What is sudden cardiac death, I've used the term
recurrently, but I haven't really explained that,
so my apologies.
Sudden cardiac death depends on the
definition of where you read it,
but it's an unexpected death from a
cardiac cause, either without symptoms
or within 1 to 24 hours of symptom onset.
And the EKG that's demonstrated below is
one that shows normal p and QRS complex,
and then suddenly there's nothing.
That's to make the point, actually, that
the vast majority of sudden cardiac death
is due to an arrhythmia and not necessarily
due to actual myocardial damage.
Of causes for sudden cardiac death, 80 to 90 percent
are going to be due to coronary artery disease.
It can also be due to remote injury leading to
scarring, which may then lead to arrhythmias
And then in the younger patient populations
who have a sudden cardiac death,
it's usually non atherosclerotic
causes as we'll talk about.
Sudden cardiac death is often the first
manifestation of ischemic heart disease,
and it can be a manifestation of limiting
flow atherosclerosis such as shown here,
present in most cases.
It may be due to remote healed
myocardial infarct so that fibrosis
will not allow the propagation of cell
signaling cell to cell to cell
because of that dense area of scarring.
And in roughly 40% of cases of sudden
cardiac death, all we can find is
evidence of an old remote infarct.
Nothing new, but an old remote one with
fibrosis that is impeding normal signaling.
And then we can have in about 10%
of cases of sudden cardiac death,
there is an acute plaque disruption that is
probably causing an acute myocardial infarct,
but the patient dies so acutely we don't see
the histologic evidence of myocyte necrosis.
We don't see the actual infarct because
the cells die and the patient dies
before we have a chance to
have the histologic changes.
Hereditary or acquired abnormalities
of the cardiac conduction system
can have non-atherosclerotic causes.
Congenital coronary artery abnormalities.
So this is not really atherosclerosis,
but this may be a coronary artery
that courses in the wrong place and is prone to
being compressed by other extrinsic structures.
Mitral valve prolapse probably
by causing relative ischemia,
the papillary muscle that's
associated with that prolapse in valve
can also be a cause for sudden cardiac death.
Sarcoidosis because of the inflammation and
the focal scarring within the myocardium
can be another non-atherosclerotic
cause of sudden cardiac death.
Myocarditis with inflammation and
focal cellular damage and necrosis
can be a cause of arrhythmias.
And dilated or hypertrophic cardiomyopathies
where we're getting individual cardiac myocytes
that are big with a relative
area of central ischemia because
we don't increase the capillary density, are also
prone to having sudden development of arrhythmias.
Myocardial hypertrophy is an otherwise
independent risk factor for sudden cardiac death.
And again, as the individual cardiac
myocytes enlarge, as a response to
systemic hypertension as a
response to aortic stenosis,
those individual cardiac myocytes
get bigger and bigger and bigger.
The capillary density around them doesn't change,
so the diffusion distance for oxygen and nutrition
is increased with the expanding size
of the individual cardiac myocytes.
And as a result of that, we have
an area of relative ischemia,
hypoxia in the middle of those cells.
Now, since we're having to
conduct currents of calcium
and sodium and potassium throughout the cell,
dysfunctional ATP in a local area of the cell
may make it prone to aberrant signaling and
therefore becoming a nidus for arrhythmia.
In young individuals, myocardial
hypertrophy, typically in the setting of
hypertrophic cardiomyopathy, is a common
cause of sudden cardiac death in youth.
And when we have an athlete, otherwise healthy
and viable athlete die tragically at a young age,
it's often in association with
myocardial hypertrophy and actually
frequently in association with
Other non-atherosclerotic causes of sudden
cardiac death, and these are not even arrhythmias,
these are just other causes
that you should be aware of.
So a pericardial tamponade and accumulation
of fluid acutely around the heart
will prevent the heart from being
able to expand during diastole, it won't fill.
It will contract fine, but won't fill, and that
can be an acute cause of sudden cardiac death.
Non-atherosclerotic in general.
Pulmonary embolism, another cause.
So if I have a big pulmonary embolus and I am not
able to get blood from the right side of the body
to the left side of the body, and
I'm not getting oxygenated blood
to the left side of the body,
you will have a sudden death.
Other systemic, metabolic and
hemodynamic alterations can do this.
Patients who have a severe renal insufficiency
can develop such severe metabolic acidosis
or hyperkalemia or hypercalcemia that they then
have a non atherosclerotic sudden cardiac death.
There's no atherosclerosis, but the vessel may
spasm and cause ischemia and can cause arrhythmias.
And vasospasm can occur in
the setting of catecholamines.
So say, from a pheochromocytoma or from cocaine,
things that can cause small vessel vasospasm.
Drugs such as cocaine and methamphetamines should
be considered in the evaluation of patients
who have a sudden death without evidence
of significant atherosclerotic disease
or other defects in the normal
structure and organization of the heart.
So lethal arrhythmias, the most common
mechanism of sudden cardiac death.
So ventricular fibrillation, clearly, I'm not
squeezing blood out of the ventricles sufficiently
to perfuse the brain or any other structure,
within two to three minutes, the patient will die.
And if there is asystole, clearly
the patient is going to die.
There may not be any obvious
infarction in the heart.
There may be no, nothing that
we can identify structurally
and yet lethal arrhythmia
makes the patient just as dead.
This is just to make that point, infarction need
not occur for sudden cardiac death to occur.
And in fact, most cases the vast
majority of cases, 90% of cases,
a fatal arrhythmia is triggered by electrical
instability or irritability of the myocardium
and not by infarction.
How can we treat this?
Well if we know that a patient is prone to
sudden cardiac death by whatever testing,
family history, long QT, short QT, etcetera,
we can do pharmaceutical intervention
to try to regularize the heartbeat
and minimize the arrhythmias.
We can also put implantable
cardioverter defibrillators, ICDs.
These detect arrhythmias, everything from asystole
all the way up to ventricular fibrillation,
atrial fibrillation, et cetera
depending on how they're programed,
they will fire and restart the heart.
And those are the dominant
ways by which we treat this.
With that, we've covered a lot of territory having
to do with whether a heartbeat is regular or not.