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The following electronic only articles are published in conjunction with this issue of Heart.   Physical activity is a major contributor to the ultra low frequency components of heart rate variability J M Serrador, H C Finlayson, R L Hughon Objective—To investigate the link between changes in level of physical activity and the pattern of heart rate variability during long term ambulatory monitoring. Design—Heart rate variability was measured simultaneously with a quantitative indicator of muscle activity by electromyography (EMG) in five men and five women while they did activities typical of daily life or while they rested for 2–3 hours. Spectral and cross spectral analyses were performed on both variables with standard fast Fourier transform. Results—There was a marked reduction in spectral power in the ultra low frequency band (< 0.003 Hz) on going from active to rest conditions for both heart rate variability (men 6187 (1801) v 410 (89) ms2/Hz; women 4056 (1161) v 2094 (801), mean (SEM); p < 0.01) and EMG (p < 0.001). Cross spectral analysis showed a strong positive gain between the EMG and heart rate variability signal that was virtually eliminated in the resting condition (p < 0.01). A sex-by-condition effect (p = 0.06) was noted with a reduction in total spectral power for heart rate variability during rest in men, while it increased slightly in women. Conclusions—There is a quantitative link between muscle activation and heart rate variability in the lowest frequency band. Voluntary restriction of physical activity in healthy young subjects caused marked reduction in spectral power in the lowest frequency band which is often used to assess patient prognosis. The findings strongly suggest that studies of ambulatory heart rate variability should always include an indication of physical activity patterns. (Heart1999;82:e9) balloon dilatation for congenital aortic stenosis: report of 90 cases (1986–98) A Borghi, G Agnoletti, O Valsecchi, M Carminati Objective—To review 12 years of experience of balloon aortic valvoplasty in childhood. Design—Early and mid-term clinical and instrumental evaluation of 104 consecutive balloon aortic valvoplasties performed from 1986 to 1998. Setting—A tertiary referral centre for congenital heart disease. Patients—90 patients with congenital aortic stenosis: 20 neonates (group 1), 16 infants (group 2), and 54 children (group 3). Interventions—Balloon aortic valvotomy. Main outcome measures—Doppler and peak to peak aortic gradient before and after valvoplasty, degree of aortic regurgitation before and after valvoplasty, early and late mortality, need for repeat intervention or surgery. Results—Balloon aortic valvoplasty produced a gradient reduction of > 50% in 59 patients, 12 having a residual peak to peak gradient of > 50 mm Hg. Early mortality included three procedure related and six procedure unrelated deaths. There were no intraprocedural deaths. Grade III aortic regurgitation occurred in 20 patients. Five non-lethal complications occurred. At a mean follow up of 5.1 (group 1), 5.7 (group 2), and 7.6 years (group 3), survival was 75%, 88%, and 96%, respectively. Redilatation was performed in three patients in group 1, one in group 2, and 10 in group 3. Surgery was necessary for six in group 1, one in group 2, and eight in group 3. Freedom from events at last follow up was 50%, 75%, and 64%, respectively. There was a residual maximum Doppler gradient of < 30 mm Hg in 22 patients and > 60 mm Hg in 23; 50 patients have mild to moderate aortic regurgitation. Conclusions—Balloon aortic valvoplasty is effective and repeatable and offers good palliation for congenital aortic stenosis in childhood. (Heart1999;82:e10) young man with a heavy heart P Davey, Benson A 34 year old man presented with acute chest pain. His ECG was very abnormal but stable and he was treated with opiate analgesia. When his condition did not improve, chest radiography and cardiac ultrasound were performed. Both revealed metal dense deposits in the heart. On questioning, the patient revealed that he had self injected with mercury 15 years before. Self injection of elemental mercury is rare but well described and normally used by those who are suicidally depressed or who seek to improve sexual or athletic performance. Intravenous mercury may be deposited in the right heart and can result in ECG abnormalities, which may later be mistaken for changes due to coronary or other cardiac disease and result in inappropriate medication and hospitalisation. (Heart1999;82:e11)