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PubMed1976

Electrophysiologic effects of atropine on human sinus node and atrium.

Electrophysiologic studies were conducted in 17 patients without apparent sinus node disease before and after intravenous administration of 1 to 2 mg of atropine. Mean values in milliseconds (+/- standard error of the mean) before and after administration of atropine were as follows: sinus cycle length 846 +/- 26.4 versus 647 +/- 20.0 (P less than 0.001); sinus nodal recovery time 1,029 +/- 37 versus 774 +/- 36 (P less than 0.001); mean calculated sinoatrial (S-A) conduction time 103 +/- 5.7 versus 58 +/- 3.9 (P less than 0.001); mean P-A interval 34 +/- 1.5 msec versus 31 +/- 1.5 (P less than 0.05); mean atrial effective and functional refractory periods during sinus rhythm 285 +/- 11.3 versus 238 +/- 7.9 and 331 +/0 11.6 versus 280 +/- 8.6, respectively (P less than 0.001 for both); mean atrial effective and functional refractory periods measured at equivalent driven cycle length 239 +/- 7.7 versus 213 +/- 7.4 and 277 +/- 11.4 versus 245 +/- 9.5, respectively (P less than 0.001 for both). In conclusion, atropine shortened sinus cycle length, sinus nodal recovery time and calculated S-A conduction time. The shortening of atrial refractory periods with atropine implies that vagotonia prolongs atrial refractoriness in man.

Adult↗
PubMed1991

RETRACTED: Acute preoperative hemodilution in cardiac surgery: volume replacement with a hypertonic saline-hydroxyethyl starch solution.

Preoperative hemodilution (HD) is a recommended practice in cardiac surgery that conserves blood and reduces the complications of homologous blood transfusion. In 45 patients undergoing myocardial revascularization, HD was performed preoperatively. Withdrawn volume (10 mL/kg) was replaced either by a new hypertonic saline (HS) solution prepared in hydroxyethyl starch (HES) (2,400 mOsm/L, HS-HES group, n = 15) or by a standard low molecular weight hydroxyethyl starch solution (6% HES 200/0.5, HES group, n = 15) to maintain baseline PCWP (acute normovolemic hemodilution [ANH]). Fifteen comparable patients without HD served as controls. Significantly less HS-HES (210 +/- 20 mL) than HES 6% (890 +/- 90 mL) was necessary to sustain hemodynamics during HD. Stable cardiocirculatory conditions were obtained even after termination of bypass. Fluid balance during cardiopulmonary bypass as well as in the postoperative period was significantly lower in HS-HES-treated patients. With regard to hemodynamics, CI increased most in the HS-HES group (+36%), whereas systemic vascular resistance was lower in these patients. Right ventricular ejection fraction increased only in HS-HES patients (+15%). However, sodium concentration as well as osmolarity increased after volume replacement with HS-HES, without exceeding normal values. None of the patients suffered from organ failure. Pulmonary gas exchange (PaO2) was less compromised in the HS-HES patients. There were no renal function differences between the groups. In conclusion, HS solution prepared in HES is an attractive alternative for blood substitution in cardiac patients undergoing acute hemodilution for blood conservation.

Atrial Function, Right↗
PubMed1996

Noninvasive assessment of right heart function by 81mKr equilibrium radionuclide ventriculography in chronic pulmonary diseases.

Noninvasive multigated equilibrium radionuclide ventriculography with krypton-81m (81mKr) was used to assess right heart relaxation in patients with chronic pulmonary diseases (CPD). The subjects consisted of 30 patients with CPD and 8 patients free of cardiopulmonary diseases admitted to our department. A region of interest (ROI) was selected on both the right atrium (RA) and right ventricle (RV). A time activity curve was obtained for each ROI. As a diastolic index of the right heart performance, the right atrial early emptying rate (RAER) was obtained from the right atrial time activity curve, while the right ventricular rapid filling rate (RVRFR) was obtained from the right ventricular time activity curve. The mean RAER was significantly lower in CPD patients compared with the control (CPD, 9.5 +/- 4.5; control, 16 +/- 3.4%/100 ms). Similarly, the mean RVRFR was significantly lower in CPD patients compared with the control (CPD, 27.3 +/- 9.9; control, 34 +/- 8.5%/100 ms). A strong negative correlation was noted between the mean pulmonary arterial pressure (mPAP) and RAER (r = -0.77; p < 0.001) and between the mPAP and the RVRFR (r = -0.63; p < 0.001). Our results suggest that RAER and RVRFR measured by 81mKr are clinically useful in the noninvasive assessment of right heart relaxation in patients with CPD.

