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Biomedical subjects

S Talbot

Publications and source records attributed to S Talbot.

At least 55 records · Page 3Linked to original sources
PubMed1978

Differentiation of irregular rhythms by frequency distribution analysis.

Distinctive electrocardiographic patterns for atrial fibrillation, sinus rhythm and atrial extrasystoles, sinus arrhythmia and atrial flutter were found by analysing the frequency distribution of cycle lengths of the electrocardiogram. Frequency distribution analysis, demonstrated that atrial fibrillation is not completely irregular, but shows more long cycles than expected by chance and often a mode at the lower end of the distribution. Irregular atrial flutter is similar. Sinus arrhythmia has more variable organization, but usually there is a centrally situated mode with decreasing observations to the two extremities, and positive skewing. Examples of sinus rhythm and atrial extrasystoles usually have a mode at the upper end of the distribution with a secondary concentration of observations at the lower extremity. Ratios derived from the frequency distributions were of value in differentiating these arrhythmias. It is suggested that such information will improve computer identification of arrhythmia.

Arrhythmia, Sinus↗
PubMed1977

QRS voltage of the electrocardiogram and Frank vectorcardiogram in relation to ventricular volume.

Left ventricular volumes were estimated in 59 patients, who were investigated by single plane ventriculography and coronary arteriography. The relation of the left ventricular end-diastolic volumes to the QRS voltage of the 12-lead electrocardiograms and Frank vectorcardiograms was examined. It was found that the maximum spatial QRS voltage and the R wave voltage of leads V5 and V6 in patients without left ventricular hypertrophy were inversely correlated with end-diastolic volume. This inverse relation of QRS voltage and left ventricular volume may explain loss of QRS voltage with dilatation of the heart. In patients with left ventricular hypertropy QRS voltage is usually positively correlated with the degree of hypertrophy, but there is no significant correlation in the presence of cardiac dilatation. If the results of this study are extrapolated to patients with left ventricular hypertrophy and cardiac dilatation, then the inverse correlation of volume and QRS voltage may reduce the diagnostic sensitivity of unipolar chest lead and vectorcardiographic criteria of left ventricular hypertrophy.

Cardiac Volume↗
PubMed1977

Prognostic importance of ventricular extrasystoles in acute myocardial infarction.

Ventricular arrhythmias were recorded in 233 patients in a prospective study of patients with acute myocardial infarction. In over 95% of patients antiarrhythmic therapy was not given until the onset of ventricular tachycardia, ventricular fibrillation, or persistent idioventricular rhythm. There was a mortality of 18% during the patients' stay in hospital. The most important features of ventricular ectopic activity, which preceded these severe ventricular arrhythmias in the first 48 hr, were multiformity, variation of coupling intervals of larger or equal to 0-1 sec, the R-on-T phenomenon, double ventricular extrasystoles and ventricular bigeminy. The number of a single ventricular extrasystoles per minute was related to the probability of these severe ventricular arrhythmias but to a lesser degree. It was found that if all the patients with the first two prognostic features that if all the patients with the first two prognostic features were removed, the number of single ventricular extrasystoles was not of significant import and the other features were less important. Three-quarters of the severe arrhythmias occurred in the first 24 hr and during this period 60% were preceded by either multiform ventricular extrasystoles or extrasystoles with variable coupling. The importance of these findings in relation to prophylactic therapy is discussed.

Acute Disease↗
PubMed1977

Diagnosis of ventricular conduction defects.

A total of 1342 electrocardiograms demonstrating intraventricular conduction defects were reviewed. Criteria for distinguishing different types of conduction defects and combinations of such defects are presented. The time of intrinsicoid deflection was of great value and may be used to distinguish lesions of the main fascicles and peripheral Purkinje conduction defects. However multiple peripheral defects affecting a large area of myocardium can produce a pattern identical to left bundle branch block. It is suggested that intrinsicoid deflection time should be measured from the beginning of the QRS to the onset of the longest downslope at or after the peak of the R wave. It should be carefully related to the voltage of the dominant wave of the QRS complex in each lead. If intrinsicoid deflection is delayed in a limb lead that does not show the maximum voltage of the QRS, a peripheral left ventricular conduction defect is present; but if the lead does show the maximum voltage of the QRS, the defect may be central or peripheral. Another useful electrocardiographic feature was the direction of both the initial and terminal QRS forces in the 12-lead electrocardiogram. Such analysis often resolved the diagnosis of hemiblocks when the axis was indeterminate.

Arrhythmias, Cardiac↗
PubMed1977

Sequential analysis of supraventricular arrhythmias and its value in the differentiation of irregular rhythms.

