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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Failure to capture:

    • – Pacing spike is not followed by a depolarization

  • Oversensing:

    • – Typically, the T wave or skeletal muscle potentials are sensed as depolarization, and a pacing spike is not initiated

  • Pacemaker-mediated tachycardia:

    • – Pacing at or near the programmed upper tracking rate limit secondary to retrograde conduction of the ventricular complex to the atrium, which is sensed as a P wave

  • Lead fracture is suspected when there is high lead impedance

  • Lead insulation failure leads to low lead impedance

  • Electromagnetic interference (eg, MRI scanners) may interfere with pacemaker function

GENERAL CONSIDERATIONS

  • Component failure can be intermittent, and a complete evaluation may not identify the problem initially

  • Activity before the clinical event is useful and should be sought

  • Pacemaker interrogation is critical in the evaluation

  • A complete evaluation includes history, examination, indication for pacemaker insertion, and review of imaging studies

  • Medications influence the pacing thresholds and should be examined

  • Lead dislodgement usually occurs soon after implantation

  • Exit block is a chronic problem, presumably related to fibrosis disturbing the electrode–myocardium interface (reduced by steroid-eluting leads)

  • Perforation and metabolic alteration (including medication) may raise pacing thresholds

  • Air in the pocket may result in pacing failure of unipolar pacemaker

  • Loose set screw manifests as failure to pace or capture

  • Overall, pacemakers are extraordinarily reliable; component failure is rare

  • Diaphragmatic stimulation is rare but may occur, in particular with biventricular devices

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Dizziness

  • Syncope

  • Fatigue

  • Palpitations secondary to excessive response from a sensor-driven pacemaker

PHYSICAL EXAM FINDINGS

  • Usually no change in findings

  • Myopotential oversensing can be brought on by isometric maneuver

  • Diaphragmatic pacing may be observed

DIFFERENTIAL DIAGNOSIS

  • Lead dislodgement

  • Loose connection between the lead and the pulse generator

  • Metabolic abnormalities such as hyperkalemia

  • Antiarrhythmic medication adverse effects

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Cardiac biomarker if undersensing is an issue and is not explained by other conditions

  • Basic metabolic panel to evaluate the causes of undersensing or failure to capture

ELECTROCARDIOGRAPHY

  • ECG with rhythm strip to identify the problem

IMAGING STUDIES

  • Echocardiogram may be useful when there is an intervening event such as myocardial infarction

  • Chest x-ray may help in evaluating lead fracture and definitely macrodislodgement

  • CT scan and echocardiogram may be helpful in cardiac perforation

DIAGNOSTIC PROCEDURES

  • Device interrogation

TREATMENT

CARDIOLOGY REFERRAL

  • Electrophysiologic evaluation is recommended for all patients

HOSPITALIZATION CRITERIA

  • Depends on underlying problem

  • If patient is pacemaker dependent, hospitalization is recommended

MEDICATIONS
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