Adult↗
PubMed2005

Effect of transcatheter atrial septal defect closure in children on left ventricular diastolic function.

The acute impact of transcatheter atrial septal defect (ASD) closure on left ventricular (LV) diastolic function was assessed in 15 consecutive children, and pre- and postclosure data were compared with those in a matched group of controls. The data indicate that transcatheter ASD closure leads to an immediate improvement in LV diastolic function as assessed by septal myocardial Doppler tissue imaging and LV inflow velocity propagation. The improvement in LV diastolic properties correlates with the degree of right ventricular volume overload.

Adolescent↗
PubMed2001

Hemodynamic changes with right lateral decubitus body positioning in the tilted porcine heart.

BACKGROUND: In beating-heart coronary surgical procedures, exposure of posterior vessels through sternotomy causes cardiac function to deteriorate. We hypothesized that turning the subject to the right lateral decubitus position before cardiac retraction improves exposure of posterior vessels and preserves cardiac pump function on displacement. METHODS: Eight 80-kg open-chest pigs were instrumented with catheter-tip manometers. After a stepwise 60-degree turn to the right lateral decubitus position of the body, the heart was retracted anteriorly to 90 degrees with a suction stabilizer. RESULTS: Right lateral body positioning caused an approximately 45-degree right deviation of the apex, thereby exposing the left atrial groove. Stroke volume, mean arterial pressure, right atrial pressure, and right ventricular end-diastolic pressure increased to 106% +/- 5% (mean +/- standard error of the mean, p = 0.31), 106% +/- 3% (p = 0.01), 129% +/- 8% (p = 0.001), and 171% +/- 14% (p = 0.002), respectively, compared with control values. In contrast, left atrial pressure decreased to 73% +/- 6% (p = 0.007), whereas left ventricular preload remained unchanged (110% +/- 8%, p = 0.26). Additional anterior displacement to 90 degrees fully exposed the posterior vessels, and stroke volume decreased to 90% +/- 3% (p = 0.01) and mean arterial pressure to 93% +/- 5% (p = 0.07) at the expense of further increased right ventricular preload (256% +/- 28%, p < 0.001). CONCLUSIONS: By placing the subject in the right lateral decubitus position, exposure through sternotomy of posterior vessels in the beating porcine heart was facilitated while mean arterial pressure was maintained.

Animals↗
PubMed1975

[On the mechanism of valve plane (author's transl)].

A detailed description of the functional sequence and mechanism of the valve plane movements is given as an extension of the studies on the functional morphology of cardiac movements. The valve plane mechanism is driven in the small, rapidly beating heart by the contraction of the external and internal spiral fibres of the myocardium which decreases the width of the chamber. The atrium is enlarged during systole by the descent of the valvular ring towards the apex. The auricular apendices must act as a compensation reservoir giving the atrial wall the necessary freedom of movement within the pericardial dome. Under these working conditions (hypovolaemia, decreased venous return pathophysiological consequences are discernible as subendocardial bleeding secondary to increased sliding movement of the inner layer of the myocardium against the middle layer. Chamber dilation as a consequence of endocardial fibrosis is explained as a result of progressive rigidity of endo-epicardial fixation. These structural changes progressively impair the systolic-diastolic changes in wall thickness.

Animals↗
PubMedDate not supplied

A prospective study of left atrial spontaneous echo contrast and thrombus in 100 consecutive patients referred for balloon dilation of the mitral valve.

