Interactions of antiarrhythmic drugs and implantable devices in controlling ventricular tachycardia and fibrillation

Ventricular fibrillation (VF) has been induced at implantable cardioverter defibrillator (ICD) implant to ensure reliable sensing, detection, and defibrillation. Despite its risks, the value was self-evident for early ICDs: failure of defibrillation was common, recipients had a high risk of ventricular tachycardia (VT) or VF, and the only therapy for rapid VT or VF was a shock. Today, failure of defibrillation is rare, the risk of VT/VF is lower in some recipients, antitachycardia pacing is applied for fast VT, and vulnerability testing permits assessment of defibrillation efficacy without inducing VF in most patients. This review reappraises ICD implant testing. At implant, defibrillation success is influenced by both predictable and unpredictable factors, including those related to the patient, ICD system, drugs, and complications. For left pectoral implants of high-output ICDs, the probability of passing a 10 J safety margin is approximately 95%, the probability that a maximum output shock will defibrillate is approximately 99%, and the incidence of system revision based on testing is < or = 5%. Bayes' Theorem predicts that implant testing identifies < or = 50% of patients at high risk for unsuccessful defibrillation. Most patients who fail implant criteria have false negative tests and may undergo unnecessary revision of their ICD systems. The first-shock success rate for spontaneous VT/VF ranges from 83% to 93%, lower than that for induced VF. Thus, shocks for spontaneous VT/VF fail for reasons that are not evaluated at implant. Whether system revision based on implant testing improves this success rate is unknown. The risks of implant testing include those related to VF and those related to shocks alone. The former may be due to circulatory arrest alone or the combination of circulatory arrest and shocks. Vulnerability testing reduces risks related to VF, but not those related to shocks. Mortality from implant testing probably is 0.1-0.2%. Overall, VF should be induced to assess sensing in approximately 5% of ICD recipients. Defibrillation or vulnerability testing is indicated in 20-40% of recipients who can be identified as having a higher-than-usual probability of an inadequate defibrillation safety margin based on patient-specific factors. However, implant testing is too risky in approximately 5% of recipients and may not be worth the risks in 10-30%. In 25-50% of ICD recipients, testing cannot be identified as either critical or contraindicated.

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“…In general, sodium channel blocking drugs increase DFTs 155,156 . Lidocaine has a profound effect on DFTs 164,165 .…”

Section: Factors That Influence Required Defibrillation Shock Strengtmentioning

confidence: 99%

“…61 In general, sodium channel blocking drugs increase DFTs. 155,156 Lidocaine has a profound effect on DFTs. 164,165 Its volume of distribution is reduced in heart failure, and its half life is markedly prolonged in the presence of inadequate hepatic perfusion or liver disease.…”

Section: Antiarrhythmic Drugsmentioning

confidence: 99%

The Dilemma of ICD Implant Testing

Swerdlow

Russo

DeGroot

2007

Pacing Clinical Electrophis

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130

112

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“…Antiarrhythmic drugs are prescribed commonly to ICD patients 75–78 . Serious drug‐ICD interactions associated predominantly with the use of sodium‐ or potassium‐channel blocking (Vaughn‐Williams class IA, IC, or III) drugs have been reviewed 7,76,79 and are summarized in Table II. These interactions must be considered when antiarrhythmic drug treatment is initiated or the dose is altered 7 …”

Section: Troubleshooting Interactions With Icdsmentioning

confidence: 99%

Advanced ICD Troubleshooting: Part II

Swerdlow

Friedman

2006

Pacing Clinical Electrophis

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Failure to Deliver Therapy or Delay of TherapyAbsent or delayed therapy may be caused by programmed values (including human error), ICD system performance, or a combination of the two. The most common causes are ICD inactivation, VT slower than the programmed detection interval, SVT-VT discriminators, undersensing, and intradevice software interactions. Pacemaker-ICD interactions, once important, are now rare due to incorporation of dual-and triple-chamber pacemakers in ICDs. ICD InactivationIf detection is programmed OFF for surgery using electrocautery, reprogramming must be performed at the end of the procedure, a fact easily forgotten, especially in outpatient surgery. One study reported an unexplained 11% annual incidence of transient suspension of detection. 1 Medtronic ICDs sound an audible Patient Alert TM 6 hours after the ICD is programmed "off" to alert the patient to the possibility of inadvertent. 2 VT Slower Than the Programmed Detection IntervalIn most ICD patients, VT with cycle lengths >400-450 ms are tolerated well, while repeated inappropriate therapies are not. However, slow VT may be catastrophic in patients with severe LV dysfunction or ischemia. 2 All SVT-VT discrimination algorithms (except ELAs) 3-5 deliver less inappropriate therapies if the VT detection interval is programmed to a shorter cycle length so that fewer SVTs are evaluated. To prevent underdetection of irregular VT, the VT detection interval should be set at least 40-50 ms longer than the slowest predicted VT for consecutive-interval counting and 30-40 ms longer for X-of-Y or interval + interval-average counting. 5 It should be a longer cycle length if rapidly conducted SVT is unlikely or SVT-VT discrimination is reliable at long cycle lengths (ELA ICDs). A long VT detection interval is important in patients with advanced heart failure, Address for reprints: Charles D.

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