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Thorax
Published in Bobby Krishnachetty, Abdul Syed, Harriet Scott, Applied Anatomy for the FRCA, 2020
Bobby Krishnachetty, Abdul Syed, Harriet Scott
The conducting system is the unique tissue specific to the heart and has specialised cardiac muscle. It generates and transmits impulses that regulate cardiac contraction. The sinoatrial node (SA node) is situated in the upper part of the crista terminalis, within the myocardium, to the right of the SVC opening. It is also called the pacemaker of the heart as it initiates and modulates the heart rate and transmits impulses to the atria and the ventricles.The atrioventricular node (AV node) is situated in the endocardium, near the atrial septum, immediately above the opening of the coronary sinus. It receives electrical impulses that originate in the SA node and transmits them to the bundle of His.The atrioventricular bundle of His transmits impulses to the walls of the ventricles. It first transits along the membranous part of the interventricular septum and then divides at the junction of the muscular and membranous parts of the interventricular septum. The subendocardial branches are the Purkinje fibres, specialised cardiac fibres, which then ascend within the muscular walls of the ventricles.
Role of muscarinic receptors in cardiovascular regulation in SHR
Published in H. Saito, Y. Yamori, M. Minami, S.H. Parvez, New Advances in SHR Research –, 2020
The heart is parasympathetically inervated by the preganglionic rami cardiad which originate from both sides from the vagus nerve. Fibers of the right side predominantly inérvate the right atrium and the sinus node while fibers from the left side innervate the atrioventricular node. Thus, stimulation of the right vagus maily influences heart rate, while stimulation of the left vagus nerve has an impact on the atrioventricular conduction time.
Non-ischemic Cardiomyopathy and Ventricular Arrhythmias
Published in Andrea Natale, Oussama M. Wazni, Kalyanam Shivkumar, Francis E. Marchlinski, Handbook of Cardiac Electrophysiology, 2020
Matthew C. Hyman, Gregory E. Supple
Bundle branch re-entrant ventricular arrhythmias are a distinct, but important clinical entity found in both ischemic and non-ischemic cardiomyopathies. The majority of bundle branch re-entry ventricular arrhythmias are found in ischemic cardiomyopathies, though they can also be found in NICM as well (40% and 25%, respectively according to a large cohort).54 The underlying critical substrate for this arrhythmia is the presence of an underlying conduction abnormality. This conduction abnormality can be either a fixed or functional block in the His Purkinje system.55 In either case, when a patient has differential conduction down the bundle branches, this predisposes the patient to re-entrant arrhythmias using the right and left limbs of the conduction system. This is analogous to the differential conduction seen in the atrioventricular node where slow and fast pathways allow for sustained AV nodal reentrant tachycardias.
Management of congenitally corrected transposition from fetal diagnosis to adulthood
Published in Expert Review of Cardiovascular Therapy, 2023
Due to abnormal position of the atrioventricular node and its connection to the atrioventricular bundle in ccTGA, cardiac conduction disorders are common and permanent pacemaker therapy is frequently required [27]. Unless contraindicated (patient’s size, unrepaired associated lesions), the transvenous system can be implanted. Subpulmonary univentricular pacing was shown to be associated with deterioration of sRV and exacerbation of tricuspid valve regurgitation [59,60]. Study on 53 patients with dual-chamber univentricular pacemakers revealed an improvement after upgrading to biventricular pacing [60]. However, some observations provided different results [61]. Transvenous implantation of an sRV lead is possible in ccTGA patients with suitable anatomy assessed by advanced cardiac imaging [62]. Alternatively, surgical placement of ventricular pacing leads or a hybrid approach can be performed. According to Pediatric and Congenital Electrophysiology Society (PACES) and Heart Rhythm Society guidelines, cardiac resynchronization therapy (CRT) can be useful for adults with sRV function ≤35%, sinus rhythm, complete right bundle branch block with QRS ≥150 ms (spontaneous or paced) and NYHA class II-IV [63]. The benefit of CRT in patients with sRV dysfunction without conduction disturbances is unclear.
Comparison of methods for delivering cardiac resynchronization therapy: electrical treatment targets and mechanisms of action
Published in Expert Review of Medical Devices, 2023
Florentina Simader, Ahran Arnold, Zachary Whinnett
Atrial fibrillation (AF) may contribute to or be the primary cause of heart failure. It may adversely impact cardiac function via the following mechanisms: (i) loss of the contribution of atrial contraction to ventricular filling; (ii) tachymyopathy: rapid conduction of AF to the ventricles may lead to long periods of a high ventricular rate, leading to ventricular impairment; (iii) irregularity in RR interval [25]. This third mechanism of irregularity of intervals between ventricular contractions is increasingly being recognized as a trigger for developing ventricular impairment. The trigger for this harmful effect is thought to be mediated by post-extra-systolic potentiation, which refers to an increase in contractility that is associated with Ca2+ overload [26]. Tachymyopathy and RR irregularity due to AF can be treated with pacemaker implantation combined with atrioventricular node ablation and, therefore, represent a further potential electrical treatment target for pacing therapy for heart failure.
The future of cardioneuroablation in cardiovascular medicine
Published in Expert Review of Cardiovascular Therapy, 2022
Tolga Aksu, Asad Khan, Henry Huang
In patients with atrioventricular block, the PMLGP should also be targeted because postganglionic nerves from the PMLGP extend toward the interatrial septum and presumably supply the atrioventricular nodal region [67]. We have recently demonstrated that ablation around the PMLGP resulted in 1:1 atrioventricular conduction in 13 (76.4%) of 17 patients with persistent second-degree AVB [11]. Although atrioventricular node injury during GP ablation has not been reported, we should be aware of the possibility of such a complication during ablation of PMLGP around the coronary sinus ostium. To avoid or decrease the risk of atrioventricular node injury ablation for PMLGP, it is recommended to begin ablation from the left atrium. However, ablation may need to be extended to the right atrium around the coronary sinus or other GP sites if desired atrioventricular response is not achieved after ablation via the left atrium. Also, radiofrequency application should be stopped as soon as possible in case of signs of atrioventricular node injury.