Review Question - QID 218262

This patient with a history of coronary artery disease with stent placement is found to have paradoxical splitting (P2 before A2, with splitting more pronounced on expiration). This suggests a conduction delay to the left ventricle, which may be seen in a left bundle branch block (LBBB) as seen in Figure D.

The A2 and P2 components of S2 separate (split) during inspiration under normal physiologic conditions. Increased venous return to the right ventricle and decreased left-sided filling during inspiration lead to a longer right ventricular ejection time. In turn, this is appreciated as a delay of P2 after A2 of between 20 and 60 milliseconds. Paradoxical or reversed splitting of S2 occurs when P2 precedes A2 during inspiration. During expiration, the sounds may become single. The two main causes of paradoxical splitting are conduction and hemodynamic disturbances. Delays in conduction to the left ventricle compared to the right ventricle can lead to paradoxical splitting. These processes include Wolff-Parkinson-White syndrome (pre-excitation of the right ventricle), right ventricular pacing, and a left bundle branch block. Prolonged left ventricular ejection fraction such as in aortic stenosis, may also lead to paradoxical splitting. However, paradoxical splitting can often be difficult to appreciate in practice, as P2 may often be inaudible due to the systolic aortic stenosis murmur.

Gray discusses the etiology, mechanism, and utility of the paradoxical splitting of the second heart sound and presents the phonocardiograms of 40 cases. The author found that paradoxical splitting was found in all cases of left bundle-branch block (LBBB), half of cases of aortic stenosis, and one-third of cases of patent ductus arteriosus studied. The author recommends the auscultation for paradoxical splitting of S2 at the second or third left intercostal space to help distinguish LBBB from other causes of wide splitting.

Figure/Illustration A shows an EKG from a patient with atrial fibrillation (AF). Characteristics features of AF include the irregularly irregular R-R intervals (blue arrows), absence of P waves, and disorganized baseline electrical activity (yellow arrow).

Figure/Illustration B shows an EKG from a patient with an incomplete right bundle branch block (RBBB). Characteristics features of incomplete RBBB include slightly prolonged QRS of 110 ms (yellow box) and an rSr’ in V1 (blue boxes).

Figure C shows a normal EKG.

Figure/Illustration D shows an EKG from a patient with a LBBB. Note the prolonged QRS duration (yellow box), the rS in V1 and V2 (blue box), and broad, notched R wave in V5 and V6 (green boxes) that are typically found in LBBB.

Figure/Illustration E shows an EKG from a patient with right ventricular hypertrophy (RVH). Note the right axis deviation (yellow boxes indicating a downward QRS in lead I and an upward QRS in lead aVF), dominant R wave in V1 (>7mm tall, blue box), and dominant S wave in V6 (> 7mm deep, green box) typically found in RVH.

Incorrect Answers:
Answer 1: Figure A shows an EKG from a patient in atrial fibrillation (AF). Cardiac auscultation in patients with AF will reveal an irregularly irregular rhythm, as well as a variable S1.

Answer 2: Figure B shows an EKG from a patient with an incomplete RBBB. An ostium secundum type atrial septal defect can cause incomplete RBBB by increasing right-sided flow, thus leading to increased right ventricular (RV) pressures and defects in right-sided electrical conduction. Patients with an ASD would be expected to have wide and fixed splitting of S2 throughout the respiratory cycle. Additionally, S1 splitting can sometimes be appreciated in patients with a RBBB.

Answer 3: Figure C shows a normal EKG from a patient in sinus rhythm. On cardiac auscultation, physiologic splitting of S2 would be expected. Therefore, the pulmonic component of S2 would be auscultated after the aortic component of S2; splitting would be more pronounced on inspiration.

Answer 5: Figure E shows an EKG with evidence of RV hypertrophy and right axis deviation. This EKG would be consistent with pulmonic stenosis. In pulmonic stenosis, there would be expected to be wide splitting of S2 that is increased on inspiration.

Bullet Summary:
In paradoxical splitting of S2, P2 occurs before A2 in expiration; causes of paradoxical splitting include aortic stenosis and delayed conduction to the left ventricle such as in left bundle branch block (LBBB).