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Certain types of medications may put divers at risk for a dangerous cardiac rhythm. A study published in the Mayo Clinic Proceedings (Ackerman, M, et al. Mayo Clin.Proc. 74:1088, 1999) identified an abnormality in the heart electrical system that puts swimmers and divers at risk for sudden death. The inherited disorder is called the Long Q-T Syndrome, and is identified by specific genes that cause the abnormality. [The Q-T interval is a time interval on the electrocardiogram that represents the period when the heart muscle membranes "recharge" after each heart beat.]
Drugs Can Prolong the Q-T
interval
The combination of a slow heart rate from water
immersion
(diving bradycardia) and a prolonged Q-T interval is known to induce a
dangerous cardiac arrhythmia. There are cardiac and other drugs
that
prolong the Q-T interval, and would also impart a risk for divers who
may
develop a slow heart rate . The responsible cardiac drugs are
certain
of the drugs used to control abnormal heart rhythms. These medications
would be used for treatment of atrial fibrillation, atrial flutter or
ventricular
tachycardia.
Psychotropic medications
Other drugs include some commonly used psychotropic
medications,
the tricyclic antidepressants (TCA), imipramine and desipramine. The
major
cardiovascular and electrophysiologic effects of the commonly used
psychotropic
drugs are listed in Table
I. The ECG effects of TCA administration include an
increase
in heart rate (20-25%), prolongation of the PR interval (5-10%
increase),
increase in QRS duration (7-25%), and prolongation of the QT interval
(3-10%).
Torsade de pointes
Although medications can potentially cause sudden,
unexpected
death by a variety of mechanisms (seizures, central nervous system
depression,
coronary artery spasm), cardiac arrhythmias are the most frequent
cause.
In particular, a unique form of ventricular tachycardia termed torsade
de pointes has been recognized as the arrhythmia responsible for
the
so-called pro-arrhythmic effect of several anti-arrhythmia drugs and
recent
evidence has pointed to a similar mechanism in syncope and deaths
related
to other medications and in the familial long QT syndromes. The
common
feature of these conditions is delayed repolarization of the myocardium
(related to abnormal sodium or potassium currents) with resultant
prolongation
of the QT interval of the ECG. This appears to leave the myocardium
vulnerable
to ventricular tachycardia, primarily in the setting of bradycardia,
but
occasionally associated with exercise.
Drug Interactions due to
the
cytochrome P450 system
Many psychotropic medications are metabolized by the
cytochrome P450 system, an enzyme system which may be inhibited by a
multitude
of medications (Table
II). Adverse effects have occurred when the P450 system is
inhibited,
leading to elevated levels of medications which prolong the QT interval
and produce ventricular tachycardia (torsade de pointes). Most notable
have been related to torsade de pointes from non-sedating histamine
blocking
agents such as terfenadine (Seldane) and astemizole (Hismanal). Many of
these episodes were associated with co-administration of other
medications
such as macrolide antibiotics or imadazole antifungal agents (Table
II). Other classes of medications that inhibit or are metabolized
by
the P450 cytochrome system include antidepressants, calcium channel
blockers,
histamine blockers, gastrointestinal motility agents, and steroids.
Prolongation
of the QT interval and torsades de pointes have been reported while
taking
cisapride.
Antiarrhythmic drugs of Class Ia (disopyramide, procainamide, quinidine) and Class III (amiodarone, sotalol) likewise prolong the QT interval and concomitant use of psychotropic medications is not recommended
Predive History-taking
important
Before initiating therapy with psychotherapeutic agents
or allowing diving, a careful history should be obtained with special
attention
to symptoms such as palpitations, syncope, or near-syncope. Medication
use (prescribed and over-the-counter) should be determined. The family
history should be reviewed with reference to the long QT syndrome or
other
causes of sudden, unexplained death. Detection of these symptoms or
risk
factors warrants a cardiovascular evaluation by a cardiologist prior to
initiation of therapy.
Until more data are available, it seems prudent to obtain an ECG at baseline before starting TCAs or phenothiazine therapy (primarily to detect unsuspected instances of long QT interval syndrome), and one when steady-state is achieved. If the sustained resting heart rate is > 130 bpm, the PR interval > 200 msec, QRS > 120 msec, QTc > 460 msec, or symptoms such as palpitations, near-syncope or syncope develop, alternative therapy may need to be considered along with cardiology consultation.
Concomitant use of psychotropic drugs and other drugs that are metabolized by or inhibit the P450 enzyme system should be avoided.
Disclaimer
(No representations are made that in any way offer a diagnosis, treatment or cure for any illness or condition, either discussed or implied. Answers to questions are offered as information only and should always be used in conjunction with advice from your personal diving physician. I take no responsibility for any conceivable consequence which might be related to any visit to this site.)
This page is compiled and maintained by
Ernest S Campbell, MD, FACS
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