Heart Disease in the First Week of Life: Arrhythmias, by Dr. Michael Freed.
Introduction.
My name is Michael Freed and I'm a Pediatric Cardiologist at Boston Children's Hospital
and at Harvard Medical School.
So we finished murmurs.
Let's go to arrhythmias.
In the newborn period, the heart can beat too fast, too slow, or irregular.
Irregular Heart Rate.
Let's start with irregular.
I think this is by far the most common.
I used to get a lot of calls from primary care doctors around that they were in the
nursery, they listened to a child they were going to discharge, the heart rate that was
irregular, they got an electrocardiogram, and the baby was having atrial or ventricular
premature beats, what should they do?
I always told them the same thing.
That if the baby otherwise looks okay, and doesn't have a murmur or heart failure or
cyanosis, if it's still there in a month, just give me a call and we'll figure out what
to do.
I think it's probably benign.
I think that babies have very high catechol levels and one of the auxiliary pacemakers
just fires off and gives you frequent extra heartbeats-- even sometimes bigeminy or trigeminy.
As long as they're not having runs of ventricular tachycardia or have symptoms from it, I think
it's benign.
Over the next few days or weeks, as the catechol levels, these things usually calm down and
are not a problem in the future.
And we've not seen any long term problems from this.
Bradycardia.
When I'm talking about too slow, I mean rates in the 60s and 70s.
These are almost all from congenital complete heart block.
And kids with congenital complete heart block come in two different flavors: one with heart
disease-- and these are usually L-transpositions or some other form of complicated congenital
heart disease-- or without heart disease, or without structural heart disease.
And these are almost all maternal lupus or anti-nuclear antibodies that somehow attack
the conduction system.
But these kids raise a question: why do these kids with heart rates that are so slow do
okay?
In utero, the stress response is to increase heart rate.
And these kids can't really do that.
There are not very many catecholamine receptors, so they don't have much of an ability to deal
with stress.
Why do kids with heart rate do so well?
Well, we don't really care much about heart rate.
What we're really interested in is cardiac output.
And cardiac output is a function of heart rate and stroke volume.
And what happens is these kids are just able to increase their stroke volume significantly
so they can make up for the deficit in heart rate.
When you're born, the work of the heart doesn't change very much.
OK, the work of the heart is generating a pressure and pumping a volume of blood.
The old pressure volume loop that you probably learned about in medical school-- the work
of the heart is the area inside this curve.
And when you're born, the pressure doesn't change very much.
The fetus is generating a pressure of 70 or 80 millimeters above amniotic fluid as you
are when you're born.
And the volume doesn't change very much.
So the work of the heart doesn't change very much.
So these children who did OK in utero with congenital heart block usually do okay after
they're born as well.
They only get into trouble when they really have to increase their cardiac output significantly,
which interestingly can usually deal with feeding and toddling around.
In our area, they tend to get into trouble in Kindergarten or first grade with town soccer.
The kids with congenital heart disease, however, they can get into difficulty much sooner.
Because remember, they've really maximized their stroke volume.
So even a relatively simple disease like ventricular septal defect, when the pulmonary resistance
drops, they start developing a significant left-to-right shunt.
And these kids have already maximized their stroke volume.
So they have great difficulty if they do have structural heart disease.
So our job, as a cardiologists or as primary care doctors, is to figure out, of these kids
with congenital heart block, which have structural heart disease.
If they have structural heart disease, then you have to watch them very carefully because
they don't tolerate it very well.
The ones without structural heart disease, as I mentioned, usually don't get into difficulties
in the perinatal period and frequently go long periods of time before actually needing
any help, usually a pacemaker.
Tachycardia.
Too fast-- when I'm talking about too fast, usually talking about greater than 200 beats
per minute.
These are usually supraventricular tachycardias.
Can be atrial flutter, and very infrequently atrial fibrillation.
I would say this is probably 90%, 9%, and 1%.
Atrial fibrillation's quite uncommon because usually you don't have large enough-- you
need a large atrium to support the electrical fibrillatory waves.
So we don't really see that very often in the newborn.
These newborns can be quite sick, with a very, rapid heart rate that shortens diastolic filling
of the coronary arteries.
And in addition to the very fast heart rate, they can get an ischemic congestive heart
failure component.
This may occur in utero with intrauterine supraventricular tachycardia, probably the
number one cause of fetal hydrops in developed countries, where Rh incompatibility has been
virtually eliminated.
The number one issue is to get them out of SVT.
Some children will break spontaneously, others require vagal maneuvers, or an intravenous
injection of adenosine at a dose of 0.1 milligrams per kilogram, with an increase to 0.2 milligrams
per kilogram for subsequent doses if the initial medication is not sufficient.
For a few where the adenosine is not effective, external cardioversion may be required.
Some children, with a relatively short re-entry window may not develop supraventricular tachycardia
again.
These children are usually followed with medications such as beta blockers, for a year or so, and
if no further episodes occur, the medicine is discontinued.
For some children with the larger re-entry window, the supraventricular tachycardia can
be terminated, but within moments they go back into the abnormal rhythm.
This group may be particularly difficult to treat.
Medications, usually beta blockers such as sotalol, a beta blocker with class three antiarrhythmic
effects, or Flecanide, a class one C antiarrhythmic, or both drugs in combination may be necessary
to change the refractory period sufficiently, so they don't go back into the abnormal rhythm.
These children may be problematic, and a consultation with a pediatric cardiac electrophysiologist
is probably the best approach.
This concludes our video on Clinical Presentation of Congenital Heart Disease in the First Week
of Life: Arrhythimias.
Please continue with the next video in this series, Clinical Presentation of Congenital
Heart Disease in the First Week of Life: Cyanosis.
Thank you.
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