Sigfus Gizurarson

Localized rotational activation in the left atrium during human atrial fibrillation: Relationship to complex fractionated atrial electrograms and low-voltage zones

BACKGROUND In humans, the existence of rotors or reentrant sources maintaining atrial fibrillation (AF) and the underlying electroanatomic substrate has not been well defined. OBJECTIVE Our aim was to determine the prevalence of localized rotational activation (RotA) in the left atrium (LA) during human AF and whether complex fractionated atrial electrograms (CFAEs) or low-voltage areas colocalize with RotA sites. METHODS We prospectively studied 32 patients (mean age 57 ± 8 years; 88% with persistent AF) undergoing AF catheter ablation. Bipolar electrograms were recorded for 2.5 seconds during AF using a roving 20-pole circular catheter in the LA. RotA was defined as sequential temporal activation of bipoles around the circular catheter. Bipolar electrogram fractionation index and bipolar voltage were used to define CFAEs and low-voltage areas, respectively. RESULTS In 21 (66%) patients, 47 RotA sites were identified. Few (9%) lasted 2.5 seconds (cycle length 183 ± 6 ms), while the majority (91%) were nonsustained (duration 610 ± 288 ms; cycle length 149 ± 11 ms). RotA was most common in the pulmonary vein antrum (71%) and posterior LA (25%). CFAEs were recorded from 18% ± 12% of LA area, and most (92% ± 7%) were not associated with RotA sites. However, 85% of RotA sites contained CFAEs. Very low voltage (<0.1 mV) areas comprised 12% ± 10% of LA area and were present in 23% of RotA sites. CONCLUSIONS In patients with predominantly persistent AF, localized RotA is commonly present but tends to be transient (<1 second). Although most CFAEs do not colocalize with RotA sites, the high prevalence of CFAEs and very low voltages within RotA sites may indicate slow conduction in diseased myocardium necessary for their maintenance.

Effects of Renal Artery Denervation on Ventricular Arrhythmias in a Postinfarct Model

Background— The therapeutic potential of renal denervation (RDN) for arrhythmias has not been fully explored. Detailed mechanistic evaluation is in order. The objective of the present study was to determine the antiarrhythmic potential of RDN in a postinfarct animal model and to determine whether any benefits relate to RDN-induced reduction of sympathetic effectors on the myocardium. Methods and Results— Pigs implanted with single-chamber implantable cardioverter defibrillators to record ventricular arrhythmias (VAs) were subjected to percutaneous coronary occlusion to induce myocardial infarction. Two weeks later, a sham or real RDN treatment was performed bilaterally using the St Jude EnligHTN basket catheter. Parameters of ventricular remodeling and modulation of cardio–renal sympathetic axis were monitored for 3 weeks after myocardial infarction. Histological analysis of renal arteries yielded a mean neurofilament score of healthy nerves that was significantly lower in the real RDN group than in sham controls; damaged nerves were found only in the real RDN group. There was a 100% reduction in the rate of spontaneous VAs after real RDN and a 75% increase in the rate of spontaneous VAs after sham RDN (P=0.03). In the infarcted myocardium, presence of sympathetic nerves and tissue abundance of neuropeptide-Y, an indicator of sympathetic nerve activities, were significantly lower in the RDN group. Peak and mean sinus tachycardia rates were significantly reduced after RDN. Conclusions— RDN in the infarcted pig model leads to reduction of postinfarction VAs and myocardial sympathetic effectors. This may form the basis for a potential therapeutic role of RDN in postinfarct VAs.

The effect of left ventricular pacing on transmural activation delay in myopathic human hearts

