Relation between QT and RR intervals.
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Adult↗
Biomedical subjects
K Venkataraman
Publications and source records attributed to K Venkataraman.
Effects of amiodarone on the circadian rhythm and power spectral changes of heart rate and QT interval: significance for the control of sudden cardiac death.
Effects of chronic amiodarone therapy on the circadian rhythmicity and power spectral changes of heart rate and QT intervals from Holter recordings were evaluated in three groups of patients: group 1 baseline (n = 10); group 2, treated for 3 to 6 months (n = 11); and group 3, treated for > 1 year (n = 13). Amiodarone reduced heart rate, which reached steady state at 3 to 6 months; bradycardia was evident during the entire 24 hours. The corrected QT (QTc) interval increased as a function of treatment duration. It was 457 +/- 39, 530 +/- 28 (p < 0.001), and 581 +/- 36 (p < 0.0002) msec for groups 1, 2, and 3, after 6 months, respectively. The circadian rhythmicity of QTc was abolished in group 3. Power spectral analysis showed a tendency for amiodarone to reduce both R-R and QT interval variabilities, suggesting inhibition of autonomic control on the heart by the drug. The effectiveness of amiodarone against ventricular arrhythmias may result in part from the sustained bradycardia in concert with continuous uniform prolongation of myocardial repolarization.
Aged↗
Amiodarone toxicity. II. Desethylamiodarone-induced phospholipidosis and ultrastructural changes during repeated administration in rats.
The contribution of desethylamiodarone (DEA), principal metabolite of the antiarrhythmic drug amiodarone, to the major side effects of amiodarone is unclear. The effects of repeated DEA administration to rats on tissue drug accumulation, ultrastructural changes, and phospholipid concentrations were studied. Two groups (n = 8/group) of male Sprague-Dawley rats (250 g body wt) were administered a 5% aqueous solution of DEA (Dose I, 40 mg/kg/day; Dose II, 60 mg/kg/day) intraperitoneally for 21-23 days, while a third group (control, n = 8) received saline. DEA levels were significantly higher with Dose II compared to Dose I in the lung, liver, kidney, spleen, heart, and serum while the tissue to serum ratios were similar with both doses for all tissues except the heart. DEA administration caused a significant elevation in the lipid phosphorus levels of liver, lung, and alveolar macrophages compared to control levels. A strong positive correlation (p less than 0.01) was found between tissue DEA levels and lipid phosphorus for the above tissues. Electron microscopy revealed the presence of lipid inclusion bodies in liver, lung, and alveolar macrophages of DEA-treated rats. A dose-dependent increase in the percentage of vacuolar surface area was found in the lung and alveolar macrophages. The tissue ultrastructural changes after repeated DEA dosing were qualitatively similar to our previous findings with amiodarone. Increased lung and liver phospholipid levels with repeated DEA doses may result from a potent inhibitory action of DEA on tissue phospholipase A as has been observed by others in in vitro studies.
Amiodarone↗
Circadian rhythmicity of rate-normalized QT interval in hypothyroidism and its significance for development of class III antiarrhythmic agents.
Lengthening of repolarization and refractoriness occurs in hypothyroidism; it is associated with a reduced probability of arrhythmias, with the converse occurring in hyperthyroidism. Because the QT interval and its circadian rhythmicity relative to heart rate is poorly defined in man, we used our new computer-assisted technique to measure QT interval in our analysis of 24-hour Holter tapes before and after (8 to 12 weeks) thyroxine (T4) replacement in 10 patients with hypothyroidism; the findings were compared to those in 6 normal control subjects. QTc interval was prolonged (p less than 0.02) and heart rate decreased (p less than 0.005) during the hypothyroid state. Data were analyzed for circadian rhythmicity by repeated-measures analysis. Circadian variation in QTc and heart rate was statistically significant during hypothyroid and euthyroid states (p less than 0.001) as well as in control subjects, but the circadian rhythmicity of QTc interval and heart rate were out of phase; the maximum prolongation of QTc occurred between midnight and 6 A.M., at a time when heart was at its lowest. QTc interval remained significantly prolonged after 8 to 12 weeks of T4 replacement, when biochemical indexes of hypothyroidism had returned to normal values. The computer-assisted QTc interval determination technique that we used, and our data on the circadian rhythmicity of QTc and heart rate, have significant implications for the development of new class III antiarrhythmic agents.
