Amiodarone inhibits cardiac ATP-sensitive potassium channels.

INTRODUCTION: ATP-sensitive K+ channels (K(ATP)) are expressed abundantly in cardiovascular tissues. Blocking this channel in experimental models of ischemia can reduce arrhythmias. We investigated the acute effects of amiodarone on the activity of cardiac sarcolemmal K(ATP) channels and their sensitivity to ATP. METHODS AND RESULTS: Single K(ATP) channel activity was recorded using inside-out patches from rat ventricular myocytes (symmetric 140 mM K+ solutions and a pipette potential of +40 mV). Amiodarone inhibited K(ATP) channel activity in a concentration-dependent manner. After 60 seconds of exposure to amiodarone, the fraction of mean patch current relative to baseline current was 1.0 +/- 0.05 (n = 4), 0.8 +/- 0.07 (n = 4), 0.6 +/- 0.07 (n = 5), and 0.2 +/- 0.05 (n = 7) with 0, 0.1, 1.0, or 10 microM amiodarone, respectively (IC50 = 2.3 microM). ATP sensitivity was greater in the presence of amiodarone (EC50 = 13 +/- 0.2 microM in the presence of 10 microM amiodarone vs 43 +/- 0.1 microM in controls, n = 5; P < 0.05). Kinetic analysis showed that open and short closed intervals (bursting activity) were unchanged by 1 microM amiodarone, whereas interburst closed intervals were prolonged. Amiodarone also inhibited whole cell K(ATP) channel current (activated by 100 microM bimakalim). After a 10-minute application of amiodarone (10 microM), relative current was 0.71 +/- 0.03 vs 0.92 +/- 0.09 in control (P < 0.03). CONCLUSION: Amiodarone rapidly inhibited K(ATP) channel activity by both promoting channel closure and increasing ATP sensitivity. These actions may contribute to the antiarrhythmic properties of amiodarone.

Atrial arrhythmia following a biatrial approach to mitral valve surgery.

The biatrial approach to exposing the mitral valve during surgery has the potential for improving visualization of the valve with minimal cardiac manipulation. This procedure, involving a right atriotomy and an extended transseptal incision, may isolate the sinus node from its normal blood supply and autonomic innervation. Thirty-eight consecutive patients undergoing this procedure were examined. Twenty-two of these patients (58%) were admitted in normal sinus rhythm and 15 (40%) were in atrial fibrillation (AF) or atrial flutter. Of the 22 patients admitted in normal sinus rhythm, only 3 patients remained in this rhythm at discharge. Fourteen of the 22 patients were discharged in a slow, low atrial rhythm. All of the patients admitted in AF were discharged in AF. Of the 14 patients discharged in a low atrial rhythm, the rhythm persisted in eleven patients (80%) at a mean of 6-month follow-up. The routine use of this transseptal approach to mitral valve surgery needs further assessment in light of the predictable loss of the sinus mechanism.

Mapping reentry around atriotomy scars using double potentials.

Supraventricular arrhythmias, often seen in patients after cardiac surgery, may be associated with scars produced in the atria at the time of surgery. Double potentials, found in the presence of functional or anatomical block, can define the limits and critical regions of a reentrant circuit associated with the atriotomy scars. We describe six patients with seven distinct atrial tachycardias in whom atriotomy scars were successfully mapped during intraatrial reentry utilizing the presence and interelectrogram relationship of observed double potentials. The reentrant circuit was mapped in all patients by following the relationship between double potentials along the surgical scar, assuming that they would be widely split in the middle of the scar and merge into a single continuous fractionated potential at the apex of the scar. At this site, atrial pacing was performed to entrain the tachycardia and confirm the participation of the atriotomy scar in the clinically relevant atrial tachycardia. Radiofrequency ablation was performed from the site of electrogram fusion to the nearest anatomical obstacle. Five of seven atrial tachycardias were successfully ablated utilizing this technique over a mean follow-up of 10 months. We proposed that these double potentials and their interelectrogram relationship are an effective means of mapping atriotomy scars and guiding successful radiofrequency ablation.

Endoventricular remodeling of left ventricular aneurysm. Functional, clinical, and electrophysiological results.

BACKGROUND: Recent advances in surgical techniques for the repair of left ventricular aneurysms (LVAs) include the use of an endoventricular patch to exclude the aneurysm cavity. This technique has replaced conventional linear plication of the aneurysm. The endoventricular patch technique remodels the left ventricular cavity to a more physiological geometry that improves function. METHODS AND RESULTS: From December 1989 through November 1993, 45 patients underwent an LVA repair with an endoventricular patch. This procedure was performed in association with coronary artery bypass grafting in 40 patients. Twenty-eight patients (62.2%) also had nonguided encircling subendocardial incisions. Operative procedures included 7 emergency operations, 3 concomitant valve procedures, and a mean of 2.2 bypass grafts per patient. Eight patients had previous cardiac operations. Hospital mortality was 15.6% (7/45) for all patients and 9.1% (3/33) for nonemergent revascularization and LVA repairs. Ejection fraction improved from a mean of 25.8% preoperatively to 37.8% postoperatively; the mean New York Heart Association classification improved from 3.5 to 1.5. Of patients known to have preoperative arrhythmias (inducible or sudden death), 69% were not inducible postoperatively without antiarrhythmic medication. Survival from late cardiac death (including death of unknown origin) was 86.5% at 2 years. Freedom from documented ventricular arrhythmias was 94.3% at 2 years. CONCLUSIONS: These results indicate that the patch endoaneurysmorrhaphy technique can provide an excellent functional and physiological outcome in patients with LVAs and severely impaired ventricular function.

