The effects of rate and irregularity on sympathetic nerve activity in human subjects.

BACKGROUND: We have recently shown that atrial fibrillation is associated with an increase in sympathetic nerve activity (SNA) compared with sinus rhythm. It remains unclear, however, whether these findings are true at various rates and whether the magnitude of sympathoexcitation is related to the degree of irregularity. OBJECTIVE: To determine the role of irregularity in mediating the SNA changes at various pacing rates. Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, P < .001) but that MAP and DBP did not change significantly. METHODS: Using custom-made software, atrioventricular sequential pacing with predetermined rates (100, 120, and 140 bpm) and irregularities (standard deviation = 0%, 5%, 15%, and 25% of mean cycle length) was performed in 23 patients referred for electrophysiologic evaluation. Pacing at each rate/irregularity was performed for 2 minutes, with 2 minutes of recovery in between. Systolic, diastolic, and mean arterial blood pressure (SBP, DBP, and MAP), central venous pressure (CVP), and SNA were measured at baseline and during pacing. RESULTS: Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, P < .001 but that MAP and DBP did not change significantly. A significant correlation was found between the pacing irregularity and SNA, with greater sympathoexcitation noted at greater degrees of irregularity (r = 0.2, P = .04). A five-variable linear model using DBP, MAP, CVP, and degree of pacing irregularity to predict SNA was highly statistically significant (r = 0.46, P < .001). After controlling for hemodynamic changes, for every 1% increase in irregularity, there was a 6.1% increase in SNA. CONCLUSION: We have shown that greater degrees of irregularity cause greater sympathoexcitation and that the effects of irregular pacing on SNA are independent of the hemodynamic changes.

A novel approach for EIT regularization via spatial and spectral principal component analysis.

Electrical impedance tomography, EIT, is an imaging modality in which the internal conductivity distribution of an object is reconstructed based on voltage measurements on the boundary. This reconstruction problem is a nonlinear and ill-posed inverse problem, which requires regularization to ensure a stable solution. Most popular regularization approaches enforce smoothness in the inverse solution. In this paper, we propose a novel approach to build a subspace for regularization using a spectral and spatial multi-frequency analysis approach. The approach is based on the construction of a subspace for the expected conductivity distributions using principal component analysis. It is shown via simulations that the reconstructed images obtained with the proposed method are better than with the standard regularization approach. Using this approach, the percentage of misclassified finite elements was reduced up to twelve fold from the initial percentages after five iterations. The advantage of this technique is that prior information is extracted from the characteristic response of an object at different frequencies and spatially across the finite elements.

Case report: Radiofrequency catheter ablation of typical atrial flutter and the atrioventricular junction via the superior vena caval approach in a patient with a congenital absence of an inferior vena cava.

The absence of an inferior vena cava is a rare congenital condition often without clinical significance. Alternative venous approaches are often needed to treat these patients. We report a case of successful ablation of both isthmus dependent flutter and the AV junction using the superior vena cava in a patient with an inferior vena cava anomaly.

Carvedilol produces sustained long-term benefits: follow-up at 12 years.

The authors measured long-term outcomes of patients who initiated carvedilol between 1990 and 1992 to test the hypothesis that carvedilol produces sustained benefits in heart failure patients. The study population consisted of 57 patients who completed a carvedilol placebo-controlled phase II trial. Patients were given open-label carvedilol and were titrated to the maximum dose. Patients were assessed by serial multigated acquisition, echocardiography, and symptom scores. Survival was assessed for all patients and censored as of January 1, 2004. Survival for ischemic vs nonischemic patients was compared using the log-rank test and further compared using Cox regression, controlling for covariates. Etiology of heart failure was ischemic in 15 patients and nonischemic in 42 patients. Median follow-up was 12.9 years. Resting left ventricular ejection fraction (LVEF) and heart failure symptom scores improved at 4 months of treatment and were sustained at 24 months. Left ventricular internal diameter in systole (LVIDS) and left ventricular internal diameter in diastole decreased significantly at 4 and 8 months, respectively, and LVIDS continued to improve at 24 months. Overall mortality was 43% in nonischemic patients and 73% in ischemic patients. In a multivariate analysis, ischemic etiology and baseline LVEF were significant predictors of mortality. Carvedilol produces sustained improvements in left ventricular remodeling and symptoms. Long-term survival is good, particularly in nonischemic patients.

Klebsiella pneumoniae: a rare cause of device-associated endocarditis.

Intravascular infections involving implanted pacemakers and defibrillators are being seen with increasing frequency. This report describes a case of intravascular infection of an implanted defibrillator with Klebsiella pneumoniae, an unusual pathogen for pacemaker or defibrillator infection.

The magnitude of sinus cycle length change during ventricular tachycardia is predictive of successful antitachycardia pacing.

BACKGROUND: Despite the wide use of antitachycardia pacing (ATP) in patients with implantable cardioverter defibrillators (ICDs), predictors of ATP success remain poorly understood. We hypothesize that the degree of sympathoexcitation, as measured by the sinus cycle length (SCL) shortening during ventricular tachycardia (VT), is a predictor of ATP success. METHODS AND RESULTS: The charts of 462 patients with dual-chamber ICDs were reviewed. A total of 88 events in 26 patients met the inclusion criteria and were analyzed. The mean SCL during the 4 seconds preceding the VT onset (SCL-baseline), and during the 4 seconds prior to ATP delivery (SCL-VT) was measured. The percent shortening in SCL was calculated as ((SCL-baseline) - (SCL-VT))/(SCL-baseline) x 100. Patients were classified into the ATP-success and ATP-failure groups depending on the VT(s) response to ATP. Using a t-test analogue for clustered data, patients in the ATP-success group exhibited a greater shortening in SCL when compared with the ATP-Failure group (5.8% compared to 4.7%, P = 0.007). The successful ATP events displayed an average SCL shortening of 6.0% compared to 1.8% in the unsuccessful ATP events (P = 0.029). When the events were analyzed, the sensitivity and specificity of a shortening in SCL of >10% in predicting ATP success were 0.29 and 1. CONCLUSION: We have shown that the SCL change during VT, a marker of the autonomic changes that accompany a tachycardia, is useful in predicting ATP success. Our findings suggest that analysis of the SCL during VT might play a role in future programming of ATP in patients with ICDs.

Initiation and use of beta-blockers in class IV heart failure.

Treatment of patients with heart failure caused by left ventricular systolic dysfunction using b-adrenergic receptor antagonists (or b-blockers) results in improvements in symptoms, hemodynamics, left ventricular remodeling, morbidity, and mortality. Most patients studied in prospective, randomized placebo-controlled trials have had New York Heart Association (NYHA) functional class II or III symptoms. The efficacy of b-blockers in treating NYHA class IV patients is not as well-established. This review summarizes the published experience regarding the use of b-blockers in patients with advanced heart failure. Although treatment requires considerable care, the data support attempts at initiation of b-blockers in this group of patients.