The dicrotic notch is a small, brief dip in the arterial blood pressure waveform that marks the moment the aortic valve snaps shut at the end of each heartbeat. It sits between the peak of systolic pressure and the long decline of diastolic pressure, acting as the boundary line between the heart’s pumping phase and its resting phase. Though it looks like a minor wiggle on a monitor screen, the notch carries a surprising amount of clinical information, from how stiff your arteries are to whether a critically ill patient is responding to treatment.
What Produces the Notch
For decades, the standard textbook explanation was straightforward: blood briefly flows backward toward the heart once the left ventricle stops contracting, and this backflow slams the aortic valve shut, producing a momentary pressure dip. That story is not quite wrong, but the physical mechanism turns out to be more nuanced than a simple door swinging closed.
Research using high-speed imaging and echocardiography established that the notch originates primarily from the aortic valve itself. In a healthy valve, the leaflets distend slightly as blood decelerates and then snap back into their closed position, and it is this elastic recoil that generates the characteristic pressure deflection. When the valve is diseased, the recoil pattern changes, but the notch still traces back to valve motion rather than to stretching and rebounding of the aortic walls themselves.1The American Journal of Cardiology. Valve origin of the aortic incisura A more recent hypothesis goes further, proposing that the rapid deceleration of the entire valve apparatus at the instant of closure creates an acceleration-driven pressure transient, supported by calculations from computed tomography scans of the human aorta.2PubMed. Mechanics of the dicrotic notch: An acceleration hypothesis
Echocardiographic studies have pinned down the timing with precision. The valve reaches its fully closed position at the point of zero forward flow, and this event precedes the audible second heart sound (the familiar “dub” of a stethoscope) by roughly 4 to 10 milliseconds.3PubMed. Hemodynamic correlates of the normal aortic valve echogram. A study of sound, flow, and motion The notch itself is essentially the pressure fingerprint of that closure event. By the time the sound travels through the chest wall, the valve has already been shut for a few milliseconds.
Why the Notch Looks Different Depending on Where You Measure
If you place a pressure sensor directly in the aorta, the dicrotic notch is sharp and unmistakable. Move the sensor out to the brachial artery in the arm, and the waveform looks different: the main systolic peak is taller and sharper, and the crisp notch you saw centrally has smoothed out or shifted into a gentler diastolic wave. This transformation is not a measurement error. As the pressure pulse travels away from the heart and into smaller, more muscular arteries, wave reflections from branch points and vessel tapering reshape the waveform. Pulse-wave modeling of the human arm arterial system accurately predicts these changes, including the disappearance of the aortic incisura and the emergence of a broader diastolic wave further downstream.4PubMed. Pulse-wave model of brachial arterial pressure modulation in aging and hypertension
This matters practically because clinicians reading a radial artery line in the wrist are looking at a waveform that has already been reshaped by the vascular tree. The notch there is not the same clean marker of aortic valve closure that it is centrally. Recognizing where a waveform was recorded helps avoid misinterpreting a blunted notch as a sign of pathology when it is really just the physics of wave propagation doing its thing.
How Aging and Arterial Stiffness Erase the Notch
One of the most consistent findings across vascular research is that the dicrotic notch fades with age. Young, healthy arteries are compliant and elastic, so the pressure wave bounces and reverberates in a way that preserves a clear notch. As arteries stiffen over the years, the pulse wave travels faster, reflected waves arrive earlier and merge with the systolic peak, and the notch gets progressively blunted or disappears altogether.5PLOS Digital Health. Vascular age estimation using a consumer wearable sleep tracker
A study examining retinal blood velocity waveforms across age groups quantified this starkly. Among young adults, about 70% had a visible dicrotic notch, compared with roughly half of middle-aged adults and only about 14% of older adults. The decline was statistically significant and held up even in people without hypertension.6PubMed Central. Retinal Blood Velocity Waveform Characteristics With Aging and Arterial Stiffening in Hypertensive and Normotensive Subjects The notch, in other words, is partly a marker of vascular youth. Its absence does not necessarily signal disease in an older person, but in a younger person, a blunted notch may raise a flag about premature arterial stiffening.
Researchers have begun exploring whether the notch could serve as a low-cost screening tool for vascular age. Consumer wearable devices that use optical sensors already capture pulse waveforms from the wrist or finger, and the presence or morphology of the dicrotic notch in those tracings correlates with measures of arterial stiffness.7PLOS Digital Health. Vascular age estimation using a consumer wearable sleep tracker The idea is appealing because it would require no blood draw and no special equipment beyond the fitness tracker someone already owns, though the technology is still being validated.