The aim of this study was to determine the clinical, echocardiographic, and hemodynamic predictors of left atrial spontaneous echo contrast (SEC) and thrombus, respectively, in patients referred for balloon dilation of the mitral valve and to establish the relationship between the two phenomena in this group of patients. One hundred consecutive patients (mean age 57 +/- 14 years) referred for mitral balloon (Inoue) dilation were studied prospectively with transthoracic and transesophageal (83 biplane and 17 single plane) echocardiography (TEE) combined with spectral and color Doppler modalities, immediately before the procedure. TEE was repeated within 24 hours of valvotomy in the first 55 patients. All patients also underwent comprehensive left- and right-sided heart catheterization. TEE was performed successfully in 96 patients. SEC was detected in all 65 patients in atrial fibrillation and in 14 (45%) of 31 patients in sinus rhythm. Patients with SEC were significantly older (61 +/- 13 vs 45 +/- 12 years; p < 0.001) and had larger left atrial volume (98 +/- 48 vs 64 +/- 24 ml; p < 0.001), higher mitral valve echocardiographic scores (7.4 +/- 3.2 vs 5.3 +/- 2.6; p = 0.016), lower cardiac output (3.5 +/- 1.1 versus 4.6 +/- 0.9 L/min; p < 0.001), lower peak systolic pulmonary vein flow velocity (SVm) (24 +/- 12 versus 45 +/- 11 cm/sec; p < 0.001), and correspondingly lower systolic velocity-time integral (4.0 +/- 2.6 vs 7.9 +/- 2.9 cm; p < 0.001) than had patients without SEC. There were no significant associations between SEC and either mitral valve area or anticoagulant therapy. SVm and atrial fibrillation were found to be independent predictors of SEC. In patients in sinus rhythm, SVm was the only independent predictor of SEC. After mitral balloon dilation, SEC disappeared in only two of 35 patients in atrial fibrillation and in five of eight patients in sinus rhythm. Significant mitral regurgitation occurred in the two patients in atrial fibrillation. TEE detected left atrial thrombus in 14 patients. Thrombus was significantly associated with age, mitral valve area, and the severity of SEC. The latter was found to be an independent predictor of thrombus. Two patients in sinus rhythm had evidence of left atrial mechanical dysfunction. Both patients had left atrial SEC and one had thrombus in the appendage. It is concluded that SEC in patients with severe mitral stenosis is dependent on left atrial systolic function and peak systolic pulmonary vein velocity. It is not related to mitral valve area or anticoagulant therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed2002

Cardiac resynchronization therapy restores optimal atrioventricular mechanical timing in heart failure patients with ventricular conduction delay.

We characterized the relationship between systolic ventricular function and left ventricular (LV) end-diastolic pressure (LVEDP) in patients with heart failure (HF) and baseline asynchrony during ventricular stimulation. The role of preload in the systolic performance improvement that can be obtained in HF patients with LV stimulation is uncertain.We measured the maximum rate of increase of LV pressure, LVEDP, aortic pulse pressure (PP) and the atrioventricular mechanical latency (AVL) between left atrial systole and LV pressure onset in 39 patients with HF. Two subgroups were identified: "responder" if PP improved, or "nonresponder."Maximum hemodynamic improvement occurred at an atrioventricular (AV) delay that did not decrease LVEDP. Left ventricular and biventricular (BV) stimulation increased systolic hemodynamics significantly, despite no significant increase in LVEDP. All parameters decreased when the LVEDP was decreased by shorter AV delay. Left ventricular and BV stimulation provided better hemodynamics than right ventricular (RV) stimulation. For the nonresponder subgroup, systolic hemodynamics only worsened during AV delay shortening. For the responder subgroup, optimum PP was achieved when AVL was near zero. Restoration of optimal left atrial-ventricular mechanical timing partly contributes to the hemodynamic improvements observed in this patient subgroup. However, preload alone cannot explain the differences seen between RV and BV stimulation and the contradictory PP decreases even at maximal preload in the nonresponder subgroup. These results may be explained by a site-dependent mechanism such as the degree of ventricular synchrony. Caution should be taken in these patients when optimizing AV delays using echocardiography techniques that focus on LV inflow.

Atrial Function, Left↗
PubMed2000

Clinical and echocardiographic predictors of left atrial clot and spontaneous echo contrast in patients with severe rheumatic mitral stenosis: a prospective study in 200 patients by transesophageal echocardiography.

