The dip sign is a specific finding in cardiac hemodynamics that provides insight into the heart’s ability to fill with blood. This pattern is observed when evaluating pressure changes inside the ventricles during the relaxation phase known as diastole. This sign indicates an unusual pressure dynamic, suggesting the heart’s filling process is physically restricted. Understanding this distinct pressure tracing helps physicians identify underlying conditions that impair the normal expansion of the heart muscle or the surrounding sac.
What the Dip Sign Represents in Heart Function
The dip sign, often called the “dip and plateau” or “square root sign,” represents abnormal pressure dynamics within the ventricles during diastole. This phase begins when the mitral and tricuspid valves open, allowing blood to rush from the atria into the ventricles. On a pressure tracing, it is defined by a rapid and deep fall in ventricular pressure immediately following valve opening.
This initial, sharp pressure drop is the “dip,” reflecting the sudden rush of blood into the chamber after contraction. Following this rapid early filling, the pressure trace abruptly reverses direction and rises sharply. The pressure then levels off and remains elevated for the remainder of diastole, forming the “plateau.”
The resulting waveform resembles a square root symbol. This characteristic shape signifies that while initial filling is unimpeded, the volume the ventricle can ultimately hold is severely limited. The pressure remains high and fixed during the later filling phase because the chamber cannot expand further.
The Hemodynamic Events Causing the Dip
The physiological mechanism creating the dip sign relates directly to restricted ventricular compliance—the inability of the heart muscle or surrounding tissue to stretch. The deep “dip” occurs because the atria, under high pressure from upstream congestion, force blood rapidly into the ventricles when the valves open. This quick movement causes a momentary drop in ventricular pressure.
This rapid filling phase is quickly terminated by an external or internal constraint on the ventricle. In certain diseases, the heart is encased by a stiff, non-stretching layer, or the heart muscle itself is rigid. Once the ventricle reaches the maximum volume allowed by this constraint, further filling is immediately met with sharp resistance.
This abrupt halt causes the intraventricular pressure to rise dramatically and sustain a high pressure for the duration of the filling period, forming the “plateau.” This highlights a severe restriction on the heart’s ability to relax and expand in the middle and late stages of diastole, fixing the heart’s total diastolic volume.
Diagnosing Pericardial and Myocardial Disease
The dip and plateau sign is highly characteristic of diseases that compromise ventricular filling, primarily Constrictive Pericarditis (CP) and Restrictive Cardiomyopathy (RCM).
In Constrictive Pericarditis, the stiff, often thickened pericardium—the sac surrounding the heart—acts as a rigid shell preventing the ventricles from expanding fully. The heart muscle may remain healthy, but its movement is physically restricted by this outer layer.
Restrictive Cardiomyopathy, by contrast, is a disease where the heart muscle itself becomes stiff and non-compliant, often due to infiltration by abnormal proteins or tissue. In both conditions, the heart’s ability to relax and accept blood is impaired, leading to the characteristic pressure tracing. Differentiating between CP and RCM is important because Constrictive Pericarditis can often be cured surgically by removing the constricting pericardium.
While the dip sign is similar in both, other specific hemodynamic findings are necessary for a final diagnosis. For instance, in CP, the elevated diastolic pressures in all four heart chambers are often nearly equal, known as pressure equalization. The dip sign serves as a powerful initial indicator that one of these severe diastolic filling disorders is present.
Tools Used to Visualize the Dip Sign
The most definitive method for visualizing the dip sign is invasive cardiac catheterization, which allows physicians to directly measure pressure tracings inside the ventricles. During this procedure, a catheter is threaded into the heart chambers to record pressure changes throughout the cardiac cycle. The resulting graph directly displays the rapid early dip followed by the sustained plateau pattern.
While catheterization provides the most accurate pressure data, non-invasive imaging offers indirect evidence. Doppler echocardiography, an ultrasound of the heart, measures the speed and pattern of blood flow entering the ventricles. This technique shows the rapid acceleration of blood flow during early diastole (causing the dip), followed by an abrupt deceleration as the restricted volume is reached.
The exaggerated movement of the septum during respiration is another sign often seen with constrictive physiology that complements the pressure tracing. These non-invasive tools provide sufficient detail for diagnosis in many cases, but the invasive pressure tracing remains the gold standard for confirming the characteristic dip and plateau sign.