Distinctive electrocardiographic patterns for atrial fibrillation, sinus rhythm, and atrial extrasystoles and sinus arrhythmia were found by analysing the sequential distribution of cycle lengths. Sequential analysis demonstrated similarities between those arrhythmias, accounting for confusion between them, but it could also be used to demonstrate important differences. Utilizing information from both the frequency distribution and the sequential distribution of cycle lengths has improved the accuracy of computer identification of 20-sec arrhythmia recordings from 58.4 to 70.5%, when all supraventricular arrhythmias recorded on acute medical admissions were considered. It is suggested that such information will improve arrhythmia identification based on P wave analysis. From this analysis a classification of irregular rhythms has been proposed. An irregular rhythm may or may not be totally irregular. If there is lack of sequential dependency an arrhythmia should be described as nonperiodic. If there are distinct cycle lengths which are most frequent, the rhythm may be described as modal and there may thus be bimodal or trimodal rhythms which are irregular. Sinus rhythm with atrial extrasystoles may show a combination of these features. This can be described as a bimodal nonperiodic rhythm. If there is neither sequential dependency nor distinct modality the rhythm may be described as an irregular nonperiodic rhythm, e.g. some examples of atrial fibrillation. Sinus arrhythmia is an irregular periodic rhythm.

Arrhythmia, Sinus↗
PubMed1976

Diagnostic criteria for computer-aided electrocardiographic 15-lead system. Evaluation using 12 leads and Frank orthogonal leads with vector display.

The criteria for the diagnosis of myocardial infarction and ischaemic heart disease by an automated 15-lead computer-aided electrocardiographic system were examined using electrocardiograms of 543 patients. Errors in the electrocardiographic diagnosis were evaluated for each lead system (Frank orthogonal 3-lead, 12-lead, and hybrid 15-lead) using clinical and catheterization data for definitive diagnosis before review of the electrocardiograms and their reports. The effects of combinations of these diagnoses and additional ventricular conduction defects were also studied. Myocardial infarction and left ventricular hypertrophy were more reliably diagnosed using 3-lead and 12-lead systems together than with either system alone. The most sensitive criteria for anterior infarction were a Q/R ratio in Z less than 0-1 and loss of the first 20 ms of anterior forces in the horizontal and sagittal planes of the vectorcardiogram. However, false positive results were frequent, particularly in association with left ventricular hypertrophy, non-specific intraventricular conduction defects, and left bundle branch system block. Our V lead criteria were more specific whether or not these associated conditions were present. No single criterion with an acceptable false positive rate could be found to be sensitive for inferior infarction in all situations. Our most sensitive criteria were those based on the limb leads, and the presence of superior forces for the first 30 ms in the frontal plane of the vectorcardiogram, but these were better in combination. Limb lead criteria were the most specific. False positive results for inferior infarction were more frequent in the presence of left ventricular hypertrophy or ventricular conduction defects other than left anterior hemiblock. ST and T wave abnormalities were more apparent in the 12 leads than in the orthogonal leads. Specificity and sensitivity of criteria were poor, and specificity was decreased and sensitivity was not significantly improved by combining 3-lead with 12-lead criteria. Because of frequent measurement errors of ST, T, and also Q waves by the computer programme, in practice we have achieved increased sensitivity in the diagnosis of ischaemia and infarction with the combination of 3-lead and 12-lead systems. It is concluded that errors of diagnosis by a computer-aided system can be reduced by using multiple leads and that both 12-lead and orthogonal 3-lead systems are necessary for optimal computer diagnosis of left ventricular hypertrophy, myocardial infarction, and ischaemia.

Adult↗
PubMed1976

Association of ventricular extrasystoles and ventricular tachycardia with idioventricular rhythm.

Patients with acute myocardial infarction were monitored for ventricular arrhythmias in the first 48 hours. Idioventricular rhythm (rate less than 100/minute) occurred in 35 out of 224 patients (15.6%) during the first day and in 13 out of 192 patients not receiving treatment on the second day (6.8%). This arrhythmia was frequently preceded by late ventricular extrasystoles, which often showed variation of their coupling intervals to the preceding QRS. Double ventricular extrasystoles separated by larger than or equal to 600 ms were also precursors of idioventricular rhythm. Idioventricular rhythm at times could be described as an escape rhythm, but on other occasions it was undoubtedly an accelerated rhythm. Spontaneous changes in the idioventricular cycle length were frequent on single one-minute electrocardiographic recordings. The rate of the dominant rhythm in patients with episodes of idioventricular rhythm was significantly slower than the heart rate of patients without this arrhythmia. Idioventricular rhythm was more frequent in patients with inferior infarction. Idioventricular rhythm sometimes preceded ventricular tachycardia but there was only a significant association between ventricular tachycardia and idioventricular rhythms with rates of over 75/minute. Irregular idioventricular rhythm frequently accelerated to ventricular tachycardia. It is suggested that the term benign idioventricular rhythm be reserved for those rhythms below 75/minute, and that the term rapid idioventricular rhythm should be used for rhythms between 75 and 120/minute. The rate of idioventricular rhythm is related to the probability of development of life-threatening ventricular arrhythmias during the first 48 hours after myocardial infarction.

