Left atrial pressure and dominant frequency of atrial fibrillation in humans.

BACKGROUND: Atrial stretch is thought to play a role in the development of atrial fibrillation (AF). However, the precise mechanism by which stretch contributes to AF maintenance in humans is unknown. OBJECTIVE: The purpose of this study was to determine the impact of left atrial (LA) pressure on AF frequency in patients undergoing catheter ablation of AF. METHODS: The subjects of this study were 58 consecutive patients with persistent AF (n = 40) or paroxysmal AF (n = 18) undergoing LA ablation. LA pressure was measured before ablation. Both atria and the coronary sinus were mapped, and regional dominant frequency (DF) was determined. RESULTS: Mean LA pressure in the persistent AF group was significantly higher than in the paroxysmal AF group (18 ± 5 vs 10 ± 4 mmHg, P <.0001). Mean DF in the persistent AF group was also higher than in the paroxysmal AF group (6.36 ± 0.51 Hz and 5.83 ± 0.54 Hz, P = .0006). In patients with persistent AF, there was a significant correlation between LA pressure and DF at the LA appendage (r = 0.55, P = .0002). DF(max) was found at the LA appendage region in 24 (60%) of the 40 patients with persistent AF (P = .0006). In multivariate analysis, LA pressure was the only independent predictor of DF(max) in the LA appendage (P = .04, odds ratio 1.41, 95% confidence interval 1.02-1.94). CONCLUSION: Higher LA pressure in patients with persistent AF implies that these patients are more vulnerable to stretch-related remodeling than are patients with paroxysmal AF. The DF of AF was directly related to LA pressure in patients with persistent AF. This finding suggests that atrial stretch may contribute to the maintenance of AF in humans by stabilizing high-frequency sources.

Percutaneous epicardial left atrial appendage closure: preliminary results of an electrogram guided approach.

BACKGROUND: Pharmacologic therapies to prevent stroke in atrial fibrillation (AF) have numerous limitations, prompting the development of device-based therapies. We investigated whether an electrogram-based approach using a novel hollow suture can safely capture and ligate the left atrial appendage (LAA). METHODS AND RESULTS: A novel system for closure of the LAA within the confines of the closed pericardium with a single sheath puncture was tested in 4 dogs. The tool used to grasp the appendage was fitted with electrodes and utilized electrical navigation to identify and confirm LAA capture. A hollow suture preloaded with a mechanical support wire to permit its manipulation and fluoroscopic visualization was advanced over the grasper, and the wire removed after the suture was positioned. The LAA was successfully closed in all dogs. In 2 dogs, after closure, a thoracotomy was performed and the LAA amputated without bleeding, confirming closure integrity. Necropsy confirmed closure in all animals. CONCLUSIONS: Using electrical navigation, percutaneous epicardial LAA ligation with a remotely tightened suture was performed successfully within the confines of the intact pericardial space. This technique may allow decreasing the risk of stroke in AF patients without the need for thoracotomy or an endocardially placed prosthetic device.

Hypotensive activity of the ethanol extract of Pavetta crassipes leaves.

Pavetta crassipes leaf is routinely used locally in Nigeria for the management of respiratory disorders and hypertension. The hypotensive and other cardiovascular effects of Pavetta crassipes were investigated in cats and rats. The effects of the extract on rat and cat blood pressures, isolated rat atria, rat portal vein, isolated rat aorta and rat vas deferens were studied. Specific receptor antagonists (atropine, mepyramine, phentolamine, propranolol) were used to elucidate the underlying mechanism(s) involved in the cardiovascular changes induced by P. crassipes. The results revealed that the ethanolic extract of Pavetta crassipes lowered the blood pressures of cats and rats in a dose dependent manner. The extract also caused a concentration-dependent decrease in the force of contraction of the isolated rat atria and rat portal vein. The decreases in blood pressure values were attenuated in the presence of a beta-adrenoceptor antagonist, propranolol. The extract also attenuated isoprenaline-induced contraction of the rat atria. However, the extract did not affect contractions evoked by KCl, norepinephrine and 5-HT on the rat aorta. Pavetta crassipes contains biologically active substances that may be useful in the management of hypertension.

Cardiovascular effects of isorhamnetin and quercetin in isolated rat and porcine vascular smooth muscle and isolated rat atria.

Isorhamnetin and quercetin produced endothelium-independent vasodilator effects in rat aorta, rat mesenteric arteries, rat portal vein and porcine coronary arteries. The effects of the two flavonoids were similar in arteries stimulated by noradrenaline, KCl, U46619 or phorbol esters but the two flavonoids were more potent in the coronary arteries than in the aorta. At high concentrations, they also induced a positive inotropic effect in isolated rat atria. Therefore, at least part of the in vivo effects of quercetin may result from its conversion to isorhamnetin which is the main metabolite of quercetin found in plasma. The arterial, venous and coronary vasodilator effects may contribute to the protective effects of flavonoids in ischaemic heart disease observed in epidemiological studies.

Attenuation of interatrial conduction using right atrial septal catheter ablation.

OBJECTIVES: We sought to characterize a method of attenuating interatrial conduction using radiofrequency ablated lesions applied to the right atrial septum. BACKGROUND: Interatrial conduction occurs in specific zones. Recent data suggest that interatrial conduction can be important in triggering and sustaining atrial fibrillation. Therefore, a method for attenuating interatrial conduction may have therapeutic value. METHODS: In 13 healthy pigs, interatrial conduction was evaluated before and after sequential ablation of the right atrial septum, targeting interatrial conduction zones. In six animals, zone 1 (crista terminalis and limbus) was ablated first, followed by ablation of zone 2 (fossa ovalis and coronary sinus ostium). In the other seven animals, the order of ablation was reversed. Electrophysiologic and pathologic findings were correlated. RESULTS: After ablation of zone 1, interatrial conduction was slowed, but there was no block. After ablation of zone 2, conduction was unchanged. After ablation of both zones, complete block was observed in four animals, and there was left atrial quiescence. In the remaining nine animals, incomplete block was observed, with marked conduction slowing or block during sinus rhythm and pacing. Ablation did not adversely affect atrioventricular node conduction, nor did it facilitate sustenance of an atrial arrhythmia. Pathologic analysis revealed that complete interatrial conduction block was associated with confluent ablation of both targeted zones. CONCLUSIONS: Catheter ablation of the right atrial septum attenuated interatrial conduction without disturbing atrioventricular conduction.