What the Notch Tells Clinicians at the Bedside
In intensive care units and operating rooms, doctors and nurses watch arterial waveforms on monitors constantly. The dicrotic notch is not just an anatomical curiosity there; it provides real-time clues about what is happening inside the cardiovascular system. Detecting it within each cardiac cycle is essential for estimating cardiac output, calculating how fast the pulse wave moves through the arterial tree, measuring how long the left ventricle spends ejecting blood, and feeding data into machine-learning models that predict blood pressure changes.8PubMed Central. An algorithm to detect dicrotic notch in arterial blood pressure and photoplethysmography waveforms using the iterative envelope mean method
The shape and position of the notch also help distinguish different kinds of cardiovascular trouble. Simulation studies have shown that waveform features describing the notch correlate well with specific types of hemodynamic instability, whether the problem is insufficient blood volume returning to the heart, poor heart muscle contraction, or excessive resistance in the blood vessels.9PubMed Central. Distinct morphologies of arterial waveforms reveal preload-, contractility-, and afterload-deficient hemodynamic instability: An in silico simulation study A trained eye can sometimes spot these patterns before lab results or echocardiograms confirm the diagnosis.
Reading the Notch in Septic Shock
Sepsis is one clinical scenario where the dicrotic notch earns its keep. Patients in septic shock often develop a rapid heart rate, and clinicians need to figure out whether that fast rate is a helpful compensatory response or a sign that the heart muscle itself is struggling. Standard ultrasound measurements of the heart sometimes cannot tell the difference.
A study of septic shock patients found that the pressure difference between the systolic peak and the dicrotic notch could discriminate between these two situations. Patients whose hearts had adequate contractile reserve showed a higher gap between systolic pressure and dicrotic notch pressure at baseline, around 53 mmHg, compared with about 40 mmHg in those whose hearts were already weakening. When a drug was given to slow the heart rate, the gap held steady in the stronger group but dropped sharply in the weaker group, exposing a hidden loss of heart muscle function that conventional echo had not detected.10Biomedical Signal Processing and Control. Systolic-dicrotic notch pressure difference can identify tachycardic patients with septic shock at risk of cardiovascular decompensation following pharmacological heart rate reduction The notch, in this context, served as an early warning system.
How Drugs Reshape the Waveform
Vasoactive medications, the drugs used to tighten or relax blood vessels in critically ill patients, visibly alter the dicrotic notch. Vasopressors like norepinephrine increase vascular tone, and studies have observed that after their administration the notch tends to become more prominent and shifts toward a morphology associated with healthier waveforms. Vasodilators like nitroglycerin have roughly the opposite effect, opening up the vasculature and changing the balance between forward flow and wave reflections.11European Heart Journal. Acute Cardiovascular Care. Reservoir-excess pressure analysis, aiding critical care management by revealing subtle changes in vasomotor status, is closely linked to dicrotic notch morphology
Pulse-wave modeling predicted these drug effects decades before they were mapped in detail at the bedside. The same models that explain how the waveform changes shape as it travels from the aorta to the wrist also reproduce the waveform distortions caused by pharmacologically induced vasoconstriction and vasodilation.12PubMed. Pulse-wave model of brachial arterial pressure modulation in aging and hypertension For clinicians, the practical takeaway is that a sudden change in the notch’s appearance may signal that a vasoactive drug is working, wearing off, or that the patient’s vascular tone has shifted for some other reason, sometimes before blood pressure numbers on the monitor move appreciably.
The Notch During Valve Replacement Procedures
One of the more novel uses of the dicrotic notch has emerged in the cardiac catheterization lab during transcatheter aortic valve implantation, the procedure where a new valve is threaded into the heart through a blood vessel rather than through open-chest surgery. A common complication is paravalvular regurgitation, meaning blood leaks around the edges of the newly placed valve. Detecting this leak during the procedure, rather than after, gives operators a chance to fix it in real time.
A study found that when a clear dicrotic notch reappeared on the arterial waveform after the new valve was deployed, it was a strong signal that the valve was seated well and not leaking significantly. Among patients who had a visible notch, only about 8% showed significant regurgitation, compared with roughly 33% of those without a notch. When the notch was present and diastolic blood pressure remained at or above 40 mmHg, the rate of significant leaking dropped to about 3%.13University of Helsinki. Association between dicrotic notch and paravalvular regurgitation during the TAVI procedure The notch essentially serves as a quick visual check, available on the same monitor the operator is already watching, without needing to pause the procedure for additional imaging.
