The changing face of echocardiography

Friday, February 1, 2019

 

Introduction

2019 Transthoracic Echocardiography (TTE) barely resembles my memories of TTE as a student Physiological Measurements Technician (PMT).

As student at Leicester Royal Infirmary I was privileged to be part of the generation who, in the early 1980’s, trained in the use of "single crystal" TTE, or "1D" echocardiography. This was an era where the abstract nascent examination was conducted in mysterious darkened rooms and imaging technology was of more interest to the physicists, and physiological measurements technicians than today’s cutting-edge cardiologists and the wider medical community.

 

Professor Feigenbaum, in front of an early M-mode echo machine

(Previously Dr Feigenbaum, widely seen as the “Father” of clinical diagnostic echocardiography).

 

Why cardiac physiologists became echocardiographers

Acoustic heterogeneity (code for difficult patients and incoherent or uninterpretable images) meant that parasternal examinations were highly subject and operator dependant. The examination time and diagnostic yield meant echocardiography was not a skillset appropriate for busy cutting-edge cardiologists to routinely pursue. It’s practical and technical challenges saw it become more the preserve of senior physiological measurements technicians(PMTs). For Senior PMT’s, echocardiography was a creative challenge and a welcome diversification from the activity of performing the ubiquitous 12 lead Electro-Cardio Graph (ECG).

 

1D echocardiography

Imaging formats were restricted to:

  • The abstract and limited A-mode (amplitude-mode, now obsolete); invaluable to guide instrumentation settings optimising overall gain, TGC’s, compression to optimise the B-mode output.
  • B-mode (brightness mode, the fundamental building block of all ultrasound tissue imaging); higher screen brightness values (Z modulation) representing stronger reflective interfaces. B-mode could be swept across a screen generating a depth graph of anatomical reflectors like ocean bed sonar.
 
 


M-mode showing Mitral Stenosis

M-mode. (Motion mode) represented on screen or inscribed on a thermal/photographic paper output, derived from a dynamic B-mode with the transducer held still. Consequent changing depth of the moving structures gave a time motion representation of the heart. Outputs obtained by sweeping the B-mode beam across a persistence CRT (cathode ray tube / TV screen) or moving a light sensitive chart paper under the B-mode array.

  • Four M-mode traces constituted the routine adult TTE examination – all from the parasternal window to reveal the basal aspects of left and right heart. Primarily favouring analysis of left heart components and hence adult acquired heart disease – paediatric cardiologists were not on-board. The incident pulsed ultrasound transmitted orthogonally (90 degrees for maximal reflection) in respect of the target structures below:
    • 1 M-mode of aortic valve, revealed the RVOT, Aortic Root (sinus dimensions), and LA dimensions.
    • 2 M-mode of mitral valve, revealed proximal RVOT, Proximal LV walls and chamber with anterior and posterior leaflet movement.
    • 3 M-mode of left ventricle, revealed RV basal, LV walls proximal mid and chamber sizes and allowed assessment of proximal LV radial systolic function.
    • 4 M-mode sweep from 1 through to 3 to show continuity of structures, confirm orthogonal relationship and identify presence of pericardial or pleural effusions.

 

Technology 2D (first commercial 1970’s)

A-mode would become obsolete once the 2D revolution became established. The limitations of 1D abstract "oceanography" would become a distant memory once the revolution in the shape of sector imaging became established. M-mode with its temporal and measurement qualities would still hold value even in today’s TTE adult exam. Around 1982 the Leicester Royal Infirmary obtained its first 2D echocardiography machine. This was my first encounter with a mechanical sector probe. Two-dimensional imaging was now reaching non-specialist hospitals allowing sectioning of the heart, to show continuity of structures and real-time anatomy. Additional to the parasternal window it allowed coherent imaging from four new windows of acquisition:

  • The apical window, allowing assessment of all four chambers from pulmonary veins to ventricular apexes (today the window with the highest diagnostic yield).
  • The suprasternal window allowing visualisation of aortic arch, PA branches LA and pulmonary veins.
  • The subcostal/subxiphoid window allowing visualisation of abdominal structures including vasculature, full anatomical visualisation of the mediastinal structures including the heart.

 

2D still image sections from the 4 main "window positions"

The right parasternal window (not shown above) allowing assessment of the proximal ascending aorta and root.

Adult echocardiography gained with the advent of 2D. However, hampered by the poor echogenicity of its subjects, the gains were not heralded sufficient for cardiologists to pick up the probe. Necessity and utility being the key drivers for human endeavour, busy cardiologist’s endeavours and demands centred on the high volume of:

  1. Ischaemic heart disease making coronary angiography the bread and butter of tertiary centres
  2. Haemodynamic assessment of valve disease making diagnostic cardiac catheter with coronary angiography

This meant PMT’s develop their skills further and dominated the provision of echo in the UK.

Paediatric cardiology had little interest in 1D echo. However, its strong requirement for complex morphological identification made 2D sectioning a gold mine and so a must. However, paediatric cardiologists didn’t have the time to divert to the rapid expansion of this new system, hence PMT’s developed further and became the experts in the UK through to the mid to late 80’s. However, this would change as the ubiquity of echocardiography in paediatric cardiology started to emerge.

ICS Diagnostics has a wealth of experience. By partnering with us you will be able to access the latest technology in echocardiography and our suite of services such as training and mentoring.

To read more about our full service, click here.

Mr James Ashman
Head of Physiology Services, ICS Diagnostics