The reliability of intermittent ECG sampling in arrhythmia detection

Although intermittent ECG sampling is a commonly used method for arrhythmia detection there are no controlled studies of its efficiency. In the present study a continuous ECG was recorded for three hours in 52 patients with ventricular tachyarrhythmias. All ECGs were interpreted minute to minute to get the true arrhythmia content. Intermittent ECG samples were simulated by analyzing the first two and first five minutes of every 15 minutes in the ECG material. Two minute long ECG samples were also used every 30 minutes. The 15 and 30 minute long periods were classified as containing arrhythmias or not according to the arrhythmia content of the samples. These findings were subsequently compared with the true arrhythmia content. The arrhythmia detection rate depends on the sampling time and true arrhythmia occurrence. The distribution of arrhythmias within the periods was also of importance. With a five minute long ECG sample about 80% of the intervals containing any type of ventricular tachyarrhythmia will be detected. This is reduced to about 50% when one minute long ECG strips are used. Infrequent types of VPCs such as R on T or ventricular tachycardia are very poorly detected also when sampling as much as one-third of the total time. The study also included a comparison between the results obtained from the clinical material and the results obtained by the use of computerized arrhythmia models. It is concluded that intermittent ECG sampling besides a low detection rate for infrequent arrhythmias and short ECG samples, also brings a risk of underestimating or overemphasizing the arrhythmia occurrence depending on a periodic type of arrhythmia distribution among the patients. These factors make intermittent ECG sampling an unsuitable method for evaluating antiarrhythmic drugs.

The effect of therapeutic doses of lidocaine hydrochloride on the effective refractory period of the right ventricle in man

The effect of lidocaine on the effective refractory period of the right ventricle (EVRP) was measured in 10 patients using the extra stimulus technique of progressive introduction of premature stimuli until a response could not be elicited. In four patients lidocaine produced a significant decrease in the EVRP, in a further four patients there was no change, and in the remaining two patients lidocaine produced a significant increase in the EVRP. The effect of the drug on the EVRP could not be correlated with the serum potassium levels. The reasons for the variable effect of lidocaine are attributed to the different action of lidocaine on different components of conduction within the ventricle.

A rapid and specific method for isolation of thiol-containing peptides from large proteins by thiol-disulfide exchange on a solid support

Activated thiol-Sepharose [agarose-(glutathione-2-pyridyl disulfide) conjugate] has been used to immobilize proteins with a single or a few thiol groups via disulfide bridges. The immobilized proteins were subsequently proteolytically degraded. After washing, the thiol-containing peptides were eluted with a reducing agent. A single preparative paper electrophoresis, occasionally after a modification such as oxidation, was sufficient to obtain pure peptides in good yields. The method was applied to the major parvalbumin from hake muscle (a protein with 108 amino acid residues and one cysteine residue), to mercaptalbumin from bovine serum (565 residues and one cysteine), and to human serum ferroxidase [EC 1.16.3.1; iron (II):oxygen oxidoreductase] (ceruloplasmin) (1065 residues and three cysteines). The use of the technique, e.g., as a simple means of obtaining homologous peptides in related proteins, is discussed.

Plasma concentrations and urinary excretion of the antiarrhythmic quaternary ammonium compound QX-572 in man

A quantitative thin layer chromatographic (TLC) method has been developed for determination of the antiarrhythmic quaternary ammonium compound N,N-bis (phenylcarbamoyl methyl) dimethylammonium chloride (QX-572) in biological materials. Prior to chromatography QX-572 was transferred into chloroform as perchlorate by ion pair extraction. Tritium-labelled QX-572 was used as the internal standard and a TLC scanning spectrophotometer equipped with a linear detector system afforded the required accuracy, specificity and simplicity. The method was used to determine QX-572 in plasma from 11 patients with various cardiac diseases who received QX-572 8 mg/kg body wt. as an intravenous infusion over 30 min. There was a rapid initial decay of the plasma levels from 11.0+/-1.1 mug/ml (mean+/-SE) at the end of infusion to 3.5+/-0.5 mug/ml after 30 min. 240 min after commencement of the infusion the plasma level was 0.7+/-0.1 mug/ml. In these patients 22+/-2% (mean+/-SE) of the total administered dose of QX-572 was excreted unchanged in urine during the 24 hours following infusion of the drug. A second group of 28 patients with acute myocardial infarction also received QX-572 8 mg/kg body wt. Their plasma levels did not differ significantly from those found in the first group of patients. There was a poor correlation between the amount of QX-572 administered and plasma level at the end of the infusion. The study has provided some preliminary data about the pharmacokinetics of QX-572, but before a detailed analysis can be done data from longer periods of observation is required. The present results suggest that in future QX-572 can be administered in a standardized dosage, what would be advantageous in practice.