Optical Sensors and Wearable Technology
You do not need an arterial catheter to see a version of the dicrotic notch. Photoplethysmography, the optical sensing technology built into pulse oximeters and smartwatches, measures relative changes in blood volume in the small vessels of your fingertip or wrist. The resulting waveform is not an exact replica of the central arterial pressure curve, but it preserves many of its features, including the notch. Algorithms designed to locate the notch in these optical signals can extract useful information about cardiac timing and vascular health without any needle or catheter.14International Journal of Computer Applications. Novel Notch Detection Algorithm for Detection of Dicrotic Notch in PPG Signals
The challenge is that the notch in a photoplethysmography signal is often faint, noisy, or shifted compared with what you would see on an invasive arterial line. Automated detection algorithms have to contend with motion artifacts, skin tone variations, and the natural blunting that comes from measuring at the periphery rather than centrally. Recent work using iterative signal processing methods has improved detection accuracy across both invasive arterial waveforms and optical signals.15PubMed Central. An algorithm to detect dicrotic notch in arterial blood pressure and photoplethysmography waveforms using the iterative envelope mean method Machine-learning models trained on annotated waveforms can now locate the notch with average errors around 6 milliseconds, which is precise enough to derive downstream metrics like arterial stiffness indices that closely match human-annotated results.16Biomedical Signal Processing and Control. PulseAI: An automated machine learning-based augmentation index detector for arterial stiffness monitoring from cuff-based measurements
This accuracy matters because the whole point of finding the notch in a wearable signal is to calculate something useful from it. If the notch is mislocated by even 20 or 30 milliseconds, downstream estimates of ejection time or stiffness can be thrown off significantly. As algorithms improve, the prospect of passive, continuous vascular health monitoring from a wristband moves from theoretical to genuinely practical.
Timing Mechanical Heart Support
The dicrotic notch has a long-standing role in one of the more dramatic interventions in cardiology: the intra-aortic balloon pump. This device is a long balloon threaded into the aorta that inflates and deflates in sync with the heartbeat. It inflates during diastole to push blood forward into the coronary arteries and deflates just before the next heartbeat so the left ventricle faces less resistance when it ejects. Getting the timing right is critical, and the dicrotic notch is the landmark that tells the device when diastole begins.
Because the balloon pump needs to inflate within milliseconds of diastole starting, predicting where the notch will fall within each individual heartbeat, rather than just detecting it after the fact, becomes important. Research into real-time prediction algorithms found that the notch’s timing varies only slightly from beat to beat, even in patients with irregular heart rhythms, making reliable intra-beat prediction feasible for driving balloon inflation timing.17PubMed. Performance of a real-time dicrotic notch detection and prediction algorithm in arrhythmic human aortic pressure signals An inflation command that arrives a fraction of a second too early fights against the heart; one that arrives too late misses the window for boosting coronary perfusion. The notch, small as it is on the screen, is the pivot point for the entire device’s effectiveness.
Common Misconceptions
One widespread misunderstanding is that the dicrotic notch is caused by blood bouncing off the closed aortic valve. This “water hammer” image is intuitive but does not hold up. Experimental evidence from animal models showed that a simple backward wave reflection from the valve cannot account for the notch’s characteristics, which is what led researchers to explore valve-apparatus acceleration as the underlying mechanism.18PubMed. Mechanics of the dicrotic notch: An acceleration hypothesis The difference is subtle but real: the notch comes from the valve’s own elastic behavior during closure, not from a reflected pressure wave crashing against it.
Another common confusion is between the dicrotic notch and the dicrotic wave. The notch is the downward dip; the dicrotic wave is the small upward bounce that follows it. In peripheral arteries, the notch may vanish but the dicrotic wave can remain or even become more prominent, which sometimes leads to the two features being conflated. Clinicians and textbooks occasionally use the terms loosely, which does not help. If someone tells you the dicrotic notch has “disappeared” in an older patient’s radial artery tracing, what they usually mean is that the sharp central notch has been smoothed out by wave propagation and arterial stiffening into a broader, gentler undulation. The hemodynamic event it represents, aortic valve closure, is still happening on schedule.
A third misconception is that the notch is a fragile curiosity visible only on expensive hospital monitors. Optical sensors in pulse oximeters and consumer wearables routinely capture it, and as detection algorithms improve, the notch is increasingly being used outside the ICU for purposes its original describers never imagined, from estimating your vascular age while you sleep to flagging early signs of arterial disease from a smartwatch.19PLOS Digital Health. Vascular age estimation using a consumer wearable sleep tracker