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Offir Paz

Publications and source records attributed to Offir Paz.

6 recordsLinked to original sources
PubMed2006

Detection of T-wave alternans using an implantable cardioverter-defibrillator.

BACKGROUND: Microvolt T-wave alternans (TWA) increases acutely prior to ventricular tachycardia (VT) or ventricular fibrillation (VF) in computer simulations and animal models, suggesting that TWA may provide a warning for VT/VF in patients with an implantable cardioverter-defibrillator (ICD). OBJECTIVES: The purposes of this study were to develop a method for analyzing TWA recorded from ICD electrograms (EGMs) and to evaluate the degree of concordance between EGM TWA and TWA recorded from the surface ECG. METHODS: We developed a software program to measure EGM TWA in the frequency domain and then used simulated EGMs to determine the effects of ICD signal processing, electrical noise, and variation in the EGM fiducial point on the recorded amplitude and K score (signal-to-noise ratio) of TWA. We then applied this method to analyze TWA simultaneously using both surface ECGs and ICD EGMs during incremental pacing in 25 ICD patients. Pacing modes and EGM sources were varied in repeated trials. EGMs with dynamic range adjusted to achieve a large T wave were telemetered to a digital Holter recorder and measured offline. ECG TWA was analyzed using a commercial system. A positive (+) ECG test had sustained alternans >or=1.9 microV with K score >or=3. Stored EGMs were reviewed for VT/VF during a 6-month follow-up period. RESULTS: Simulations demonstrated that the EGM method accurately identified TWA >or=10 microV. Overall, 10 (40%) patients had at least one ECG TWA+ test and 15 patients (60%) had no ECG TWA+ tests. The maximum value of TWA was greater in EGMs than in ECGs (median 64 microV vs 2.2 microV, P <.0001). EGM TWA was greater in ECG TWA+ tests than in ECG TWA- tests (169 +/- 175 microV vs 71 +/- 61 microV, P <.001). Using a sustained EGM TWA threshold of 30 microV, EGM TWA was concordant with ECG TWA in 63 (84%) of 75 analyzed tests (P <.0001) and predicted ECG TWA results with 85% sensitivity and 84% specificity. Both ECG and EGM TWA predicted VT/VF during follow-up (ECG: P = .006; EGM: P = .035). CONCLUSION: The amplitude of TWA is at least 10 times greater on ICD EGMs than on surface ECGs. EGM and ECG TWA have substantial concordance and comparable predictive value for spontaneous VT/VF. These observations support the hypothesis that ECG and EGM TWA detect the same electrical alternans phenomenon.

Aged↗
PubMed2006

[Brugada syndrome--unique ECG pattern].

In 1992, the Brugada brothers, cardiologists from Spain, described 8 patients who survived sudden cardiac death and had a unique ECG pattern. Electrocardiographically characterized by a distinct ST-segment elevation in the right precordial leads. The syndrome is associated with a high risk for sudden cardiac death in young and otherwise healthy adults. Since then, thousands of cases were published. The syndrome is still under-diagnosed which has a serious implication on patient's prognosis. We described one patient who was misdiagnosed at the ER.

Adult↗
PubMed2005

Canine model of paroxysmal atrial fibrillation and paroxysmal atrial tachycardia.

Both autonomic nerve activity and electrical remodeling are important in atrial arrhythmogenesis. Therefore, dogs with sympathetic hyperinnervation, myocardial infarction (MI), and complete atrioventricular block (CAVB) may have a high incidence of atrial arrhythmias. We studied eight dogs (experimental group) with MI, CAVB, and sympathetic hyperinnervation induced either by nerve growth factor infusion (n = 4 dogs) or subthreshold electrical stimulation (n = 4 dogs) of the left stellate ganglion. Cardiac rhythm was continuously monitored by a Data Sciences International transmitter for 48 (SD 27) days. Three normal control dogs were also monitored. Six additional normal dogs were used for histology control. Paroxysmal atrial fibrillation (PAF) and paroxysmal atrial tachycardia (PAT) were documented in all dogs in the experimental group, with an average of 3.8 (SD 3) episodes/day, including 1.3 (SD 1.6) episodes of PAF and 2.5 (SD 2.2) episodes of PAT. The duration averaged 298 (SD 745) s (range, 7-4,000 s). There was a circadian pattern of arrhythmia onset (P < 0.01). Of 576 episodes of PAF and PAT, 236 (41%) episodes occurred during either sustained or nonsustained ventricular tachycardia (VT). Among these 236 episodes, 53% started before VT, whereas 47% started after the onset of VT. Normal dogs did not have either PAF or PAT. The hearts from the experimental group had a higher density of nerve structures immunopositive (P < 0.01) for three different nerve specific markers in both right and left atria than those of the control dogs. We conclude that the induction of nerve sprouting and sympathetic hyperinnervation in dogs with CAVB and MI creates a high yield model of PAF and PAT.

Animals↗
PubMed2005

Differential beta-adrenoceptor expression induced by nerve growth factor infusion into the canine right and left stellate ganglia.

BACKGROUND: Nerve growth factor (NGF) infusion into the right stellate ganglion (RSG) is antiarrhythmic, while NGF infusion into the left stellate ganglion (LSG) is proarrhythmic in dogs with myocardial infarction (MI) and complete atrioventricular block (CAVB). This functional asymmetry suggests differential neural remodeling. OBJECTIVES: To test the hypothesis that NGF infusion into the RSG and the LSG can lead to differential beta-adrenoceptor (beta-AR) expression in dogs with MI and CAVB. METHODS AND RESULTS: We performed immunostaining to quantify beta(1)-AR and beta(3)-AR immunoreactivity in six dogs with MI and CAVB, nine dogs with MI, CAVB, and NGF infusion to the LSG, six dogs with MI, CAVB, and NGF infusion to the RSG, and six normal dogs. There was significantly increased beta(3)-AR immunoreactivity in dogs with NGF infusion into the LSG and significantly decreased beta(3)-AR immunoreactivity in dogs with NGF infusion into the RSG compared with controls and with the MI and CAVB group. There were no significant differences in beta(1)-AR immunoreactivity among these four groups. To determine protein and mRNA expression of beta-ARs, we created MI and CAVB and infused NGF into the LSG in six additional dogs. The noninfarcted left ventricle free wall was harvested 1 week later. The protein level and receptor density of beta(3)-AR (but not beta(1)- or beta(2)-AR) significantly increased in these six dogs compared with normal controls. CONCLUSIONS: We conclude that NGF infusion into the RSG and the LSG in dogs with MI and CAVB induced differential beta(3)-AR expression in the left ventricular myocardium.

Animals↗
PubMedDate not supplied

Cardiac resynchronization therapy: overcoming ventricular dyssynchrony in dilated heart failure.

Despite optimal medical therapy, dilated heart failure is associated with a dismal prognosis and relentless progression. Intraventricular conduction delay or bundle branch block is a marker of heart failure progression and worsening prognosis. Patients fitting this profile have been shown to benefit from a specific form of cardiac pacing now referred to as cardiac resynchronization therapy (CRT). This monograph is an in-depth review of the theory and consequences of ventricular dyssynchrony in dilated heart failure, and provides an overview of the major clinical trials of CRT. Practical considerations for achieving ventricular resynchronization are discussed, with an emphasis on biventricular pacing.

Bundle-Branch Block↗