Pacemaker Rhythms

Pacemaker Rhythms ECG Interpretation #317

Introduction Part 1

Rhythms are often named according to the source of the electrical activity in the heart or the structure where the problem is occurring.
Pacemaker Rhythms are aptly named due to the locus of stimulation coming from an artificial impulse generator called a pacemaker.
The most common pacemakers may deliver an electrical impulse to the right atrium, right ventricle or both.
Artificial pacemakers are often implanted as a result of either a failure of the higher (faster) pacemakers within the heart or an irregular rhythm resulting in decreased cardiac output.
Remember, the fastest electricity in the heart (regardless of location or source) will dictate the heart rate.

Each rhythm in this category will share unique a morphologic feature which separate them from all other rhythms.
Pacemaker rhythms are identified by the presence of a conspicuous vertical mark known as a “spike”.
If the spike precedes the P wave, it is referred to as an Atrial Pacemaker rhythm.
If the spike precedes the ventricular depolarization, it is referred to as a Ventricular Pacemaker rhythm.
If there is a spike prior to the P wave and the ventricular depolarization, it is referred to as an AV (atrioventricular sequential) Pacemaker rhythm. Note: QRS complexes in Ventricular and Atrioventricular Pacemaker rhythms will have a wide, bizarre appearance (just like ventricular rhythms) and typically measure 0.12 seconds or greater.
After learning the unique features just described, it is simply a matter of recalling the unique feature and associating it with the corresponding waveform.

During implantation, pacemakers are programmed by the physician to provide electrical impulses at a specific strength of impulse (enough to cause depolarization) and with a certain rate to maintain cardiac output within a specific normal range.
Many pacemakers also are programmed to “sense” the inherent electrical activity occurring within the heart, so the device only turns on when needed and does not compete with the patients own natural electrical activity.
Sensing capability is an important safety feature in pacemakers to ensure the electrical impulse provided by the pacemaker does not inadvertently occur during the vulnerable period of repolarization (relative refractory period).

Unfortunately not all pacemakers work the way they should. According to Pub Med, an article titled “Complications related to permanent pacemaker therapy” (http://www.ncbi.nlm.nih.gov/pubmed/10353129): In a group of patients studied at Kuopio University Hospital, inadequate capture or sensing was observed in 7.4% of the patients.
A variety of problems can occur when is comes to pacemakers. The wire may not embed in the endocardium or pull out post-procedure, the device may oversense or undersense or fail to capture.

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