Salim F. Idriss

Arrhythmias in a contemporary fontan cohort: prevalence and clinical associations in a multicenter cross-sectional study.

OBJECTIVES Our aim was to examine the prevalence of arrhythmias and identify independent associations of time to arrhythmia development. BACKGROUND Since introduction of the Fontan operation in 1971, long-term results have steadily improved with newer modifications. However, atrial arrhythmias are frequent and contribute to ongoing morbidity and mortality. Data are lacking regarding the prevalence of arrhythmias and risk factors for their development in the current era. METHODS The Pediatric Heart Network Fontan Cross-Sectional study evaluated data from 7 centers, with 520 patients age 6 to 18 years (mean 8.6 +/- 3.4 years after the Fontan operation), including echocardiograms, electrocardiograms, exercise testing, parent-reported Child Health Questionnaire (CHQ) results, and medical history. RESULTS Supraventricular tachycardias were present in 9.4% of patients. Intra-atrial re-entrant tachycardia (IART) was present in 7.3% (32 of 520). The hazard of IART decreased until 4 to 6 years post-Fontan, and then increased with age thereafter. Cardiac anatomy and resting heart rate (including marked bradycardia) were not associated with IART. We identified 3 independent associations of time to occurrence of IART: lower CHQ physical summary score (p < 0.001); predominant rhythm (p = 0.002; highest risk with paced rhythm), and type of Fontan operation (p = 0.037; highest risk with atriopulmonary connection). Time to IART did not differ between patients with lateral tunnel and extracardiac conduit types of Fontan repair. Ventricular tachycardia was noted in 3.5% of patients. CONCLUSIONS Overall prevalence of IART was lower in this cohort (7.3%) than previously reported. Lower functional status, an atriopulmonary connection, and paced rhythm were determined to be independently associated with development of IART after Fontan. (Relationship Between Functional Health Status and Ventricular Performance After Fontan-Pediatric Heart Network; NCT00132782).

The restitution portrait: A new method for investigating rate-dependent restitution

Introduction: Electrical restitution, relating action potential duration (APD) to diastolic interval (DI), was believed to determine the stability of heart rhythm. However, recent studies demonstrate that stability also depends on long‐term APD changes caused by memory. This study presents a new method for investigation of rate‐ and memory‐dependent aspects of restitution and for assessment of mapping models of APD.

A miniaturized catheter 2-D array for real-time, 3-D intracardiac echocardiography

The design, fabrication, and characterization of a 112 channel, 5 MHz, two-dimensional (2-D) array transducer constructed on a six layer flexible polyimide interconnect circuit is described. The transducer was mounted in a 7 Fr (2.33 mm outside diameter) catheter for use in real-time intracardiac volumetric imaging. Two transducers were constructed: one with a single silver epoxy matching layer and the other without a matching layer. The center frequency and -6 dB fractional bandwidth of the transducer with a matching layer were 4.9 MHz and 31%, respectively. The 50 /spl Omega/ pitch-catch insertion loss was 80 dB, and the typical interelement crosstalk was -30 dB. The final element yield was greater than 97% for both transducers. The transducers were used to acquire real-time, 3-D images in an in vivo sheep model. We present in vivo images of cardiac anatomy obtained from within the coronary sinus, including the left and right atria, aorta, coronary arteries, and pulmonary veins. We also present images showing the manipulation of a separate electrophysiological catheter into the coronary sinus.

Real-time three-dimensional intracardiac echocardiography.

Using catheter-mounted 2-D array transducers, we have obtained real-time 3-D intracardiac ultrasound (US) images. We have constructed several transducers with 64 channels inside a 12 French catheter lumen operating at 5 MHz. The transducer configuration may be side-scanning or beveled, with respect to the long axis of the catheter lumen. We have also included six electrodes to acquire simultaneous electrocardiograms. Using an open-chest sheep model, we inserted the catheter into the cardiac chambers to study the utility of in vivo intracardiac 3-D scanning. Images obtained include a cardiac four-chamber view, mitral valve, pulmonic valve, tricuspid valve, interatrial septum, interventricular septum and ventricular volumes. We have also imaged two electrophysiological interventional devices in the right atrium, performed an in vitro ablation study, and viewed the pulmonary veins in vitro.

