We
live in the era of non-invasive imaging in medicine. The top rankers in the
nation-wide competitive exam for post-graduate medical education invariably
choose radiology as their specialization of choice.
What is Cardiac Imaging?
Imaging
is the main pillar of congenital heart disease (CHD) diagnosis and congenital heart disease treatment. A century earlier CHD was suspected clinically and diagnosed on an autopsy
performed after the child died.
Even
four decades earlier, CHD was diagnosed by cardiac catheterization and
angiography. This was an invasive procedure which carried a small but definite
risk of adverse events. Thankfully, advances in
non-invasive imaging have allowed a more accurate and safe diagnosis of CHD in
neonates, infants and young children.
The
three modalities which we use most commonly in clinical practice are the echocardiogram, the computerized tomogram (CT) and cardiac magnetic resonance imaging (CMR).
There is a peculiar challenge in imaging the heart
unlike other organs of the body. The brain, liver, kidneys and gut remain
static for the most part. However, the heart is a dynamic organ which first
relaxes to receive blood (a phase termed diastole) and then contracts to push
the blood out (a phase termed systole). This process is termed the cardiac
cycle which comprises of both systole and diastole. Each of the four chambers
of the heart (the two upper chamber called atria and the two lower chambers
called ventricles) go through this cardiac cycle tens of thousands of time
every day.
In
addition to the three standard dimensions of length, breadth and depth, the
heart needs to be studied in time as well to understand the changes happening
during each phase of the cardiac cycle. An ideal imaging modality should
provide accurate information about the various parts of the heart in the
traditional dimensions (termed spatial resolution – a modality which provides
high quality images of the cardiac chambers is said to have good spatial
resolution) and also be capable of tracking the changes in the chambers with
time (termed temporal resolution). It suffices to say that no single modality
available today offers superior spatial and temporal resolution. Pediatric cardiologists,
hence, resort to a combination of imaging modalities to obtain all the information
required before subjecting a child with CHD to surgery.
Echocardiogram: The Most
Common Method
The
echocardiogram is the most commonly performed investigation in the pediatric
cardiology and may be considered “the workhorse” of a busy pediatric cardiac
practice. The echocardiogram uses ultrasound waves to image the heart.
Our
ear is attuned to hearing sounds of frequencies between 20 to 20000 hertz (20
Hz to 20 kHz). Sounds of frequencies above this value are used by bats to move
(a process called echolocation). When the sound waves hit a barrier, they are
reflected back. The bats analyze the reflected waves
to understand the location of barriers and avoid them while flying. Medical
ultrasound analyses the sound waves reflected from the various organs of the
body and reconstructs them using
a computer algorithm to provide images of
the organs in a digital screen. The sound waves used in cardiac imaging vary from
1000000 to 14000000 (1MHz to 14 MHz). Two-dimensional ultrasound has excellent
spatial resolution and temporal resolution. It is readily available and
relatively inexpensive compared to other imaging modalities. It is hence the
first imaging modality of choice in all children with suspected or known CHD.
The echocardiogram is performed by a pediatric
cardiologist or a trained pediatric cardiac sonographer. A typical echo study
takes between 5 to 30 minutes. The room is kept relatively dark to enable the
cardiologist to see the screen better. This is comparable to switching off the
lights in a cinema hall.
Making Echocardiogram
Comfortable for Children
The children are made to lie on a comfortable couch.
Most children above 4 years of age are co-operative during a study. This
process can be further enabled by talking to the child, putting the child at
ease and continuing to engage the child in conversation during the study.
However, it is often a challenge to obtain a study in
younger children. Toddlers become intimidated by the darkness in the room. The
cardiologist uses a gel to act as an interface between the echo probe and the
body. This enables them to see the structures better. The gel is often cold and
uncomfortable for younger children. Cardiologists have worked out a number of
techniques to facilitate this process. Children younger than 6 months of age
often go to sleep immediately after a feed. Hence the parents are encouraged to
feed the baby. The sleeping baby is then wrapped in a warm blanket to make him
or her comfortable. A soother in the mouth also helps to relax the baby.
Older infants and toddlers can be distracted by making
them watch their favorite cartoons. Sometimes children are more confident while
lying in their mother’s lap and the study can then be performed in this
fashion.
However frequently, children of this age group will need to be put to sleep by
administering medications. In most centers, the medicines used are Tricoflos,
chloral hydrate or melatonin. The use of this medicine is safe and will not
harm of the child. However, the child’s breathing and heart rate will need to
be monitored for a short while. Children go to sleep within half an hour of
administering the medicine and remain asleep for 1 – 2 hours.
Conclusion
It helps when the parents are explained about the
process of congenital heart disease treatment and their confidence is gained. It allows them to be actively
involved in calming the baby and makes the job easier for everyone involved.
Comments
Post a Comment