Effects of ultrasound energy application on cardiac performance in open-chest Guinea pigs.

BACKGROUND: Although ultrasound (US) is widely used in cardiology, little is known about the effects of US energy on cardiac performance. This study aimed to investigate the mechanical effects of high-intensity continuous US energy (1.0 MHz with 3 different intensities) on cardiac performance. METHODS AND RESULTS: Either left ventricular (LV) pressure or aortic blood flow (ABF) was evaluated in open-chest guinea pigs (n=30) under surface ECG monitoring. LV systolic pressure and ABF increased significantly (ie, maximum percent increases in these parameters were 2.5%, 3.1% and 7.1% for LV systolic pressure and 9.4%, 4.9% and 8.8% for mean ABF at intensities of 0.06, 0.67 and 2.90 W/cm2, respectively). LV end-diastolic pressure was reduced significantly by US (5.3+/-0.9 to 4.8+/-0.8, 5.5 +/-1.3 to 4.8+/-1.0 and 5.8+/-2.0 to 5.0+/-1.2 mmHg, respectively), indicating positive inotropic and lusitropic effects and resultant ABF augmentation. Local temperature was not significantly changed. ECG showed neither chronotropic action nor arrhythmogenesis. CONCLUSIONS: Although the basic mechanisms of these phenomena remain unclear, this pilot study of the short-term effects of US energy on cardiac performance suggests the possibility of physical therapy for heart failure.

Extracellular potassium dependent negative dromotropic action of nicorandil in guinea pig myocardium.

Although the antiarrhythmic action of nicorandil is drawing an increasing attention, dromotropic effect of this agent is unclear. Therefore, this was investigated by microelectrode technique to the superfused guinea pig papillary muscle to record the action potential and extracellular potential during conduction. The correlation of myocardial internal longitudinal resistance (r1) assumed to reflect the global gap junctional resistance, maximum rate of rise of the action potential upstroke (Vmax), and conduction velocity was examined under the alterations of external potassium concentrations ([K+]e; ranging from 3.0 to 12.0 mM) in the presence or absence of 100 microM nicorandil. In the minimum [K+]e, nicorandil caused significant (p < 0.05) hyperpolarization and reduction in Vmax. Negative dromotropic action of nicorandil was slight but significant (p < 0.05) in low (3.0 mM) [K+]e but was not evident in physiologic (5.4 mM) or elevated (9.0 to 12.0 mM)[K+]e. In conclusion, nicorandil exerts negative dromotropic action as [K+]e decreased, which was accounted for by the cable analysis and may contribute to the prevention of low [K+]e-induced arrhythmia.

Bezold-Jarisch-like reflex during Brockenbrough's procedure for radiofrequency catheter ablation of focal left atrial fibrillation: report of two cases.

Brockenbrough's puncture technique has been widely conducted in the electrophysiologic laboratory. We report here two cases exhibiting a rare complication of this procedure, which arose during the conduct of catheter ablation using radiofrequency energy delivered to the pulmonary vein for the treatment of focal left atrial fibrillation. These cases exhibited marked sinus bradycardia and profound hypotension, suggestive of a Bezold-Jarisch-like reflex, observed immediately after Brockenbrough's procedure but before radiofrequency application. ST elevation in the inferior leads was also observed in spite of normal coronary angiograms. This unanticipated transient complication was treated by intravenous administration of atropine, which had no influence on the ablation procedure or prognosis. This is speculated to be attributable to the elevation of vagal tone caused by the mechanical effects of transseptal puncture on the interatrial vagal network.

Reentrant atrial tachycardia originating from the superior vena cava.

A 52-years old man with a previous pericardiotomy for idiopathic constrictive pericarditis underwent catheter ablation for drug-resistant atrial tachycardia (AT). The mechanism of the AT was considered as reentry because of resetting response and the entrainment phenomenon during AT. We introduced a 64-electrode basket catheter into the superior vena cava (SVC) during AT to obtain precise mapping. A fractionated potential preceding local atrial electrogram was recorded in the SVC. The earliest activation site of the potential was located at the anterior aspect of the SVC, 2 cm above the SVC-right atrium junction determined fluoroscopically. The fractionated potential at this site preceded the onset of the P wave by 115 msec. Radiofrequency catheter ablation at this site eliminated the tachycardia. At 6 months follow-up, the patient is free of AT. Reentrant AT involving the SVC is a candidate of RF ablation. Multielectrode basket catheter is useful for a detailed mapping of the SVC.