ECG 1a. The ECG above belongs to a 65 years-old woman who had been implanted DDDR type pacemaker 2 weeks ago.
As seen in the middle of the tracing, the pacemaker senses the atrial depolarization (P wave) by its atrial electrode and after
waiting for a pre-programmed AV delay (150 msec),
ventricular electrode gives stimulus (spike) which fails to produce a wide
QRS complex at the expected time
(pacemaker fails to capture the ventricle). Thereafter, a short-lasting narrow QRS complex
nodal escape rhythm
arises. In this patient, the cause of failure to capture is displacement of the tip of right ventricular
electrode.

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ECG 1b. Another ECG from the same patient, before realignment of the ventricular electrode. Since the electrode in the right
atrium is functioning properly, the pacemaker always senses atrial depolarization (P wave) and gives
stimulus (spike) from the
ventricular electrode
after 150 msec. However it fails to produce wide QRS complex at the expected time since the tip of the
ventricular electrode does not contact the myocardium. When it recurs
for the second time a narrow QRS complex nodal
escape beat arises. Thereafter,
the ventricular electrode succeeds in stimulating the ventricle (capturing the ventricle)
and produces a pacemaker induced wide QRS complex
.

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ECG 1c. The same patient's ECG, still before revision of the electrode. Since the electrode in the right atrium is functioning
properly, the pacemaker always senses atrial depolarization (P wave) and gives
stimulus (spike) from the ventricular electrode
after 150 msec. However it fails to produce wide QRS complex at the expected time since the tip of the ventricular electrode
does not contact the myocardium. When it recurs
for the second time a narrow QRS complex nodal escape beat arises .
Thereafter, the ventricular electrode succeeds in stimulating the ventricle (capturing the ventricle) for 5 cardiac cycles and
produces pacemaker-induced wide QRS complexes.

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ECG 1d. The above ECG was recorded after repositioning the ventricular electrode. Now, the pacemaker is functioning
normally. Since atrial rate (P wave rate) is fast enough (above the preprogrammed lower limit of the atrial rate of the
pacemaker), the atrial electrode does not stimulate the right atrium. Therefore no spike is seen before the P waves.
As mild change in atrial rate is normal, a change of the interval between pacemaker-induced QRS complexes
following the P waves is also normal.

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ECG 2. Pacemaker dysfunction.
Blue arrows show the spikes which successfully resulted in ventricular stimulation.
Red arrow
shows the spike which did not succeed in depolarizing the ventricles (pacing dysfunction, failure to capture).
Green arrow shows the ventricular premature beat.

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ECG 3. Pace dysfunction.
Blue arrows show the spikes which successfully resulted in ventricular stimulation.
Red arrows show the spikes (pacing dysfunction) which did not succeed in depolarizing the ventricles.
Green arrows show the ventricular escape rhythm.

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