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Case 2 

Case 2
Chapter:
Case 2
Author(s):

Haran Burri

DOI:
10.1093/med/9780198727774.003.0002
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date: 05 March 2021

Introduction to the case

An 82-year-old woman had been implanted with a single-chamber ventricular pacemaker 6 years ago for atrial fibrillation (AF) with symptomatic bradycardia. She presented to the hospital with shortness of breath and twitching of the left pectoral region. Her pacemaker follow-up, performed 6 months ago, had been completely normal. The results of the device follow-up performed at that time are shown in Table 2.1, and the electrocardiogram (ECG) recorded at admission is shown in Figure 2.1.

Table 2.1 Device settings and tested parameters

Programming

Mode

VVIR

Rate

60-110bpm

Pacing output (bipolar)

2.5V/0.4ms

Sensitivity setting (bipolar)

2.8mV

Tests

Battery voltage

2.71V

Battery impedance

1200 ohms

Lead impedance (bipolar)

625 ohms

Capture threshold (bipolar)

1.2V/0.4ms

Sensing threshold (bipolar)

6.8mV

Question

What do you observe?

  1. A Ventricular undersensing

  2. B Ventricular oversensing

  3. C Ventricular non-pacing

  4. D Both A and C are correct

Answer

  1. A Ventricular undersensing

The pacing spikes in Figure 2.2 occur at exactly 60bpm (the baseline rate), with all spikes showing ventricular undersensing and non-capture. This should not be confused with non-pacing, which refers to the lack of delivery of a pacing spike where one is expected.

  • ➊ This beat could be interpreted as normal device function with pseudofusion, as the spike occurs almost simultaneously with the QRS complex. With pseudofusion, the pacing spike occurs at, or shortly after, QRS onset, but before the depolarization wavefront has reached the lead dipole. The pacing spike occurs during the myocardial refractory period and therefore does not capture the ventricle.

  • ➋ The ventricular spike occurs on the T-wave which may be potentially pro-arrhythmic, but this is not the case here, as there is no capture.

Figure 2.2 Annotated ECG recorded at admission

Figure 2.2
Annotated ECG recorded at admission

Comments

Subclavian crush

A chest X-ray showed complete lead section due to subclavian crush (Figure 2.3A). A chest X-ray had been performed shortly before the previous device follow-up by the patient’s general practitioner for cough and already showed signs of lead damage (Figure 2.3B).

Figure 2.3 Chest X-rays showing complete lead section due to subclavian crush (a) and evidence of lead damage 7 months ago, when device parameters were normal (b).

Figure 2.3
Chest X-rays showing complete lead section due to subclavian crush (a) and evidence of lead damage 7 months ago, when device parameters were normal (b).

This case illustrates how normal parameters (including impedance) do not rule out damage to a lead. This is of particular relevance in pacemaker-dependent patients who may be experiencing symptoms compatible with device dysfunction and in whom a chest X-ray and Holter recording should be performed if device interrogation does not elucidate the problem.

Subclavian crush may result from medial subclavian puncture and may be avoided by favouring axillary vein puncture or cephalic vein cutdown for lead implantation.