubleshooting process, particularly when dealing with a single chamber ICD. 

A 63-year-old male received a single chamber ICD for symptomatic VT. He comes into the office for his first follow-up and the device has recorded several events from the prior day. The tracing below is representative. 

Implantation of transvenous ICD systems employs techniques similar to those used for permanent pacemaker implantations, and is discussed in detail in a separate chapter in this book. Connecting ICD leads to the device is slightly different than connecting pacemaker leads to pacemaker generators. All ICD pulse generators have at least three ports for single chamber devices (four ports for dual chamber devices, and five ports for CRT-D). One LV port is for the pace/sense IS-1 terminal pin, and two are for the defibrillation coil (usually DF+ and DF-). The second DF port may be capped if a single coil... 

Optimal ICD device selection (single chamber, dual chamber, triple chamber) remains an issue regarding patient outcomes and cost-effectiveness. 

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. 

While upgrading a patient with CHF and a single chamber pacemaker to a biventricular ICD the following image is obtained. 

The thresholds of right and left ventricular pacing leads can be difficult to assess in ICDs that do not have separate programmability for each output. This is because the morphology change of the QRS complex on a single surface ECG rhythm strip can be very subtle when capture is lost in a ventricular chamber. Also, since many of the patients for which a CRT device has been implanted have a native left bundle branch block (LBBB) pattern on their surface ECG, the RV capture and native QRS complexes can look remarkably similar. 

A 70-year-old male with ischemic cardiomyopathy (BF 20%) and complete heart block was upgraded from a dual-chamber pacemaker to ICD due to inducible VT (225 b.p.m.). He comes into the office for evaluation after receiving his first shock. The ICD is programmed as a single-zone device, VF > 185 b.p.m. (all 31J shocks), and is not committed. You interrogate the ICD and find the following recorded event. 

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