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Modification of sinus node function by epicardial laser irradiation in dogs
L Littmann1, R H Svenson, J J Gallagher
1Laser and Applied Technologies Laboratory, Heineman Medical Research Center, Charlotte, North Carolina.
Abstract:
This study tested the feasibility of neodymium:YAG laser photocoagulation of selected sinus node areas to depress sinus rate responsiveness. In 14 open-chest dogs, origin of the sinus impulse (O point) was electrically mapped from the epicardium before and during isoproterenol infusion. Epicardial laser photocoagulation was applied to the O point observed during isoproterenol infusion and stepwise to remapped new O points until a 30 +/- 5% decrease in heart rate occurred. Long-term effects were assessed by Holter monitoring and electropharmacologic testing preoperatively and up to 10 weeks or 6 months. Mean (+/- SEM) percent decreases were observed at 10 weeks in the following parameters: average 24-hour heart rate, 17.4 +/- 5.0%; maximum heart rate on Holter, 30.5 +/- 3.5%; heart rate during pharmacologic autonomic blockade, 32.7 +/- 3.5%; and maximum heart rate on isoproterenol, 23.1 +/- 4.6% (all p less than 0.01). Curves with pacemaker recovery time plotted against control cycle length remained unchanged. Holter monitoring did not show excessive bradycardic episodes even after administration of propranolol. In three control dogs (sham operation), sinus node function remained unchanged. Histologic study of the irradiated area showed replacement by inflammatory cells, fibrosis, and cartilage formation with surrounding normal cells and occasional cells resembling pacemaker-like cells at the caudal end of the sinoatrial node. This study suggests that 1) map-guided graded laser photocoagulation of sinus node regions showing earliest activation during catecholamine stimulation successfully limits maximum heart rates without causing significant bradycardia, 2) the effects are long lasting, and 3) the remaining pacemaker behaves like the sinus node. Laser modification of sinus node function could become a form of nonpharmacologic heart rate control in patients with coronary artery disease undergoing surgery and in the syndrome of inappropriate sinus tachycardia.
Insights
Map-guided laser photocoagulation effectively reduced heart rate in dogs by targeting the sinus node. This long-lasting, non-pharmacologic approach shows promise for heart rate control in specific patient groups.
Area of Science:
- Cardiovascular Physiology
- Interventional Cardiology
- Medical Device Technology
Background:
- Tachycardia and inappropriate sinus tachycardia are significant clinical concerns.
- Current treatments for heart rate control often involve pharmacologic interventions with potential side effects.
- Non-pharmacologic strategies for modulating heart rate are under investigation.
Purpose of the Study:
- To assess the feasibility of using neodymium:YAG laser photocoagulation to modify sinus node function.
- To determine if targeted laser treatment can reduce sinus rate responsiveness.
- To evaluate the long-term efficacy and safety of this intervention for heart rate control.
Main Methods:
- Electrophysiological mapping of the sinus impulse origin (O point) in open-chest dogs.
- Graded epicardial laser photocoagulation applied to identified O points during isoproterenol infusion.
- Assessment of heart rate changes, Holter monitoring, and electropharmacologic testing for up to 6 months.
Main Results:
- Laser photocoagulation successfully decreased heart rate by 17-33% across various parameters at 10 weeks (p<0.01).
- Long-term effects were sustained, with no excessive bradycardia observed, even after propranolol administration.
- Histological analysis revealed localized tissue changes with preserved surrounding functional cells.
Conclusions:
- Map-guided laser photocoagulation of the sinus node is a feasible method for limiting maximum heart rates.
- The procedure demonstrates long-lasting efficacy and a favorable safety profile, avoiding significant bradycardia.
- This technique offers a potential non-pharmacologic heart rate control strategy for conditions like inappropriate sinus tachycardia.
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