Intracardiac echocardiography (9 MHz) in humans: methods, imaging views and clinical utility.

A new low-frequency (9 MHz, 9 Fr) catheter-based ultrasound (US) transducer has been designed that allows greater depth of cardiac imaging. To demonstrate the imaging capability and clinical utility, intracardiac echocardiography (ICE) using this lower frequency catheter was performed in 56 patients undergoing invasive electrophysiological procedures. Cardiac imaging and monitoring were performed with the catheter transducer placed in the superior vena cava (SVC), right atrium (RA) and/or right ventricle (RV). In all patients, ICE identified distinct endocardial structures with excellent resolution and detail, including the crista terminalis, RA appendage, caval and coronary sinus orifices, fossa ovalis, pulmonary vein orifices, ascending aorta and its root, pulmonary artery, RV and all cardiac valves. The left atrium and ventricle were imaged with the transducer at the limbus fossa ovalis of the interatrial septum and in the RV, respectively. ICE was important in identifying known or unanticipated aberrant anatomy in 11 patients (variant Eustachian valve, atrial septal aneurysm and defect, lipomatous hypertrophy, Ebstein's anomaly, ventricular septal defect, tetralogy of Fallot, transposition of the great arteries, disrupted chordae tendinae and pericardial effusion) or in detecting procedure-related abnormalities (narrowing of SVC-RA junction orifice or pulmonary venous lumen, atrial thrombus, interatrial communication). In patients with inappropriate sinus tachycardia, ICE was the primary ablation catheter-guidance technique for sinus node modification. With ICE monitoring, the evolution of lesion morphology with the three imaging features including swelling, dimpling and crater formation was observed. In all patients, ICE was contributory to the mapping and ablation process by guiding catheters to anatomically distinct sites and/or assessing stability of the electrode-endocardial contact. ICE was also used to successfully guide atrial septal puncture (n = 9) or RA basket catheter placement (n = 4). Thus, ICE with a new 9-MHz catheter-based transducer has better imaging capability with a greater depth. Normal and abnormal cardiac anatomy can be readily identified. ICE proved useful during electrophysiological mapping and ablation procedures for guiding interatrial septal puncture, assessing placement and contact of mapping and ablation catheters, monitoring ablation lesion morphological changes, and instantly diagnosing cardiac complications.

ICD-antiarrhythmic drug and ICD-pacemaker interactions.

Antiarrhythmic drugs and separate bradycardia pacing systems are prescribed commonly in patients with implantable cardioverter defibrillators (ICDs). Adverse effects of antiarrhythmic drugs on ICD function and adverse interactions between ICDs and pacemakers have been documented. The effect of antiarrhythmic drugs on the defibrillation threshold (DFT) in patients has not been well assessed. Most studies have been performed in animal models in which cardiac function was normal and drug doses were supraphysiologic. In addition, most studies have utilized monophasic defibrillation shock waveforms and epicardial lead systems. Despite the lack of clinical data applicable to current defibrillation systems, it appears that chronic amiodarone administration causes a significant DFT increase. In addition, antiarrhythmic drugs can influence antitachycardia pacing and tachycardia sensing. Defibrillation shocks can cause transient failure of pacemaker sensing and pacing, and cause spurious pacemaker reprogramming. Pacemaker function can result in ICD oversensing, leading to inappropriate therapy, or cause ICD undersensing, potentially resulting in failure to deliver therapy during ventricular fibrillation. The susceptibility of an ICD to undersensing appears related to the amplitude of the pacing stimulus artifact recorded by the ICD rate-sensing circuit and to the characteristics of the fibrillation electrogram. Preliminary data suggest that undersensing of ventricular fibrillation by current ICDs is an unlikely event.

Lower frequency (5 MHZ) intracardiac echocardiography in a large swine model: imaging views and research applications.

Our previous investigation indicated that, in the 50-114-kg weight range, the swine model provides transeosophageal echocardiographic normal values for cardiac structures comparable to those found in human adults. Intracardiac echocardiographic imaging using a 12.5-MHz ultrasound catheter is limited, due to ultrasonic attenuation. Transesophageal echocardiographic imaging of the right heart is also limited with its anterior anatomic location. To further study the utility of intracardiac imaging, we placed a 5-MHz (30 Fr) multiplane transducer at the junction of the superior vena cava and right atrium, in the right atrium and right ventricle in 8 closed-chest swine (weight 129 +/- 61 kg). In each animal, complete whole heart imaging was obtained, with tomographic views including the cardiac 4-chamber, right atrium, right ventricle and outflow, left atrium and ventricle, and basal great vessels. Major intracardiac anatomic landmarks (i.e., crista terminalis, right atrial appendage, coronary sinus orifice, interatrial septum, tricuspid valve, right ventricular outflow, pulmonary veins, mitral valve and left ventricular papillary muscles) were visualized in every swine. Thus, this 5-MHz multiplane transducer, as a prototype for a steerable low-frequency intracardiac ultrasound catheter, improved both whole heart and individual cardiac structure imaging from a single intracardiac location. Further technological development and refinement is needed for routine use in research and clinical imaging practice.