From tube to transducer

The original 1976 profiles needed a catheter threaded into the heart. That is fine in intensive care. It is not something you do to an outpatient every few months.

What changed is that ultrasound got good enough to estimate the same things from the outside. The paper states that invasive assessment in critically ill patients has been replaced by non-invasive evaluation, and argues that echo can now sort patients into the four profiles well enough to guide treatment.

This part is about the specific measurements. If you have ever looked at an echo report and seen a line of abbreviations, some of these are what they mean.

Measuring "wet": the pressure signals

Doppler ultrasound measures the speed of blood flow. From the pattern of flow through the mitral valve, the valve between the left atrium and left ventricle, you can infer how stiff and pressurised the ventricle is as it fills.

The key measurements the paper names:

E/e′ ratio. "E" is the speed of blood rushing into the ventricle early in filling. "e′" (said "e prime") is how fast the heart muscle itself moves at the same moment. When the ratio of E to averaged e′ climbs above 14, it reliably reflects raised filling pressure. The paper calls E/e′ the most robust echo stand-in for high left ventricular filling pressure, and higher values are linked to disease progression and worse outcomes.

E-wave deceleration time. This is how quickly that early rush of blood slows down. When it shortens to under 150 milliseconds, it points to high filling pressures and worse prognosis. When treatment reverses these changes, it goes with normal pressures and better outcomes.

In the paper's summary of recent research, patients whose E/e′ was above 14, the wet profiles, had the worst short and long term outcomes. If they also had low cardiac index, cold and wet, it was worse again.

Measuring "wet": the lung scan

There is a second, simpler way to spot congestion. Lung ultrasound.

When fluid builds up in lung tissue, the ultrasound picks up artefacts called B-lines, vertical streaks that show up where the lung should look dark. Count the B-lines and you get a semi-quantitative measure of how congested the lungs are.

What I find striking is how well these simple streaks track everything else. The paper notes B-lines are associated with clinical signs of congestion, natriuretic peptide levels, echo signs of high filling pressure, enlarged left atrium and raised pulmonary artery pressure.

And there is a practical finding worth knowing: residual congestion on lung ultrasound at the time of hospital discharge identifies people at higher risk of readmission or death, regardless of their heart failure type. Going home still a bit wet is a risk factor in itself.

Measuring "warm" or "cold": the flow

For cardiac output, echo uses two measurements at the left ventricular outflow tract, the channel blood passes through as it leaves the heart:

  • The diameter of that channel
  • The velocity time integral (VTI), essentially the distance a column of blood travels with each beat

Multiply the area by the distance and you get stroke volume, the amount pumped per beat. Multiply that by heart rate and you get cardiac output. Adjust for body size and you get cardiac index.

The paper mentions that some researchers suggest an outflow VTI under 15 cm or a stroke volume index under 30 ml/m² as practical cut-offs for reduced output.

Why this matters beyond the ICU

The strongest point in this section is about ambulatory patients.

In a study of outpatients with reduced ejection fraction on drug treatment, those whose filling pressures stayed high or got worse, and who also had low cardiac index, had the worst outcomes. Patients whose filling pressures improved over time saw their forward flow improve too, which likely contributed to their better clinical status.

In the REVERSE trial of cardiac resynchronisation therapy, patients with raised filling pressures had higher risk of death and of heart failure getting worse. And when treatment unloads the heart by lowering filling pressure, cardiac output can go up.

The message running through all of it: echo does not just describe your heart. Tracked over time, it shows whether treatment is actually changing the pressures and flows that decide how you do.

Two tools, one picture

The paper's real proposal is combining echo with the natriuretic peptide testing from Parts 3 and 4. It describes their complementary nature as able to outweigh their individual limitations.

At one end of the spectrum you have normal flow, normal filling pressures and dry peptide levels. At the other you have low flow, high pressures and wet levels. Most patients sit somewhere between, and the combination lets a clinician place them more precisely than either tool alone.

A question worth asking

Most standard echo reports for heart failure patients already include E/e′ and often some measure of outflow. They rarely get explained.

If you have a report, look for E/e′. If it is over 14, ask what that means for your filling pressures and treatment. If there is a VTI, ask whether it suggests your output is normal or reduced. And if you have been admitted for heart failure, ask whether you had a lung ultrasound before discharge.

These are not awkward questions. They are exactly what your echo was measuring. You are just asking to hear the answer.

This series discusses a peer-reviewed clinical review. Nothing here is medical advice. Heart failure treatment should always be guided by your own cardiology team.