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Optimised cardiac rhythm therapy: AV pacing technologies for physiological stimulation

AV pacing, or atrioventricular stimulation, represents a fundamental therapeutic strategy in modern pacemaker technology and enables the restoration of physiological heart rhythms in patients with atrioventricular block and sick sinus syndrome. This sequential stimulation technique coordinates the contraction sequences between the atria and ventricles for optimal haemodynamic performance.

Physiological principles of AV stimulation

Sequential cardiac stimulation

Dual-chamber pacing: AV pacing uses coordinated stimulation of the atrium and ventricle to maintain the physiological excitation sequence. The programmable AV delay between atrial and ventricular stimulation optimises ventricular filling and maximises cardiac output.

Atrioventricular synchronisation: Maintaining atrial transport function through AV pacing increases stroke volume by 15-30% compared to ventricular pacing alone. This haemodynamic improvement is particularly important in patients with impaired left ventricular function.

AV delay optimisation

Programmable AV intervals: Modern pacemakers allow individual adjustment of the AV delay between 100-300 milliseconds. The optimal AV time varies from patient to patient and depends on factors such as atrial size, ventricular function and medication.

Frequency-adaptive AV delay: Physiological pacemakers automatically adjust the AV time to the heart rate, with shorter AV intervals at higher frequencies mimicking natural heart physiology.

Modern AV pacing modes

DDD/DDDR programming

Dual-chamber modes: Atrioventricular pacing is primarily implemented in DDD or DDDR modes, which offer both atrial and ventricular sensing and pacing functions. These modes ensure AV synchronisation at variable intrinsic rhythms.

Mode switch function: In the event of supraventricular tachyarrhythmias, modern systems automatically switch from AV-synchronous to ventricular pacing (mode switch) to prevent inadequate rate transmission.

The fundamental AV stimulation characteristics include:

  • Atrial tracking: synchronisation of ventricular stimulation with intrinsic atrial activity
  • AV sequential pacing: Coordinated pacing of both chambers in sinus node dysfunction
  • Frequency adaptation: Sensor-controlled frequency adjustment in case of chronotropic incompetence
  • Upper rate behaviour: Algorithms to prevent excessive ventricular rates

Controlled ventricular pacing

MVP algorithms: Modern AV pacing systems use controlled ventricular stimulation to minimise unnecessary ventricular stimulation. These algorithms dynamically extend programmed AV times to promote intrinsic AV conduction.

SafeR mode: Special algorithms combine the advantages of single-chamber atrial stimulation (AAI) with the safety of DDD pacing through continuous AV conduction monitoring.

Clinical indications and patient selection

Atrioventricular block management

Complete heart block: Atrioventricular pacing is the standard therapy for permanent AV block III° to restore haemodynamically effective heart rhythms. AV sequential pacing optimises ventricular filling despite the absence of intrinsic AV conduction.

Intermittent AV block: In paroxysmal higher-degree AV block, atrioventricular pacing systems enable backup pacing during conduction disturbances while maintaining intrinsic rhythms in symptom-free phases.

Postoperative applications

Temporary AV stimulation: After heart surgery, AV pacing is often used to optimise cardiac output. Studies show maximum cardiac output increase at AV intervals between 100 and 225 milliseconds.

Cardiac surgery convalescence: Temporary AV pacing systems support haemodynamic stabilisation in the postoperative phase by optimising heart rate and AV synchronisation.

Technical implementation

Electrode positioning

Right atrial electrode positioning: Optimal atrial electrode placement in the right heart ear or atrial septum ensures stable P wave sensing and reliable atrial stimulation for effective AV pacing.

Ventricular electrode optimisation: Modern AV pacing systems use alternative stimulation sites such as the septum or His bundle region to minimise pacing-induced dyssynchrony.

Programming parameters

AV delay settings: Individual AV time programming is based on echocardiographic optimisation of ventricular filling. Paced and sensed AV delays are often programmed differently to compensate for atrial conduction delays.

Frequency adaptation programming: AV pacing systems integrate activity sensors for physiological rate increase during physical exertion, maintaining AV synchronisation across the entire frequency range.

Monitoring and troubleshooting

ECG interpretation

Stimulation artifact detection: Atrioventricular stimulation shows characteristic stimulation artifacts before P waves (atrial stimulation) and QRS complexes (ventricular stimulation). The temporal relationship between atrial and ventricular spikes corresponds to the programmed AV delay.

Capture evaluation: Successful atrial capture is indicated by P waves after atrial stimulation artefacts, while ventricular capture is confirmed by QRS complexes after ventricular spikes.

Dysfunctions

AV dissociation: Loss of AV synchronisation due to inadequate sensing or stimulation failure can lead to pacemaker syndrome with haemodynamic deterioration.

Upper rate limitation: In fast atrial rhythms, AV pacing systems activate Wenckebach behaviour or 2:1 blocking to prevent excessive ventricular rates.

Clinical outcomes and evidence

Haemodynamic advantages

Cardiac output optimisation: Clinical studies demonstrate 15-25% higher cardiac output values with atrioventricular pacing compared to VVI pacing by maintaining atrial contraction and optimising ventricular filling.

Exercise tolerance: Patients with atrioventricular pacing show improved exercise capacity and quality of life through physiological rate adaptation and preserved AV synchronisation.

Long-term results

Atrial fibrillation prevention: AV pacing reduces the incidence of atrial fibrillation compared to pure ventricular stimulation by maintaining physiological atrial activation and avoiding retrograde AV conduction.

Heart failure progression: Minimising unnecessary ventricular stimulation through AV pacing algorithms slows the development of pacing-induced cardiomyopathy.

Atrioventricular pacing – future developments

AV pacing technologies are constantly evolving through the integration of more physiological pacing patterns, improved sensing algorithms and adaptive AV delay optimisation. Future systems will offer automatic AV time adjustment based on continuous haemodynamic monitoring.

His bundle pacing and left bundle branch area pacing complement traditional AV pacing by providing even more physiological ventricular activation. These developments aim to maintain natural excitation propagation while maintaining AV synchronisation.

Modern AV pacing systems represent the gold standard for patients with AV conduction disorders by combining haemodynamic optimisation with long-term event prevention and improved quality of life.

 

Note: This article is for informational purposes only and does not replace specialist cardiological advice. The implementation of AV pacing requires specialised expertise in rhythmology and pacemaker technology.