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Biomedical subjects

S M Cobbe

Publications and source records attributed to S M Cobbe.

At least 145 records · Page 8Linked to original sources
PubMed1990

Lipid peroxidation during myocardial ischaemia induced by pacing.

Oxygen derived free radical generation can be shown in experimental models of myocardial ischaemia and reperfusion and may cause cellular damage by peroxidizing polyunsaturated membrane phospholipids. An attempt was made to quantify human intracardiac lipid peroxidation during transient myocardial ischaemia by measuring the aortic and coronary sinus concentrations of malondialdehyde (a marker of lipid peroxidation) before, during, and after incremental pacing. Twenty six patients were paced until they had severe chest pain or 2 mm ST segment depression or they reached a paced rate of 180 beats/min. They were divided into two groups according to whether or not lactate was produced during pacing. Twelve patients (group 1), all with coronary artery disease, produced myocardial lactate during pacing. None of the other 14 patients (group 2), half of whom had coronary disease, produced lactate during pacing. Concentrations of malondialdehyde in the aorta and coronary sinus were significantly higher in group 1 than in group 2. Five minutes after the end of pacing coronary sinus malondialdehyde concentrations in group 1 had increased significantly from baseline values. There were no changes with time in the coronary sinus concentration of malondialdehyde in group 2 or in the aorta in either group. The negative malondialdehyde extraction ratio in group 1 suggests that intracardiac lipid peroxidation occurs during transient human myocardial ischaemia.

Adult↗
PubMed1990

Study of serum C-reactive protein concentration in cardiac failure.

The serum concentration of C-reactive protein was prospectively assessed in 37 patients with various degrees of heart failure. The serum concentration of C-reactive protein was higher than normal in 26 (70%) patients. The concentration was directly related to the severity of heart failure and the stage of decompensation. Hepatic cell damage is the most likely stimulus to cytokine production and hence release of C-reactive protein in heart failure. Heart failure is an additional cause of raised serum concentration of C-reactive protein but the pathological importance of this feature is not yet known.

Aged↗
PubMed1990

Verapamil or adenosine for the immediate treatment of supraventricular tachycardia.

A comparison of verapamil with adenosine for the immediate treatment of supraventricular tachycardia was made from a retrospective review of 164 spontaneous episodes of paroxysmal tachycardia in 43 patients. Verapamil administered to 33 patients restored sinus rhythm in 91 of 112 episodes (81 per cent). Hypotension occurred in 9 per cent of episodes. Adenosine terminated 94 per cent of episodes of supraventricular tachycardia in 25 patients. The arrhythmia recurred shortly after adenosine restored sinus rhythm in 20 episodes. Transient side effects were common. Fifteen patients were treated with both agents. Adenosine was successful in all, but verapamil failed to restore sinus rhythm at least once in seven of the 15 patients. Early recurrence of tachycardia occurred in five of these after adenosine, but in only one after verapamil. Verapamil and adenosine are both effective in the treatment of supraventricular tachycardia; adenosine has the higher success rate and is safer, but transient symptoms are common and arrhythmias may recur.

Adenosine↗
PubMed1989

Infective endocarditis caused by Streptococcus agalactiae.

We report a series of five cases of infective endocarditis caused by Streptococcus agalactiae (group B streptococcus) in Glasgow over a 30 month period. There were three males and two females mean age 48.6 years (range 28-63 years). Only one patient had previous valvular heart disease. The infections were characterised by an acute presentation and an aggressive course with major arterial emboli. Despite early diagnosis and appropriate intravenous antibiotics three patients died, one after valve replacement and two before surgery could be undertaken. The remaining two patients had successful valve surgery and have recovered. S. agalactiae endocarditis is an uncommon but important condition which carries a high mortality. The infection is difficult to control with antibiotics alone and therefore early surgery may be indicated.

Adult↗
PubMed1989

An animal model for the chronic study of ventricular repolarisation and refractory period.

We have developed a simple model permitting stable, chronic measurements of ventricular repolarisation and refractory period to be made in conscious, unsedated, unrestrained animals. The model utilises the ventricular paced evoked response, recorded from permanent pacemaker electrodes implanted into the right ventricle of New Zealand White rabbits. After a "bedding in" period of 18-21 d, measured variables are stable for long periods; the stimulus to T wave interval of the evoked response remains stable up to at least 150 d after electrode insertion. The principal advantage of the model lies in the control of heart rate by pacing, eliminating the requirement for unreliable methods of correction of repolarisation data for sinus rate. Surgical techniques are straightforward. The model can also be used for studies involving recordings of the intrinsic (non-paced) intracardiac electrogram, as the quality of the signal obtained is consistently superior to standard methods of recording the electrocardiogram in animals. The stimulus-T interval of the paced evoked response has been found to correlate significantly (r = 0.96) with action potential duration measured by transmembrane microelectrode recordings in the isolated, arterially perfused interventricular septum.

Action Potentials↗
PubMed1989

Value and limitations of adenosine in the diagnosis and treatment of narrow and broad complex tachycardias.

