What syndrome is characterized by a diastolic flattening of the LV posterior wall observed on m-mode?

The syndrome characterized by diastolic flattening of the left ventricular (LV) posterior wall observed on M-mode echocardiography is indeed constrictive pericarditis. This condition occurs when the pericardium—the fibrous sac surrounding the heart—becomes thickened and fibrotic, which restricts the heart's ability to fill properly during diastole.

In constrictive pericarditis, the impaired filling leads to characteristic echocardiographic findings. The flattening of the LV posterior wall during diastole is a consequence of the increased pressure within the pericardial space that artificially compresses the heart, affecting its geometry. This is a key feature that helps differentiate constrictive pericarditis from other conditions that may also lead to diastolic dysfunction but do not exhibit the same M-mode findings.

Overall, recognizing these specific echocardiographic traits is crucial for accurate diagnosis and effective management of the underlying cause of the symptoms presented by the patient.