[[File:Wiggers Diagram.svg|thumb|400px|[[Wiggers diagram]] of various events of a [[cardiac cycle]], with ''2nd'' heart sound at bottom.]]
{{Short description|Detailed explanation of Split S2 in cardiology}}
A '''split S2''' is a finding upon auscultation of the [[Heart sounds#S2|S2 heart sound]].<ref name="urlThe Auscultation Assistant - Split S2">{{cite web |url=http://www.wilkes.med.ucla.edu/SplitS2main.htm |title=The Auscultation Assistant - Split S2 |work= |accessdate=2009-01-09}}</ref>
It is caused when the closure of the [[aortic valve]] (A<sub>2</sub>) and the closure of the [[pulmonary valve]] (P<sub>2</sub>) are not synchronized during inspiration. The second heart sound (S2) is caused by the closure of the aortic and pulmonic valves, which causes vibration of the valve leaflets and the adjacent structures. The aortic valve closes slightly before the pulmonic, and this difference is accentuated during inspiration when S2 splits into two distinct components (physiological splitting). During expiration, the pulmonic valve closes at nearly the same time as the aortic, and splitting of S2 cannot be heard.
==Split S2==
[[File:Heart sounds diagram.png|thumb|Diagram of heart sounds, including S2 splitting]]
'''Split S2''' refers to the phenomenon where the second heart sound (S2) is audibly divided into two distinct components. This occurs due to the asynchronous closure of the [[aortic valve]] (A2) and the [[pulmonary valve]] (P2) during the cardiac cycle. The splitting of S2 is a normal physiological occurrence that can vary with respiration.
Exercise increases the intensity of both the aortic and pulmonic components of S2, whereas deep inspiration increases the intensity of the pulmonic component only.
==Physiology==
The second heart sound, S2, is primarily produced by the closure of the semilunar valves, which include the aortic and pulmonary valves. During inspiration, the negative pressure in the thoracic cavity increases venous return to the right side of the heart, leading to a delay in the closure of the pulmonary valve. This results in the splitting of S2 into two audible components: A2 and P2.
==Physiological split==
===Normal Splitting===
'''During inspiration''', the chest wall expands and causes the intrathoracic pressure to become more negative (think of a vacuum). The increased negative pressure allows the lungs to fill with air and expand. While doing so, it also induces an increase in venous blood return from the body into the right atrium via the superior and inferior venae cavae, and into the right ventricle by increasing the pressure gradient (blood is being pulled by the vacuum from the body and towards the right side of the heart). Simultaneously, there is a reduction in blood volume returning from the lungs into the left atrium (the blood wants to stay in the lungs because of the vacuum surrounding the lungs, and [[Pulmonary vascular resistance|PVR]] is lower because of lung expansion). Since there is an increase in blood volume in the right ventricle during inspiration, the pulmonary valve (P<sub>2</sub> component of S<sub>2</sub>) stays open longer during ventricular systole due to an increase in ventricular emptying time, whereas the aortic valve (A<sub>2</sub> component of S<sub>2</sub>) closes slightly earlier due to a reduction in left ventricular volume and ventricular emptying time. Thus the P<sub>2</sub> component of S<sub>2</sub> is delayed relative to that of the A<sub>2</sub> component. This delay in P<sub>2</sub> versus A<sub>2</sub> is heard as a slight broadening or even "splitting" of the second heart sound; though it is usually only heard in the pulmonic area of the chest because the P<sub>2</sub> is soft and not heard in other areas.
In healthy individuals, the splitting of S2 is most pronounced during inspiration and diminishes during expiration. This is known as "physiological splitting." During inspiration, the increased venous return to the right heart delays the closure of the pulmonary valve, while the aortic valve closure remains relatively unchanged.
'''During expiration''', the chest wall collapses and decreases the negative intrathoracic pressure (compared to inspiration). Therefore, there is no longer an increase in blood return to the right ventricle versus the left ventricle and the right ventricle volume is no longer increased. This allows the pulmonary valve to close earlier such that it overlaps the closing of the aortic valve, and the split is no longer heard.
