Drug effects on the sinus node. A clinical perspective

Methylxanthine Derivatives in the Treatment of Sinus Node Dysfunction: A Systematic Review

While the chronotropic effects of theophylline and aminophylline are well-known, their clinical application in the treatment of sinus node dysfunction has not been established in a review. The purpose of this systematic review is to evaluate the efficacy and safety of methylxanthines in the treatment of bradyarrhythmias associated with sinus node dysfunction. A systematic review was conducted in accordance with PRISMA guidelines on Embase, PubMed, MEDLINE, Cochrane Central, Web of Science, SciELO, Korean Citation Index, Global Index Medicus, and CINAHL through June 2023. A total of 607 studies were identified through the literature search. After applying the inclusion and exclusion criteria, 14 studies were included in this review. The causes of bradyarrhythmias involving the sinoatrial node included acute cervical spinal cord injury, coronavirus disease of 2019, carotid sinus syncope, chronotropic incompetence, heart transplant, and chronic sinus node dysfunction. Theophylline and aminophylline were shown to be effective for increasing heart rate and reducing the reoccurrence of bradyarrhythmias. The data on symptom resolution was conflicting. While many case studies reported a resolution of symptoms, a randomized controlled trial reported no significant difference in symptom scores between the control, theophylline, and pacemaker groups in the treatment of sick sinus syndrome. The incidence of adverse effects was low across all study designs. The data suggests methylxanthines may be useful as an alternative or bridge to nonpharmacologic pacing; however, dosing has yet to be established for various indications. Overall, methylxanthines proved safe and effective as a pharmacologic therapy for bradyarrhythmic manifestations of sinus node dysfunction.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Declining into failure: the age-dependent loss of the L-type calcium channel within the sinoatrial node

BACKGROUND

The spontaneous activity of pacemaker cells in the sinoatrial (SA) node controls heart rate under normal physiological conditions. Clinical studies have shown the incidence of SA node dysfunction increases with age and occurs with peak prevalence in the elderly population. The present study investigated whether aging affected the expression of Ca(v)1.2 channels and whether these changes could affect pacemaker activity, in turn leading to age-related SA node degeneration.

METHODS AND RESULTS

The SA node region was isolated from the right atrium of guinea pigs between birth and 38 months of age. Immunofluorescence studies showed Ca(v)1.2 protein was present as punctate labeling around the outer membrane of atrial cells but was absent from the center of the SA node. The area lacking Ca(v)1.2-labeled protein progressively increased from 2.06+/-0.1 (mean+/-SEM) mm2 at 1 month to 18.72+/-2.2 mm2 at 38 months (P<0.001). Western blot provided verification that Ca(v)1.2 protein expression within the SA node declined during aging. Functional measurements showed an increased sensitivity to the L-type calcium blocker nifedipine; SA node preparations stopped beating in 100 micromol/L nifedipine at 1 day old, compared with 30 micromol/L at 1 month and 10 micromol/L at 38 months of age. Furthermore, the amplitude of extracellular potentials declined within the center and periphery of the SA node during aging.

CONCLUSIONS

The present data show Ca(v)1.2 channel protein decreases concurrently with reduced spontaneous activity of the SA node with increased age, which provides further evidence of mechanisms underlying the age-related deterioration of the cardiac pacemaker.