Transcript Distribution of QTc values for patients with and without long QT

A typical day at work
October 29th, 2009
So, you get to work, and go to see
your first patient…

21-year-old female with a history of
"seizure" disorder. She had one of
these events. She has the following
ECG…
Long QT

Reading the QT interval

Causes

What to watch out for
Upper limits of normal

Male – 0.44

Female – 0.46

Look for longest interval on the ECG

Do it manually!
You’ve been recognized as an
astute diagnostician and
prognosticator

As such, in addition to your regular
responsibilities, you’ve been asked to
predict the future…
Uh oh – Diagnosis? Treatment?
Treatment: Torsades de Pointes

Defibrillation

Magnesium

Overdrive pacing
After helping the patient back in to
a rhythm more compatible with life,
you do a chart review of
medications. Any concerning?





1.
2.
3.
4.
5.
Biaxin
Amiodarone
Seroquel
Zofran
Mefloquine
Causes of long QT

1. Congenital

2. Acquired
Acquired

A) Drugs

B) Lytes

C) Intracranial – CVA, SAH

D) Cardiac pathology (ischemia, CHF, myocarditis)

E) Severe bradycardia

F) Anorexia

G) Thyroid – hyper or hypo

(Aust Prescr 2002;25:63–5)
Drugs, drugs, drugs
Lots of drugs implicated in acquired
long QT –
1.
Antibiotics – macrolides,
fluoroquinolones
2.
Antipsychotics – haldol, risperdal,
seroquel, fluphenazine, clozaril
3.
Antiarrhythmic – amiodarone,
sotalol, procainamide
4.
Antinausea - domperidone, zofran
More drugs…





Antifungals – fluconazole,
ketoconazole
Antidepressants – TCAs, SSRIs
Antimalarials – quinidine,
mefloquine, chloroquine
Moral of the story – if it’s Anti
Something, it may be Pro – long
QTc.
www.QTdrugs.org
You’re asked to take a phone call
from a hospital administrator. He
tells you that resources are limited.

AHS wants you to tighten up your
investigations. It has mandated that
you can only do one test on your
next patient, who has the following
ECG:
Lytes and long QT

1. Hypokalemia

2. Hypomagnesemia

3. Hypocalcemia
Next in the triage list…

25 year old guy passed out while he
was swimming. He feels fine now
and wants to go home. He has the
following ECG…
He happens to mention…



His father died suddenly when he was
30
He’s had multiple fainting spells
before
What do you want to do?
Congenital - LQTS



1 in 2500-5000 people
Collection of genetically distinct
disorders
Results from mutations in cardiac
potassium and sodium ion channels
(channelopathies)
Congenital LQTS forms




Romano-Ward
Jervell and Lang-Nielsen
Andersen
Timothy
Precipitants of arrhythmias in
patients with LQTS






Variety of adrenergic stimuli Exercise
Emotion
Loud noise
Swimming (cold water)
Sleep may also precipitate
Your next patient…


Doesn’t have a heart problem!
40 year old woman with chest pain –
turns out it’s a pneumothorax but in
the process of working her up, you
do an ECG which shows an incidental
QTc of 450. Are you worried about
this?
Effect of clinical setting on the relative probability of having long QT syndrome
(LQTS).
Johnson, J N et al. Br J Sports Med 2009;43:657-662
Copyright ©2009 BMJ Publishing Group Ltd.
Distribution of QTc values for patients with and without long QT
syndrome (LQTS).
Johnson, J N et al. Br J Sports Med 2009;43:657-662
Copyright ©2009 BMJ Publishing Group Ltd.
LQTS Probability Score
(Schwartz score)














Clinical history of syncope with stress – 2 points
Clinical history of syncope without stress – 1 point
Congenital deafness – 0.5 points
Family history of long QT syndrome – 1 point
Unexplained sudden death of 1st degree family
member < 30 years – 0.5 points
QTc 450-460 – 1 point
QTc 460-480 – 2 points
QTc >480 – 3 points
Torsades de Pointes – 2 points
3 leads with notched T waves – 1 point
T wave alterans – 1 point
Bradycardia < 2nd percentile for age – 0.5 points
Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic criteria for
the long QT syndrome. An update. Circulation 1993;88:782–784.
On your way to see your next patient you run in
to your CCU colleague. He pimps (presents) you
with the following scenario…
 Previously healthy 49-year-old man who
presents with progressive muscle
weakness and constipation. He has no
chest pain or dyspnea. The ECG is most
consistent with?
 A) Hypokalemia
 B) Hyperkalemia
 C) Hypocalcemia
 D) Hypercalcemia
 E) Hypothyroidism
Short QT




Much shorter list:
Hypercalcemia
Digoxin
Hereditary short QT
Well done, doctor

Once again, you’ve stamped out
disease. Patients and staff alike
cheer as you leave the department.
References


1. European Heart Journal February 20, 2007 Clinical diagnosis of long
QT syndrome: back to the caliper. Tom Rossenbacker1 and Silvia G.
Priori2
2. Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic criteria
for the long QT syndrome. An update. Circulation 1993;88:782–784.

3. www.QTdrugs.org

4. Johnson, J N et al. Br J Sports Med 2009;43:657-662

5. Aust Prescr 2002;25:63–5

6. ECG Wave-Maven www.ecg.bidmc.harvard.edu/maven

7. Uptodate.com