Effects of resynchronization therapy on sympathetic activity in patients with depressed ejection fraction and intraventricular conduction delay due to ischemic or idiopathic dilated cardiomyopathy.

This study assesses the effect of biventricular pacing on sympathetic nerve activity (SNA) in patients with depressed ejection fraction and intraventricular conduction delay (IVCD). Biventricular pacing has been shown to result in hemodynamic improvement in patients with depressed ejection fraction and IVCD. The effect of biventricular pacing on SNA, however, remains unclear. A total of 15 men with a mean ejection fraction of 25 +/- 4% were enrolled. Arterial pressure, central venous pressure and SNA were recorded during 3 minutes of right atrial (RA) pacing and RA-biventricular pacing. Pacing was performed at a rate 5 to 10 beats faster than sinus rhythm, with an atrioventricular interval equal to 100 ms during RA-biventricular pacing. RA-biventricular pacing resulted in greater arterial pressures (p <0.05) than RA pacing (146 +/- 15/83 +/- 11 vs 141 +/- 15/80 +/- 10 mm Hg). There were no differences in central venous pressures between the 2 pacing modes (p = 0.76). SNA was significantly less during RA-biventricular pacing (727 +/- 242 U) than during RA pacing (833 +/- 332 U) (p <0.02). Furthermore, there was a positive correlation between baseline QRS duration and the decrease in SNA noted with RA-biventricular pacing (r = 0.58, p = 0.03). Biventricular pacing results in improved hemodynamics and a decrease in SNA compared with intrinsic conduction in patients with left ventricular dysfunction and IVCD. If the current findings are also present with chronic biventricular pacing, then this form of therapy may have a positive impact on mortality.

Echocardiographic Recognition of Left Ventricular Mural Thrombus.

Left ventricular (LV) mural thrombus is a well recognized complication of acute myocardial infarction. In survivors of infarction, its incidence is influenced by the location and magnitude of infarction: it occurs often in patients with large anterior Q wave infarctions, particularly in the presence of LV apical akinesis or dyskinesis. Although radionuclide imaging with indium-111-labeled platelets, computed tomography, and magnetic resonance imaging may be used to identify LV mural thrombus, two-dimensional echocardiography is the technique of choice for assessing its presence, shape, and size, and recent technical advances in echocardiographic methodology, such as high-frequency, short-focal-length transducers, have improved the echocardiographic assessment of LV mural thrombus. In the patient in whom a mural thrombus is identified, acute and chronic anticoagulation (with heparin and warfarin, respectively) is indicated: first, to prevent further thrombus formation and, second, to reduce the incidence of systemic embolization.

Novel use of atrial overdrive pacing to rapidly differentiate junctional tachycardia from atrioventricular nodal reentrant tachycardia.

BACKGROUND: Distinguishing between junctional tachycardia (JT) and atrioventricular nodal reentrant tachycardia (AVNRT) is essential to minimize unnecessary catheter ablation and the risk of heart block during treatment of AVNRT. OBJECTIVE: The purpose of this study was to investigate whether the tachycardia response to atrial overdrive pacing at a cycle length (CL) slightly shorter than tachycardia CL can differentiate between JT and AVNRT. We hypothesized that atrial overdrive pacing would transiently suppress JT but would entrain AVNRT. METHODS: Twenty-one patients in whom AVNRT was induced and atrial overdrive pacing during either AVNRT or JT was attempted were included in the study. We predicted that, upon cessation of atrial overdrive pacing, an atrial-His-His-atrial (AHHA) response would identify JT and an atrial-His-atrial (AHA) response would identify AVNRT. RESULTS: A total of 8 JT and 21 typical AVNRT were induced. Atrial overdrive pacing was attempted in all cases of JT and in 16 cases of AVNRT. An AHHA response was observed in 100% (8/8) of JT cases. In 2 cases of AVNRT, atrial overdrive pacing repetitively terminated the tachycardia. In the remaining patients with AVNRT, an AHA response was observed in 100% (14/14) of cases. When a response was able to be elicited, atrial overdrive pacing was 100% sensitive and 100% specific for differentiating JT from AVNRT. CONCLUSION: Atrial overdrive pacing during tachycardia can rapidly differentiate JT from AVNRT, which can improve the safety and efficiency of catheter ablation of these arrhythmias.