Pacing spikes

Fig. 1.11 Twelve lead ECGs demonstrating bipolar and unipolar atrial and ventricular pacing. With unipolar pacing, there are prominent atrial and ventricular pacing spikes (stimulus artifact).

After VF induction the asynchronous pacing spikes can be seen marching through the surface lead strip. The pacing spikes do not have any effect on the detection of VF as can be seen by noting the absence of undersensing on the marker channels. 

An atrial pacing spike sensed by the ventricular channel outside of the blanking period is a form of. ... 

First, the patient s AF is undersensed by the pacemaker as evidenced by the presence of atrial pacing. The first, second, third, and sixth atrial pacing spikes from the permanent pacemaker are oversensed as ventricular events by the ICD. This causes each of the subsequent paced QRS complexes from the pacemaker to fall into the ICD s VF detection zone. The first QRS is also double detected (sensed by the RV and LV leads at a different time). 

This phenomenon represents one of the other significant pacemaker/ICD interactions that can occur besides undersensing of VF. In fact if the atrial and ventricular pacing spikes are sensed at a fast enough rate the ICD can detect what it thinks is a tachyarrhythmia and deliver treatment. 

Pacemakers are identified on the ECG by a wide QRS (>0.11) and the presence of pacing spikes . Pacing spikes (Fig. 8.3) are small vertical lines seen just before either the P wave, the QRS complex or both. 

The location of the spikes helps to identify the type of pacemaker system in situ. A spike before a P wave denotes atrial pacing, whereas one before the QRS complex identifies ventricular pacing. Spikes before both P waves and QRS complexes can be either dual chamber (atria and ventricle) or Bi-v pacing. As both chambers are synchronized in the Bi-v system only one spike is usually visible. Figures 8.4 and 8.5 show single and dual chamber pacemaker systems. 

Fig. 8.4 Single chamber ventricular pacing (spikes before QRS complex)...

Fig. 8.6 Feiilure to Sense. Arrows show presence of pacing spikes on the ECO appearing at various points in the intrinsic cardiac cycle...

The pacemaker fires but fails to pace the myocardium. This can again be dangerous for the patient as they can be subject to the condition the pacemaker was inserted to treat if the pacemaker fails to work correctly. This is seen on the ECG by the presence of pacing spikes without a subsequently paced QRS complex or P wave (Fig. 8.7). 

This is the complete absence of pacing spikes and paced complexes where expected. The ECG often shows a gap in between complexes. This can be problematic for patients as it can decrease cardiac ontpnt (Fig. 8.8). 

Pacanakers can be identified on the ECG by the presence of pacing spikes. Pacing spikes indicate which of the heart s chambers are being paced. Pericarditis can be identified by widespread ST segment elevation in multiple leads, with a concave shape. 

ECG may show pacing spikes anywhere in the cycle, as shown below. 

Gragin, G.E. Clark, J.R. Pace, C.B. Comparison of Physically and Chemically Dispersed Crude Oil Toxicity Under Continuous and Spiked Exposure Scenarios, MSRC Technical Report Series Report 94-015, Marine SpiU Research Corporation, Washington, DC, 1994. 

Fig. 19.16 The Medtronic 9790 programmer generates a uniform amplitude pacemaker spike in response to any high-frequency transient. Although the paced rhythm can be seen in the background, the multiple pacing stimuli are arising from an unknown source extrinsic to the pacemaker and distorted the recording markedly impeding the pacing system evaluation.

An Ml pacemaker senses and paces only the atria. As shown in the shaded area below, a P wave follows each atrial spike (atrial depolarization).The QRS complexes reflect the heart s own conduction. 

A Wl pacemaker senses and paces the ventricles. When each spike is followed by a QRS complex (depolarization), as shown here, the rhythm is said to reflect 100% capture. 

Remember Visibihty of spikes depends on pacing polarity and type of lead. 

Knowing whether your patient has an artificial pacemaker will help you avoid mistaking a ventricular paced beat for a premature venticular contraction (PVC). If your facility uses a monitoring system that eliminates artifact, make sure the monitor is set up correctly for a patient with a pacemaker. Otherwise, the pacemaker spikes may be eliminated as well. 

If your patient has intermittent ventricular pacing, the paced ventricular complex will have a pacemaker spike preceding it, as shown in the shaded area of the top electrocardiogram... 

ECC) strip. You may need to look in different leads for a bipolar pacemaker spike because it s small and may be difficult to see. What s more, the paced ventricular complex of a properly functioning pacemaker won t occur early or prematurely it will occur only when the patient s own ventricular rate falls below the rate set for the pacemaker. 

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