Color Atlas and Synopsis of Electrophysiology, 1st Ed.


Kelly M.W. McDonnell, DO, Shawn Campbell, MEM, Kenneth A. Ellenbogen, MD, FHRS


A 75-year-old man is seen in the emergency department after receiving multiple shocks from his ICD. He has a history of symptomatic bradycardia, coronary artery disease, ischemic cardiomyopathy, ejection fraction of 20%, and New York Heart Association class II heart failure. A dual chamber ICD was implanted 5 years earlier for primary prevention. The patient has a history of nonsustained ventricular tachycardia with no history of previous ICD therapy delivery. He denies change in medications or clinical status. He has had consistent follow-up with normal device function and lead parameters since implant. Evaluation of the clinical event is demonstrated with the interval plot in Figure 74-1 and the electrograms in Figure 74-2. This demonstrates the appearance of multiple ventricular-sensed events accelerating into the ventricular fibrillation zone and the delivery of multiple shocks during a single event prior to termination.


FIGURE 74-1 Interval plot showing multiple shocks for a patient with a lead fracture. The v-v intervals are less than 200 ms and are non-physiologic.


• This is a case of nonphysiologic ventricular-sensed events on the ventricular lead resulting in the classification of ventricular fibrillation and delivery of therapy. Careful evaluation of all telemetered information is required to fully evaluate and classify therapy as appropriate or inappropriate.

• A complete evaluation includes assessment of lead integrity (sensing, impedance, and threshold values), lead parameter trends, device implant history, and imaging studies.

• The differential diagnosis of these events includes both physiologic and nonphysiologic events, such as ventricular fibrillation, lead noise, and electromagnetic interference (EMI).


The delivery of appropriate therapies is the pièce de résistance of ICDs. The delivery of multiple shocks can lead to great psychological distress; including depression for patients. When this occurs secondary to oversensing of nonphysiologic events, patients can develop fear and distrust of the reliability of the device designed to save their lives. Rapid intervention to prevent further shocks is essential. If therapy is found to be inappropriate secondary to noise, immediately inactivate all therapies while the patient and the device are evaluated.

The etiology of lead noise can be differentiated based on the number of leads demonstrating noise.

• Noise that is sensed on multiple leads suggests EMI.

• Noise sensed on a single lead can occur secondary to loose set screw, lead fracture, conduction failure, lead dislodgement, or air in the header.

Lead noise can represent lead integrity failure. In 2011, 150 386 new right ventricular ICD leads were implanted in the United States.1 Lead failure is estimated to occur in 0.58% per year of modern ICD lead implants.2


The approach to determining the etiology of noise artifact in this case includes assessing multiple aspects of the device.

• Clinical history: The patient’s history may provide key insight into the etiology of the noise artifact. Inquiry into possible sources of EMI should be made; including magnetic sources, TENS units, or operation of high voltage equipment.

• Implant information: Evaluate the device indication, implant techniques, leads used, or need for device revisions. Timing of noise from device implant or generator change should also be identified.

• Electrocardiogram (ECG): A 12-lead ECG should be performed on all patients with implantable devices. This allows for evaluation of the paced morphology. In particular, it is essential in patients with biventricular devices to assess pacing morphology. It is also useful to compare the implant ECG to the presenting ECG. Sudden change of a right ventricular-paced morphology from a left to right bundle branch block pattern may suggest lead migration or septal perforation.


FIGURE 74-2 Intracardiac electrograms from patient with prior dot plot (74-1) showing noise. The tracing shows the typical sporadic, intermittent, high frequency non physiologic signals recorded from the sensed bipolar electrogram.

• Chest X-ray (CXR): Ideally the implant CXR should be compared to a current CXR to assess the device system. The CXR should be used to assess the device location, course of the lead near the clavicle and first rib junction, evaluation of the header with visualization of the lead pin across the set screw, lead integrity with breach of the insulation, and the position of the leads in the cardiac chambers. Comparison with the original CXR will assist with identification of lead position changes or dislodgement. The CXR may also identify defects in the lead or positioning of the lead in the header of the pulse generator.

• Interrogation: A complete device interrogation should be performed on all patients who are identified with lead integrity issues. Lead parameters, programming, trends, histograms, and mode switches should all be clearly assessed. The diagnostic evaluation should also include further maneuvers to exclude myopotential sensing.

 Images Sensing counters: Attention should be paid to sensing counters, which will rapidly identify nonphysiologic-sensed signals, which are termed “short V-V intervals” in Medtronic devices. These counters identify ventricular-sensed events that occur at very short cycle lengths and are suggestive of lead damage (Figure 74-3).


FIGURE 74-3 Interrogated data for patient with the lead fracture showing an elevated sensing integrity counter.

