Implantable Cardioverter-Defibrillator Programming and Troubleshooting

Clinical History

As in all other areas of medicine, the keystone to diagnosis is the clinical history. Historical clues suggesting ICD malfunction, although by themselves nondiagnostic, provide the basis for a presumptive diagnosis and suggest further avenues of inquiry. For example, repeated shocks in an asymptomatic patient suggest false signal detection or an atrial arrhythmia. Certain body positions associated with ICD shocks suggest the possibility of lead fracture or lead instability. ICD model, manufacturer, date of implantation, lead type and location, antiarrhythmic drug history, presence or absence of symptoms of heart failure or angina preceding therapy, and other clues are important, because any or all of these factors may have relevance and can be related to ICD therapy. The presence of an implanted pacemaker with an ICD raises the specter of device-device interaction, a scenario that was only of historical interest in the last two decades but may now be seen again as pacemakers are implanted in patients with subcutaneous S-ICDs, and vice versa. Therapy during exercise raises the possibility of sinus tachycardia or of atrial fibrillation (AF) with a rapid ventricular response. Palpitations may signal either supraventricular tachycardia (SVT) or VT.

Physical Examination

The physical examination may be helpful in pinpointing the exact cause of ICD malfunction. For example, for a patient who reports that certain body positions or movements elicit ICD shocks, reproducing the precise maneuver or the exact circumstances known to elicit the shocks, while simultaneously telemetering the device, may prove the diagnosis of lead failure. Occasionally, patients are reluctant to allow the examiner to do this because the prospect of an ICD shock is psychologically threatening. In such circumstances, the ICD may be placed in a monitor mode, either by programming or with the use of a magnet to suspend tachyarrhythmia detection, at the same time assuring the patient that shock delivery will not occur. The assessment of recordings from the ICD in these situations is discussed later.

Because a common point of lead fracture occurs where transvenous ICD leads pass between the clavicle and first rib, manipulation of the device pocket or the lead entry point in the pectoral area may elicit electrical noise artifact, indicating lead conductor fracture. Similar artifacts may occur with a loose connection of the set-screw to the lead terminal pin in the ICD pulse generator header. Again, make-break potentials can be demonstrated by noninvasive telemetry, as discussed later.

Other diagnostic clues may be provided by the physical examination, such as detection of an irregular pulse suggestive of AF, which may be readily confirmed by an electrocardiogram. Congestive heart failure is often associated with exacerbation of ventricular arrhythmias. Therefore eliciting symptoms and signs of left ventricular decompensation suggests a possible cause for worsening arrhythmias.

Electrocardiographic Recordings

Objective evidence of the event precipitating ICD therapy, or of an arrhythmia with absence of the expected ICD response, can be extremely helpful and is usually diagnostic ( Fig. 38-1 ). In the days before the availability of stored electrograms (EGMs), such evidence was rarely available unless the patient was hospitalized and monitored at the time of the event. Fortunately, this is now a problem of the past. Nevertheless, even when EGMs are available, they can sometimes be inconclusive or confusing. In addition, if multiple ICD detections have occurred for any reason, including lead failure, SVT, or a VT or VF storm, EGM documentation of the initial event leading to detection may be overwritten because of limited device memory.

Device Telemetry

The advent of device telemetry has revolutionized and greatly simplified analysis of arrhythmias and events suspected of representing ICD malfunction. Early devices (e.g., Ventak, Cardiac Pacemakers [CPI/Guidant], St. Paul, MN) were able to emit sounds or beeps synchronous with ventricular EGM detection, enabling identification of oversensing or undersensing. When recorded with a phonocardiogram, a so-called “beep-o-gram” was produced. Although helpful, these crude attempts at telemetry were quickly supplanted by advances that enabled detailed information, such as R-R intervals and ventricular EGMs, to be telemetered ( Fig. 38-2 ). The complexity and sophistication of these diagnostic tools are increasing with the new generation of ICDs. The addition of the atrial channel has greatly simplified analysis of arrhythmic events ( Fig. 38-3 ).

Other diagnostic information is now routinely available from all ICDs, including battery voltage, pacing and sensing lead impedances, charge times, high-voltage lead impedance, and frequency and timing of ventricular events. The finding of a depleted battery, lead impedance out of range (either too high or too low), and R-R intervals can lead to correct diagnoses. The latter is extremely important, because nonphysiologic intervals (short) raise the suspicion of make-brake electrical noise artifact. One device (Medtronic, Minneapolis, MN) records information regarding both impedance changes ( Fig. 38-4 ) and nonphysiologic R-R intervals (“sensing integrity counter” [SIC], Medtronic, Minneapolis, MN).

