Pacemaker Therapy for the Optimization of Fontan Circulation
Article ID: CJ-23-0963
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Article ID: CJ-23-0963
Pacemakers (PM) significantly affect cardiac output and dynamically alter hemodynamics (Figure 1). The determinants of cardiac output are heart rate, contractility, preload, and afterload,1 of which PMs affect 3: heart rate, contractility, and preload. The heart rate can be regulated through alterations of the pacing rate provided by the PM. The PM can also influence systemic ventricular preload by atrioventricular (AV) sequential pacing or changing the AV interval. The pacing rate and AV sequential pacing/AV interval indirectly affect contractility. Due to the force–frequency relationship, cardiac contractility increases as the heart rate increases, reaching a peak and then decreasing.2 According to the Frank–Starling Law, cardiac contractility also increases as preload increases.2 Furthermore, ventricular pacing directly affects ventricular contractility by altering ventricular synchronicity. Each of these factors differentially affect the failing heart compared with the nonfailing heart. Hemodynamics can be optimized or further compromised depending on the PM setting, the position of the pacing lead, and the method of ventricular pacing.
Effects of pacemaker (PM) on cardiac output. Solid and dotted orange arrows respectively indicate the direct and indirect effects of PM. AV, atrioventricular.
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The effects of a PM and the determination of optimal PM settings in Fontan circulation have yet to be established. Recent reports about the use of PM in Fontan circulation, while informative, have not fully addressed these issues.
In this issue of the Journal, Shin et al evaluate the prognostic risk factors for Fontan patients with PM implantation and show that a wide QRS complex led to adverse outcomes in Fontan patients.3 With or without a PM, a wide QRS complex is harmful to the Fontan circulation. Wide QRS complexes are associated with a lower aerobic exercise capacity in Fontan patients,4 and even with a less rapid heart rate they can cause hemodynamic deterioration of Fontan circulation during supraventricular tachycardia.5 Wide QRS complexes are also associated with stronger interventricular dyssynchrony and decreased ventricular ejection fraction with single-ventricular physiology.6
Single-site ventricular pacing creates a wide QRS complex and adversely affects ventricular synchronicity. Therefore, cardiac resynchronization therapy is occasionally indicated in such patients with single-ventricular physiology. In patients who undergo the Fontan operation, biventricular motion swinging between the ventricles is frequently observed during single-site ventricular pacing, representing the interventricular dyssynchrony that occurs with the single-ventricular physiology in the presence of 2 ventricles.7,8 A permanent PM was determined to be a significant predictor of late death in Fontan patients according to a meta-analysis,9 and a high ventricular pacing burden was associated with a poor prognosis, including death and necessity of heart transplantation.10 This data lend credence to the current study by Shin et al.3
The introduction of a PM in a patient with Fontan circulation also can optimize or further compromise hemodynamics, although parameters have yet to be established. The author suggests 3 points for the use of PM for the optimization of Fontan circulation (Figure 2). First, minimize the QRS complex duration and optimize ventricular synchrony during ventricular pacing. The ventricular lead position is critical in achieving these goals. Apical ventricular pacing is recommended because it has been associated with a better prognosis than placement at other pacing sites.11 Unnecessary ventricular pacing should be avoided. When ventricular dyssynchrony due to pacing is present, cardiac resynchronization therapy should be promptly implemented regardless of symptoms. Second, maintain AV synchrony by atrial pacing or through the adjustment of the AV interval. Junctional rhythm due to sinus node dysfunction is a major late complication of the Fontan circulation, which leads to elevation of central venous pressure due to the loss of AV synchrony.12,13 Atrial pacing is known to improve the hemodynamics in this situation and the most recent guidelines present PM implantation as a Class I recommendation for sinus node dysfunction in Fontan circulation.14 Additionally, the AV interval to maintain AV synchrony must be carefully set in a manner different from that of a normally structured heart.15 Third, set the pacing rate to fit the patient’s activity level; decrease at rest and increase during activity. The optimal heart rate for Fontan circulation is still unknown, but optimization of the rate response function is necessary to provide adequate cardiac output during a wide range of activities.
Pacemaker (PM) settings for the optimization of Fontan circulation. AV, atrioventricular; CRT, cardiac resynchronization therapy; SND, sinus node dysfunction.
Previous studies have demonstrated a worse prognosis after PM implantation in Fontan circulation patients. As the goal is to improve the patient’s quality of life and survival rate, it is important to consider the timing, location, and settings of the PM, with regard to the individual’s anatomic and hemodynamic characteristics, and to make adjustments that are consistently beneficial.
The author declares that there are no conflicts of interest.