Cardiac Complexes, Premature↗
PubMed1976

Exertional hypotension due to postganglionic sympathetic blocking drugs.

Debrisoquine, guanethidine and bethanidine may produce troublesome hypotensive symtoms related to exertion. Thirteen patients with such symptoms were exercised on a treadmill and the response of blood pressure and heart rate was compared to that of thirty patients without these symptoms, who were exercised to the same extent. There was a slight drop of systolic and diastolic pressures on standing in both groups, but after exertion there was a significantly greater drop of systolic pressure in the group with symptoms than in the asymptomatic group. The diastolic pressure after exertion was significantly lower in the group with symptoms. It was impossible to predict from the standing blood pressure levels at rest which patients would develop hypotensive symptoms after exertion. All three drugs had a similar negative chronotropic effect at rest and on exercise. It is suggested that patients are exercised during control of hypertension in order to identify those prone to exertional hypotension. Patients with such hypotension should be exercised on each attendance before the blood pressure is measured. Treatment other than postganglionic sympathetic blocking drugs should be employed whenever possible in patients with milder hypertension.

Bethanidine↗
PubMed1976

Influence of ventricular conduction defects on ventricular repolarisation and coupling intervals of ventricular extrasystoles.

In all conduction disorders of the left ventricle the Q-T interval is prolonged in relation to the prolongation of the QRS duration, but the S-T interval (measured from the end of the S wave) is within normal limits. Right ventricular conduction defects are associated with prolongation of the Q-T interval, but the S-T interval in incomplete and complete right bundle branch block is subnormal. In the absence of a broad QRS, the Q-T and S-T intervals are not prolonged in left anterior hemiblock. However, an associated non-specific left intraventricular conduction defect or right bundle branch block does prolong the QRS and thus the Q-T interval. The S-T interval is normal or subnormal in the presence of right bundle branch block and left anterior hemiblock confirming that left anterior hemiblock does not effect the Q-T interval and repolarisation. In the presence of any conduction defect which prolongs the QRS duration, extrasystoles have longer coupling intervals. The coupling intervals are longer in the presence of left bundle branch block than right bundle branch block. It is postulated that this is due to the differences in the time of depolarisation and thus repolarisation of the left ventricle.

Bundle-Branch Block↗
PubMed1976

Angina in hypertensive patients. With particular reference to the negative chronotropic effects of sympatholytic therapy.

There was no significant difference in the blood pressure and heart rate response of hypertensive patients with and without angina to standardised exercise on a treadmill before and after anti-hypertensive treatment. There was no improvement in exercise tolerance in the hypertensive patients with angina treated with bethanidine, debrisoquine or guanethidine despite a reduction of resting and exercise heart rates after treatment. The negative chronotropic effect of these sympatholytic drugs was less than that of oxprenolol or propranolol, but the hypotensive response was greater. Both of these beta-receptor blocking drug produced an an improvement in exercise tolerance in patients with angina either alone or in combination with other hypotensive therapy. The best control of blood pressure and angina was often achieved by a combination of a sympatholytic drug and beta-receptor blocking drug. In hypertensive patients treated for several years, angina at presentation was occassionally reduced by reduction of blood pressure. Later onset of angina appeared to be unrelated to control of hypertension but to be due to coincidental coronary occlusion. There was no evidence that myocardial infarction was precipitated by postural or exercise hypotension although these effects occasionally precipitated angina.

Adrenergic beta-Antagonists↗
PubMed1975

Electrical axis and voltage criteria on left ventricular hypertrophy.

The voltage criteria of left ventricular hypertrophy were studied in 229 hypertensive patients undergoing treatment and 62 patients who were not treated. The limb-lead voltage criterion (R Lead aVL greater than or equal 11 mm.) was found more frequently in patients with radiographic evidence of cardiomegaly than other voltage criteria. This may have been due to a more negative axis in patients with cardiomegaly than in patients without cardiomegaly. It is possible that dilatation of the left ventricle to the left and posteriorly accentuates limb-lead criteria at the expense of V-lead criteria. Left anterior hemiblock occured in less than 10 per cent of the hypertensive patients. In 10 out of 16 patients with left anterior hemiblock, the hemiblock disappeared after treatment of the hypertension for 4 years whereas all five hemiblocks in untreated hypertensives persisted. Development of left anterior hemiblock subsequently occurred in only one patient with treatment and one without treatment over a 4-year period.

