Thil Yoganathan

Magnesium and arrhythmias after coronary artery bypass surgery

Arrhythmias are very common after cardiac surgery and are multifactorial. Magnesium is receiving increased consideration in the management of supraventricular and ventricular arrhythmias. This study was designed to evaluate the role of magnesium in preventing arrhythmias in hypokalemic (K < 3.5 mEq/L) and normokalemic (K > 3.5 mEq/L) patients with normal renal and ventricular function after coronary artery bypass grafting (CABG). One hundred forty patients ranging from 32 to 71 years of age who were scheduled for CABG were studied. They were divided into four groups: group I (control) received no magnesium; group II received 10 mg/kg of magnesium sulfate intravenously before cardiopulmonary bypass (CPB); group III received 10 mg/kg of magnesium soon after CPB; group IV received 10 mg/kg of magnesium before and after CPB. Serum potassium and catecholamine levels, as well as serum and urine magnesium levels, were measured and the incidence and type of arrhythmias were determined. There was a statistically significant difference in the occurrence of arrhythmias between the groups studied. The incidence of arrhythmias was highest in groups I and II and lowest in group IV (12 patients in group I, 14 in group II, 5 in group III; and 1 in group IV). Magnesium levels were higher in group IV than any other group studied after completion of surgery. There was no difference in serum and urine magnesium levels between the hypokalemic and normokalemic patients within each group. Serum magnesium returned to normal in all patients after 48 hours. Therefore, it appears that administration of magnesium during and after cardiac surgery reduces the incidence of arrhythmias in hypokalemic and normokalemic patients.

Left ventricular diastolic function after coronary artery bypass grafting: A correlative study with three different myocardial protection techniques

BACKGROUND This study was designed to examine the effect of myocardial protection on diastolic function after cardiac operations. METHODS Subjects were patients with normal preoperative diastolic function who were scheduled for coronary artery bypass grafting. Group I received anterograde cardioplegia; group II received anterograde and retrograde cardioplegia; and group III was protected with ventricular fibrillation and intermittent aortic crossclamping. Operations were performed with mild hypothermia and ventricular venting through the left superior pulmonary vein in all cases. Left ventricular diastolic function was evaluated with pulsed-wave Doppler transesophageal echocardiography (samples at the mitral valve leaflet: four-chamber view) and left superior pulmonary vein flow velocity. The flow patterns were stored on videotape and sent to an independent investigator for analysis. Left ventricular ejection fraction was calculated with transesophageal echocardiography (short-axis view, two-dimensional and M-mode). RESULTS Left ventricular diastolic function, as measured by the ratio between the peak velocities during early filling and atrial contraction and by systolic diastolic superior pulmonary venous flow ratio, was significantly impaired in all three groups 5 minutes after discontinuation of cardiopulmonary bypass. At 1 hour after operation, these values had returned to control levels only in group III. There was an increased incidence of supraventricular arrhythmias in group III. There were no significant hemodynamic differences among the three groups. CONCLUSIONS Left ventricular diastolic function was severely impaired after cardiopulmonary bypass. The degree of impairment depended on the myocardial protection used. The impairment in diastolic function was less when ventricular fibrillation and intermittent aortic crossclamping were used, and greater when anterograde and retrograde cardioplegia were used.

Histamine Blockade and Cardiovascular Changes Following Heparin Administration During Cardiac Surgery

Large doses of heparin given as a bolus may produce hypotension; however, conflicting reports exist about the mechanisms involved. This study was undertaken to determine the role of histamine in beef lung heparin-induced hypotension and the efficacy of histamine-receptor blockade in attenuating this undesirable side effect in patients undergoing cardiac surgery. Two hundred patients with good ventricular function were studied after they were randomized into four equal groups. Group I (control) received no histamine-receptor blockade, group II received 1 mg/kg of diphenhydramine 30 minutes prior to heparin administration, group III received 5 mg/kg of cimetidine 4 hours and again 30 minutes before heparin administration, and group IV received 1 mg/kg of diphenhydramine 30 minutes prior to heparin administration and 5 mg/kg of cimetidine 4 hours and 30 minutes before heparin administration. Hemodynamic variables, plasma histamine, and ionized calcium levels were measured before and after heparin administration. Significant hypotension occurred in group I patients after heparin administration. Mean arterial pressure decreased from 95 +/- 5 to 67 +/- 1.5 mm Hg (P less than 0.005) after 1 minute and to 85 +/- 2 mm Hg (P less than 0.05) at 4 minutes. Those changes were significantly greater than in group II (P less than 0.025) and Group IV (P less than 0.005) patients, in whom no significant hypotension was found. In group III, mean arterial pressure decreased from 92 +/- 3 to 75 +/- 1 mm Hg (P less than 0.05) after 1 minute and returned toward baseline values after 4 minutes. Histamine levels increased significantly in all groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicardipine or nitroglycerin in patients with failed percutaneous coronary angioplasty: effect on myocardial diastolic function