 Images Lead diagnostics and trends: Sudden changes in a lead parameter typically indicate acute fracture or dislodgement of the lead, versus slow, chronic changes that may indicate changes at the electrode myocardial interface or lead failure. It is important to know that data trends are developed by daily measurements on the leads and represent only a single point in time and do not collect continuous information about lead function. Therefore, lead integrity problems may not be highlighted if there is intermittent noise or artifact (Figure 74-4).


FIGURE 74-4 Telemetry data showing normal right ventricular (RV) and superior vena cava (SVC) defibrillation impedance.

• Lead recalls: It is prudent to have knowledge of all lead recalls or leads with a higher failure rate. Although all leads carry a risk of lead failure, leads with particular problems should be assessed regularly and have active alerts in place to rapidly identify problems with the lead function.

This patient has lead noise secondary to a lead fracture. His intrinsic rhythm can be seen through the noise artifact (Figure 74-5). He has a Sprint Fidelis RV defibrillation lead with a previously recognized increased risk of lead failure.


FIGURE 74-5 Intracardiac tracing (atrial electrogram on top, RV pace/sense electrogram in the middle and marker channel on bottom showing noise and non physiologic signals on the right ventricular electrogram.


The initial management of this patient includes disabling therapy for VT/VF to prevent further unnecessary shocks. He will then need replacement of the ICD lead. The options are replacement of the ICD lead with a new ICD lead if the vein is patent, placement of a new pace-sense lead (again assuming the vein is patent), or lead extraction of the failed ICD lead and placement of a new ICD lead.

Device algorithms have been designed to deal with lead noise. These algorithms include noise reversion algorithms, lead noise algorithms, and lead integrity alerts (LIA).

• Noise reversion algorithms protect against pacing inhibition from artifact sensing. The response to sensed-rapid signals suggestive of nonphysiologic artifact is transient reversion to asynchronous pacing. These algorithms are more difficult to implement in ICDs due to the need to recognize ventricular fibrillation and the risk of undersensing ventricular fibrillation and withholding appropriate therapy.

• Lead noise algorithms (RV lead noise) compares near field electrograms to far field electrograms to determine the presence of noise when short V-V events occur. Noise should be isolated to the near field electrogram (RV tip to RV ring sensed channel in a dedicated bipolar ICD lead). If short V-V intervals are noted on both near field and far-field electrograms, then one must be concerned about EMI, noise not limited to the ICD rate sense component, or a true ventricular arrhythmia. If the event is classified as noise, a timeout window is initiated for a nominal 45 seconds, during which detection and therapy is withheld. After the timeout period is completed, redetection is initiated.

• Lead integrity alerts (LIA) are in place to identify possible lead failures and were created for the Sprint Fidelis lead. When two of the three components have fallen outside of the normal parameters, an audible alert sounds for the patient and a transmitted report will be sent to the physician if remote monitoring is being utilized. The components are:

 Images Greater than 30 short V-V intervals (≤130 ms) in 3 days.

 Images Abnormal RV lead impedance, defined as a significantly higher or lower value then the calculated baseline. Specifically, a 75% increase or 50% decrease from baseline.

 Images Nonsustained ventricular episodes (>2 events) with >5 intervals that are shorter then 220 ms.

If noise has been identified and is determined to not be due to lead failure, programming changes can be made. Sensitivity can be increased, but testing to make certain that ventricular fibrillation can still be sensed is mandatory. The VT/VF detection intervals or durations can also be extended. If there is significant concern or proof of lead failure, then ICD lead replacement is necessary.


Patients with lead concerns should be followed very closely and have remote monitoring for early identification of a problem. Efforts should be made for early intervention and lead revision. After lead revision, the patients will require regular follow-up per standard guidelines for device implants.


1. Kremers MS, Hammill SC, Berul CL, et al. The National ICD Registry Report: version 2.1 including leads and pediatrics for years 2010 and 2011. Heart Rhythm. 2013;10(4):e59-e65.

2. Kalahasty G, Ellenbogen KA. Management of the patient with implantable cardioverter-defibrillator lead failure. Circulation. 2011;123:1352-1354.

3. Al-Ahmad A, Ellenbogen KA, Natale A, Wang PJ. Pacemakers and Implantable Cardioverter Defibrillators. Minneapolis, MN: Cardiotext; 2010.

4. Ellenbogen KA, Kay GN, Lau CP, Wilkoff BL. Clinical Cardiac Pacing, Defibrillation and Resynchronization Therapy. 4th ed. Philadelphia, PA: Elsevier; 2011.

5. Swerdlow CD, Gunderson BD, Ousdigian KT, et al. Downloadable algorithm to reduce inappropriate shocks caused by fractures of implantable cardioverter-defibrillator leads. Circulation. 2008;118:2122-2129.