This article reviews the left ventricular pressure (LVP) morphology and identifies problematic morphology and the cause of the morphology abnormality.  The LVP cycles is typically used to report endpoints pertaining to inotropy (contractility) and lusitropy (relaxation).  Ponemah reports dP/dtmax (dLVP/dt_max) as an index of contractility.  Indices of lusitropy are dP/dtmin (dLVP/dt_min) and Tau.

NOTE: Please refer to Surgical Manuals and Videos for PhysioTel, PhysioTel HD, and PhysioTel Digital Implants or watch the PhysioTel Digital Surgical Video Large Animal Left Ventricular Pressure (LVP), Blood Pressure (BP), and ECG for large animal surgeries and HD-S21 Surgical Video Rat Left Ventricular Pressure (LVP), Blood Pressure (BP), and ECG for rat surgeries.  Please refer to following article for mouse LVP DSI recommendation for Mouse Left Ventricular Pressure using Implantable Telemetry.

Typical morphology of the LVP signal

Figure 1 shows a typical LVP morphology.  One characteristic of typical LVP morphology is Left Ventricular End Diastolic Pressure (LVEDP) is between 0-15 mmHg.  Also, dp/dt_max occurs between midway to 2/3 of upstroke of the LVP signal.  After the upstroke of the LVP cycle, the top of the LVP signal is relatively flat.  

Abnormal Morphology

Spikes during Systole on LVP cycle and/or near or at end of diastole going negative 

Figure 3 & 4 below show peaks or spikes on the LVP cycle during systole. 

Placement of catheter

This is can be indicative of the catheter being squeezed during a contraction.  The catheter tip is potentially touching either the free ventricular wall or the intraventricular septum.  Systolic measurement should not be reported from these cycles.  When this happens shortly after surgery, it is recommended to evaluate your surgical approach.  

Catheter not fully hydrated or Clot forming in catheter tip

In addition, this can happen if the catheter isn’t fully hydrated before insertion.  It can also occur if the tip of the catheter was bent during insertion, causing gel at the tip to be extruded and leaving a void for blood to fill in and organize.  This can sometimes be easy to do during a challenging insertion.  If the catheter isn’t removed and re-gelled prior to re-insertion, a clot can form.    Please see Preventing Clots in the Catheter Tip

Portions of waveform showing negative pressures

One common reason you may see negative pressure is due to the squeezing of the gel during surgery upon inserting the catheter into the heart.  If a large amount is removed, you'll likely be able to see the abnormal morphology during surgery.  If a small amount of gel squeezed, a morphology change will likely not be seen until a clot forms (~1-2 weeks post surgery).  Please see Preventing Clots in the Catheter Tip for more information. 

Low LV dP/dtmax (index of contractility)

When a LVP cycle reports low dP/dtmax, this is typically seen when there is an artifact on the LVP cycle during the upstroke.  The derived parameter of dP/dt_max is reported as the maximum derivative of the LVP cycle during systole. Figure 4 shows the dP/dtmax validation mark occurring early during the upstroke and the derivative waveform derivative goes to zero (time point is marked with a red arrow) at this time. 

When this occurs, within the Ponemah software, you can specify a derivative window within the LVP analysis module. 

The Derivative Window defines the range of samples over which the LVP’s derivative signal is calculated. This window acts as a smoothing function for the derivative by calculating across a larger range. Using a value of 0ms will provide the derivative between two consecutive points, whereas entering a larger value may provide the derivative across non-consecutive points.  For example, if sampling at 1000 Hz, the time between consecutive points is 1ms. By choosing a Derivative Window of 2ms, the derivative will be calculated across every other point.

Radiograph/Fluoroscopy

The LVP collar is radiopaque; therefore can be visualized using radiograph or fluoroscopy.  With these imaging techniques, the depth and angle of the catheter tip can be visualized and improvements on surgical techniques can be addressed.  

References