Discussion
PPM malfunction is an infrequent cause for recurrent
syncope.1 PPM malfunction due to electrical connection
problems such as a loose set screw or lead-header malapposition, is
distinctly uncommon. 2, 3, 4, 5
The chest radiograph revealed that the RV lead terminal pin was not
fully inserted into or engaged in the pacemaker header (Figure 2). This
was suspected as the potential cause for the intermittent noise. The
patient was brought to the electrophysiology laboratory for lead
revision. Failure of complete lead terminal pin insertion was confirmed
intra-op (Figure 3). Both set screws were set but the distal set screw
was not fully contacting the terminal pin. The RV lead was extensively
tested using the pacing system analyzer revealing a bipolar threshold of
0.6 V at 0.4 msec and a pacing impedance of 630-660 Ω. New lead
insertion or lead extraction was not performed and the RV lead was fully
reinserted into the header and both set screws were tightened. At 22
months follow-up, the patient is asymptomatic without syncope or
lightheadedness and device function is normal.
Oversensing in cardiovascular implantable electronic devices (CIEDs) can
be defined as sensing of signals that are not caused by local
depolarizations and is often due to physiologic or non-physiologic
causes2. Non-physiologic causes of oversensing, often
referred to as noise, include electromagnetic interference (EMI), lead
failure, lead-header connection problems, myopotentials, and sensing of
extraneous pacemaker signals, such as those emitted by the minute
ventilation sensor.6, 7
Determining the cause of noise requires a step-by-step approach and
often involves a process of elimination. For example, if noise is due to
EMI (external source), it should be recorded on all channels which was
not the case in our patient. Lead component failure (fracture or
insulation breach) is the most common cause of non-physiologic
oversensing and is often associated with changes in impedance, sensing
or threshold. 2 Lead parameters were stable in our
patient. Oversensing of myopotentials (either due to diaphragm or
pectoral muscle) is often provocable with maneuvers such as deep
inspiration, isometrics, or straining.3 None of these
maneuvers elicited noise in our patient. Noise due to oversensing of
minute ventilation signals are also high frequency, intermittent and may
resemble those seen in our patient, but the Ingenio pacemaker has not
been involved in the recent Boston Scientific safety
advisory.8
Lead-header connection problems such as loose set screw or terminal
pin-header malapposition most often present soon after implantation. Our
case is unusual in its late presentation resulting in recurrent syncope
14 months after the initial implant. Because noise due to lead-header
connection problems is rare, it is often overlooked, but can be
recognized by its characteristic appearance − typically high frequency,
intermittent, with saturation of the amplifier. 9, 10Because of the intermittent make-or-break behavior of the connection
problem, changes in impedance, sensing and threshold may not always be
present.
Recurrent syncope after PPM implantation is a common problem, often
leading to emergency room visits, but is rarely due to PPM malfunction.
In a study evaluating 162 patients presenting with syncope after PPM
implantation, device malfunction was responsible for less than 5%
(8/162) of the episodes.1 Premature battery or primary
lead failure were responsible for all 8 cases and required either
generator change or new lead insertion. No lead-header connection
problems were noted. The etiology of the syncope was not found in
> 50% of patients in this cohort but hemodynamic causes
such as orthostasis were suspected.
The evaluation of a patient who presents with recurrent syncope after
CIED implantation includes device interrogation in addition to
orthostatic vital signs, electrocardiogram and routine laboratory
data.1 Chest radiography (CXR) is often performed in
the evaluation of PPM malfunction. While not systematically studied, the
reported yield of routine CXR is low. 1,11 This is
likely due to the fact that a lead insulation breach, micro-fracture or
micro-dislodgement are usually not visible on CXR. However, in our
patient, the CXR was valuable in helping find the cause for the noise.
Since CXR is a modality that is readily available, non-invasive and
relatively inexpensive, it has value and should be performed in the
evaluation of PPM malfunction.