Cardiac resynchronization therapy

Earl Bakken, co-founder of Medtronic, 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 routine stimulation site was the right ventricular apex (Stellbrink 2024).

Since 1988, programmable pacemakers have been classified by the International Nomenclature of Pacemaker Systems, the so-called NBG code (Bauch 2002).

In 2002, Bristow et al. published a study of cardiac resynchronization therapy in patients with heart failure, the so-called COMPANION study, as did Cleland et al. in 2005 in the so-called CARE HF study. The biventricular pacemaker systems (BVP) also contain a third electrode cable that is placed on the left side wall of the heart (Antwerpes 2014).

Cardiac resynchronization therapy (CRT) is an invasive form of treatment for chronic heart failure (Herold 2023) in which the myocardial contraction processes are optimized by means of electrical stimulation (Klotz 2015).

In patients with left bundle branch block, there is impaired electrical excitation in the left ventricle, as the posterolateral wall is excited much later. This leads to hemodynamic changes and a so-called rocking motion of the left ventricle. Left bundle branch block and heart failure influence each other. (Gotzmann 2024).

In CRT, atrial-controlled biventricular electrical stimulation is used to synchronize the atrioventricular, interventricular and intraventricular contraction sequences. This initially results in a complete bundle branch block with reverse remodeling, which leads to

• a decrease in ventricular volume
• an increase in pumping capacity of up to 15%
• an improvement in mitral valve insufficiency
• a reduction in mortality (Herold 2023)

Indications for performing CRT are:

• NYHA ≥ 2 despite optimal drug treatment
• EF ≤ 35 %
• Widened QRS complex
  • With left bundle branch block ≥ 130 ms
  • For non-left bundle branch block ≥ 150 ms
• Life expectancy > 1 year (Herold 2023)

In exceptional cases, CRT can also be performed in patients with atrial fibrillation if the following conditions are met

• NYHA class III- IV despite optimal drug therapy
• Almost complete biventricular stimulation
• QRS complex ≥ 130 ms
• LVEF ≤ 35 % (2023 guidelines)

Dyssynchronies are also frequently found in patients with heart failure and preserved ejection fraction. However, the benefit of CRT in these patients has not yet been sufficiently proven (Guidelines 2023).

Procedure

In cardiac resynchronization therapy, a pacemaker probe is inserted transvenously via a suitable branch of the coronary sinus into the area of the posterolateral wall of the left ventricle (Gotzmann 2024). The operation time is approx. 90 min and is therefore almost twice as long as with conventional pacemakers (Guidelines 2023).

Ventricular dyssynchrony, which leads to increased mortality, is found in approx. 33% of all patients with heart failure in stage NYHA III- IV with reduced ejection fraction. CRT is indicated for these patients (2023 guidelines).

In 2015, a CRT pacemaker was implanted in 12,500 patients (Guidelines 2023).

A non-synchronous contraction intraventricularly (between the walls of the left ventricle) or interventricularly (between the ventricular chambers) reduces the mechanical efficiency of the contraction, leads to an impairment of systolic function and has a negative effect on ventricular filling. (Kasper 2015).

CRT can be associated with the following complications:

• Bleeding
• Pocket hematoma
• Failure of the unit
• Dislocation of the probes
• infection
• Pericarditis
• Pneumothorax (2023 guidelines)

In patients with heart failure with preserved sinus rhythm and asynchronous action of both ventricles with LBBB, CRT leads to significantly improved performance function and a significantly improved quality of life in up to two thirds of patients (Klotz 2015)

Patients with CRT should present p.o. for the first time after 1 - 3 months. Further checks depend on the patient's clinical condition and should be carried out every 3 - 6 months (Butter 2015).

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