Newer ICDs from all major manufacturers are capable of remote device telemetry from the patient's home. This capability offers two advantages over exclusively office-based interrogation. The first advantage is the ability to interrogate the ICD following a shock more quickly and easily. The second advantage is the ability to discover arrhythmias that may be asymptomatic ( Fig. 38-5 ). The third advantage is that most remote monitoring frequently assesses lead impedance changes and other parameters that may herald lead failure. The TRUST: Lumos-T Reduces Routine Office Device Follow-Up study showed that remote monitoring with automatic daily surveillance provides early detection of device events. Once a potential lead failure is identified by the device, the physician can be notified quickly, often quickly enough to intervene before lead failure produces a clinical event (i.e., shock for lead fracture). The CONNECT Trial demonstrated that remote follow-up of ICD significantly reduced the time from onset of clinical events (new onset atrial or ventricular arrhythmias, lead or device integrity problems) to clinical decisions compared with usual outpatient clinic follow-up. The role of remote monitoring in helping troubleshooting management is more extensively discussed in a separate chapter ( Chapter 40 ). Unfortunately, some device failures occur with adverse events happening so rapidly such as inappropriate shocks that early notification is impossible. Notably, even if mechanisms such as audible tones are available for patient notification, with increasing age more patients are unable to hear the alerts.

Radiographic Evidence

Radiographic evidence is helpful if lead malposition, dislodgment, or fracture is suspected ( Figs. 38-6 through 38-9 ). It is recommended, whenever possible, that chest radiographs taken immediately after ICD implantation be compared with radiographs obtained at the time of a problem. Such comparisons may reveal lead malposition and displacement when none is suspected. Radiographs can also be helpful in demonstrating conductor fracture or pin connectors improperly positioned in the header. Examining the radiographic “signature” of the device can help identify the device type when the patient is unaware of the ICD model or type. Knowledge of unique failure modes, such as “migration” of set screws (travel of the right ventricular fixation screw into the channel lumen during shipment) in particular families of ICDs, is of course desirable. Figures 38-6 and 38-7 show examples of lead dislodgment. Because the distal end of the lead is close to the tricuspid annulus (see Fig. 38-6A ), both atrial and ventricular signals are recorded (see Fig. 38-6B ). This leads to “double-counting,” which for a given heart rate, the ventricular channel registers twice the actual heart rate, satisfying the high rate detection requirement and leading to administration of a shock (see Fig. 38-6B ). Figure 38-7 shows a similar example, but the electrical artifacts are more disorganized and irregular, presumably because the lead is more free-floating. Figure 38-8 shows an example of disruption of a transvenous ICD lead as it passes between the clavicle and first rib. Figure 38-9 is an example of fracture of a subcutaneous ICD lead that was placed due to an elevated defibrillation threshold (DFT). The chest x-rays were obtained following an elevated impedance check on routine interrogation. Device revision was required.

Chest radiography may sometimes clearly show lead perforation, whether it be subacute or chronic. However, because accurate diagnosis in these situations can be critical given the competing risks of unnecessary device revision and unexpected device failure, 3D echocardiography and computed tomography scanning can be used to further evaluate lead perforation when questions arise.

Care must be taken to learn the appearance of the welds of the springs, because they can be mistaken for fracture if their usual appearance of being offset from the central axis of the lead is not appreciated ( Fig. 38-10 ). An unusual cause of lead failure, and sometimes failure of telemetry, occurs in “twiddlers”; in these cases, a lead is twisted and fractured ( Fig. 38-11 ) or the ICD is inverted. Lead perforation can occur subacutely or rarely chronically, leading to several problems including undersensing of ventricular arrhythmias, failure to convert ventricular arrhythmias, and failure of pacing as the lead tip exits the myocardium ( Fig 38-12 ).

Figure 38-13 shows chest x-rays obtained on a patient with an S-ICD. Proper positioning of the S-ICD can and the S-ICD lead is important to ensure an optimal shock vector.

Multiple Shocks

Multiple shocks ( Table 38-1 ) may be the result of incessant VT/VF, repetitive VT/VF, oversensing of T waves, electromagnetic interference, electrical noise artifacts from a fractured conductor or myopotentials in the case of insulation failure, or SVT including sinus tachycardia, AF, atrial flutter, or another mechanism. Sometimes the ICD itself can be proarrhythmic ( Box 38-1 ).