Hello, my name is Gary Dhillon. I'm a board-certified Pediatric Cardiologist, and a
current Clinical Fellow in Critical Care Medicine at the Department of Anesthesiology, Critical Care
and Pain Medicine at Boston Children's Hospital, at the Harvard Medical School. And today,
I'll be discussing Long QT syndrome, and pearls for the anesthesiologist and intensivist.
I have no disclosures for this presentation. This lecture is purely for educational purposes. And
the information provided in this lecture should not be used as a replacement for the expertise
advice of cardiology, anesthesiology, and intensive care consultations.
The objectives of this presentation will be to provide a brief review of Long QT syndrome,
review how to calculate a corrected QT, a review of electrocardiogram examples of Long QT syndrome,
and a discussion of peri-operative considerations in patients with
Long QT syndrome. Long QT syndrome affects approximately 1 in 2,500 patients.
It can be inherited in both autosomal dominant and recessive fashions, with variable penetrance.
The first manifestation can be sudden cardiac death in up to 10% to 12%,
and in some studies, has been shown to potentially account for upwards of 10%
or more of SIDS mortalities-- sudden infant death syndrome mortalities.
Mortality can be upwards of 21% within the first year of a syncopal episode, if left untreated.
40% of patients with Long QT syndrome don't demonstrate QT prolongation on a baseline EKG.
And as a baseline, a normal QTc in males is defined as less than 440 milliseconds.
Whereas, a normal QTc in females is defined as less than 460 milliseconds.
I've listed here the three most common types of Long QT syndrome-- types 1, 2,
and 3. And as you can see here, in each row, you have a different type that I'll discuss shortly.
I've listed, at the very end, the different mutations that are involved. With Long QT syndrome
type 1, it's due to a KCNQ1 mutation. Long QT type 2 is due to a KCNH2 mutation. And Long QT type 3
is due to an SCN5A mutation. If you may recall, it has been discussed in a previous channelopathy
lecture, SCN5A is also seen in Brugada syndrome mutation, the difference being with
Brugada syndrome, the mutation in the SCN5A sodium channel ion gene is a loss of function in Brugada.
Whereas, in Long QT type 3, is a gain of function in the SCN5A gene.
The other types, Type 1 and 2, are due to a loss of function in the potassium ion channel gene,
with KCNQ1 and H2, respectively with types 1 and 2. The frequency decreases from type 1 to type 3
in gene positive diagnosed patients with Long QT syndrome.
Long QT type 1 is seen in approximately 30% to 35%. Long QT type 2 is seen in approximately
25% to 30%. And type 3 is seen in approximately 5% to 10%. As you can see here,
in the middle of this table, are characteristic EKG findings in Long QT syndrome.
As the name of the syndrome indicates, what you'll expect to see, is a long QT interval. With type 1,
the characteristic QT segment has an early peaking T wave, coming soon after the QRS complex.
With Long QT type 2, the T wave is not as early peaking and has a saddleback-shaped appearance.
And in Long QT type 3, the T wave has a late peaking appearance to it.
And in all three of these, as the name indicates, the QTc
will be measured as prolonged, compared to baselines, in males and females.
And lastly, a very important aspect of these three different types of disease processes is
the underlying factors that can trigger lethal cardiac events. In all of these,
exercise, emotional stress responses, and periods of high vagal tone-- such as sleep-- can trigger
life-threatening events. However, in each type, certain triggers are more common than others.
For type 1, exercise is the most common trigger in approximately 68% of patients.
In type 2, emotional stress is the most common trigger, in upwards of 49%.
In Long QT type 3, periods of high vagal tone, such as sleep, are the most common trigger.
In type 1, it's also important to note that although exercise, in general,
is a very common trigger event, it has been noted in studies that swimming, in particular,
as a certain type of exercise, tends to be more common in this population as a triggering event
for cardiac events. A general thing to keep in mind, as a way to remember the
most common triggers for life-threatening events in Long QTs type 1, 2 and 3, are the words swim,
startle and sleep for types 1, 2 and 3. So swim, or exercise, for type 1, startle, or
emotional stress responses, for type 2, and then sleep, or high periods of vagal tone, for Type 3,
are generally the most common triggering events.
