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Digitalis and the sick sinus syndrome. Clinical and electrophysiologic documentation of severe toxic effect on sinus
Insights
This study found that digoxin can cause severe sinus node dysfunction in patients with a history of mitral valve replacement. Caution is advised when prescribing digoxin to patients with sick sinus syndrome.
Area of Science:
- Cardiology
- Electrophysiology
Background:
- Sick sinus syndrome (SSS) is a complex cardiac arrhythmia.
- Mitral valve replacement (MVR) is a common cardiac surgical procedure.
- Digitalis preparations are often used in cardiac patients.
Purpose of the Study:
- To investigate the effects of digoxin on sinus node function in a patient with a history of MVR.
- To evaluate the electrophysiologic response to digoxin in a patient with pre-existing sinus node abnormalities.
Main Methods:
- Clinical and electrophysiologic studies were performed before and after digoxin administration.
- Intravenous digoxin was administered at a dose of 1.025 mg/24 hrs.
- Sinus node function was assessed through various electrophysiologic tests.
Main Results:
- Digoxin administration led to a significant increase in resting sinus cycle length.
- Marked abnormalities in response to overdrive pacing were observed post-digoxin.
- Prolonged sinus pauses exceeding six seconds occurred even at slow pacing rates.
Conclusions:
- Digoxin can precipitate severe sinus node dysfunction in susceptible patients, even at therapeutic doses.
- This case highlights the need for caution when using digitalis preparations in patients with SSS, despite prior reports of tolerance.
- Electrophysiologic studies are crucial for assessing the risk of digoxin toxicity in patients with complex cardiac histories.
Abstract:
Digoxin, in a common clinical dose and at a low serum level, brought out severe manifestations of sinus node dysfunction in a patient who had previously undergone successful mitral valve replacement. This report presents the results of extensive clinical and electrophysiologic studies of this patient before and after a digoxin challenge. In the absence of cardiac glycoside, the only demonstrable abnormalities of sinus node function were mild resting sinus bradycardia and failure to respond to atropine administration. Responses to isoproterenol administration, programmed premature atrial stimulation, and overdrive pacing at several cycle lengths were normal. Following the administration of intravenous digoxin, 1.025 mg/24 hrs, the resting sinus cycle length increased and the response to overdrive pacing became markedly abnormal. The latter was followed by sinus pauses in excess of six seconds, even at relatively slow overdrive pacing rates. The electrophysiologic and clinical implications of these data are discussed. It is suggested that despite previous reports that digitalis preparations are relatively well tolerated by patients with sick sinus syndrome, caution should be used when administering these drugs to this group of patients.
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