Prevalence, characteristics and natural course of inappropriate sinus tachycardia.

AIMS: To study the prevalence, characteristics and natural course of inappropriate sinus tachycardia (IST). METHODS AND RESULTS: The prevalence and characteristics of IST were evaluated in a random sample of 604 middle-aged subjects. Seven of the subjects (1.16%) fulfilled the contemporary diagnostic criteria of IST. The systolic (147+/-11 mmHg vs. 130+/-13 mmHg, P<0.001) and diastolic ambulatory blood pressures (92+/-7 mmHg vs. 81+/-8 mmHg, P<0.001) were higher among the subjects with IST than among the controls. The other laboratory, echocardiographic and personality measurements, with the exception of the hostility score (10+/-2 vs. 8+/-3, P<0.001), revealed no differences between the groups. The natural course and prognosis of the disorder was assessed among the subjects fulfilling the IST criteria and nine previously diagnosed IST patients. During a mean follow-up of 6.0+/-2.4 years, none of the subjects developed any clinical or echocardiographic evidence of structural heart disease despite ongoing palpitations, and there was no significant reduction in the 24-h average HR (9+/-2 bpm vs. 89+/-8 bpm, P=0.204). CONCLUSION: The prevalence of IST in a middle-aged population was higher than previously assumed. Despite the chronic nature of the disorder, the prognosis of IST was benign. The causal relationship between IST and hypertension and/or hostile personality type remains speculative.

Fractal analysis of heart rate variability and mortality after an acute myocardial infarction.

The recently developed fractal analysis of heart rate (HR) variability has been suggested to provide prognostic information about patients with heart failure. This prospective multicenter study was designed to assess the prognostic significance of fractal and traditional HR variability parameters in a large, consecutive series of survivors of an acute myocardial infarction (AMI). A consecutive series of 697 patients were recruited to participate 2 to 7 days after an AMI in 3 Nordic university hospitals. The conventional time-domain and spectral parameters and the newer fractal scaling indexes of HR variability were analyzed from 24-hour RR interval recordings. During the mean follow-up of 18.4 +/- 6.5 months, 49 patients (7.0%) died. Of all the risk variables, a reduced short-term fractal scaling exponent (alpha(1) <0.65), measured by detrended fluctuation analysis, was the most powerful predictor of mortality (univariate relative risk 5.05, 95% confidence intervals [CI] 2.87 to 8.89, p <0.001). A low scaling exponent alpha(1) predicted death in the patients with and without depressed left ventricular function (p <0.001 and p <0.01, respectively). Several other HR variability parameters also predicted mortality in univariate analyses, but in a multivariate analysis after adjustments for clinical variables and left ventricular ejection fraction, alpha(1) was the most significant independent HR variability index that predicted subsequent mortality (relative risk 3.90, 95% CI 2.03 to 7.49, p <0.001). Short-term fractal scaling analysis of HR variability is a powerful predictor of mortality among patients surviving an acute myocardial infarction.

Impaired negative chronotropic response to adenosine in patients with inappropriate sinus tachycardia.

INTRODUCTION: Adenosine is an endogenous nucleoside that has an important role in the diagnosis and treatment of several cardiac arrhythmias. However, its effects on inappropriate sinus tachycardia (IST) are not well established. METHODS AND RESULTS: In this study, the response to intravenous adenosine (0.1 to 0.15 mg/kg) was studied in 18 patients (age 46+/-15 years) with IST. In a subset of patients (n = 5), the direct effects of adenosine were assessed during pharmacologic beta-adrenergic and cholinergic blockade. Atrial cycle length (ACL) was measured before adenosine injection, at the time of the greatest cycle length prolongation, and during the maximum rebound acceleration of heart rate. Eighteen subjects (age 46+/-11 years) with normal sinus rhythm undergoing clinically indicated electrophysiologic study served as controls. Adenosine did not terminate IST in any patient. The maximum dose of adenosine prolonged the sinus interval significantly, from 780+/-128 msec to 985+/-225 msec (P < 0.001) in the control subjects. In contrast, adenosine caused no significant lengthening of atrial cycle length (527+/-69 msec vs 590+/-148 msec; P = NS) in the patients with IST. Similar difference in the response to adenosine was seen during the pharmacologic autonomic blockade. The reflex increase of the sinus rate (rebound effect) was greater in the control subjects than in the patients with IST (21.2%+/-9.7% vs 8.5%+/-8.8%; P < 0.001). CONCLUSION: The usual negative chronotropic effect of adenosine was impaired in the patients with IST. This may have important diagnostic implications and provide new insight into the mechanism(s) of IST.