Treatments for Long QT syndrome tend to be beta blockade, as a first line therapy.
It's most effective in type 1. And it's generally initiated if a long QTc is present, even if the
patient is asymptomatic. In Long QT type 2, beta blockade has been shown to be less effective,
with cardiac arrest occurring in 6% to 7% of patients despite
the use of beta blockade. And in type 3, even less effective, with cardiac
arrest present in upwards of 10% to 15% of the population, despite the use of beta blockade.
Sodium channel blockade-- and in particular, mexiletine-- in some studies has been shown
to provide some benefit in Long QT type 3. And along with beta blockade,
additional treatments also include lifestyle modification
and prevention of certain triggers in this Long QT population. For example, in general,
we tend to prohibit competitive sports in this population, as they can be triggers
for life-threatening cardiac arrest events in all three types, but in particular for type 1.
In type 2, this population tends to be more sensitive to abnormal potassium levels in serum,
as a trigger for life-threatening events. So as with all of these, but particular for type 2,
normalizing electrolyte derangements becomes very common. As you may recall, a startle response
or a periods of emotional stress tend to be the more common trigger for Long QT type 2.
So in particular for Long QT type 2, having discussions with the family regarding things like
not having alarms in the bedroom, or certain types of alarms that are sudden and jolting that
could result in a startle response that could trigger a life-threatening event are important
discussions to have with these families. There are indications for ICD placement in this population,
as well as indications for left cardiac sympathetic denervation in high risk
populations who've shown life-threatening cardiac arrest or ventricular arrhythmias.
An important website, not only for clinicians, but also for patient and patient families,
is crediblemeds.org or torsades.org, which provides a list of medications
that are known to cause Long QT-- that are useful in the Long QT population
and are also useful, in general, in patients that have drug-induced Long QT syndrome,
who were admitted to hospitals when a clinician is trying to identify certain medications.
They need to be discontinued or held in patients when a long QT is noted on EKG.
I've listed here a calculation for how we go about calculating a QTc interval. As you can see here,
we have a general EKG strip with a P wave, QRS, T wave, and the ST segment here. The general
leads that are used to calculate a QTc are Lead II or V5. You first calculate the QT interval.
And as a brief reminder, on an EKG, every small box is equivalent to 40 milliseconds.
And every large box, which includes five small boxes, is 200 milliseconds.
So first, you calculate the beginning of the QRS to the end of the T wave.
To identify exactly where to measure at the end of the T wave, you can draw a imaginary tangential
line along the descending slope of the T wave. And where it intersects the baseline, would be the end
of the QT interval. So the beginning of the QRS to the end of the T milliseconds and the R-R interval
that you calculate is the preceding R-R interval, prior to the QT interval that you calculated.
And using Bazett's Formula, the QTc is equal to the QT interval divided by the square root of
the preceding R-R interval. And if you didn't happen to have a calculator in front of you,
or were trying to identify just by sight if a QT was theoretically prolonged, a general measure you
can use is to look at the R-R interval and to ask yourself, does that QT interval end
at least halfway between the R-R interval? If it does, or if it ends after the halfway
point between the R-R interval, then it may likely be a prolonged QT.
However, after that point, it still is very important to provide an exact calculation
for how many milliseconds that corrected QT interval is.
I've listed here two examples, the first example being a long QT. So as you'll see here--
and for this purpose, we'll focus on Lead II at the top left EKG-- you will see that the QT,
if you were to just eyeball it, ends beyond the halfway point between the R-R interval.
And if calculated, you would find it to be greater than 460 milliseconds, indicating it is a long QT.
Secondly, you'll also note that this T wave is an early peaking T wave,
that is more consistent with Long QT type 1. And this next EKG, that you'll see here,
shows one of the characteristic findings in Long QT that is classically seen as a life-threatening
cardiac event, which is an oscillation around the points-- torsades de pointes--
which is polymorphic ventricular tachycardia that varies from a large
amplitude QRS complexes to small amplitude QRS complexes, and goes back and forth.