Adult↗
PubMed1975

Measuring ventricular extrasystoles.

Uniform ventricular extrasystoles can be divided into three types: fixed coupling, parasystole, and variable non-parasystolic coupling. Frequency distributions of coupling intervals of ventricular extrasystoles were determined from long electrocardiographic recordings of 51 patients with variable coupling. These distributions were of five types: (a) two distinct coupling intervals, (b) a preponderance of extrasystoles with short coupling intervals and less frequent extrasystoles with progressively longer coupling, (c) a preponderance of long coupling intervals and less frequent extrasystoles with progressively shorter coupling, (d) an even distribution and (3) a central distribution. Interectopic intervals were measured in these electrocardiograms (ECGs). Parasystole was found only in three recordings. It is recommended that the diagnosis of parasystole be made only if the degree of variation of the ectopic cycle (both when it is manifest and when it is concealed) is less than the variation of the coupling intervals. When the ECGs with variable non-parasystolic coupling were compared with 44 ECGs with fixed coupling, it was found that variable coupling was associated with abnormalities of the basic electrocardiographic contour, multiformity of extrasystoles and repetitive extrasystoles.

Cardiac Complexes, Premature↗
PubMed1975

Factors predisposing to postural hypotensive symptoms in the treatment of high blood pressure.

Symptoms due to orthostatic and exertional hypotension occurred in 23-4 per cent of 448 hypertensive patients treated with guanethidine, debrisoquine, or bethanidine. Symptoms were significantly more frequent in patients treated with guanethidine than in those treated with bethanidine or debrisoquine. Women rather than men and patients with radiological evidence of cardiomegaly, electrocardiographic evidence of left ventricular hypertrophy, or ST/T wave changes, developed these symptoms significantly more often than other patients. A raised blood urea was found more frequently in patients with postural hypotensive symptoms. Characteristically guanethidine produced early morning postural hypotensive symptoms, wheras hypotensive symptoms caused by bethanidine and debrisoquine occurred at other times of the day and particularly one to two hours after tablet ingestion. Debrisoquine and guanethidine had a significantly greater negative chronotropic effect than bethanidine. It is suggested that negative chronotropic effects of these drugs may potentiate hypotensive symptoms in patients with cardiovascular, renal, or cerebrovascular disease. It should be possible to minimize symptoms of postural hypotension by attention to predisposing factors and selection of treatment accordingly.

Bethanidine↗
PubMed1975

Characteristics of ventricular extrasystoles and their prognostic importance: a reappraisal of their method of classification.

The concept of two different types of extrasystoles, parasystolic and coupled, depends upon two distinguishing characteristics of these beats. The characteristics of the parasystolic extrasystoles are the invariability of the ectopic cycle together with their independence from the basic rhythm. Coupled extrasystoles demonstrate a dependence upon the basic rhythm although they may express some degree of ectopic variability. The degree of variation of the interectopic interval or its common denominator measures the irregularity of the ectopic parasystolic rhythm. The variation of coupling intervals describes the dependence of the ectopic beat upon the basic rhythm. In a study of 719 electrocardiograms with ventricular extrasystoles, about one-third of the extrasystoles appeared intermediate between these types since they had both variable coupling intervals and variable interectopic intervals. Some of these had total variability of coupling intervals and of the interectopic intervals (random non-parasystolic coupling), and others had limited variation of coupling intervals when expressed in relationship to the total duration of electrical diastole (approximate non-parasystolic coupling). Both these ectopic types appeared to be associated with cardiac disease, and repetitive ventricular extrasystoles. Left bundle branch type extra-with fixed coupling. There were no obvious relationships between the contour and the type of coupling of ventricular extrasystoles. Left bundle branch type extrasystoles with vertical or right axis were the most frequent, particularly in normal subjects, but in the presence of cardiac disease there were more electrocardiograms with right bundle branch type extrasystoles. Extrasystoles in the presence of underlying conduction defects were usually of opposite configuration to this defect. The contour of uniform extrasystoles did not appear to predispose to serious ventricular arrhythmias but multiformity of extrasystoles was an important prognostic indicator. It is suggested that variability of contour and coupling are important signs of inhomogenous conduction and may precede the onset of severe ventricular arrhythmias. Random nonparasystolic coupling and marked multiformity indicate a more sinister arrhythmic state.

Bundle of His↗