The objective of this study was to prospectively investigate various clinical and echocardiographic variables to predict the left atrial and left atrial appendage clot and spontaneous echo contrast in patients with severe rheumatic mitral stenosis. We studied 200 consecutive patients (112 males and 88 females; mean age 29.6+/-9.6 years). Left atrial clot and spontaneous echo contrast were present in 26 and 53.5% of cases, respectively. There were no significant differences in the mitral valve area, mean transmitral diastolic gradient and left ventricular ejection fraction between patients with and without clot. Patients with clot were older (34.4+/-11.4 vs. 28.2+/-8.5 years, P<0.001), had longer duration of symptoms (41. 4+/-36.0 vs. 28.8+/-22.9 months, P<0.001), more frequent atrial fibrillation and spontaneous echo contrast (69.2 vs. 16.9%, P<0. 00001 and 76.9 vs. 45.3%, P<0.00001, respectively) and larger left atrial area and diameter (41.0+/-12.7 vs. 29.9+/-7.4 cm(2), P<0.00001 and 53.9+/-8.3 vs. 47.6+/-7.4 mm, P<0.0001, respectively) as compared to patients without clot. Similarly patients with spontaneous echo contrast were older (31+/-10.4 vs. 27.8+/-8.3 years, P<0.01), had more frequent atrial fibrillation (48.6 vs. 9.7%, P<0.0001), left atrial clot (37.4 vs. 12.9%, P<0.0001), larger left atrial area and diameter (37.6+/-11.2 vs. 28.1+/-6.7 cm(2), P<0.00001 and 52.2+/-8.3 vs. 45.9+/-6.5 mm, P<0.00001, respectively) and smaller mitral valve area (0.77+/-0.14 vs. 0.84+/-0.13 cm(2), P<0.01) as compared to patients without spontaneous echo contrast. There were no significant differences in the mean transmitral diastolic gradient and left ventricular ejection fraction. On multiple regression and discriminant function analysis, atrial fibrillation and left atrial area were independent predictors of left atrial clot formation. In a subgroup of patients with sinus rhythm, larger left atrial area and presence of spontaneous echo contrast were significantly associated with the presence of clot in left atrium and appendage. We conclude that in patients with severe mitral stenosis, the presence of atrial fibrillation and in the subgroup of the patients with sinus rhythm the presence of large left atrium (> or =40 cm(2)) and spontaneous echo contrast were associated with higher risk of clot formation in the left atrium and might be benefited by prophylactic anticoagulation.

Adolescent↗
PubMed1975

Some evidence for the maturity of peripheral adrenergic nerves in new-born guinea-pigs.

The fluorescence histochemical technique of Falck and Hillarp revealed a similar distribution and density of peripheral adrenergic nerves in new-born and adult guinea-pigs. The accumulation of tritiated noradrenaline by tracheae from new-born guinea-pigs, assumed to be uptake into adrenergic nerves, was not less than the accumulation by tracheae from adult animals. There was equal potentiation by cocaine (1 x 10(-5)M) of responses to noradrenaline on tracheal chain preparations taken from new-born and adult guinea-pigs. The evidence supports the hypothesis that the guinea-pig has a functional, well differentiated peripheral adrenergic nervous system at birth. This would account for the apparent inability to produce a long-lasting sympathectomy by administration of 6-hydroxydopamine to new-born guinea-pigs.

Animals↗
PubMed2001

Radiofrequency ablation at the coronary sinus ostium interrupts the vagal efferent input to the atrioventricular node in the canine heart.

The fat pad at the junction of the inferior vena cava and inferior left atrium is the area of convergence of vagal projections into the atrioventricular node (AVN) region. The present study investigated whether radiofrequency (RF) ablation applied to the area around the coronary sinus (CS) ostium would impair vagal input to the AVN in the canine heart. Twenty-four dogs were anesthetized by sodium pentobarbital and RF energy was delivered at 20W for 5-10s. In the baseline state without vagal stimulation (10Hz, 2ms), the electrophysiological variables did not change significantly after RF ablation. Vagally induced changes in the sinus cycle length and effective refractory period of the right atrium and left ventricle did not differ after RF ablation. However, the effects of vagal stimulation on the AVN function were impaired after RF ablation to the CS area from the ostium to 10mm within the ostium. After ablation was applied to the fast pathway area, the vagally induced changes in the AVN function decreased, but these changes were not affected after RF ablation in the slow pathway area. RF ablation in the vicinity of the CS would attenuate vagal input to the AVN.

Animals↗
PubMed1991

Successful surgical treatment of atrial fibrillation. Review and clinical update.

