Catheter Ablation for Atrial Flutter: Current Concepts and Results

Soil moisture controls on phenology and productivity in a semi-arid critical zone

The Earth's Critical Zone, where physical, chemical and biological systems interact, extends from the top of the canopy to the underlying bedrock. In this study, we investigated soil moisture controls on phenology and productivity of an Acacia woodland in semi-arid central Australia. Situated on an extensive sand plain with negligible runoff and drainage, the carry-over of soil moisture content (θ) in the rhizosphere enabled the delay of phenology and productivity across seasons, until conditions were favourable for transpiration of that water to prevent overheating in the canopy. Storage of soil moisture near the surface (in the top few metres) was promoted by a siliceous hardpan. Pulsed recharge of θ above the hardpan was rapid and depended upon precipitation amount: 150mm storm(-1) resulted in saturation of θ above the hardpan (i.e., formation of a temporary, discontinuous perched aquifer above the hardpan in unconsolidated soil) and immediate carbon uptake by the vegetation. During dry and inter-storm periods, we inferred the presence of hydraulic lift from soil storage above the hardpan to the surface due to (i) regular daily drawdown of θ in the reservoir that accumulates above the hardpan in the absence of drainage and evapotranspiration; (ii) the dimorphic root distribution wherein most roots were found in dry soil near the surface, but with significant root just above the hardpan; and (iii) synchronisation of phenology amongst trees and grasses in the dry season. We propose that hydraulic redistribution provides a small amount of moisture that maintains functioning of the shallow roots during long periods when the surface soil layer was dry, thereby enabling Mulga to maintain physiological activity without diminishing phenological and physiological responses to precipitation when conditions were favourable to promote canopy cooling.

Mechanisms and medical management of patients with atrial flutter

Type I atrial flutter is due to reentrant excitation, principally in the right atrium. The standard ECG remains the cornerstone for its clinical diagnosis. Acute treatment should be directed at control of the ventricular response rate and, if possible, restoration of sinus rhythm. Radiofrequency catheter ablation therapy provides the best hope of cure, although atrial fibrillation may subsequently occur after an ostensibly successful ablative procedure. Alternatively, antiarrhythmic drug therapy to suppress recurrent atrial flutter episodes may be useful, recognizing that occasional recurrences are common despite therapy. Radiofrequency ablation of the His bundle ablation with placement of an appropriate pacemaker system may be useful in selected patients.

Mechanisms of atrial flutter: implications for ablative therapy

Much has been learned about atrial flutter mechanisms from studies in animal models and in patients. In fact, it seems virtually always due to some form of reentry. Furthermore, it seems likely that there is more than one location of the atrial flutter reentrant circuit in patients, although the reentrant circuit in most instances of atrial flutter seems to be activation up the interatrial septum and then down the posterior right atrial free-wall. Other locations of the reentrant circuit may include the right atrial free-wall alone or the tricuspid valve annulus, among others. Resolution of this awaits better mapping data from human studies. Clearly, an understanding of mechanism is central to achieving effective ablation. Thus, if it is possible to identify a critical aspect or aspects of the atrial flutter mechanism vulnerable to therapy with ablative energy, effective treatment using ablative techniques should be successful.

NASPE/ACC/AHA/ESC medical/scientific statement special report--clinical investigation of antiarrhythmic devices: a statement for healthcare professionals from a Joint Task Force of the North American Society of Pacing and Electrophysiology, the American College of Cardiology, the American Heart Association, and the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology

The goal of radiofrequency catheter ablation and the criterion for efficacy is the elimination of arrhythmogenic myocardium. The application of radiofrequency current in the heart clearly results in lower morbidity and mortality rates than thoracic and cardiac surgical procedures in general, and comparisons of therapy with radiofrequency catheter ablation and therapy with thoracic and cardiac surgical procedures in randomized clinical trials are unwarranted. Trials of radiofrequency catheter ablation versus medical or implantable cardioverter defibrillator therapy may be indicated in certain conditions, such as ventricular tachycardia associated with coronary artery disease. Randomized trials are recommended for new and radical departures in technology that aim to accomplish the same goals as radiofrequency catheter ablation. Surveillance using registries and/or databases is necessary in the assessment of long-term safety and efficacy.

Clinical investigation of antiarrhythmic devices. A statement for healthcare professionals from a joint task force of the North American Society of Pacing and Electrophysiology, the American College of Cardiology, the American Heart Association, and the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology

The goal of radiofrequency catheter ablation and the criterion for efficacy is the elimination of arrhythmogenic myocardium. The application of radiofrequency current in the heart clearly results in lower morbidity and mortality rates than thoracic and cardiac surgical procedures in general, and comparisons of therapy with radiofrequency catheter ablation and therapy with thoracic and cardiac surgical procedures in randomized clinical trials is unwarranted. Trials of radiofrequency catheter ablation versus medical or implantable cardioverter-defibrillator therapy may be indicated in certain conditions, such as ventricular tachycardia associated with coronary artery disease. Randomized trials are recommended for new and radical departures in technology that aim to accomplish the same goals as radiofrequency catheter ablation. Surveillance using registries and/or databases is necessary in the assessment of long-term safety and efficacy.