Effect of Rapid Pacing and T-Wave Scanning on the Relation Between the Defibrillation and Upper-Limit-of-Vulnerability Dose-Response Curves

BACKGROUND The critical-point and upper-limit-of-vulnerability (ULV) hypotheses predict that the ULV dose-response curve should be steeper and to the right of the defibrillation (DF) curve. Yet, some recent experimental data contradict this prediction. Two studies are presented that test two explanations for the contradiction: (1) Testing at a single point in the T wave underestimates the ULV dose-response curve and (2) ULV testing at normal heart rates does not mimic the mechanical or electrical state of the heart in ventricular fibrillation (VF). METHODS AND RESULTS A nonthoracotomy lead system with a biphasic waveform was used throughout. In eight dogs, the dose-response curve widths (a measure of steepness) were compared between DF data and ULV data gathered at the peak (ULVPK), middownslope (ULVDWN), midupslope (ULVUP), and all times (scanning or ULVSCN) in the T wave. In another eight dogs, ULV data (ULVRAP) were gathered by scanning the T wave after 15 rapidly paced beats (166- to 198-ms pacing interval). The rapid pacing interval was chosen to more closely mimic the hemodynamics and activation rate of early VF. ULV data (ULVSTD) at normal heart rates were gathered for all animals. In the first study, scanning significantly reduced the ULV curve width (ULVSCN, 63.5 +/- 29.7 V; ULVPK, 81.9 +/- 45.2 V; ULVDWN, 116 +/- 36.5 V; DF, 105 +/- 22.0 V; P < .03) and significantly shifted the ULV curve to the right (ULV80 SCN, 410 +/- 62.6 V; ULV80 PK, 266 +/- 35.3 V; ULV80 DWN, 355 +/- 80.4 V; DF80, 427 +/- 60.9 V; P < .001). The subscript 80 signifies that the subject was left in normal sinus rhythm 80% of the time after that stimulus strength was delivered. In the second study, the ULVRAP curve was shifted dramatically to the right, the average ULV50 RAP being greater than the average DF90. Furthermore, 92% of the ULVRAP VF inductions occurred between 10 ms before and 50 ms after the peak of the T wave, suggesting that scanning of the entire T wave may not be necessary. CONCLUSIONS With a single rapidly paced ULV sequence with limited T-wave scanning, it may be possible to estimate highly effective defibrillation doses with few VF episodes and high-voltage stimuli.

Electrocardiographic response to enzyme replacement therapy for Pompe disease

Purpose: Electrocardiogram (ECG) abnormalities are universal in infantile Pompe disease or glycogen storage disease type II, a fatal genetic muscle disorder caused by deficiency of acid α-glucosidase (GAA). Hallmarks of this disease include a shortened PR interval, an increased QT dispersion (QTd), and large left ventricular (LV) voltages. We evaluated the effect of recombinant human GAA (rhGAA) enzyme replacement therapy (ERT) on these ECG parameters in patients with infantile-onset Pompe disease.Methods: A total of 134 ECGs were evaluated from 19 patients (5 females and 14 males) with a median age of 5.5 months at the time of enrollment in open-label clinical trials exploring the safety and efficacy of ERT at a single center from 1999 to 2004. rhGAA was purified from genetically engineered Chinese hamster ovary cells overproducing GAA and infused intravenously at doses ranging from 10 mg/kg per week to 20 to 40 mg/kg every 2 weeks in patients with infantile-onset Pompe disease. The PR interval, QTd (longest to shortest QT), and LV voltage (SV1+RV6) were blindly determined by two independent observers.Results: The median follow-up period was 6 months (range 2–30 months). The PR interval lengthened from 83 (42–110) ms to 107 (95–130) ms (P < .001), and the QTd decreased from 83 (40–125) ms to 53 (20–80) ms (P = .003). There were significant decreases in LV voltage (67 [17–83] mV vs. 48 [18–77] mV, P = .03), which correlated with decrease in LV mass on two-dimensional echocardiogram. There was no evident change in the QTc interval (429 [390–480] ms vs. 413 [370–450] ms, P = not significant).Conclusion: rhGAA ERT for infantile Pompe disease results in an increase in PR interval and a decrease in both the QTd and the LV voltage. These results suggest that these ECG parameters may be useful markers of the severity of cardiac disease and the response to ERT treatment in patients with infantile Pompe disease.