Atrial fibrillation is the most common of all sustained cardiac arrhythmias, yet it has no effective medical or surgical therapy. During the past decade, multipoint computerized electrophysiological mapping systems were used to map both experimental and human atrial fibrillation. On the basis of these studies, a new surgical procedure was developed for atrial fibrillation. Between September 25, 1987, and July 1, 1991, this procedure was applied in 22 patients with paroxysmal atrial flutter (n = 2), paroxysmal atrial fibrillation (n = 11), or chronic atrial fibrillation (n = 9) of 2 to 21 years' duration. All patients were refractory to all antiarrhythmic medications, and each patient failed to receive the desired therapeutic benefits of an average of five drugs administered preoperatively. There were no operative deaths and all perioperative morbidity resolved. All 22 patients have been successfully treated for atrial fibrillation with surgery alone. Three patients developed one late isolated episode of atrial flutter at 5, 6, and 15 months postoperatively, and each of these patient's symptoms is now controlled by a single antiarrhythmic drug. Preservation of atrial transport function has been documented in all patients postoperatively, and all have experienced marked clinical improvement.

Adult↗
PubMed1995

[Effects of isorhynchophylline on physiological characteristics of isolated guinea pig atrium].

Isorhynchophylline (Iso) inhibits the automaticity and contractile force of isolated guinea pig atrium in a concentration-dependent manner, 30 mumol/L markedly depresses adrenaline-induced automaticity, 10 mumol/L prolongs functional refractory period and decreases excitability. Furthermore, 10 mumol/L of Iso reduces the effect of ouabain on contractile force in left atrium and 0.3 mmol/L markedly inhibits the response to paired stimulation.

Alkaloids↗
PubMed1992

[Correlation analysis between plasma atrial natriuretic peptide and cardiac function in blood deficiency syndrome].

The function of ANP in the cardiovascular regulation is very similar with the TCM theory of "the Heart governs blood circulation". Using the method of cardiac impedance to check cardiac output and the method of radioimmunoassay (RIA) to check plasma ANP, the result showed that in the status of Blood Deficiency Syndrome, cardiac function was impaired, there were reduced kinemia and stroke volume, as well as markedly raised plasma ANP and peripheral resistance. The above-mentioned indexes were significantly different from those of normal group (P < 0.01). Using multivariate regression analysis, cardiac output was negatively correlated with the plasma ANP (P < 0.05). 23 cases with Blood Deficiency Syndrome showed normal hemoglobin, but an evidently changed cardiac output and plasma ANP were closely related with the level of the Blood Deficiency. Both parameters might serve as the objective basis to reflect the level of Blood Deficiency to facilitate the clinical diagnosis of the patient.

Adult↗
PubMed1997

Vagal reflex is not responsible for changes in airway and lung tissue mechanics due to vascular engorgement in young piglets.

Eleven open-chest piglets were studied to examine the effects of vascular engorgement on partitioned airway and lung tissue mechanics, and to investigate the role of vagal denervation on lung function during engorgement. Alveolar pressure was measured using alveolar capsules. Pulmonary elastance (EL) and resistance (RL), airway (Raw), and tissue (Vti) resistance were calculated during mechanical ventilation. Acute fluid administration with polygeline (10 mL/kg boluses up to a total of 30 mL/kg) resulted in an increase of RL with increases in both Raw and Vti. Vti rose 2-3-fold in comparison with Raw. To increase left atrial pressure, a balloon catheter was inserted into the left atrium of the heart and inflated with different volumes. The responses of EL, RL, Raw and Vti were comparable to those with acute fluid load. Alterations in pulmonary mechanics were closely correlated to mean pulmonary artery blood pressure. In another six animals the effect of vagotomy on vascular engorgement was studied. Vagotomy did not alter baseline airway or tissue mechanics. Furthermore, vagotomy did not influence the change of pulmonary mechanics to fluid load or increase of left atrial pressure. Our data indicate that in young piglets vascular engorgement causes alterations in airway and lung tissue mechanics that are not dependent on vagal influences.

Airway Resistance↗
PubMedDate not supplied

[Phonocardiographic and Doppler echocardiographic study on the mechanism of the presystolic murmur in mitral stenosis, especially the relationship to mitral inflow dynamics].