===Wide Splitting===
Wide splitting of S2 can occur in conditions that delay right ventricular emptying, such as [[right bundle branch block]] or [[pulmonary stenosis]]. In these cases, the delay in P2 is more pronounced, leading to a wider interval between A2 and P2.
It is physiologically normal to hear a "splitting" of the second heart tone in younger people, during inspiration and in the "pulmonary area", i.e. the 2nd ICS (intercostal space) at the left edge of the sternum.
===Fixed Splitting===
Fixed splitting of S2 is characterized by a constant interval between A2 and P2, regardless of the respiratory cycle. This is often associated with an [[atrial septal defect]] (ASD), where the left-to-right shunt maintains a constant volume load on the right ventricle, leading to a persistent delay in P2.
===Steps===
===Paradoxical Splitting===
# Chest wall expands during inspiration
Paradoxical splitting, or "reversed splitting," occurs when the interval between A2 and P2 is greater during expiration than inspiration. This can be seen in conditions that delay left ventricular emptying, such as [[left bundle branch block]] or [[aortic stenosis]]. In these cases, A2 is delayed, causing the split to be more pronounced during expiration.
# Intrathoracic pressure becomes more negative to form a vacuum
# Venous return from the body to the right heart increases, venous return from the lungs to the left heart decreases
===Analysis of pressure===
==Clinical Significance==
According to Harrison's Principles of Internal Medicine, "Normally, blood pressure falls during inspiration (equal or less than 10 mmHg), due to an increase in blood flow into the right ventricle with displacement of the interventricular septum to the left, decreasing left ventricular filling and cardiac output".<ref name="isbn0-07-149619-X">{{cite book |author1=Loscalzo, Joseph |author2=Charles M. Wiener |author3=Bloomfield, Gerald T. |author4=Fauci, Anthony S. |author5=Braunwald, Eugene |author6=Dennis L. Kasper |author7=Hauser, Stephen L |author8=Longo, Dan L. |title=Harrison's principles of internal medicine: self-assessment and board review |publisher=McGraw-Hill Medical |location= |year=2008 |pages= |isbn=0-07-149619-X |oclc= |doi= |accessdate=}} Question 29 disorders of the cardiovascular system</ref>
The presence and pattern of S2 splitting can provide valuable diagnostic information about underlying cardiac conditions. Auscultation of heart sounds, including the assessment of S2 splitting, is an important component of the physical examination in cardiology.
The pressure in the right ventricle tries to open the pulmonary valve. The pressure in the pulmonary artery tries to close the pulmonary valve. Remember that the higher pressure will "win". Hence, the closure of the pulmonary valve (P<sub>2</sub>) will be delayed since the pressure in the right ventricle is increased in inspiration, opposing the pressure in the pulmonary artery and keeping it open longer than in expiration. The change in A<sub>2</sub> is not that evident. Thus P<sub>2</sub> appears after A<sub>2</sub> in inspiration.
==Related Pages==
* [[Heart sounds]]
==Pathological split==
* [[Cardiac cycle]]
* [[Aortic valve]]
The different types of split S<sub>2</sub> can be associated with medical conditions:
* [[Pulmonary valve]]
* [[Atrial septal defect]]
* Split during inspiration: normal.<ref name="PerezBotsford2007">{{cite book|author1=Mayra Perez|author2=Lindsay K. Botsford|author3=Winston Liaw|title=Deja Review: Family Medicine|url=https://books.google.com/books?id=cAakbVN9RU4C&pg=PA28|accessdate=11 November 2010|date=18 October 2007|publisher=McGraw Hill Professional|isbn=978-0-07-148568-5|pages=28–}}</ref> (See above)
* [[Right bundle branch block]]
*Wide splitting: seen in conditions that delay RV emptying (pulmonic stenosis, RBBB). Delay in RV emptying causes delayed pulmonic sound (regardless of breath); it is an exaggeration of normal splitting sounds.
