{"id":4722,"date":"2025-08-24T18:54:00","date_gmt":"2025-08-24T22:54:00","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/?post_type=chapter&#038;p=4722"},"modified":"2025-12-13T17:53:48","modified_gmt":"2025-12-13T22:53:48","slug":"cardiac-conduction-pathway","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/chapter\/cardiac-conduction-pathway\/","title":{"raw":"7p3 Cardiac Conduction Pathway","rendered":"7p3 Cardiac Conduction Pathway"},"content":{"raw":"<strong>Overview:<\/strong>\r\n<ul>\r\n \t<li>The heart\u2019s rhythm is coordinated by a specialized conduction system comprised of cardiomyocytes, not nerves.<\/li>\r\n \t<li>This system starts with the\u00a0<strong>SA node<\/strong>\u00a0(sinoatrial node), the primary pacemaker.<\/li>\r\n<\/ul>\r\n<h1><strong>SA Node (Sinoatrial Node):<\/strong><\/h1>\r\n<ul>\r\n \t<li>Located in the roof of the right atrium.<\/li>\r\n \t<li>Composed of\u00a0<strong>specialized cardiomyocytes<\/strong>\u00a0that spontaneously depolarize due to leak channels.<\/li>\r\n \t<li><strong>Pacemaker<\/strong>\u00a0of the heart: depolarizes at 80-100 beats per minute naturally.<\/li>\r\n \t<li>Under parasympathetic influence (\"rest and digest\"), the heart rate slows to 60-80 bpm.<\/li>\r\n<\/ul>\r\n<h2><strong>Electrical Wave Propagation:<\/strong><\/h2>\r\n<ul>\r\n \t<li>Depolarization spreads rapidly through\u00a0<strong>gap junctions<\/strong>\u00a0in the atrial myocardium.<\/li>\r\n \t<li>Wave travels via\u00a0<strong>internodal pathways<\/strong>\u00a0to the\u00a0<strong>AV node<\/strong>\u00a0(located at the floor of the right atrium).<\/li>\r\n \t<li>The delay at the\u00a0<strong>AV node<\/strong>\u00a0(pause) allows the atria to contract and ventricles to fill before ventricular depolarization.<\/li>\r\n<\/ul>\r\n<h1><strong>Ventricular Conduction:<\/strong><\/h1>\r\n<ul>\r\n \t<li>From the AV node, the wave moves down the\u00a0<strong>atrioventricular (AV) bundle<\/strong>\u00a0(bundle of His).<\/li>\r\n \t<li>It divides into\u00a0<strong>left and right bundle branches<\/strong>.<\/li>\r\n \t<li>The wave then spreads via the\u00a0<strong>Purkinje fibers<\/strong>\u00a0throughout the ventricular myocardium.<\/li>\r\n \t<li><strong>Synchronization:<\/strong>\u00a0All ventricular cells depolarize together via gap junctions, leading to coordinated contraction.<\/li>\r\n<\/ul>\r\n<h2><strong>Intrinsic Pacemaker Rates:<\/strong><\/h2>\r\n<ul>\r\n \t<li><strong>SA node:<\/strong>\u00a080-100 bpm (normal resting HR 60-80 bpm due to parasympathetic tone).<\/li>\r\n \t<li><strong>AV node:<\/strong>\u00a060-80 bpm (if SA node fails).<\/li>\r\n \t<li><strong>Bundle of His and Purkinje fibers:<\/strong>\u00a020-40 bpm (can support life temporarily if primary nodes are damaged but is insufficient long-term).<\/li>\r\n<\/ul>\r\n<h1><strong>Heart ANS Innervation &amp; Control:<\/strong><\/h1>\r\n<ul>\r\n \t<li><strong>Parasympathetic fibers<\/strong>\u00a0from the vagus nerve modulate the SA node, slowing HR during rest.<\/li>\r\n \t<li><strong>Sympathetic stimulation<\/strong>\u00a0increases HR during stress or activity.<\/li>\r\n<\/ul>\r\n<h1><strong>Heart Transplant Consideration:<\/strong><\/h1>\r\n<ul>\r\n \t<li>Post-transplant, the heart lacks parasympathetic innervation.<\/li>\r\n \t<li>Heart rate is typically higher (~80-100 bpm at rest).<\/li>\r\n \t<li>Surgeons cannot reattach parasympathetic nerves; they \"reconnect\" major vessels, not nerves.<\/li>\r\n<\/ul>\r\n<h1><strong>Pathophysiology &amp; Clinical Implications:<\/strong><\/h1>\r\n<ul>\r\n \t<li>If the\u00a0<strong>SA node or internodal pathways<\/strong>\u00a0are damaged or fail, the\u00a0<strong>AV node<\/strong>\u00a0becomes the secondary pacemaker.<\/li>\r\n \t<li><strong>Pacemaker implantation:<\/strong>\u00a0Used if intrinsic conduction is insufficient, especially if damage is extensive.<\/li>\r\n<\/ul>\r\nIts rate supports life but may require intervention for optimal heart function.\r\n<h1><strong>Summary:<\/strong><\/h1>\r\nThe heart\u2019s electrical activity begins with the SA node, setting a regular rhythm. The conduction system ensures synchronized contraction of atria and ventricles. Damage to primary nodes can be compensated temporarily by secondary pacemakers, but long-term support often requires a pacemaker. Understanding this pathway is crucial in diagnosing arrhythmias and designing appropriate treatments.","rendered":"<p><strong>Overview:<\/strong><\/p>\n<ul>\n<li>The heart\u2019s rhythm is coordinated by a specialized conduction system comprised of cardiomyocytes, not nerves.<\/li>\n<li>This system starts with the\u00a0<strong>SA node<\/strong>\u00a0(sinoatrial node), the primary pacemaker.