And this finding, torsades de pointes, is seen in Long QT syndrome,
and can be seen in this population, and is life-threatening. And in general,
for a persistent rhythm like this, it will not be associated with the presence of adequate
cardiac output, or would likely with a pulse in a patient. It would necessitate not only initiation
of PALS algorithm for resuscitation and cardiopulmonary resuscitation on this population,
but also, an important thing to keep in mind, if torsades is seen in a patient with
Long QT-- or even patients without previously diagnosed Long QT syndrome-- treatment with
magnesium sulfate is indicated and will provide reversal for this life-threatening arrhythmia.
So once again, Long QT syndrome, one of the life-threatening rhythms that can result
is torsades, which is an oscillation between large and small QRS complexes of polymorphic
ventricular tachycardia. And keep in mind that magnesium sulfate would be indicated
for this arrhythmia. Another important thing to consider is an EKG that you may see,
such as this for example, which may be seen in the neonate when bradycardia is noted.
And let's just focus on Lead II, for this EKG. What you'll see here is a P wave followed by QRS.
And then, you'll actually see another wave here that looks very similar to P wave morphology.
And this actually is a P wave.
So you'll see here, there's two P waves for every QRS. So you may think to yourself that this is 2:1
atrioventricular block. And the underlying pathology is that this P wave is unable to
conduct down the AV node, due to some abnormality of that AV node.
But what's also important to note is the QT segment is actually quite prolonged,
as you can see here just by eyeballing the EKG. It is at least half of the R-R interval.
So what may actually be going on here is that you have an intact AV node.
And during this long QT interval, you have a ventricular myocardium that is refractory
and cannot conduct a normal-- dallying normal conduction pathway. So you actually have a blocked
P wave that is unable to conduct, due to ventricular refractory period.
And we call this Pseudo 2:1 atrioventricular block in the presence of a long QT.
And this extreme prolongation can be seen in neonates, and is associated with a poor
prognosis. Can be seen outside of the neonatal population, as well.
In neonates with congenital Long QT syndrome, it requires medical therapy and a high suspicion
for needing an ICD. It's also associated with poor prognosis and a high risk of mortality
when this congenital Long QT syndrome is noted. Pre-operative considerations in Long QT syndrome
include certain things that may be tailored based off of the type of long QT a patient has.
In particular, if you remember Long QTs type 1 and 2-- swim and startle,
or exercise and emotional response triggers-- a sympathetic stimulation
trigger should theoretically be avoided. So consider things such as premedication,
calm induction, especially in children with stranger and separation anxiety. For Long QT
type 2, where emotional stress responses such as startling a response is important to keep in mind,
things like keeping the room quiet and preventing startling in young children.
And for Long QT type 3, when life-threatening events can occur during periods of high vagal
tone, consider monitoring these patients closely with premedication, during periods
of high vagal states intra-operatively, and then during recovery periods, as well.
In these populations, in consultation with cardiology, it's so important to discuss the
need to continue any anti-arrhythmic medications they're on in the peri-operative period. And then,
also consider not only pre-operative, but also intra-operative electronic monitoring, as well.
For intra-operative considerations, consider careful use of volatiles and succinylcholine,
as they can prolong the QTc. Propofol does not have significant QTc prolongation and can be
used safely in this population. Deep sedation during induction,
to prevent provoking sympathetic stimulation during laryngoscopy, may also be important.
And be prepared, in general, to deal with arrhythmias, such as by having
defibrillation pads available, lidocaine available for ventricular arrhythmias,
having magnesium sulfate available, as well as esmolol. And in particular, if you're considering
things like this, having electrophysiology cardiac consultants involved in high-risk patients
is important with this population. From a post-operative consideration standpoint,
consider things like a deep extubation to prevent profound sympathetic stimulation associated with
emergence with an airway, and considering in-patient monitoring, post-operatively.
So important takeaway points from this brief review of long QT-- Long QT types 1 through
3 are most common, with types 1 and 2 being due to a loss of potassium channel ion function, and
type 3 being due to a gain of sodium ion channel function. Remember, exercise, emotional stress,
and sleep for types 1, 2 and 3, and the term swim, startle, and sleep associated with types 1, 2, 3.
Remember that beta blockade is a general first line therapy for this population.
Calculations of a QTc, using Bazett's Formula, can be calculated by measuring the QT interval
in milliseconds divided by the square root of the preceding R-R interval in milliseconds. Thank you.