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.

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.

Case Reports: 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.

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.