OBJECTIVE To evaluate whether intracoronary vasodilators can improve diastolic function in 32 patients with failed percutaneous transluminal coronary angioplasty (PTCA). DESIGN Clinical trial. SETTING Single-institution, academic hospital. PARTICIPANTS Failed PTCA patients undergoing emergency coronary artery bypass grafting surgery. INTERVENTIONS Patients were divided into 2 groups: group A received 0.1 mg of intracoronary nicardipine, and group B received 20 microg of intracoronary nitroglycerin. Both drugs were administrated via a coronary dilatation perfusion catheter inserted in the catheterization laboratory by the cardiologist. Subsequently, they were continuously infused via the side port of the introducer of the pulmonary artery catheter and titrated to keep systolic blood pressure at about two thirds of the control value. Transesophageal echocardiography (Power Vision/6000, 9-mm 5MHZ Probe; Toshiba, Elmsford, NY) was used in this study. MEASUREMENTS AND MAIN RESULTS Left ventricular ejection fraction, cardiac index, tissue Doppler imaging velocity of the left ventricle and mitral annulus, and troponin levels were measured before and after administration of the 2 vasodilators and after cardiopulmonary bypass. Diastolic dysfunction was found preoperatively in all the patients and responded only to intracoronary nicardipine. Ea of mitral annulus velocity significantly increased in group A patients from 7.5 +/- 0.02 to 11.8 +/- 0.01 (p < 0.005) and decreased in group B patients from 8.0 +/- 0.03 to 7.5 +/- 0.02 after nicardipine or nitroglycerin administration. Left ventricular ejection fraction and cardiac index increased significantly (p < 0.005) only after nicardipine administration. Troponin levels were significantly lower in group A than in group B patients (p < 0.005). CONCLUSION Intracoronary nicardipine improves diastolic function and myocardial flow velocity in patients with failed PTCA undergoing emergency coronary artery bypass graft surgery.

Superoxide dismutase and hemodynamic changes following aortic crossclamp release.

Release of an aortic crossclamp usually results in hypotension which is mainly due to hypovolemia from sequestration of fluid in the tissues and the release of vasoactive substances (ie, bradykinin, free radicals) that increase capillary permeability. The purpose of this study was to evaluate superoxide dismutase (SOD), a free-radical scavenger, as a pharmacologic technique to prevent hemodynamic changes following aortic crossclamping and release. Fourteen mongrel dogs were studied and divided into two groups. The aorta was clamped for 60 minutes. Group A received NaHCO3, 3.5 mEq/kg, and SOD, 15,000 U/kg; while group B received only NaHCO3, 3.5 mEq/kg, prior to aortic crossclamp release. There was a statistically significant difference in cardiac output, systolic blood pressure, systemic and pulmonary vascular resistances, and arterial oxygen tension between the two groups following aortic crossclamp release. Cardiac output increased from 2.2 +/- .05 to 2.5 +/- .03 L/min (P < .05) after declamping, and returned toward preclamping baseline values after five minutes in group A. In group B, cardiac output decreased from 2.3 +/- .05 to 2.1 +/- .01 (P < .005) after declamping and remained unchanged five minutes later. No statistically significant changes in PaO2 occurred in group A, while there was a significant decrease in PaO2 in group B after crossclamp release. In group B, PaO2 decreased from 95 +/- 7 to 70 +/- 1 mmHg (P < .005) after crossclamp release. Bradykinin levels were almost identical in both groups studied. It is concluded that SOD significantly decreases the cardiovascular changes following aortic crossclamp release.

Pulse oximetry during pulmonary artery banding

In children with a ventricular septal defect and congestive heart failure, banding of the pulmonary artery (PA) causes equalization of right and left ventricular pressures, reduces the volume of the left-to-right shunt, and diminishes the work of the left ventricle and the engorgement of the pulmonary vessels. However, banding the PA too tightly usually produces hypoxemia by reversing the left-to-right shunt and causes severe hemodynamic changes. A series of 14 infants is reported who underwent PA banding during which a pulse oximeter was used as an early indicator of excessively tight PA banding. Significant hemodynamic changes occurred in eight infants in whom the PA banding was too tight. This consisted of hypotension and bradycardia three to four minutes after the banding. The eight patients also showed significant desaturation of the blood after application of the band, with the arterial hemoglobin saturation (SaO2) dropping from a preband value of 98 +/- 6% to a postband value of 80 +/- 2%. The decrease in SaO2 preceded the hypotension and bradycardia by two to three minutes in all cases. When the band was removed, the hemodynamic and SaO2 changes returned toward baseline. Subsequently, a less tight band was applied; this was associated with a smaller decrease in SaO2, an elevation of blood pressure, and no bradycardia. This was considered to be acceptable banding. The right ventricle/PA pressure gradient significantly decreased after acceptable banding, and a gradient higher than 45 mmHg was usually associated with hypoxemia.