Adult↗
Mosquito fauna of medical importance in Kumbakkarai: a tourist spot near Madurai (Tamil Nadu).
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Animals↗
Tissue drug accumulation and ultrastructural changes during amiodarone administration in rats.
Pulmonary and hepatotoxicity are the two major side effects of chronic amiodarone therapy. We studied the accumulation of amiodarone and its principal metabolite, desethylamiodarone, in lung and liver of rats treated ip for 21 to 23 days with either 40 or 80 mg/kg/day amiodarone. The ultrastructural changes in liver, lung, and alveolar macrophages in saline controls and in rats on the two amiodarone dosage regimens were investigated. There was a dose-dependent increase in amiodarone and desethylamiodarone levels in serum and in tissues. The desethylamiodarone/amiodarone ratios in liver and lung, but not in serum, increased significantly with increasing dose. Serum also contained another metabolite, monodeiodinated desethylamiodarone. Increase in vacuolization and presence of whorled lamellar inclusion bodies in alveolar macrophages occurred with an increase in dose and higher lung amiodarone and desethylamiodarone levels. Electron microscopy of the liver of amiodarone-treated rats revealed the presence of large inclusion bodies partially filled with amorphous material in the cytoplasm. The quantitative relationship of the above changes to organ toxicity and to phospholipidosis that accompanies amiodarone administration remains to be established.
Amiodarone↗
Effect of propranolol on the QT intervals of normal individuals during exercise: a new method for studying interventions.
A new method was used to study the effect of a single dose of propranolol on the QT intervals during exercise in 11 normal volunteers. They exercised maximally on a bicycle ergometer and repeated the test after taking propranolol (40 mg) by mouth two hours before. Electrocardiograms were continuously recorded on magnetic tape and the cardiac cycle length (RR interval) and the QT interval were measured every five seconds by a computer aided method. The RR-QT data from each test during the exercise phase were analysed by an exponential formula, QT = A - B x exp (-k x RR) and by Bazett's formula, QT = K x square root of (RR). Three reference QT intervals, QTc1, QTc2, and QTc3, estimated at RR = 400, 700, and 1000 ms respectively from the regression curves of both formulas were compared. The exponential formula, which consistently gave a better fit with the data, showed that propranolol had a biphasic action on the QT intervals during exercise. It significantly prolonged the mean (SD) interval at longer cycle lengths (from 287 (27) to 305 (18) ms at RR = 1000 ms and shortened it at shorter cycle lengths (from 198 (14) to 179 (16) ms at RR = 400 ms). In contrast, Bazett's formula did not show any significant effect when the same raw data were used. The exponential formula can be adapted to study other interventions or conditions that affect QT intervals.
Adult↗
The small right coronary artery: angiographic implications--case reports.
Two patients with small right coronary arteries are presented. Possible complications during coronary angiography and methods of preventing them are discussed. It is stressed that the time of occlusion of the artery by the catheter tip should be kept to a minimum. The use of newly available angiographic catheters with side holes is also illustrated.
Aged↗
Effect of ethanol on regional myocardial blood flow and hemodynamics, before and after coronary artery ligation in dogs.
