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PURPOSE-Neuregulins (NRG) are growth factors that bind to receptors of the erbB family, and are known to mediate a number of processes involved in diverse tissues. Neuregulin-1β is expressed in skeletal muscle and is activated by exercise. We hypothesized that NRG-1β might circulate in the bloodstream and increase as a consequence of physical activity. A study was conducted in healthy subjects to determine if NRG-1β is immunodetectable in human serum, and if so whether levels relate acutely or chronically to exercise.METHODS-Nine healthy men underwent three bouts of exercise of varying degrees of intensity on a bicycle ergometer over a period of three weeks. Cardio-respiratory fitness was determined by measurement of maximal oxygen uptake (VO 2 max). Serum was sampled prior to and immediately after each session (up to 30 minutes post) and serum NRG-1β was quantified utilizing an indirect sandwich ELISA assay developed in our lab.RESULTS-Across subjects, mean serum NRG-1β levels ranged from 32 ng/mL to 473 ng/mL. Individual subjects showed relatively stable levels during the study period that did not change acutely after exercise. Serum NRG-1β demonstrated a positive correlation with VO 2 max (r2=0.49, p =.044).CONCLUSIONS-These preliminary observations suggest that at least in healthy men, serum NRG-1β is an indicator of cardio-respiratory fitness and does not change acutely with exercise.

BackgroundMost literature for cryoablation of atrioventricular nodal reentry tachycardia (AVNRT) is based on −30 degree celsius cryomapping with 4 & 6 mm distal electrode catheters. The cryomapping mode is not available on the 6 mm cryocatheter in the United States. We describe a technique for ‘pseudo’ mapping at −80° using a 6 mm cryocatheter and report on short and long term outcomes.MethodsA retrospective analysis of all index cases (n = 253) of cryoablation of AVNRT at a single North American institution during the period of 2003–2010 was performed. The majority of cases utilized a 6 mm distal electrode tip catheter. Long term follow up (2.4 ± 1.8 years) was performed via review of the medical record and by questionnaire or telephone if necessary.ResultsAcute ablation success was achieved in 93% of cases, with transient conduction defects noted in 39% of cases, and long term conduction defects in 1.6% of cases (4 patients with PR prolongation, 2 of which were permanent). General anesthesia, male gender and presence of structural heart disease were more common in the acute failure cohort. The recurrence rate for AVNRT was 8%. These patients tended to be younger and had more transient A-V conduction defects during the index procedure than those without a recurrence.ConclusionsIn conclusion, anatomic cryoablation of AVNRT utilizing a 6 mm electrode catheter with mapping performed at −80° Celsius is a safe procedure with good long term efficacy. Transient A-V block during the index procedure increases the risk of late recurrence.

Atrioventricular nodal reentrant tachycardia (AVNRT) is usually associated with a good prognosis. This is a case of a 57-year woman who presented with supraventricular tachycardia that spontaneously deteriorated to polymorphic ventricular tachycardia (PVT). The PVT terminated without treatment after 16 seconds. Extensive cardiac evaluation including echocardiography, stress testing, coronary angiography, and cardiac magnetic resonance imaging did not reveal any structural heart disease. Electrophysiology testing demonstrated typical AVNRT which was successfully treated with cryoablation. The clinical ventricular tachycardia could not be reproduced despite the use of an aggressive induction protocol and isoproterenol. Postablation, exercise treadmill testing did not provoke any tachyarrhythmia. The patient is doing well 13 months later. In summary, we present the rare finding of a moderately fast, typical AVNRT degenerating to a long run of PVT, in the absence of any detectable heart disease or other etiology for PVT.