3D Echo and Invasive Pressure Synchronization

Generating Real Time, Multi Cycle Pressure Volume Loops

Dariusz Mroczek

, Kyong-Jin Lee

Juan Pablo Sandoval

, Helene Houle

Andreea Dragulescu, Lee Benson

and Rajiv R. Chaturvedi

Hospital for Sick Children, Toronto, Canada,

Siemens Medical Solutions USA, Inc., Ultrasound Division, Malvern, U.S.A.

1 BACKGROUND

The ventricular pressure-volume loop (PVL) relates

intracardiac pressure changes as a function of

volume changes during the cardiac cycle and is a

convenient method to understand major

determinants of myocardial performance. Acquiring

PVL is not simple in human models, the main

limitation being accurate volume measurement.

Traditionally PVL is obtained using conductance

catheterization which is based on the measurement

of the electrical conductivity of the blood volume by

placing a multiple electrode catheter along the long

axis of the ventricle (either right or left) during

catheterization and delivering an alternating current

between the most proximal and distal electrodes. -1-

Although conductance catheterization is considered

the gold standard for pressure volume relationship

acquisitions, this technology and equipment is

difficult to use and time consuming.

There has been considerable development in

three-dimensional echocardiography and more

recently display of cardiac structures in real time

rather than as offline reconstructed images from

multiple 2D echocardiographic slices. An important

clinical application of three-dimensional real-time

echocardiography (3D-RTE) includes delineation of

ventricular morphology and volume quantification -

2,3-

2 OBJECTIVES

Our objective was to explore the feasibility of using

3D-RTE together with cardiac catheterization to

determine ventricular function derived from PVL.

We established that success of our experiment

depends on several components and overall

reproducibility of our technique. Consequently we

identified signal synchronization (volume and

pressure), optimal sampling rate and the possibility

of multicycle acquisition as crucial requirements.

3 METHODS

3.1 Data Flow Diagram

3.2 Equipment

During cardiac catheterization ventricular volume

was attained by 3D RTE using the Siemens Acuson

SC2000 ultrasound system (Siemens Medical

Solutions USA Inc., Mountain View, CA) with a

4Z1c real-time volume imaging transducer (2.8

MHz). The SC2000 has a unique ability to produce

up to about 40 complete volumes per second in a

true real time acquisition mode. It is capable of

forming 64 parallel beams in real time and

processing of 160M voxels per second. Volume data

sets are free of multi-cycle averaging, regional

interpolation and “stitching” interference.

Ventricular pressure was obtained by a high

fidelity pressure cathether (Micro-Tip®, Millar,

Houston, Texas) which was advanced into the left or

right ventricle. Millar catheter frequency response is

greater than 10 kHz and the pressure signal was

acquired at 16 bit resolution by DT9804 (Data

Translation Inc) analog to digital converter.

All pressure, trigger and ECG signals were

recorded with Notocord hemodynamic software

(Notocord Systems, France, v 4.2).

Mroczek D., Lee K., Pablo Sandoval J., Houle H., Dragulescu A., Benson L. and R. Chaturvedi R..

3D Echo and Invasive Pressure Synchronization - Generating Real Time, Multi Cycle Pressure Volume Loops.

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

3.3 Functional Integration and

Acquisition

Data was collected in children and adolescents with

congenital heart disease aged 0-18 years that

underwent cardiac catheterization for interventional

purposes. Different ventricular sizes and

morphologies were included.

Pressure and 3D volume data set acquisitions

were synchronized by common ECG source and

activated by foot-switch signal. In addition the

pressure signal was interfaced to the ultrasound

system and displayed in real time for reference.

Notocord software recorded real time pressure, ECG

and trigger spike that initiated the volume recording.

This trigger signal with the conjunction of ECG

established proper cardiac cycle and a reference

point (R wave) of the first collected volume. The

typical length of a complete volume data set was

between three to five cardiac cycles.

3.4 Post Processing and Data Plot

Ventricular volume quantification and analysis was

done offline using Siemens software with the

combination of automatic ventricular volume

detection and manual user correction (Figure 1). The

produced ventricular volume curve was exported to

a text file. Based on this extract, the number of

individual volumes per acquisition time defined

absolute sampling frequency for pressure signal

extraction. Furthermore, the pressure raw data from

the trigger marker combined with QRS and with the

same duration as a ventricle volume acquisition was

resampled and averaged using imaging volume

resolution (Figure 2). The produced pressure extract

had the same time resolution as the acquired 3D

ventricular volume. As a result, absolute values of

both tracings could be plotted on the same XY axis.

Figure 1.

Figure 2.

4 RESULTS

PVL generated with this technique had reasonable

resolution and demonstrated expected physiological

characteristics. The real time volume sampling rate

was sufficient to obtain accurate pressure-volume

relationships of systolic and diastolic cardiac

performance. Synchronisation between these

different physiological sources was proven to be

feasible and reproducible in different congenital

heart conditions and after cardiac interventions.

4.1 PVL Examples

Figure 3: Right ventricle PVL after interventional

procedure (acute response).

Figure 4: PVL generated in a patient under varying

degrees of ventricular preload.

5 DISCUSSION

This described method is effective in acquiring PVL

and creates a platform for full integration and

synchronization of functional imaging and

hemodynamic data. It eliminates the use of costly

conductance catheters (a variety of them are usually

needed for full spectrum of ventricle sizes),

exposure to high frequency currents, flexibility of

ventricle volume selection and it does not rely on

complex volume calibration as is the case for

conductance systems.

Post-procedure analysis requires several steps

but can easily be integrated further and could

eventually become a built-in feature wherein

pressure-volume relationships could be calculated

instantaneously during a procedure.

The opportunity to synchronize 3D-RTE and

pressure data with a less invasive method such as

this one will allow clinicians to obtain valuable

insight of myocardial performance in a more simple

and accessible way. Furthermore, the pressure data

could potentially be used to gate volume acquisition

and immediately obtain the end-diastolic pressure

volume relationship (EDPVR) and end-systolic

pressure volume relationship (ESPVR).

It is acknowledged that development in integration

and automation is ongoing.

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