The effects on regional myocardial blood flows (RMBF) and hemodynamics due to ethanol administered before and after acute coronary artery ligation (CAL) in 18 anesthetized dogs were studied. Ethanol was administered to seven dogs (group I) prior to CAL and to six dogs (group II) after CAL; five dogs (group III, control) received only saline before and after CAL. Uniform blood ethanol levels (180 +/- 30 mg/dl) were maintained in groups I and II after initial ethanol administration. In these groups the heart rate and rate-pressure product (which reflects myocardial oxygen consumption) remained stable, but pulmonary arterial pressures were elevated. Other hemodynamic parameters remained stable in all groups. Ethanol caused a significant transmural increase of RMBF (p less than 0.001) in both groups I and II. In group II the increase was significant in both nonischemic and ischemic tissues, with no apparent redistribution of flow among the myocardial layers. The percentage increase of RMBF due to ethanol was highest in group II nonischemic tissue (95-107%) compared to the corresponding ischemic tissue (57-60%) and the group I myocardial tissue (36-47%) prior to CAL (p less than 0.001). The observed differences between ethanol pre- and posttreatments suggest different interactions between ethanol and catecholamines. The results also confirm that vasodilatory reserve is present in the acutely ischemic myocardium and that the local availability of ethanol is important for coronary vasodilatation.
Animals↗
Effects of diltiazem on cation transport across erythrocyte membranes of hypertensive humans.
The effects of the calcium antagonist diltiazem on diastolic blood pressure and various parameters of erythrocyte membrane cation transport were evaluated in hypertensive patients with diastolic blood pressure between 95 and 110 mm Hg in a placebo-controlled, double-blind parallel study. Twenty-one patients completed the study; 13 received placebo, while 8 received diltiazem. Diastolic blood pressure, intracellular sodium and calcium concentrations, ouabain-sensitive Na+,K+-adenosine triphosphatase (ATPase) activity, and net sodium efflux and potassium influx across red blood cell membranes were examined in both groups at the end of placebo run-in, at the end of the titration phase, and at the completion of study. In the placebo group, none of the parameters changed significantly. In the drug-treated group, diastolic blood pressure declined by approximately 10% (placebo, 95.1 +/- 8.9; drug-treated, 86.9 +/- 4.9 mm Hg; p less than 0.03) at the end of the study. There were also reductions in intracellular sodium (placebo, 7.9 +/- 1.8; drug-treated, 5.2 +/- 0.4 mmol/L cells; p less than 0.002) and calcium (placebo, 13.5 +/- 1.6; drug-treated 10.8 +/- 3.3 mumol/L cells; p less than 0.03) concentrations, accompanied by a simultaneous rise in the activity of the ouabain-sensitive Na+,K+-ATPase of erythrocyte membranes (placebo, 7.1 +/- 1.1 X 10(-2); drug-treated, 9.0 +/- 0.6 X 10(-2) microM inorganic phosphate/hr/mg; p less than 0.001) at the end of the study. However, no significant change in the ouabain-insensitive moiety of the ATPase pump was found. Diltiazem treatment increased net sodium efflux and potassium influx.(ABSTRACT TRUNCATED AT 250 WORDS)
Blood Pressure↗
Efficacy and safety of nicardipine for chronic, stable angina pectoris: a multicenter randomized trial.
Nicardipine, a new calcium channel blocking drug of the dihydropyridine family, was administered to 63 patients at a dose of 30 or 40 mg 3 times daily in a multicenter, randomized, double-blind, placebo-controlled, crossover trial. Nicardipine midly increased heart rate (HR) at rest and midly decreased the blood pressure (BP) at rest. When generally similar responses to the 30- and 40-mg doses were averaged, nicardipine produced a 7% increase in peak exercise HR, which was balanced by a 6% decrease in peak exercise BP. Thus, no change occurred in the exercise HR-BP product. With nicardipine, treadmill exercise duration increased 9%, time to angina increased 15%, time to 1-mm ST-segment depression increased 16%, and oxygen consumption at peak exercise increased 13%. Mean anginal frequency declined, as did mean weekly sublingual nitroglycerin consumption, but not significantly. There were more cardiovascular side effects with nicardipine than with placebo, with at least 3 patients having increased angina judged by investigators as probably related to the drug. Vasodilatory side effects were also more frequent with nicardipine, but were generally mild and well tolerated; the drug had to be discontinued in only 1 patient, because of vasodilatory effects. Nicardipine is effective and generally well tolerated in patients with chronic stable angina.
