Paradoxical Motion of the Septum

Paradoxical septal motion, often referred to as "septal bounce," is an echocardiographic finding where the interventricular septum moves atypically during specific phases of the cardiac cycle. In a normal heart, the septum thickens and moves toward the left ventricle (posteriorly) following electrical depolarization, then moves back toward the right ventricle (anteriorly) during diastole. When this motion is paradoxical, the septum deviates from this pattern, often shifting due to changes in pressure gradients between the two ventricles or electrical conduction delays.

Why It Happens (Causes)

Cardiac Conditions

Left Bundle Branch Block (LBBB): Reversal of normal septal depolarization causes the right ventricle to contract before the left, displacing the septum posteriorly in early systole (often called "septal beaking").
Cardiac Surgery: A very common occurrence after "open" heart procedures (30%–100% of cases), potentially due to the loss of pericardial restraint, surgical inflammation, or translational error from the heart moving anteriorly.
Pericardial Disease:
- Constrictive Pericarditis: Characterized by a "double wobble" or rapid early diastolic shift toward the left ventricle, typically exaggerated during inspiration.
- Cardiac Tamponade: Similar to constriction, impaired ventricular filling leads to respiratory-dependent septal shifting.
Mitral Stenosis: Severe narrowing of the mitral valve reduces left ventricular filling, creating a negative pressure gradient that pulls the septum toward the left ventricle in early diastole.
Septal Ischaemia: Impaired blood flow to the septum can cause abnormal wall motion during systole.
Right Ventricle Pacing: Artificial pacing from the right heart chambers alters the electrical timing, leading to interventricular dyssynchrony similar to LBBB.
Congenital Absence of Pericardium: The lack of a restrictive sac allows for exaggerated anterior motion of the heart and paradoxical septal movement.

Pulmonary and Respiratory Conditions

Increased Right Ventricle (RV) Afterload:
- Pulmonary Hypertension/Cor Pulmonale: High pressures in the pulmonary arteries cause the RV to dilate and the septum to flatten or bow toward the left ventricle during systole.
- Pulmonary Embolism: Acute increases in RV afterload lead to similar paradoxical shifts.
Exaggerated Inspiratory Effort (Asthma/COPD): Large swings in intrathoracic pressure increase RV preload and afterload simultaneously, causing the septum to shift during the respiratory cycle.
Mechanical Ventilation: High PEEP (Positive End-Expiratory Pressure) or large tidal volumes in conditions like ARDS can excessively increase RV afterload, leading to posterior septal bowing.

Other Physiological Factors

Right Ventricle Volume Overload: Conditions such as a large atrial septal defect or severe tricuspid regurgitation cause the septum to flatten, predominantly during diastole, as the RV overfills.

Clinical Mechanics

The septum accounts for 25–40% of ventricular muscle mass and is considered a "motor" for both ventricles. Identification of a septal bounce is clinically significant because it suggests ventricular interdependence, where the filling or pressure of one ventricle directly impacts the function of the other through the shared septal wall. Utilizing M-mode imaging is often the best way to recognize these subtle timing differences and discern the specific underlying cause.

Normal M-Mode with no paradoxical motion of the septum.

In the context of post-PDA ligation LV dysfunction, there is evidence of mechanical dyssynchrony, with the interventricular septum and posterior wall reaching peak systolic contraction at different time points rather than synchronously.

M-mode (PLAX) – severe pulmonary hypertension pattern: The tracing demonstrates abnormal interventricular septal motion with septal flattening and paradoxical/posterior displacement during systole, reflecting significant right ventricular pressure overload. The septum does not move synchronously with the posterior wall, and there is reduced or altered inward excursion of the left ventricular cavity. Overall, this pattern is consistent with pressure-loaded right ventricle leading to interventricular septal shift, resulting in impaired LV geometry and filling—hallmarks of severe pulmonary hypertension physiology.

M-mode assessment: The left ventricular shortening fraction is calculated as ( 1.57 – 1.45 ) / 1.57 × 100 (1.57–1.45)/1.57×100, yielding 7.6%, consistent with severely reduced systolic function. There is paradoxical motion of the interventricular septum, characterized by anterior expansion during peak posterior wall contraction. The E–point septal separation (EPSS)—measured at the peak anterior excursion of the mitral valve leaflet—is increased (not measured here), further supporting left ventricular systolic dysfunction. In the context of LV dysfunction.

The images show parasternal long-axis M-mode tracings of the left ventricle in a neonate, demonstrating reduced systolic function. On the left, quantitative measurements reveal a left ventricular internal diameter in diastole (LVIDd) of 1.99 cm and in systole (LVIDs) of 1.63 cm, corresponding to a fractional shortening of 18%. There is some paradoxical motion of the interventricular septum. Normal FS of 28% in a term newborn (at least). From Echo 2 - Case October 2025.

References

Clancy DJ, Mclean A, Slama M, Orde SR. Paradoxical septal motion: A diagnostic approach and clinical relevance. Australas J Ultrasound Med. 2018 Feb 28;21(2):79-86. doi: 10.1002/ajum.12086. PMID: 34760507; PMCID: PMC8409894.

AJUM-21-79.pdf