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Chapter 86: Bradyarrhythmias

Which of the following statements concerning the blood supply of the electrical conduction system is false?

A. The left bundle receives its blood supply from the AV nodal artery, posterior descending artery, and branches of the left anterior descending artery

B. The sinus node receives its blood supply from the sinoatrial nodal artery arising from the right coronary artery in 60% of patients

C. The sinus node receives its blood supply from the sinoatrial nodal artery arising from the circumflex artery in 40% of patients

D. The AV node is supplied by the AV nodal artery arising from the right coronary artery in 10% of patients and from the left circumflex artery in the remaining 90%

E. The His bundle is supplied by the AV nodal artery as well as branches of the left anterior descending artery

The answer is D. (Hurst’s The Heart, 14th Edition, Chap. 86) The AV node is supplied by the AV nodal artery arising from the right coronary artery in 90% of patients, whereas the left circumflex artery provides it in the remaining 10% of patients. The sinus node receives its blood supply from the sinoatrial (SA) nodal artery arising from the right coronary artery in 59% (option B) of patients, from the left circumflex artery in 38% (option C), and from both arteries with a dual blood supply in 3%. Both the AV nodal artery and branches of the left anterior descending artery supply the bundle of His (option E). The left bundle has a rich blood supply from the AV nodal artery, posterior descending artery, and branches of the left anterior descending artery (option A).

A 25-year-old woman presents to your office in consultation for severe sinus bradycardia. Her resting ECG reveals a heart rate at 28 bpm. She is entirely asymptomatic from her bradycardia. All of the following represent possible etiologies of her sinus node dysfunction except:

A. Hormonal fluctuations during premenstrual, perimenopausal, and gestational periods

B. Mutation in the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel

C. Previous closure of an atrial septal defect of the sinus-venosus type

D. Collagen vascular disease

E. Mutation in the cardiac sodium channel gene, SCN5A

The answer is A. (Hurst’s The Heart, 14th Edition, Chap. 86) Hormonal changes have not been shown to be associated with sinus node dysfunction (SND). SND can occur in children and young adults without structural heart disease. In addition ...

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