Adult↗
Diltiazem as monotherapy for systemic hypertension: a multicenter, randomized, placebo-controlled trial.
A multicenter, randomized, placebo-controlled, parallel group study of diltiazem in essential hypertension was carried out in 77 patients (40 diltiazem, 37 placebo) with stable supine diastolic blood pressure (BP) between 95 and 110 mm Hg. Patients were withdrawn from previous antihypertensive therapy for at least 4 weeks, titrated to the optimal dose, and followed for a total of 12 weeks during therapy. A diltiazem dose of 360 mg/day was required in 85% of the patients. Average BP in all positions was significantly (p less than 0.0001) reduced by diltiazem compared with placebo. With diltiazem, average supine BP fell from 156/100 mm Hg at baseline to 141/87 at end titration and 145/90 mm Hg at week 12, whereas average standing BP fell from 152/101 mm Hg to 136/90 and 143/91 mm Hg, respectively, at those times. There was no significant change in heart rate at week 12. Diltiazem tended to be more effective in older patients, but caused no increase in orthostatic BP drop. There were no statistically significant changes in BP in the placebo group. Two patients receiving placebo and 1 patient receiving diltiazem discontinued therapy as a result of adverse effects, and overall, side effects were only slightly more common with diltiazem treatment. Thus, diltiazem was effective and well tolerated single therapy for mild to moderate systemic hypertension and appears to compare favorably to most agents being used.
Age Factors↗
QT interval revisited.
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Electrocardiography↗
Knotting of a bypass graft catheter: report of a case.
A case of knotting of a bypass graft catheter during coronary arteriography is presented. An arteriotomy had to be done to remove the catheter. A possible mechanism causing this complication and precautions to avoid it are described.
Angiography↗
Nicardipine for stable angina pectoris.
Nicardipine, 30 and 40 mg thrice daily, was administered to 66 patients with stable angina pectoris in a multicentre, randomised, double-blind, cross-over trial. With nicardipine therapy, duration of exercise and cumulative oxygen consumption increased, while times to onset of angina and 1 mm ST segment depression were prolonged. Anginal frequency and nitroglycerin consumption declined with use of nicardipine, but this did not reach statistical significance. Resting heart rate increased slightly and resting blood pressure decreased. Two patients on nicardipine and one on placebo sustained acute infarction. Otherwise, side effects were generally mild and transient.
Adult↗
Longterm complications of Beall prosthetic valve: a case report.
A case of malfunctioning Beall prosthetic mitral valve causing severe heart failure is presented. The unusual aspect of this malfunction was the finding of disc dislodgment despite the absence of pathology in the disc itself. The dislodgment was caused by excessive tissue ingrowth around the suture ring. The need for close clinical follow-up of this type of prosthetic valve is emphasized.
Equipment Failure↗
Oxygen diffusion into heterogeneous tissue with combined oxygen consumption kinetics.
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Diffusion↗
Fascicular premature beats with narrow QRS in the presence of bundle-branch block.
The electrocardiogram of a sixty-two-year-old male revealed right bundle-branch block, left anterior superior fascicular block, and right precordial Q waves consistent with anteroseptal myocardial infarction. Premature beats with narrow QRS (100 ms) occurred intermittently; coupling intervals varied between 560-600 ms. His bundle electrogram confirmed the fascicular origin of the premature beats. During atrial prematuring studies, it was shown that an appropriately timed premature beat could prolong infra-His conduction time, but QRS normalization was not achieved. The possible electrophysiologic mechanisms that could result in a normal QRS complex with fascicular premature beats in this patient are discussed; a new mechanism is suggested.
Arrhythmias, Cardiac↗