Preoperative Heparin Therapy Causes Immune-Mediated Hypotension Upon Heparin Administration for Cardiac Surgery

OBJECTIVE To evaluate whether patients with positive or negative heparin antibodies who received heparin preoperatively by continuous infusion developed cardiovascular changes upon heparin administration prior to cardiopulmonary bypass. DESIGN Clinical trial. SETTING Single institution, academic hospital. PARTICIPANTS Eighty (80) patients with good ventricular function on low-dose heparin infusion prior to surgery. INTERVENTIONS Patients were divided into 2 equal groups: group A had negative heparin antibodies (% ratio < 0.26), group B had positive heparin antibodies (% ratio > 1.2). All patients received heparin, 400 units/kg, prior to institution of cardiopulmonary bypass. Cardiovascular changes, activated coagulation time (ACT), and histamine levels were measured before and 5 minutes after administration of heparin. Platelets also were counted before and 6 hours after surgery. MEASUREMENTS AND MAIN RESULTS Significant hypotension and decreased cardiac index occurred in patients with positive heparin antibodies who received heparin prior to cardiac surgery. Histamine levels increased significantly 5 minutes after heparin administration. Significant thrombocytopenia occurred 6 hours after surgery in group B patients. There was a good correlation between heparin antibodies, histamine levels, thrombocytopenia and cardiovascular changes. Group B patients also had heparin resistance as manifested by a lower ACT after the loading doses of heparin. CONCLUSION Patients with positive heparin antibodies pretreated with heparin prior to surgery developed a type of immune-mediated cardiovascular changes and postoperative thrombocytopenia.

The effects of intracoronary nicardipine on ventricular dynamics and function in patients undergoing off-pump coronary artery bypass graft surgery.

OBJECTIVE To evaluate whether intracoronary nicardipine can provide myocardial protection in patients undergoing off-pump coronary artery bypass graft surgery. DESIGN Clinical trial. SETTING Single-institution, academic hospital. PARTICIPANTS Off-pump coronary artery bypass patients with good ejection fraction. INTERVENTIONS Patients were divided into 2 equal groups: group A received 1 mL (0.1 mg) of intracoronary nicardipine before performing the distal anastomosis, and group B patients received 1 mL of NaCl in the coronary artery. Transesophageal echocardiography (PowerVision 6000, 9-mm 6-MHz probe; Toshiba, Elmsford, NY) was used in this study. MEASUREMENTS AND MAIN RESULTS Left ventricular ejection fraction, cardiac index, tissue Doppler imaging, velocity of the left ventricle and mitral annulus, and troponin levels were measured in both groups. The incidence of diastolic dysfunction as evaluated by superior pulmonary blood flow and pulsed-wave Doppler of the mitral annulus was significantly lower in group A. Tissue Doppler imaging velocity of the left ventricle and mitral annular displacement were significantly higher in the nicardipine group. Group A patients had significantly lower incidences of ST-segment changes, prolonged pharmacologic support in the postoperative period, and lower levels of troponin after surgery. CONCLUSION Intracoronary nicardipine improves ventricular function in patients undergoing off-pump coronary artery bypass surgery.

Hemodynamic changes after nafcillin administration during coronary artery bypass surgery

The hemodynamic response to nafcillin administration was studied in 45 patients with good left ventricular function and no known history of hypersensitivity to penicillin during coronary artery bypass grafting (CABG). Group I (15 patients) received 1 gram of nafcillin in 10 mL of saline as an intravenous (IV) bolus, group II (15 patients) received 1 gram of nafcillin in 50 mL of saline as a slow IV infusion over 15 minutes, and group III (15 patients) did not receive nafcillin. Hemodynamic variables and plasma histamine and catecholamine levels were measured before and after nafcillin administration, after 500 mg of CaCl2, and after 0.1 mg of phenylephrine. Bolus nafcillin administration produced profound hypotension secondary to vasodilatation with significant increases in cardiac index and decreases in systemic and pulmonary vascular resistances. Cardiac index increased from 3.15 +/- 0.3 L/min/m2 to 5.75 +/- 0.25 L/min/m2 (P less than 0.005) one minute after nafcillin administration, and remained at 5.1 +/- 0.35 L/min/m2 after administration of CaCl2 (P less than 0.005). All hemodynamic parameters returned toward control values after administration of 0.1 mg of phenylephrine, IV. Plasma epinephrine, norepinephrine, and histamine levels increased more than 100%. In group II, cardiac index increased, while systemic and pulmonary vascular resistances and mean arterial pressure decreased. However, these changes were less significant than those found in group I.(ABSTRACT TRUNCATED AT 250 WORDS)