Localization of the Origin of Arrhythmias for Ablation: From Electrocardiography to Advanced Endocardial Mapping Systems

Radiofrequency catheter ablation techniques have had a dramatic impact on the treatment of a variety of cardiac arrhythmias. However, catheter ablation of complex arrhythmias, such as intra-atrial reentry, ventricular tachycardias, and atrial fibrillation, continues to pose a major challenge. This stems from limitations of fluoroscopy and conventional catheter-based mapping techniques that limit the accurate anatomic localization of complex arrhythmogenic substrates. In this article, ECG features of complex arrhythmias are reviewed, which may facilitate the planning of an ablation procedure. The physical principles of the newly available catheter-based endocardial mapping techniques and their clinical applicability for treatment of complex arrhythmias are discussed. The role of intracardiac echocardiography to facilitate mapping and ablation is reviewed.     

EFFECTS OF SOMATOSTATIN ANALOGUE SMS 201–995 IN NORMAL MAN

Long-acting somatostatin analogues may be of benefit in certain hypersecretory endocrine and gastrointestinal disorders. The 24 h hormonal and metabolic profiles of six normal male subjects receiving a twice daily subcutaneous injection of one such analogue SMS 201-995, 50 micrograms, has been compared to that obtained following placebo injection. Spontaneous daytime peaks of GH secretion were delayed until 1400 h following SMS 201-995 but nocturnal and total 24 h GH secretion were unaffected. The nocturnal rise in thyrotrophin was abolished by SMS 201-995 but thyroid function was unaffected. Insulin levels were suppressed following SMS 201-995 and the response to meals was inhibited. Glucose intolerance followed main meals. Glucagon levels were suppressed for up to 6 h. Circulating alanine levels were raised between 1200 h and 0600 h and there were intermittent elevations in lactate, pyruvate, glycerol and 3-hydroxybutyrate. Amino acid levels, including branched chain amino acids, were also increased. All six subjects suffered gastrointestinal side-effects. SMS 201-995, 50 micrograms, given twice daily shortly before meals does not suppress 24 h GH secretion, but demonstrates significant effects on metabolism and causes side effects in normal subjects.