Single chamber pacemaker

Permanent pacing of the heart has been possible since the 1950s (Kasper 2015). Earl Bakken, co-founder of the Medtronic company, developed the first wearable pacemaker in 1957. The device was worn with a chain around the neck, and the electrodes were guided directly to the myocardium via a thoracotomy (Detho 2009).

In 1958, Senning implanted the first pacemaker. This was a simple chamber pacemaker with a fixed stimulation frequency (Gertsch 2008).

The patient, Arne Larsson, had a complete thigh block with Adam Stokes seizures, which caused him to lose consciousness up to 30 x / d. The pacemaker had to be replaced after a few hours. Although the device had to be replaced after a few hours and several times in the following weeks, Larsson was highly satisfied. He died of carcinoma at the ripe old age of 86 (Detho 2009).

Programmable pacemakers have been classified since 1988 by the International Nomenclature of Pacing Systems, the so-called NBG code (Bauch 2002).

A single-chamber pacemaker is an implantable electronic device that stimulates cardiac activity at the atrial or ventricular level (Ebert 2005).

The pacemaker system is connected to only one electrode, which is located either in the right ventricle (VVI) or in the right atrium (AAI) (Bob 2001).

Single-chamber pacemakers are the only system that can be implanted without electrodes (Herold 2022).

The single-chamber pacemaker consists of a titanium housing, the so-called pacemaker unit, which contains a lithium battery as well as the electrical circuits (Detho 2009). The aggregate is connected to an electrode placed at different locations in the heart (Bob 2001). The battery must be replaced every 5-10 years, depending on how often it is used (Detho 2009).

Single-chamber pacemakers are differentiated between:

• Atrial demand pacemaker (AAI).

In this case, perception and stimulation take place exclusively at the atrial level (Ebert 2005). Stimulation of the right atrium is indicated in the ECG by a spike of intrinsic excitations (Bob 2001). Excitation of the ventricles occurs via their own AV- conduction, so that the QRS- complex is not deformed in the ECG (Fischer 2013).

• Ventricular demand pacemaker (VVI).

Here, perception and stimulation occur exclusively at the ventricular level (Ebert 2005) and only - as the name suggests - when needed (Gazarek 2019).

The right ventricle is stimulated, the other ventricles are excited by the myocardial cells. Therefore, a left bundle-branch block-like widened QRS- complex appears in the ECG after the pacemaker spike and the positional type becomes the over-rotated left type (Bob 2001).

The VVI is the most commonly implanted pacemaker (Greten 2010).

The modes of a pacemaker are classified with a five-digit code, the International Nomenclature of Pacemaker Systems, also referred to as NBG- code (Bauch 2002). Since 2002, the following version is valid (Gazarek 2019):

• First letter:

It represents the chamber in which the pacemaker senses pacing (O: no sensing; A: atrium; V: ventricle; D: dual; S: single A or V).

• Second letter:

This represents the chamber in which sensing occurs (O: no sensing; A: atrium; V: ventricle; D: dual; S: single A or V)

• Third letter:

It denotes the response to the perception (O: no response; I: inhibitory; T: triggered; D: dual [inhibition + triggered]).

• Fourth letter:

This refers to frequency adaptation (R, rate responsive).

• Fifth letter:

5th letter refers to multisided stimulation (A: atrium; V: ventricle; D: dual)

(Gazarek 2019)

Today, almost all modern pacemakers have the ability to respond to heart rate with one of several rate sensors: activity or motion, minute ventilation or QT interval. Pacemakers are usually multi-programmable. The most commonly programmed modes of implanted single-chamber pacemakers are VVIR or DDDR, although different modes can be programmed in modern pacemakers. (Kasper 2015).

• Implantation:

After the patient has been appropriately informed:

- Chest X-ray in 2 planes

- 12-channel ECG

- Laboratory tests including coagulation values

Usually the implantation is performed under local anesthesia. The aggregate is usually placed subcutaneously on the right side, subfascial on the pectoralis major muscle. For this purpose, a 5 - 7 cm skin incision is made in Mohrenheim's pit (area of the deltoideopectoral sulcus).

For the electrode, venous access is preferably via the cephalic vein, which is usually located under the lateral border of the pectoralis major muscle (Bauch 2002), since the alternative puncture of the subclavian vein is associated with an increased complication rate of between 0.7 - 2.8% (Fröhlig 2006).