Aims Left ventricular (LV) epicardial pacing (LVEpiP) in human myopathic hearts does not decrease global epicardial activation delay compared with right ventricular (RV) endocardial pacing (RVEndoP); however, the effect on transmural activation delay has not been evaluated. To characterize the transmural electrical activation delay in human myopathic hearts during RVEndoP and LVEpiP compared with global epicardial activation delay. Methods and results Explanted hearts from seven patients (5 male, 46 ± 10 years) undergoing cardiac transplantation were Langendorff-perfused and mapped using an epicardial sock electrode array (112 electrodes) and 25 transmural plunge needles (four electrodes, 2 mm spacing), for a total of 100 unipolar transmural electrodes. Electrograms were recorded during LVEpiP and RVEndoP, and epicardial (sock) and transmural (needle) activation times, along with patterns of activation, were compared. There was no difference between the global epicardial activation times (LVEpiP 147 ± 8 ms vs. RVEndoP 156 ± 17 ms, P = 0.46). The mean LV transmural activation time during LVEpiP was significantly shorter than that during RVEndoP (125 ± 44 vs. 172 ± 43 ms, P < 0.001). During LVEpiP, of the transmural layers endo-, mid-myocardium and epicardium, LV endocardial layer was often the earliest compared with other transmural layers. Conclusion In myopathic human hearts, LVEpiP did not decrease global epicardial activation delays compared with RVEndoP. LV epicardial pacing led to early activation of the LV endocardium, revealing the importance of the LV endocardium even when pacing from the LV epicardium.

Atrial decremental evoked potentials accurately determine the critical isthmus of intra-atrial re-entrant tachycardia

Background We demonstrated the utility of Decremental Evoked Potential (DEEP) mapping in identifying critical isthmus in scar ventricular tachycardia (VT). In substrate mapping, late potentials are usually targeted. This represents fixed delays in local conduction, which might not participate in tachycardia initiation. We mapped late signals which decremented, which could allow time for the blocked areas in the scar region to regain conductivity and initiate re-entry. In sinus rhythm, a pacing train of 600 ms was delivered at late potential sites with an extrastimulus at VERP þ20 ms interval. The site showing the maximum decrement was chosen as the ablation target. DEEP mapping was more specific in identifying critical targets of scar VT ablation compared to the conventional late potential mapping. We hypothesized that, as intra-atrial re-entrant tachycardia (IART) substrate is similar to scar VT by virtue of surgical scars, DEEP mapping could be useful in identifying critical targets for ablation.

Successful cryoablation of an incessant atrial tachycardia arising from the right atrial appendage

The right atrial appendage can be the origin of focal atrial tachycardias. Their ablation can be challenging owing to the complexity of the appendage anatomy. To our knowledge, we describe the first successful solid tip cryoablation of a focal tachycardia within the right atrial appendage in a patient presenting with tachycardia-induced cardiomyopathy.

Simple and non-invasive diagnostics of a broad complex tachycardia in a device patient

A 36-year-old woman presented with paroxysmal palpitations and shortness of breath to the emergency department. She was known to have transposition of the great arteries and had undergone the Mustard operation, in addition to having a pacemaker implanted. The electrocardiogram at the time of …

Quality of atrial fibrillation ablation: "success is not final, failure is not fatal; is it the score that matters?".

In the current issue of HeartRhythm, Chinitz et al present a novel scoring system (atrial fibrillation ablation [AFA] score) for evaluating the quality and success of catheter ablation for the treatment of paroxysmal atrial fibrillation (AF). We have paraphrased the words attributed to Sir Winston Churchill to give context to the transience of the wins and losses perceived in the greater battle against the formidable opponent of AF. We did this in order to shed light, and to pause and think of the direction AF ablation— the most prolific business in interventional electrophysiology —is taking. In their article, Chinitz et al underline the fact that a scoring system that incorporates quality and success has not been available for AF ablation and that the current use of AF recurrence as an outcome measure has limitations. The AFA score takes into account disparate factors such as lesion delivery, complications, and outcomes in order to evaluate the results and quality of AF ablation and allows for comparison of different techniques. This is achieved by incorporating 6 procedural features, half of which estimate efficacy and the other three reflect the relative acute safety of the procedure. A very strong emphasis is made on the total number of procedures performed, as seen in the relatively high score achieved by radiofrequency ablation in their article compared with emerging balloon techniques (cryo and laser), even though both redo and reconduction rates are quite similar among all methods, as seen in their Table 1. Although one would consider the novelty of this score may lie (if validated against meaningful outcomes) in its value in showing differences among manufacturers, operators, techniques, and institutions, the devil is always in the details. Like all creative concepts, this concept paper raises more questions than provides solutions to the problem at hand. What would this difference in score mean to the patient we hope to care for? The user of this score will not take into account the very premise for performing the procedure, that is, symptom relief. The score will only allow for comparison of nonpharmacologic treatment strategies that strictly target the pulmonary veins and does not permit comparison of AF