Dietary lipid intake and myocardial electrophysiology.

We studied the effect of a fat-free diet on the cardiac electrophysiology of rats. Fourteen 2-week-old rats were maintained on a fat-free diet and 12 rats had a 5% soybean oil supplement to their diet. The rats were killed after 6 weeks and the hearts mounted on a Langendorff chamber. Atrioventricular (A-V) block was induced. Myocardial strength-duration (S-D) and strength-interval (S-I) curves were determined. A significant depletion of linoleic acid and elevation of palmitoleic, stearic, and oleic acids was found in the hearts obtained from rats on fat-free diet as compared with the hearts obtained from the rats on oil-supplemented diets. Hearts obtained from rats who had had the oil supplement had a shorter refractory period and an increased threshold for excitation; therefore, these hearts should be less vulnerable to cardiac dysrhythmias. Both S-D and S-I curves best fitted a logarithmic relationship. The intercepts and slopes of these curves were significantly different in the two groups. There were significant correlations between myocardial fatty acid composition (stearate and linoleate in particular) and the different electrophysiological parameters.

Smoking, morbidity, and pulmonary function in a group of ex-asbestos workers: a pilot study.

Thirty-three of 184 formerly exposed asbestos textile workers were interviewed to evaluate knowledge, attitudes, and practices concerning smoking and asbestos. Twenty-three subjects in this group also underwent physical examination to determine smoking-symptom/sign-pulmonary function interrelationships. Approximately half of the exworkers smoked, and the majority who had stopped did so mostly because of illness rather than because of knowledge concerning smoking-asbestos hazards. All workers welcomed the offer of smoking cessation programs. Smokers and exsmokers, but not nonsmokers, were at risk for obstructive-type impairments, but all three groups contained subjects with impairments interpretable as restrictive. The presence of shortness of breath, cough, râles, or decreased breathing sounds alone or in any combination greatly increased the odds that either obstructive- or possible restrictive- or mixed-type impairments would be found on spirometry. Mass screening techniques required about one hour of person time per examinee to assess health status, provide educational material on smoking, and counsel workers on referral arrangements. The findings suggest that smoking alerts, smoking cessation clinics, and medical follow-up are needed, feasible, and acceptable in Israel.

Studies on a pancreatic cardiodepressant factor.

Myocardial depressant factor (MDF) was isolated from dog pancreas after incubation at 37 degrees C for 2 hr. A highly purified preparation of MDF was obtained by paper chromatography and high voltage electrophoresis. After paper chromatography of crude homogenates of the pancreatic tissue, cardiodepressant activity was found in spot F. High voltage electrophoresis of spot F produced five separate fractions. Bioassay using isolated perfused hearts and cultures of myocytic tissue showed that only one of these spots was associated with MDF activity. This spot contained a peptide with a molecular weight of 1000-2500 consisting of nine amino acids.

T-2 toxin effect on isolated perfused rat hearts.

T-2 toxin is the major lethal component of several Fusarium fungi implicated in the disease of man and animals. We used isolated rats hearts to test the T-2 toxin cardiotoxicity. Electrodynamics and ultrastructural parameters were studied. The main changes consisted of decreased contractility and electrocardiographic abnormalities without much effect on heart rate or QRS and QT intervals. Ultrastructurally, swelling of myofibers and their mitochondria occurred and damage to the plasma membrane was seen. It is possible that the T-2 effect is mediated through soluble thiol to cause cytoplasmic calcium decrease and loss of plasma membrane integrity.

Comparative cardiac effects of three hepatobiliary radiopharmacologicals in the dog: concise communication.

Three hepatobiliary agents with an acetanilide-imidoacetic-acid moiety resembling that in lidocaine were investigated for their possible effects on contractility and conductivity in the heart and on arterial pressure and aortic blood flow. This was done in the light of lidocaine's numerous cardiac side effects. HIDA, BIDA, and DIPA, each with traces of decayed Tc-99m, were injected i.v. into anesthetized dogs with an A-V block, and their effects on the above parameters were followed until control levels were reestablished. Whereas lidocaine raises the diastolic threshold and prolongs the refractory period, the three agents tested do not prolong myocardial conductivity. Both HIDA and BIDA have an effect similar to that of lidocaine, but DIPA has no effect on the latter two parameters. Moreover, whereas lidocaine depressed myocardial contractility, blood pressure, and blood flow, HIDA has a less prominent effect on these parameters, and neither BIDA nor DIPA has any such effect. It is concluded that even though the effect of HIDA on the heart is milder than that of lidocaine, the effects of both BIDA and DIPA are even less pronounced, and they are less likely to cause cardiac side effects when similar doses are administered during nuclear medicine procedures.

Myocardial conduction time and antiarrhythmic drugs.

Complete a-v block was induced in anesthetized mongrel dogs by direct electrocoagulation of the a-v node. The ventricles were paced by steady stimulation (S1) at a rate of 100/min. and by test stimuli (S2) with varying post S1 delay. Right ventricular myocardial tension was measured from the S2 stimulation site of a specially designed miniature strain gage and from a different site by a Walton-Brodie strain gage. A reproducible time lag between the two sites could be measured by comparing the differences in mechanical response to S2 stimuli. This time difference was called delta IT. delta IT varied markedly (from 10-60 msec) when measured at different sites but no linear relationship between delta IT and the inter-gage distance could be observed. Increasing the S2 current intensity induced shortening of delta IT from 37 +/- 13 msec (mean +/- S.D.) at the threshold current to 16 +/- 10 msec (mean +/- S.D.) with 10 mA. A strength-delta IT curve could be constructed and was found to be remarkably reproducible during the experiment. Quinidine and disopyramide induced upward displacement of the curve, lidocaine did not change it while verapamil lowered the delta IT values. We suggest that delta IT can be used as a reliable indicator of myocardial conduction rate. The possible reasoning for this suggestion has been discussed.

Electrical and mechanical response in biventricular mechanical alternans.

Mechanical alternans of various degrees is produced by rapid heart rates, slower rates in failing hearts and can be brought about by a single extra systole. It has also been shown that the two ventricles may exhibit different degrees of mechanical alternation. The present study was planned to clarify the possible mechanism inducing this latter phenomenon. For this reason myocardial tension was recorded simultaneously from the two ventricles as well as through a miniature strain gage capable of measuring electrogram and myocardial tension of a small area -- just adjacent to a stimulating electrode. The heart was driven at a steady heart rate through one electrode and very late premature beats were applied at various coupling times at another site through an electrode attached to the miniature strain gage. It was found that the degree of mechanical alternans is markedly different at the sites of measurements in either ventricle. These changes could be related to the time interval elapsed between the application of the electrical stimulus and the occurrence of the mechanical response.