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Background Cardiac resynchronization therapy (CRT) and atrial ablation procedures currently lack a noninvasive imaging modality for reliable treatment planning and monitoring. Electromechanical wave imaging (EWI) is an ultrasound-based method that has previously been shown to be capable of noninvasively and transmurally mapping the activation sequence of the heart in animal studies by estimating and imaging the electromechanical wave, that is, the transient strains occurring in response to the electrical activation, at both high temporal and spatial resolutions. Objective To demonstrate the feasibility of transthoracic EWI for mapping the activation sequence during different cardiac rhythms in humans. Methods EWI was perfor`med in patients undergoing CRT and a left bundle branch block (LBBB) during sinus rhythm, left ventricular pacing, and right ventricular pacing, as well as in patients with atrial flutter (AFL) before intervention, EWI findings from patients with AFL were subsequently correlated with results from invasive intracardiac electrical mapping studies during intervention. In addition, the feasibility of single-heartbeat EWI at 2000 frames/s is demonstrated in humans for the first time in a patient with both AFL and right bundle branch block (RBBB). Results The electromechanical activation maps demonstrated the capability of EWI to localize the pacing sites and characterize the bundle branch block activation sequence transmurally in patients with CRT. In patients with AFL, the EWI propagation patterns obtained with EWI were in excellent agreement with those obtained from invasive intracardiac mapping studies. Conclusions Our findings demonstrate the potential capability of EWI to aid in the assessment and follow-up of patients undergoing CRT pacing therapy and atrial ablation, with preliminary validation in vivo.

Background— Complex fractionated atrial electrograms (CFAE) are morphologically more uniform in persistent longstanding as compared with paroxysmal atrial fibrillation (AF). It was hypothesized that this may result from a greater degree of repetitiveness in CFAE patterns at disparate left atrial (LA) sites in longstanding AF. Methods and Results— CFAEs were obtained from recording sites outside the 4 pulmonary vein (PV) ostia and at a posterior and an anterior LA site during paroxysmal and longstanding persistent AF (10 patients each, 120 sequences total). To quantify repetitiveness in CFAE, the dominant frequency was measured from ensemble spectra using 8.4-second sequences, and repetitiveness was calculated by 2 novel techniques: linear prediction and Fourier reconstruction methods. Lower prediction and reconstruction errors were considered indicative of increasing repetitiveness and decreasing randomness. In patients with paroxysmal AF, CFAE pattern repetitiveness was significantly lower (randomness higher) at antral sites outside PV ostia as compared with LA free wall sites ( P P Conclusions— In paroxysmal AF, CFAE repetitiveness is low and randomness high outside the PVs, particularly the left superior PV. As evolution to persistent longstanding AF occurs, CFAE repetitiveness becomes more uniformly distributed at disparate sites, possibly signifying an increasing number of drivers from remote PVs.

Irrigated (cooled) radiofrequency (RF) ablation has become our primary ablation tool for treating atrial fibrillation, macroreentrant atrial tachycardias, and scar-related ventricular tachycardias. As with any technology that increases ablation lesion size, there is the potential for increased risk. The methods described are a cautious approach to power titration that considers the risks of excessive heating and the lesion size needed for a particular site. Future methods of assessing lesion creation will hopefully refine energy titration to improve safety and efficacy of cooled RF ablation.

Steam pops are a risk of irrigated radiofrequency catheter ablation (RFA) and may cause cardiac perforation. Data to guide radiofrequency (RF) energy titration to avoid steam pops are limited.This study sought to assess the frequency and consequence of audible pops and to determine the feasibility of using the magnitude of impedance change to predict pops.We reviewed consecutive endocardial open-irrigated RFA for ventricular tachycardia (VT) with continuously recorded ablation data in 142 patients with structural heart disease. Steam pops were defined as an audible pop associated with a sudden spike in impedance. Ablation lesions before or after pops served as controls.From a total of 4,107 ablation lesions, 62 (1.5%) steam pops occurred in 42 procedures in 38 patients. Perforation with tamponade occurred with 1 of 62 (2%) pops. Applications with pops had a greater impedance decrease (22 +/- 7 Omega vs. 18 +/- 8 Omega, P = .001) and a higher maximum power (45 +/- 5 W vs. 43 +/- 6 W, P = .011), but did not differ in maximum catheter tip temperature (40 degrees C +/- 4 degrees C vs. 40 degrees C +/- 4 degrees C, P = .180) from applications without pops. Eighty percent of pops occurred after impedance decreased by at least 18 Omega.During VT ablation with open irrigation, audible pops are infrequent and do not usually cause perforation. Limiting RF power to achieve an impedance decrease of18 Omega is a feasible method of reducing the likelihood of a pop when perforation risk is of concern.