The cause of the "presystolic murmur" in mitral stenosis was investigated by phonocardiography and continuous wave Doppler echocardiography in 31 patients with mitral stenosis and sinus rhythm classified into two groups: 18 patients with and 13 without "presystolic murmur". 1. The "presystolic murmur" group demonstrated high frequency vibrations preceding the first heart sound coinciding with the initial low frequency component of the first heart sound recorded at the apex in both groups. 2. There were two types of "presystolic murmur": The first type observed in three of the 18 patients occurred during the accelerated phase of the atrial (A) wave of mitral inflow signals and lasted until the first heart sound. The A wave velocity in mitral inflow signals was high at the onset and peak, and rapidly decreased after the peak. The second type observed in 15 patients occurred during the decelerated phase of the A wave and lasted until the first heart sound. The A wave velocity in mitral inflow signals was low at the onset, but high at the peak and rapidly decreased after the peak. 3. The mitral orifice area tended to be smaller in all patients with "presystolic murmur". The peak flow velocity, deceleration rate of the A wave, and maximal pressure gradient across the mitral valve during atrial contraction were significantly increased in all patients with "presystolic murmur". 4. Five patients with newly developed "presystolic murmur" after amyl nitrite inhalation had an increased initial low frequency component of the first heart sound coinciding with the latter half of "presystolic murmur". The rate of increase in the peak flow velocity and the deceleration rate of the A wave were significantly larger and the maximal atrioventricular pressure gradient during atrial contraction tended to be larger in these five patients than those in five who did not develop "presystolic murmur". 5. The peak flow velocity, deceleration rate of the A wave and the maximal atrioventricular pressure gradient during atrial contraction had increased 1 year later compared with those immediately after cardioversion of atrial fibrillation, and newly developed "presystolic murmur" appeared according to the recovery of left atrial mechanical function. These results suggest that the latter half of "presystolic murmur" originates from augmentation and prolongation of the initial low frequency component of the first heart sound up to the audible range caused by the sudden deceleration of mitral inflow velocity due to left ventricular contraction, and that the early half of "presystolic murmur" is the atriosystolic murmur produced by the increase in mitral inflow velocity during atrial contraction.

Blood Flow Velocity↗
PubMed1991

Assessment of right heart function.

Growing recognition of the contribution of right heart function to cardiac output in a variety of pathologic conditions lends a new outlook to cardiac assessment, especially when cardiac output is inadequate for physiologic needs. Signs and symptoms of right heart dysfunction made by physical assessment can be validated by radiologic techniques as well as a newly available bedside method of thermodilution determination of right ventricular ejection fraction and right ventricular end-diastolic and end-systolic volumes. Assessment of right ventricular function can aid clinical decision making when pressure readings obtained by usual hemodynamic monitoring techniques are altered by changes in intrathoracic pressure or ventricular compliance. This article reviews physical assessment of right heart function, signs and symptoms of right heart dysfunction, radiographic evaluations and their limitations and introduces the thermodilution evaluation of right ventricular performance. Clinical examples are presented to illustrate the utility of this new technique along with selected nursing diagnoses and outcome criteria.

Atrial Function, Right↗
PubMed1991

Electrophysiological properties of a new antiarrhythmic agent, bisaramil on guinea-pig, rabbit and canine cardiac preparations.

Electrophysiological effects of bisaramil, a novel antiarrhythmic agent, were examined using the conventional microelectrode technique applied to cardiac multicellular preparations from guinea-pigs, rabbits and dogs and the whole-cell patch-clamp technique applied to guinea-pig ventricular myocytes. Bisaramil at 10(-6) M or higher concentrations produced a dose-dependent decrease in the maximum rate of rise (Vmax) of action potentials of guinea-pig papillary muscles without changes in resting membrane potentials. In the presence of bisaramil, trains of stimuli at rates greater than 0.1 Hz led to the use-dependent block of Vmax, which was enhanced at higher frequencies. At a concentration of 3 x 10(-6) M, the degree of use-dependent block was about 35% at 3.3 Hz, of which degree was comparable to those of 10(-4) M disopyramide and lidocaine. The development of Vmax block by bisaramil was expressed by a single exponential function in the same manner as flecainide, whereas the time courses of the block development by disopyramide and lidocaine were described by two exponentials. Recovery time constants from Vmax block were 44.1 +/- 3.4 s and 20.3 +/- 2.3 s for bisaramil and flecainide, respectively. Bisaramil at 10(-6) and 3 x 10(6) M did not change the action potential duration of guinea-pig papillary muscles and rabbit atrial muscles with a significant reduction of Vmax. No change in action potential duration can be explained by depression of both the Ca2+ and the delayed outward K+ currents by bisaramil. On the other hand, 10(-6) M bisaramil shortened action potential duration of canine Purkinje fibers at 50% and 90% of repolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

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