Effects of the quaternary ammonium compound OX-572 on ventricular tachyarrhythmias complicating acute myocardial infarction

Patients with acute myocardial infarction who developed defined ventricular tachyarrhythmias were randomly allocated to two groups. The patients (n=34) in one of the groups received the quaternary ammonium compound N,N-bis (phenylcarbamoylmethyl) dimethylammoniumchloride (QX-572) intravenously as an infusion of 8 mg/kg body weight over 30 minutes. The patients in the other group (n=33) received saline and acted as controls. The analysis of arrhythmias was based on a continuous electrocardiogram recorded in parallel to routine monitoring during the 24 hours after the start of infusion. Only the detection of ventricular tachycardia or the development of ventricular fibrillation on routine monitoring could induce a change in antiarrhythmic treatment. The incidence of patients with ventricular tachycardia recorded was significantly lower in the QX-572 group (38%) than in the control group (73%). About half the number of patients with ventricular tachycardia recorded on the continuous electrocardiogram were also detected by means of routine monitoring. The number of patients with various types of ventricular premature contractions (1-5/min, greater than 5/min, paired, multifocal, R on T), ventricular tachycardia, and rapid idioventricular rhythm were compared within successive one-hour periods. For all types of ventricular tachyarrhythmias except rapid idioventricular rhythm there was a lower incidence of arrhythmias in the QX-572 group...

Blood levels of lidocaine after various infusion rates in patients with acute myocardial infarction

Blood levels of lidocaine were estimated following two different infusion rates in patients with acute myocardial infarction. Forty-one patients received lidocaine as a bolus injection of 75 mg. directly followed by an infusion. The infusion rate was, in 16 patients, 2 mg. per minute. Blood levels of lidocaine were determined at different times up to 180 minutes after the start of drug administration. The levels in the 2 mg. per minute group were lower than had been expected and the mean level plus or minus S.E. was, after three hours, only 1.1 mug per milliliter. Many of the 2 mg. per minute petients did not, during the time period observed, reach 1.2 mug per milliliter, which has been considered as the lowest effective therapeutic level. In the 4 mg. per minute group, mean level of lidocaine already at 15 minutes was significantly higher than in the 2 mg. per minute group (1,1 plus or minus 0.14 and 0.6 plus or minus 0.05, respectively; p less than 0.05). After three hours, the mean blood level in the 4 mg. per minute group was 2.6 mug per milliliter. Although the blood levels were not followed after three hours, a careful observation did not reveal any severe toxic effects in the 4 mg. per minute group during next 21 hours. In five cases, however, lidocaine side effects were probable. These symptoms disappeared rapidly after cessation of the infusion. In order to reach therapeutic blood levels of lidocaine within a reasonable time, the infusion rate of 4 mg. per minute is recommended at least for the first three hours.

Haemodynamic effects of the antiarrhythmic quaternary ammonium compound QX-572 in man

The haemodynamic effects of N, N-bis(phenyl-carbamoylmethyl) dimethylammonium chloride (QX-572) in man were studied. A controlled study was performed to rule out a possible influence of the catheterization procedure as such on the results. Ten patients with mild to moderate aortic regurgitation were studied: based on clinical data the patients were divided into 2 groups of 5. Randomly it was decided that one group should constitute a control group receiving saline while the second group received QX-572 , MG/KG BODY WEIGHT. In both groups the administration was performed as a slow intravenous infusion during 30 minutes. Heart rate, pressures in brachial artery and right atrium, cardiac output, stroke volume, and systemic vascular resistance were determined before, during, and up to 30 minutes after completion of placebo or QX-572. These variable remained stable in the control group while QX-572 produced an increase in heart rate most pronounced at the end of the infusion period. A transient decrease in systolic and mean brachial artery pressure during the infusion, and during the same period a decrease in right atrial pressure. Cardiac output and systemic vascular resistance were unchanged by QX-572 but they were not measured during the infusion when the changes in pressures were most pronounced. QX-572 was thought to act as a peripheral vasodilator during the infusion. Left ventricular contractility was studied by means of pressure curves obtained from a catheter tip manometer placed in the left ventricle. The first derivative of the isovolumic left ventricular pressure at the highest level (45mmHg) common to all patients was used (dp/dt-45). No significant difference could be observed when comparing mean changes of dp/dt-45 for the two groups. In the control group there was a slight but significant increase in dp/dt-45 during the time of observation. In the QX-572 group the results varied between individuals. Two of the patients differed from all other patients in the control and QX-572 groups showing a decrease in dp/dt-45 which, when most pronounced at the end of the infusion period, was -31 and -28 per cent of the preinfusion levels, respectively. This decrease probably reflects reduction of contractility. It was concluded that QX-572 in a dose of 8 mg/kg body weight did not have any major haemodynamic drawbacks.

Electrophysiological effects of the antiarrhythmic agent QX-572 in the human heart with special reference to rate-induced changes in effective refractory periods

The antiarrhythmic agent, N,N-bis(phenylcarbamoylmethyl)dimethylammonium chloride (QX-572) 8 mg/kg body weight produced a decreased conduction time through the atrioventricular node but did not influence intra-atrial or intraventricular conduction. Effective refractory periods of the atrium, the atrioventricular conduction system, and the ventricle were shortened by the drug. The observed effects were present at the end of drug infusion but had disapnerbd 30 min later. The probable explanation is an increased sympathetic tone induced by QX-572.

Phenformin and pulmonary hypertension

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