Echocardiographic evaluation of the coronary sinus.

The purpose of this study was to compare transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) in the evaluation of the coronary sinus and its blood flow. Forty patients were studied by TTE and TEE. The distal coronary sinus and its right atrial communication could be identified in 21 of 40 by TTE, and in all patients by TEE. Coronary sinus diameter measurement at the right atrial communication was possible by TTE in 16 of 40, and in all patients by TEE (maximal diameter 6 to 14 mm, mean 9 +/- 2). Flow velocity measurement by pulsed Doppler was possible in 25 of 40 patients (63%) by TEE, and in none by TTE. The flow velocity pattern was similar to central vein flow velocity, with systolic and diastolic antegrade waves, and a small retrograde end diastolic wave. The coronary sinus cross-sectional area was measured in 5 patients by intravascular ultrasound. It varied in size and shape during the cardiac cycle, reaching a maximum (0.3 to 1.5 cm2) at end diastole, and decreasing by 40% to 70% at end systole. TEE is superior to TTE in the evaluation of the coronary sinus and its blood flow velocity. However, because of the variability in cross-sectional area size and shape, measurement of coronary sinus blood flow may be inaccurate.

Percutaneous left atrial to femoral arterial bypass pumping for circulatory support in high-risk coronary angioplasty.

Left atrial to femoral arterial bypass was evaluated as a means of supporting patients who were considered to be at high risk for the performance of percutaneous transluminal coronary angioplasty. A 20 French drainage catheter was inserted percutaneously into the left atrium via a modified transseptal technique. Blood was withdrawn from the left atrium and returned through a femoral arterial cannula using a roller pump. Thirteen patients were treated in this fashion with excellent circulatory support. Pump flows varied from 1.5 to 3 liters per minute and bypass time ranged from 27 to 106 min (mean = 43 +/- 17). Aortic mean pressure was well supported during balloon inflation. No significant complications were encountered. Neither an oxygenator nor a perfusionist is required. The ability to obtain direct left ventricular decompression offers a major potential advantage. Further evaluation of this technique for the support of such patients is indicated.

Comparison of cardiac catheterization and Doppler echocardiography in the decision to operate in aortic and mitral valve disease.

Clinical decisions utilizing either Doppler echocardiographic or cardiac catheterization data were compared in adult patients with isolated or combined aortic and mitral valve disease. A clinical decision to operate, not operate or remain uncertain was made by experienced cardiologists given either Doppler echocardiographic or cardiac catheterization data. A prospective evaluation was performed on 189 consecutive patients (mean age 67 years) with valvular heart disease who were being considered for surgical treatment on the basis of clinical information. All patients underwent cardiac catheterization and detailed Doppler echocardiographic examination. Three sets of two cardiologist decision makers who did not know patient identity were given clinical information in combination with either Doppler echocardiographic or cardiac catheterization data. The combination of Doppler echocardiographic and clinical data was considered inadequate for clinical decision making in 21% of patients with aortic and 5% of patients with mitral valve disease. The combination of cardiac catheterization and clinical data was considered inadequate in 2% of patients with aortic and 2% of patients with mitral valve disease. Among the remaining patients, the cardiologists using echocardiographic or angiographic data were in agreement on the decision to operate or not operate in 113 (76% overall). When the data were analyzed by specific valve lesion, decisions based on Doppler echocardiography or catheterization were in agreement in 92%, 90%, 83% and 69%, respectively, of patients with aortic regurgitation, mitral stenosis, aortic stenosis and mitral regurgitation. Differences in cardiac output determination, estimation of valvular regurgitation and information concerning coronary anatomy were the main reasons for different clinical management decisions. These results suggest that for most adult patients with aortic or mitral valve disease, alone or in combination, Doppler echocardiographic data enable the clinician to make the same decision reached with catheterization data.

High flow velocity across a complicated atrial septal defect: Doppler findings and hemodynamic correlations.

An unusually high atrial shunt flow velocity pattern was recorded in a patient whose atrial septal defect was created iatrogenically during a transatrial septal approach to aortic valvuloplasty. The flow velocity pattern measured by Doppler echocardiography was predictive of the high transatrial pressure gradient noted later at catheterization.