Identifying the evolutionary building blocks of the cardiac conduction system

Area of Science:

• Comparative anatomy
• Evolutionary biology
• Cardiovascular physiology

Background:

• Endothermic mammals and birds require high heart rates for oxygen consumption, facilitated by specialized atrioventricular node and His-Purkinje systems.
• Ectothermic vertebrates exhibit similar heart contraction patterns but lack anatomical evidence of a conduction system, posing an evolutionary puzzle given their shared ancestry with endotherms.

Purpose of the Study:

• To investigate the evolutionary building plan of the vertebrate heart conduction system.
• To compare the heart structure and electrical activation patterns of adult ectotherms with embryonic endotherms.

Main Methods:

• Utilized conserved genetic markers to analyze conduction system design in adult lizards, frogs, and zebrafish.
• Employed optical mapping to observe ventricular activation patterns in ectothermic animals.

Main Results:

• Adult ectotherms possess a conduction system design similar to embryonic mammals and chickens, featuring an atrioventricular canal muscle, a lack of fibrous insulation, and a spongy ventricle.
• Ventricular activation in ectotherms proceeds from base to apex, mirroring embryonic endotherms and the His-Purkinje system.
• Mammalian and avian ventricles uniquely develop compact walls and septa, forming a distinct conduction system from the embryonic spongy ventricle.

Conclusions:

• The study uncovers the ancestral heart structure, indicating that adult ectotherms retain building blocks of the conduction system found in embryonic endotherms.
• This suggests that the complex conduction system of adult endotherms evolved from a more basic structure present in ectothermic ancestors and early developmental stages.