Pacemaker

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Revision as of 01:53, 24 August 2009 by Drj (talk | contribs) (Failure of appropriate capture, ventricular)
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Author(s) J.S.S.G. de Jong
Moderator J.S.S.G. de jong
Supervisor
some notes about authorship


A pacemaker is indicated when the electrical impulse conduction or formation is dangerously disturbed. The paced pacemaker rhythm can easily be recognized on the ECG as it shows pacemaker spikes: vertical signals that represent the electrical activity of the pacemaker. Usually these spikes are more visible in unipolar pacing than in bipolar pacing.

In the first example image, the atria are being paced, but not the ventricles, resulting in a atrial paced rhythm. Accordingly the ventricular beat is delayed until the atrial signal has passed the AV node. In the second image the ventricles are paced directly, resulting in ventricular paced rhythm. As ventricular pacing occurs exclusively in the right ventricle the ECG shows a left bundle branch pattern. An exception to this rule is left ventricular pacing in patients with congenital anomalies and patients with an epicardial pacemaker that has been placed during surgery. Another exception is septal or RVOT placement of the pacinglead which results in a less widened to normal QRS complex.


A (used) DDDr pacemaker
Chest x-ray of a patient with a pacemaker
Ventricular paced rhythm shows ventricular pacemaker spikes
DDD paced rhythm
Atrial sensed, ventricular paced rhythm (tracking). Note the LBBB morphology with left axis deviation indicating the pacing lead in the right ventricular apex.
Atrial paced rhythm

Pacemaker Coding

Pacemakers can be categorized according to the NASPE coding system, that usually consists of 3-5 letters.

The revised NASPE/BPEG generic code for antibradycardia pacing[1]
I II III IV V
Chamber(s) paced Chamber(s) sensed Response to sensing Rate modulation Multisite pacing
O = None O = None O = None O = None O = None
A = Atrium A = Atrium T = Triggered R = Rate modulation A = Atrium
V = Ventricle V = Ventricle I = Inhibited V = Ventricle
D = Dual (A+V) D = Dual (A+V) D = Dual (T+I) D = Dual (A+V)

Commonly Used Pacemakers

The most often used codes are:

  • AAI: the atria are paced, when the intrinsic atrial rhythm falls below the pacemakers threshold
  • VVI: the ventricles are paced, when the intrinsic ventricular rhythm falls below the pacemakers threshold
  • VDD: the pacemaker senses the atrial en ventriculair events, but can only pace the ventricle. This type of pacemaker is used in patients with a reliable sinus node, but suffering from the results of an AV-block.
  • DDD: the pacemaker records both the atrial and ventricular rate and can pace one of each chambers when needed.
  • DDDR: as above, but the pacemaker has a sensor that records a demand for higher cardiac output and can adjust the heart rate accordingly.
  • Biventricular pacemakers (CRT-P): leads in both ventricles are present to synchronize contraction. The lead pacing the left ventricle is usually positioned in the coronary sinus. This cardiac resynchronization therapy can improve symptoms and survival in some heart failure patients. Several optimizing methods are being evaluated to find the most effective pacing delay between left and right ventricle, they include echocardiography, narrowest QRS finding and invasive hemodynamic measurements with pressure and flow wires.
  • ICD (Internal Cardioversion Device): this device can detect and treat Ventricular Tachycardia and Ventricular Fibrillation. ICDs are a seperate category and usually not put in the pacemaker category, although they do have a pacing function. Usually the first treatment is anti-tachy pacing (pacing at a rate +- 10% above the ventricular rate in ventricular tachycardia, which can convert the rhythm to sinus rhythm). If this is not effective an defibrillator shock is delivered, usually with 16-36 Joules of energy. ICDs can save lives in patients who have a high risk of ventricular arrhythmias. All ICDs have optional pacemaker activity to treat bradycardias. New biventricular ICDs have 3 leads: an atrial lead, a left ventricular lead and a right ventricular lead.
  • Biventricular ICDs (CRT-D): an ICD with biventricular pacing option.


Pacemaker Indications

A full list of pacemaker indications can be read in the ESC guidelines on cardiac pacing [2]. A selection of class I indications are: chronic symptomatic third- or second degree (Mobtiz I or II) atrioventricular block. Syncope with sinus node disease. Alternating bundle branch block. Persisting AV block after surgery.

ICD Indications

Atrial-sensed ventricular-paced rhythm

AV dual-paced rhythm

Pacemaker Malfunction

to be filled in ...

Failure of appropriate capture, atrial

Failure of atrial capture in a patient with atrial standstill, no P waves are seen after the atrial stimuli


Failure of appropriate capture, ventricular

Failure of ventricular capture

Failure of appropriate inhibition, atrial

Failure of appropriate inhibition, ventricular

Failure of appropriate pacemaker firing

Retrograde atrial activation

Pacemaker mediated tachycardia


External Links

Heart Rhytm Society


References

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  1. Error fetching PMID 11916002: [Bernstein]
  2. Error fetching PMID 17726042: [Vardas]
  3. Error fetching PMID 12379588: [Gregoratos]
All Medline abstracts: PubMed | HubMed