Background— Ca 2+ leak from the sarcoplasmic reticulum (SR) may play an important role in triggering and/or maintaining atrial arrhythmias, including atrial fibrillation (AF). Protein kinase A (PKA) hyperphosphorylation of the cardiac ryanodine receptor (RyR2) resulting in dissociation of the channel-stabilizing subunit calstabin2 (FK506-binding protein or FKBP12.6) causes SR Ca 2+ leak in failing hearts and can trigger fatal ventricular arrhythmias. Little is known about the role of RyR2 dysfunction in AF, however. Methods and Results— Left and right atrial tissue was obtained from dogs with AF induced by rapid right atrial pacing (n=6 for left atrial, n=4 for right atrial) and sham instrumented controls (n=6 for left atrial, n=4 for right atrial). Right atrial tissue was also collected from humans with AF (n=10) and sinus rhythm (n=10) and normal cardiac function. PKA phosphorylation of immunoprecipitated RyR2 was determined by back-phosphorylation and by immunoblotting with a phosphospecific antibody. The amount of calstabin2 bound to RyR2 was determined by coimmunoprecipitation. RyR2 channel currents were measured in planar lipid bilayers. Atrial tissue from both the AF dogs and humans with chronic AF showed a significant increase in PKA phosphorylation of RyR2, with a corresponding decrease in calstabin2 binding to the channel. Channels isolated from dogs with AF exhibited increased open probability under conditions simulating diastole compared with channels from control hearts, suggesting that these AF channels could predispose to a diastolic SR Ca 2+ leak. Conclusions— SR Ca 2+ leak due to RyR2 PKA hyperphosphorylation may play a role in initiation and/or maintenance of AF.

Background— Chronic β-adrenergic receptor (β-AR) blockade improves cardiac contractility and prolongs survival in patients with heart failure; however, the mechanisms underlying these favorable responses are poorly understood. Stress-induced activation of the sympathetic nervous system results in protein kinase A (PKA)-mediated phosphorylation of the calcium (Ca 2+ ) release channel/cardiac ryanodine receptor (RyR2), required for cardiac excitation-contraction (EC) coupling, activating the RyR2 channel, and increasing cardiac contractility. The hyperadrenergic state of heart failure results in leaky RyR2 channels attributable to PKA hyperphosphorylation and depletion of the stabilizing FK506 binding protein, FKBP12.6. We tested the hypothesis that improved cardiac muscle function attributable to β-AR blockade is associated with restoration of normal RyR2 channel function in patients with heart failure. Methods and Results— We assessed the effects of β-AR blockade on left ventricular volume using isolated perfused hearts and β-agonist responsiveness using muscle strips from patients undergoing transplantation. Twenty-four human hearts were examined, 10 from patients with heart failure treated with β-AR blockers (carvedilol, metoprolol, or atenolol), 9 from patients with heart failure without β-AR blocker treatment, and 5 normal hearts. RyR2 PKA phosphorylation was determined by back-phosphorylation, FKBP12.6 in the RyR2 macromolecular complex was determined by coimmunoprecipitation, and channel function was assayed using planar lipid bilayers. β-AR blockers reduced left ventricular volume (reverse remodeling) and restored β-agonist response in cardiac muscle from patients with heart failure. Improved cardiac muscle function was associated with restoration of normal FKBP12.6 levels in the RyR2 macromolecular complex and RyR2 channel function. Conclusions— Improved cardiac muscle function during β-AR blockade is associated with improved cardiac Ca 2+ release channel function in patients with heart failure.