In AAI, the lead is placed in the right atrial auricle (Schiergens 2018), whereas in VVI it is anchored at the base or tip of the ventricle (Bob 2001).

• 1st Atrial Demand Pacemaker (AAI).

Indications:

- Diseases of the sinus node with intact AV- conduction.

- SA blockages

However, bradyarrhythmia in intermittent atrial fibrillation should not exist (Herold 2022).

Contraindications:

- AV blockages

- Atrial fibrillation (Fischer 2013)

Advantages:

- HZV is preserved (Herold 2022) and can be increased up to 20% in some cases (Greten 2010).

• 2. ventricular demand pacemaker (VVI)

The VVI stimulates independently of the atrial rhythm (Gazarek 2019).

It can also be implanted without an electrode in certain cases - such as occlusion of the venous access, problems with the pouch due to e.g. cachexia or dementia, increased risk of infection, etc. (Glikson 2021) - as a so-called "leadless pacer" (Herold 2022). An example of this is the Micra transcatheter pacemaker system from Medtronic (El- Chami 2020).

Indications:

- Bradyarrhythmia in atrial fibrillation (Herold 2022)

- in rare cases of asystole (AV or SA block [Ebert 2005]).

Disadvantages:

- Unpleasant palpitations with possible reflex drop in blood pressure.

These occur in about 20% of VVI carriers and are called "pacemaker syndrome". It results from the non-physiological stimulation (Herold 2022).

- Aggravation of preexisting heart failure

- Worsening of the HZV (Herold 2022)

Since the introduction of an implantable cardiac stimulation device, this method of treating bradycardic arrhythmias has spread worldwide. For example, in 2004, approximately 800,000 pacemakers were implanted worldwide (Gertsch 2008).

In Germany, approximately 65,000 pacemakers are implanted per year (Detho 2009).

• 1. atrial demand pacemaker (AAI)

Here, there is a physiological sequence of atrial and ventricular contraction. When the intervention frequency is undershot, the atrium is stimulated, while the atrium's own actions inhibit the pacemaker (Herold 2022).

• 2. ventricular demand pacemaker (VVI)

With sinus rhythm maintained, ventricular pacing with the AV valve closed results in intermittent atrial grafting due to lack of synchronization between the atrium and ventricle (AV sequence) or due to the ventricular stimulus by retrograde atrial excitation (Herold 2022).

The majority of complications occur immediately after implantation or about 5 - 8 years later (Gertsch 2008). Pacemakers in general work very reliably, but various complications can still occur such as:

• Asystole
• ventricular fibrillation
• Atrial f ibrillation (Böcker 2021)
• Air embolism
• Infections
• Hematomas
• Cardiac perforation
• Pneumothorax (Kasper 2015)
• Hematothorax
• Stimulation of the pectoralis muscles (Böcker 2021)
• Stimulation of the phrenic nerve
• Detachment of the electrodes
• Rotation (intentional or unintentional) of the pacemaker pulse generator in the subcutaneous pocket, the so-called "Twiddler- syndrome" can lead to:
  • Dislocation
  • Entanglement of the electrodes around the generator
• Pacemaker syndrome with:
  • Neck pulsations
  • Palpitations
  • Fatigue
  • Increase of jugular vein pressure
  • Dizziness
  • Syncope
• Stigmata of heart failure such as.
  • edema
  • third heart murmur
  • rales (Kasper 2015)

• Acute emergencies in pacemaker wearers:
• Pacemaker tachycardia (can be terminated by magnetic rest).
• Acute coronary syndrome (complicates primary infarct diagnosis).

(Kleemann 2015)

• Complications of right ventricular apical pacing:
• dysynchronous activation of the left ventricle, which can lead to:
• Mitral valve regurgitation
• Impairment of systolic function of the left ventricle
• Stigmata of heart failure (see above).

(Kasper 2015)

In several studies, the mortality rate of elderly patients with AV block showed no difference with implantation of a VVI pacemaker compared with dual-chamber pacing (DDD).

(Kasper 2015)

Follow-up

Pacemakers - regardless of the type of unit - should be checked within 72 h and 2 - 12 weeks after implantation.

Further follow-up in a physician's office is required every 12 months for single-chamber pacemakers, and after 3 - 6 months if there are signs of battery discharge. A telemedical check-up is recommended every 6 months (Glikson 2021).

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