The following are associated with causing torsades de pointes EXCEPT:
Answer: A: Drugs that block potassium channels will prolong the QT interval and therefore predispose to torsades de pointes. Likewise, electrolyte abnormalities (hypomagnesemia, hypokalaemia and hypocalcemia) that cause long QT will also predispose. Benzodiazepines have no effect on the QT interval.
Reference:
Regarding the pharmacological treatment of cardiac dysrhythmias, which ONE of the following statements is TRUE?
Answer: B: Recurrent torsades de pointes, refractory to magnesium therapy, can be effectively managed with overdrive pacing. This can be achieved electrically, or pharmacologically with an agent such as isoprenaline. Class III agents, such as sotalol, will further prolong the QT interval and exacerbate the problem.
Lignocaine is a class 1b antiarrhythmic. Class 1 agents block the sodium channel, therefore reducing the slope of phase zero of the action potential. They are further subclassified based on their effect of the action potential duration: 1a prolong the AP duration, 1b decrease the AP duration and 1c have no effect.
The dose of adenosine may need to be increased in those patients taking methylxanthines, such as theophylline, which are competitive antagonists at adenosine receptors.
References:
Regarding Brugada syndrome, which ONE of the following statements is FALSE?
Answer: D: Brugada syndrome is a recognized cause of syncope and sudden cardiac death in young patients (especially in Asian males) with structurally normal hearts. It is inherited in an autosomal dominant manner and is associated with defects in the sodium channel. It is associated with an incomplete RBBB pattern and the ST segment elevation in the right precordial leads that is either convex and downsloping with T wave inversion or saddle shaped or concave. Patients with syncope who are suspected of having Brugada syndrome should be admitted to a monitored bed. Management is with an implantable defibrillator – there is no place for class Ia and Ic or sodium channel blocking agents.
Which ONE of the following drugs can safely be used in patients with Brugada syndrome?
Answer: C: Isoprenaline causes beta-adrenergic receptor stimulation and has a potential antiarrythmic effect in patients with Brugada syndrome. All other drugs have the potential to block sodium channels and precipitate arrhythmias.
Regarding use of adenosine in the treatment of SVT, which ONE of the following statements is TRUE?
Answer: C: Adenosine is the first-line therapy for the treatment of stable SVT in both adults and children because of its short half-life (<60 seconds) and safety profile. Its overall efficacy in converting SVT to sinus rhythm (SR) is over 90%. However, because of its short half-life, approximately one-third of the patients who are converted to SR can be expected to be reversed to SVT again within a few minutes. It has also been shown that efficacy of adenosine increases with faster heart rates. Adenosine is far superior to magnesium in reversing SVT. Reversion rate for magnesium is approximately 16%.
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