Efficient electrode spacing for examining spatial organization during ventricular fibrillation

Spatial organization has been observed during episodes of ventricular fibrillation (VF) by recording epicardial unipolar electrograms on a grid of electrodes. In such studies, the choice of spacing between electrodes is an important decision, affecting the resolution and the size of the domain to be studied. A basic tenet of sampling theory, the Nyquist criterion, states that an electrode spacing smaller than half the smallest significant wavelength is required to capture the important details of a spatially sampled process. The authors suggest a method to choose a practical interelectrode spacing by examining wavenumber power spectra of high-resolution VF data recorded from a square 11*11 array of electrodes spaced 0.28 mm apart. The plaque was sutured on the epicardium near the left ventricular apex in 7 anesthetized pigs. VF was induced with AC simulation. Unipolar extracellular electrograms were simultaneously recorded from each channel for 2 s after the induction of VF. Each signal was sampled in time at 1000 Hz. Wavenumber power spectra were calculated for 100 ms segments using the zero-delay wavenumber spectrum method, for a total of 140 power spectra. All spectra had dominant peaks at the origin and fell off rapidly with increasing wavenumber (decreasing wavelength). In all the spectra, every wavelength shorter than 1.4 mm contributed insignificant power. Furthermore, in 134 of 140 spectra (96%), insignificant power levels were associated with every wavelength shorter than 2.8 mm. These results suggest that, for unipolar extracellular electrodes, an intersensor spacing on the order of 1 mm is appropriate to study organization during early VF.<<ETX>>

Real-Time 3D Transesophageal Echocardiography

Transesophageal echocardiography (TEE) is an essential diagnostic tool in patients with poor transthoracic echocardiographic windows or when detailed imaging of structures distant from the chest wall is necessary. A real-time 3D TEE probe has been fabricated in our laboratory in order to increase the amount of information available during a transesophageal procedure. The 1 cm diameter esophageal probe utilizes a 2-dimensional, 5 MHz array at its tip with a 6.3 mm diameter aperture, including 504 active channels. The array has a periodic vernier geometry with an element pitch of 0.18 mm, built onto a multilayer flexible (MLF) interconnect circuit. In order to accommodate 504 channels within the device, a 1 m long Gore MicroFlat™ cable was utilized for wiring the MLF to the corresponding system connectors. Pulse-echo tests in a water tank have yielded a −6 dB bandwidth of 25.3%. Fully connected to the system through 3 m of cable, the probe shows an average 50 Ω insertion loss of −85 dB with a standard deviation of 4 dB, as determined through pitch-catch measurements for a sampling of 10 elements. Using the completed 3D TEE probe with the Volumetrics Medical Imaging 3D scanner, real-time volumetric images of in vivo canine cardiac anatomy have been acquired, displaying atrial views, mitral valve function and interventional catheter guidance.

Feasibility Study of Real-Time Three- Dimensional Intracardiac Echocardiography for Guidance of Interventional Electrophysiology

SMITH, S.W., et al.: Feasibility Study of Real‐Time Three‐Dimensional Intracardiac Echocardiography for Guidance of Interventional Electrophysiology. The authors tested the feasibility of real‐time three‐dimensional intracardiac echocardiography for guidance of interventional electrophysiological studies. The three‐dimensional scanner uses a matrix array ultrasound transducer of 64 channels operating at 5 MHz in a 12 Fr catheter. The system features real‐time three‐dimensional image rendering and produces up to 60 volumetric scans per second. Using an open‐chest sheep model, real‐time three‐dimensional images of anatomic landmarks were obtained, including the pulmonary veins and coronary sinus, which are of value in electrophysiological procedures. In vivo radio frequency ablation procedures in the right ventricle were also monitored, which yielded lesions of high image contrast.

The Effect of Cardiac Compression on Defibrillation Efficacy and the Upper Limit of Vulnerability

Compression Affects Defibrillation and ULV. Introduction: We determined the effects of decreasing the ventricular blood volume and altering cardiac geometry on defibrillation, the upper limit of vulnerability (ULV), and the relationship between them.