Thorax
Bobby Krishnachetty, Abdul Syed, Harriet Scott in Applied Anatomy for the FRCA, 2020
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.
Electrocardiogram
Burt B. Hamrell in Cardiovascular Physiology, 2018
Damage to the atrioventricular node, bundle of His, or both bundle branches can cause a complete failure of conduction from the atria to the ventricles. In Figure 7.20, arrows mark the location of atrial depolarizations occurring at about 100/minute. RST waves are occurring regularly, but at a much slower rate than the P waves, approximately 44/minute. The atria are depolarizing regularly at their own rate and the ventricles are doing the same, but at their own much slower rate without a fixed relationship to atrial depolarizations. A likely source of ventricular pacing in this situation are Purkinje fibers. The fourth arrow from the left marks the occurrence of an R wave likely superimposed on a P wave. Notice that the R wave is taller than the others. Several of the P waves are superimposed on T waves.
Cardiovascular physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
After passing down the right side of the interventricular septum for 1 cm, the bundle of His splits into right and left bundle branches to the right and left ventricles (the left bundle branch divides into anterior and posterior divisions). The bundle branches supply the dense network of Purkinje fibres, which innervate the ventricles. Purkinje cells are the largest-diameter cells in the heart, and their conduction velocity is fast (1–4 m/s) so that ventricular activation is rapid. The endocardial surfaces of the ventricles are activated first; early interventricular septum and papillary muscle contraction provides a firm base for ventricular contraction and prevents AV valve eversion. The cardiac action potential then spreads out to the epicardial surfaces and, as the right ventricle is thinner than the left, the outside of the right ventricle is activated first. The apical regions of the ventricles are activated before the bases, propelling blood up and out of the ventricular chambers.
Anatomical Considerations and Emerging Strategies for Reducing New Onset Conduction Disturbances in Percutaneous Structural Heart Disease Interventions
Published in Structural Heart, 2021
Mazen S. Albaghdadi, Andrew O. Kadlec, Horst Sievert, Srijoy Mahapatra, Alexander Romanov, Usman Siddiqui, Itzhak Kronzon, Michael Nguyen Young, Apostolos Tzikas, Martin B. Leon, Siew Yen Ho, Karl-Heinz Kuck
Similar to the aortic valve, the tricuspid valve is in close proximity to the conduction system, particularly the AV node, bundle of His, and right bundle branch.51 The bundle of His traverses the right trigone of the central fibrous body to reach the ventricular septum which is near the commissure of the septal and anterior tricuspid leaflets.52 Percutaneous interventions may increase the risk of injury to the conduction system; however, the incidence and prognostic significance of new onset conduction disturbances following percutaneous repair of the tricuspid valve remain unknown.51 Considering that this approach is gaining recognition as a favorable alternative to surgery,49 future studies will help to delineate the incidence and impact of arrhythmias on short-term and long-term outcomes following this intervention.
Right and left-sided infective endocarditis in an IV drug abuser
Published in Journal of Community Hospital Internal Medicine Perspectives, 2020
Maryam Nemati, Kristine Galang, Syung Min Jung
Patients with IE can also develop heart blocks. Usually, heart blocks occur when the cardiac valves on the left side of the heart are affected. The occurrence of first-degree AV blocks is clinically significant not only because these heart blocks can progress, as it did in our patient, but its presence strongly suggests a perivalvular extension of an aortic abscess [9]. Furthermore, the conduction system of the heart is easily affected due to the proximity of the aortic valve with the bundle of His in turn leading to problems with AV blocks or bundle branch blocks. It is particularly prudent to monitor these patients on telemetry as disruptions in the conduction system carry increased mortality and overall a poorer prognosis. The presence of an AV block alone carries a 97% specificity in the detection of perivalvular aortic involvement [9,10].
Transcatheter aortic valve replacement and cardiac conduction
Published in Expert Review of Cardiovascular Therapy, 2019
Satya Shreenivas, Edward Schloss, Joseph Choo, Ian Sarembock, Scott Lilly, Dean Kereiakes
Conduction abnormalities are especially common in aortic valve disease due to the anatomy of the cardiac conduction system and its proximity to the aortic valve (Figure 1). In the PARTNER trial of the Sapien TAVR valve versus medical therapy, pacemakers were present in 18.4% of patients at the time of enrollment. Further, in patients randomly assigned to medical therapy, 5% required a new pacemaker by 30 days, and this incidence increased to 7.8% at 1 year and 8.6% at 2 years [1]. Baseline PPM prevalence was similar in the high surgical risk cohort of the PARTNER trial as well (20.9%) [2]. In most cases, the bundle of His and left bundle branch frequently lie between the membranous septum and the crest of the muscular ventriculur septum which are located close to the base of the noncoronary and right coronary leaflets of the aortic valve. There appears to be anatomic variation in the location of the bundle with 50% of patients showing a predominately right located bundle, 30% with a left located bundle, and 20% with a superficial located bundle (just below endocardium) [5]. However, other anatomical studies have shown different variations with less rightward located bundles [6,7]. In addition to the anatomic location of the bundle of His, the length of the membranous septum has also been correlated with post-TAVR conduction abnormalities with a shorter membranous septum associated with higher incidence of heart block. [8] Histopathologic studies using transcatheter aortic valves have shown that mechanical damage directly to the bundle is the cause of post-procedure conduction abnormalities [9].
Related Knowledge Centers
- Action Potential
- Bundle Branches
- Cardiac Cycle
- Muscle Contraction
- Purkinje Fibers
- Atrium
- Ventricle
- Atrioventricular Node
- Cardiac Muscle
- Cardiac Conduction System