Abnormal Septal Motion (ASM): Causes & Clinical Significance

Abnormal Septal Motion (ASM) refers to paradoxical or dyssynchronous movement of the interventricular septum observed on echocardiography (M-mode, 2D, tissue Doppler) or cardiac MRI. Instead of moving smoothly toward the left ventricular free wall during systole, the septum may move away (paradoxical), show delayed thickening, or exhibit post-systolic shortening.

Common Causes and Mechanisms

Right Bundle Branch Block (RBBB): Delayed RV activation → septal flash (early systolic thickening) followed by post-systolic thickening.

Post-cardiac surgery: Pericardial constraint, epicardial pacing leads, or surgical trauma alter septal mechanics.

Condition	Mechanism of ASM
Coronary Artery Disease (CAD)	Ischemia → septal stunning, akinesis, or dyskinesis; post-systolic thickening in stunned myocardium.
Hypertrophic Cardiomyopathy (HCM)	Asymmetric septal hypertrophy → systolic anterior motion (SAM) of mitral valve, diastolic dysfunction, abnormal septal contraction/relaxation.
Ventricular Septal Defect (VSD)	Left-to-right shunt → volume overload of RV → septal flattening/paradoxical motion in diastole (volume) and systole (pressure).
Dilated Cardiomyopathy (DCM)	Global systolic dysfunction → reduced septal thickening, dyssynchrony.

Diagnostic Value

ASM is a sign, not a diagnosis. Its pattern, timing, and associated findings help identify the underlying etiology. For example:

• Septal flash + post-systolic thickening → RBBB or RV pacing.
• Paradoxical systolic motion + VSD flow on Doppler → significant shunt.
• Reduced septal thickening + global hypokinesis → DCM or ischemic cardiomyopathy.

Severity correlates with prognosis in HCM (SAM severity), DCM (dyssynchrony predicts CRT response), and CAD (stunning vs. infarction).

Management

Directed at the underlying cause:

• Revascularization (PCI/CABG) for ischemic ASM.
• ICD/CRT for cardiomyopathy with dyssynchrony.
• VSD closure (surgical or device) for hemodynamically significant shunts.
• Pacing optimization (AV/VV delay) for pacing-induced ASM.
• Medical therapy for HCM (beta-blockers, verapamil, disopyramide, mavacamten).

ASM on imaging should prompt a focused search for the etiology—it's a window into ventricular mechanics and pathology.