* [[Left bundle branch block]]
* Split during expiration: Reverse splitting indicates pathology. [[Aortic stenosis]], [[hypertrophic cardiomyopathy]], [[left bundle branch block]] (LBBB), and a ventricular pacemaker could all cause a reverse splitting of the second heart sound.<ref name="Longo2012">{{cite book|author=Dan Longo|title=Principles of Internal Medicine|publisher=McGraw Hill Medical|isbn=978-0-07-174890-2|pages=1826–1827}}</ref>
* Split during both inspiration and expiration:
** If splitting does not vary with inspiration, it is termed a "fixed split S<sub>2</sub>" and is usually due to a septal defect,<ref name="Mangione2000">{{cite book|author=Salvatore Mangione|title=Physical diagnosis secrets|url=https://books.google.com/books?id=-BmjqujomUMC&pg=PA215|accessdate=11 November 2010|year=2000|publisher=Elsevier Health Sciences|isbn=978-1-56053-164-7|pages=215–}}</ref> such as an [[atrial septal defect]] (ASD). The ASD creates a left to right shunt that increases the blood flow to the right side of the heart, thereby causing the pulmonary valve to close later than the aortic valve independent of inspiration/expiration.
** A bundle branch block either LBBB or RBBB, (although RBBB is known to be associated only with [[S1 split]]), will produce continuous splitting but the degree of splitting will still vary with respiration.
When the pulmonary valve closes ''before'' the aortic valve, this is known as a "paradoxically split S<sub>2</sub>".<ref name="Chiocca2010">{{cite book|author=Ellen Chiocca|title=Advanced Pediatric Assessment|url=https://books.google.com/books?id=3mSTPSG4c5QC&pg=PA379|accessdate=11 November 2010|date=1 March 2010|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-9165-6|pages=379–}}</ref> On physical exam, paradoxical splitting is appreciated as increased splitting on expiration relative to inspiration, versus normal splitting where inspiration will increase splitting. It is seen in conditions that delay left ventricular emptying (e.g., aortic stenosis, left bundle branch block).
Split S2 refers to the phenomenon where the second heart sound (S2) is audibly divided into two distinct components. This occurs due to the asynchronous closure of the aortic valve (A2) and the pulmonary valve (P2) during the cardiac cycle. The splitting of S2 is a normal physiological occurrence that can vary with respiration.
Physiology
The second heart sound, S2, is primarily produced by the closure of the semilunar valves, which include the aortic and pulmonary valves. During inspiration, the negative pressure in the thoracic cavity increases venous return to the right side of the heart, leading to a delay in the closure of the pulmonary valve. This results in the splitting of S2 into two audible components: A2 and P2.
Normal Splitting
In healthy individuals, the splitting of S2 is most pronounced during inspiration and diminishes during expiration. This is known as "physiological splitting." During inspiration, the increased venous return to the right heart delays the closure of the pulmonary valve, while the aortic valve closure remains relatively unchanged.
Wide Splitting
Wide splitting of S2 can occur in conditions that delay right ventricular emptying, such as right bundle branch block or pulmonary stenosis. In these cases, the delay in P2 is more pronounced, leading to a wider interval between A2 and P2.
Fixed Splitting
Fixed splitting of S2 is characterized by a constant interval between A2 and P2, regardless of the respiratory cycle. This is often associated with an atrial septal defect (ASD), where the left-to-right shunt maintains a constant volume load on the right ventricle, leading to a persistent delay in P2.
Paradoxical Splitting
Paradoxical splitting, or "reversed splitting," occurs when the interval between A2 and P2 is greater during expiration than inspiration. This can be seen in conditions that delay left ventricular emptying, such as left bundle branch block or aortic stenosis. In these cases, A2 is delayed, causing the split to be more pronounced during expiration.
Clinical Significance
The presence and pattern of S2 splitting can provide valuable diagnostic information about underlying cardiac conditions. Auscultation of heart sounds, including the assessment of S2 splitting, is an important component of the physical examination in cardiology.
