0071643192.pdf

PACEMAKERMALFUNCTION

CAUSES

■ Failure to pace

■ Failure of pacemaker to output signal

■ Wire fracture/displacement

■ Battery depletion

■ Failure of myocardium to capture signal

■ Wire fracture/displacement

■ Elevated myocardial threshold from fibrosis, metabolic derange-

ment, ischemia, hypoxia

■ Undersensing

■ Failure of pacemaker to sense native impulses → paced beats in addi-

tion to native beats.

■ Causes similar to “failure to pace”

■ Oversensing

■ Unexpected pacemaker sensing of extracardiac “false” impulses with

pacer in inhibit (“I”) mode →no paced beat.

■ False impulses may include pectoralis muscle contraction, electro-

cautery, digital cell phones.

■ Inappropriate pacemaker rate (“runaway pacemaker”)

■ Rare

■ Dual chamber pacemaker in synchronous AV pacing mode

■ PVC→retrograde atrial depolarization →sensed by atrial lead →

paced ventricular impulse →retrograde atrial depolarization, etc.

SYMPTOMS/EXAM

■ With exception of runaway pacemaker, symptoms are similar to those that

prompted pacemaker placement.

■ Syncope or near syncope

■ Dyspnea

■ Palpitations

DIAGNOSIS

■ Evaluation of rhythm strip or ECG (see Table 1.12)

■ CXR for wire fracture/displacement

■ Usually close to generator or within the heart

■ Pacemaker function/battery assessment via cardiologist

RESUSCITATION

TABLE 1.12. ECG Findings in Pacemaker Malfunction

ECG FINDING PACEMAKERMALFUNCTION

Absence of pacer spikes when indicated Failure to output signal

Pacer spikes, but no depolarization Failure to capture signal

Pacer spikes despite native beats Undersensing native beats

External motion or interference pattern Oversensing

with absence of pacer spikes