Chang Ci

ECG data compression using truncated singular value decomposition

The method of truncated singular value decomposition (SVD) is proposed for electrocardiogram (ECG) data compression. The signal decomposition capability of SVD is exploited to extract the significant feature components of the ECG by decomposing the ECG into a set of basic patterns with associated scaling factors. The signal informations are mostly concentrated within a certain number of singular values with related singular vectors due to the strong interbeat correlation among ECG cycles. Therefore, only the relevant parts of the singular triplets need to be retained as the compressed data for retrieving the original signals. The insignificant overhead can be truncated to eliminate the redundancy of ECG data compression. The Massachusetts Institute of Technology-Beth Israel Hospital arrhythmia database was applied to evaluate the compression performance and recoverability in the retrieved ECG signals. The approximate achievement was presented with an average data rate of 143.2 b/s with a relatively low reconstructed error. These results showed that truncated SVD method can provide an efficient coding with high-compression ratios. The computational efficiency of the SVD method in comparing with other techniques demonstrated the method as an effective technique for ECG data storage or signals transmission. Index Terms-Data compression, electrocardiogram, feature extraction, quasi-periodic signal, singular value decomposition.

Ventricular assist device application as a bridge to pediatric heart transplantation: a single center's experience.

OBJECTIVESnThere are limited options for mechanical circulatory support to treat end-stage heart failure in pediatric patients. Although extracorporeal membrane oxygenation is commonly used in infants and children, ventricular assist devices (VAD) provide a longer duration of support with fewer complications before recovery or as a bridge to heart transplantation (HTx), as described herein.nnnMETHODSnThis retrospective chart review of eight patients transplanted from April 2008 to December 2011, after left ventricular assist device (LVAD) implantation due to end-stage heart failure. Their mean age was 12 years (9-15 y) and mean body weight, 48 kg (20-78). All were New York Heart Association functional class IV with mean left ventricular ejection fractions less than 15%.nnnRESULTSnThe six patients (75%) received HTx after a mean LVAD support duration of 43.2 days; 2 (25%) died before a suitable heart became available. Their mean duration of LVAD support was 30 days. There were 4 (50%) who experienced clinically evident thromboembolic events: 3 (37.5%) cerebrovascular with 1 mortality and 1 (12.5%) as acute limb ischemia. Transient hemodialysis was performed in 4 (50%). Bloodstream infection identified in 6 (75%) was controlled with intravenous antibiotics. Driveline infection identified in 4 (50%) was treated successfully with local wound dressing changes and intravenous antibiotics. One 9-year-old boy died of rejection at 16 months after transplantation.nnnCONCLUSIONSnBecause of the organ shortage, pediatric patients have a low chance to undergo HTx. VAD provides long-term support for children with end-stage heart failure before a suitable heart becomes available. A thromboembolic event remains a major complication influencing their survival.

An unusual cause of chylothorax after Norwood stage one reconstruction.

We report an unusual cause of prolonged chylothorax drainage after Norwood stage one reconstruction. This 1-month-old girls chylous drainage was refractory to medical treatment. Echocardiography revealed thrombosis of the superior vena cava. Upon sternotomy to remove the thrombus, we were surprised to find the ePTFE (expanded polytetrafluoroethylene) tube previously used for selective cerebral perfusion compressing the innominate vein and the pericardium-based aortic arch. We performed a superior vena cava thrombectomy and shortened the ePTFE tube. Her chylothorax subsided gradually. We suggest that external compression of the venous drainage system should be considered in patients with prolonged chylothorax drainage. Once medical treatment fails, early surgical exploration may be helpful to stop the chylothorax.

Evolving strategies and improving outcomes of Norwood stage one reconstruction: a decade experience of a single institution in Taiwan.

AIMnThe aim of this study was to define the improvement in short-term outcome and risk factors of Norwood stage one reconstruction for hypoplastic left heart syndrome (HLHS) in Taiwan, after implementing new perioperative management strategies.nnnMETHODSnData were retrieved from a retrospective chart review of patients with HLHS treated between July 1997 and July 2007. Since we implemented new perioperative strategies in 2004, we divided our patients into two groups, early era (1997-2003) and late era (2004-2007), and compared the outcome.nnnRESULTSnWe enrolled 48 patients. In the early era group (n=28), the diagnosis was confirmed by cardiac catheterization and controlled ventilation was used to manipulate the balance between systemic and pulmonary blood flow. The survival rate was only 17.9% (5/28). Surgery was performed at 15.2+/-10.7 days, which was significantly later than in the late era group (4.6+/-4.0 days, n=20). A lower preoperative shock and more prenatal diagnoses were recorded for the late era group. RV-PA conduit was used in 17 patients in the late era group of which 12 (70.6%) survived to be discharged from hospital. The risk factor was significant TR (tricuspid regurgitation).nnnCONCLUSIONSnWith our contemporary perioperative management and change in surgical strategy, survival after first-stage palliation has improved. We believe that our HLHS experience is valuable for low volume centers and also for Asian cohorts.

Cardiac Arrest After Methylprednisolone Pulse Therapy Rescued Using Extracorporeal Membrane Oxygenation in Patients With Acute Cardiac Rejection: Two Case Reports

Patients receive methylprednisolone pulse therapy (MPT) when acute cardiac rejection occurs. Although the regimen is generally safe and effective, severe complications occasionally develop. From 1997 to 2007, there were 210 cardiac transplantation procedures performed at our hospital. Among these patients, there were 23 episodes of acute rejection treated with MPT, 10 mg/kg/d. Two patients in our series had cardiac arrest within 36 hours after initiating the therapy. Endomyocardial biopsy specimens showed International Society for Heart Transplantation grade 1B allograft rejection in both cases. Emergent intubation and cardiopulmonary resuscitation were performed. Venoarterial extracorporeal membrane oxygenation (ECMO) was used to rescue the patients. The cardiac function in both patients recovered gradually. Left ventricular ejection fraction increased from 16.2% to 47% in one patient and from 27% to 30% in the other patient. One patient was successfully weaned from ECMO after 2 days of support. The other patient was discharged against medical advice because of hypoxia-related brain death after 3 days. Both patients had a history of tachyarrhythmias before initiation of MPT. Although the relationship between mechanisms of cardiac arrest and MPT is uncertain, the risk of cardiac arrest cannot be overlooked when initiating MPT, especially in patients with a history of tachyarrhythmia. Meanwhile, ECMO can serve as a rescue method if cardiac arrest occurs.