<\/li>\n<\/ul>\n<h1><strong>SA Node (Sinoatrial Node):<\/strong><\/h1>\n<ul>\n<li>Located in the roof of the right atrium.<\/li>\n<li>Composed of\u00a0<strong>specialized cardiomyocytes<\/strong>\u00a0that spontaneously depolarize due to leak channels.<\/li>\n<li><strong>Pacemaker<\/strong>\u00a0of the heart: depolarizes at 80-100 beats per minute naturally.<\/li>\n<li>Under parasympathetic influence (&#8220;rest and digest&#8221;), the heart rate slows to 60-80 bpm.<\/li>\n<\/ul>\n<h2><strong>Electrical Wave Propagation:<\/strong><\/h2>\n<ul>\n<li>Depolarization spreads rapidly through\u00a0<strong>gap junctions<\/strong>\u00a0in the atrial myocardium.<\/li>\n<li>Wave travels via\u00a0<strong>internodal pathways<\/strong>\u00a0to the\u00a0<strong>AV node<\/strong>\u00a0(located at the floor of the right atrium).<\/li>\n<li>The delay at the\u00a0<strong>AV node<\/strong>\u00a0(pause) allows the atria to contract and ventricles to fill before ventricular depolarization.<\/li>\n<\/ul>\n<h1><strong>Ventricular Conduction:<\/strong><\/h1>\n<ul>\n<li>From the AV node, the wave moves down the\u00a0<strong>atrioventricular (AV) bundle<\/strong>\u00a0(bundle of His).<\/li>\n<li>It divides into\u00a0<strong>left and right bundle branches<\/strong>.<\/li>\n<li>The wave then spreads via the\u00a0<strong>Purkinje fibers<\/strong>\u00a0throughout the ventricular myocardium.<\/li>\n<li><strong>Synchronization:<\/strong>\u00a0All ventricular cells depolarize together via gap junctions, leading to coordinated contraction.<\/li>\n<\/ul>\n<h2><strong>Intrinsic Pacemaker Rates:<\/strong><\/h2>\n<ul>\n<li><strong>SA node:<\/strong>\u00a080-100 bpm (normal resting HR 60-80 bpm due to parasympathetic tone).<\/li>\n<li><strong>AV node:<\/strong>\u00a060-80 bpm (if SA node fails).<\/li>\n<li><strong>Bundle of His and Purkinje fibers:<\/strong>\u00a020-40 bpm (can support life temporarily if primary nodes are damaged but is insufficient long-term).<\/li>\n<\/ul>\n<h1><strong>Heart ANS Innervation &amp; Control:<\/strong><\/h1>\n<ul>\n<li><strong>Parasympathetic fibers<\/strong>\u00a0from the vagus nerve modulate the SA node, slowing HR during rest.<\/li>\n<li><strong>Sympathetic stimulation<\/strong>\u00a0increases HR during stress or activity.<\/li>\n<\/ul>\n<h1><strong>Heart Transplant Consideration:<\/strong><\/h1>\n<ul>\n<li>Post-transplant, the heart lacks parasympathetic innervation.<\/li>\n<li>Heart rate is typically higher (~80-100 bpm at rest).<\/li>\n<li>Surgeons cannot reattach parasympathetic nerves; they &#8220;reconnect&#8221; major vessels, not nerves.<\/li>\n<\/ul>\n<h1><strong>Pathophysiology &amp; Clinical Implications:<\/strong><\/h1>\n<ul>\n<li>If the\u00a0<strong>SA node or internodal pathways<\/strong>\u00a0are damaged or fail, the\u00a0<strong>AV node<\/strong>\u00a0becomes the secondary pacemaker.<\/li>\n<li><strong>Pacemaker implantation:<\/strong>\u00a0Used if intrinsic conduction is insufficient, especially if damage is extensive.<\/li>\n<\/ul>\n<p>Its rate supports life but may require intervention for optimal heart function.<\/p>\n<h1><strong>Summary:<\/strong><\/h1>\n<p>The heart\u2019s electrical activity begins with the SA node, setting a regular rhythm. The conduction system ensures synchronized contraction of atria and ventricles. Damage to primary nodes can be compensated temporarily by secondary pacemakers, but long-term support often requires a pacemaker. Understanding this pathway is crucial in diagnosing arrhythmias and designing appropriate treatments.<\/p>\n","protected":false},"author":1370,"menu_order":9,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["zoe-soon"],"pb_section_license":"cc-by-nc-sa"},"chapter-type":[],"contributor":[60],"license":[57],"class_list":["post-4722","chapter","type-chapter","status-web-only","hentry","contributor-zoe-soon","license-cc-by-nc-sa"],"part":55,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4722","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/users\/1370"}],"version-history":[{"count":5,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4722\/revisions"}],"predecessor-version":[{"id":5280,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4722\/revisions\/5280"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/parts\/55"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4722\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/media?parent=4722"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapter-type?post=4722"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/contributor?post=4722"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/license?post=4722"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}