The diagnostic and therapeutic potential of intravenous adenosine was studied in 64 patients during 92 episodes of regular sustained tachycardia. In 40 patients who had narrow complex tachycardias (QRS less than 0.12 s) adenosine (2.5-25 mg) restored sinus rhythm in 25 with junctional tachycardias (46 of 48 episodes) and produced atrioventricular block to reveal atrial or sinus tachycardia in 15. In 24 patients with broad complex tachycardias (QRS greater than or equal to 0.12 s) adenosine terminated the tachycardias in six patients and revealed atrial or sinus arrhythmias in four. The tachycardias persisted in 14 patients despite doses up to 20 mg, but adenosine allowed the diagnosis of ventricular tachycardia with retrograde atrial activation in two patients by producing transient ventriculoatrial dissociation. Diagnosis based on adenosine induced atrioventricular nodal block was correct in all patients with narrow complex tachycardias and in 92% of those with broad complex tachycardias, compared with correct electrocardiographic diagnoses in 90% and 75% respectively. Adenosine gave diagnostic information additional to the electrocardiogram in 25%. The response to adenosine in broad complex tachycardias identified those of supraventricular origin with 90% sensitivity, 93% specificity, and 92% predictive accuracy. Adenosine restored sinus rhythm in all patients with junctional reentrant tachycardias, but in 10 (35%) the arrhythmias recurred within two minutes. Symptomatic side effects (dyspnoea, chest pain, flushing, headache) were reported by 40 (63%) patients and, although transient, were severe in 23 (36%). There were ventricular pauses of over 2 s in 16% of patients, the longest pause being 6.1 s. Adenosine is of value in the diagnosis and treatment of narrow and broad complex tachycardias, but its use is limited by symptomatic side effects, a tenfold range in minimal effective dosage, occasional action at sites other than the atrioventricular node, and early recurrence or arrhythmia.

Adenosine↗
PubMed1988

Neuroendocrine changes in acute myocardial infarction.

Acute myocardial infarction is associated with complex neuroendocrine changes, including release of arginine vasopressin, norepinephrine, and epinephrine, and activation of the renin-angiotensin system. Arginine vasopressin levels are maximal on admission, and subsequently fall even in patients in whom left ventricular failure develops. Plasma levels of norepinephrine and epinephrine are at their highest on admission and return to the normal range in patients with uncomplicated infarction, but they remain significantly elevated in patients in whom left ventricular failure or late ventricular arrhythmias develop. In contrast to catecholamines and arginine vasopressin, plasma renin and angiotensin levels are within normal limits on admission in patients without complications but increase by the third day. Patients with left ventricular failure already have increased plasma levels of renin and angiotensin on admission, but further marked and persistent increases occur over the following days. All of the aforementioned hormones may interact to cause systemic or coronary vasoconstriction, which may have short-term adverse hemodynamic consequences. Furthermore, increased afterload may result in infarct expansion and left ventricular dilatation, which will impair left ventricular function still further. Interruption of the cycle of vasoconstriction and worsening left ventricular failure by angiotensin converting enzyme inhibitors may reduce the incidence of heart failure after myocardial infarction.

Aldosterone↗
PubMed1988

Comparison of the effects of chronic oral therapy with atenolol and sotalol on ventricular monophasic action potential duration and effective refractory period.

The effects of 4 weeks' therapy with atenolol, 50 mg twice daily, and sotalol, 160 mg twice daily, on ventricular monophasic action potential duration (MAPD90) and effective refractory period (VERP) are compared in a randomized cross-over study in 10 patients with stable angina pectoris undergoing elective cardiac catheterization. At matched ventricular pacing cycle lengths (range 500 to 1000 msec), MAPD90 was 29 to 42 msec (11.5% to 13.4%) longer and VERP was 21 to 32 msec (8.9% to 11.4%) longer on oral sotalol than on oral atenolol. Intravenous sotalol (100 mg) caused a significant lengthening of MAPD90 and VERP during oral atenolol therapy, while intravenous atenolol (10 mg) had no additional effect during oral sotalol therapy. The effects of sotalol on ventricular repolarization and refractory period persist over and above any adaptational response to beta-receptor blockade that may occur during chronic therapy.

Action Potentials↗
PubMed1988

The Lambeth Conventions: guidelines for the study of arrhythmias in ischaemia infarction, and reperfusion.

The Lambeth Conventions are guidelines intended to be of practical value in the investigation of arrhythmias induced by ischaemia, infarction, and reperfusion. They cover the design and execution of experiments and the definition, classification, quantification, and analysis of arrhythmias. Investigators are encouraged to adopt the conventions in the hope that this will improve uniformity and interlaboratory comparisons.

Animals↗
PubMed1988

Assessment of coronary artery bypass graft flow by intraoperative Doppler ultrasound technique.

A high frequency (10 MHz) Doppler ultrasound pencil probe was used to estimate flow in coronary artery bypass grafts in vitro and during cardiac surgery. In vitro, increasing the angle of the Doppler transducer in relation to flow caused underestimation of the Doppler derived flow, and using the external rather than internal vessel diameter to calculate cross sectional area caused significant overestimation. This overestimation was considerably greater for the internal mammary artery. Accurate flow estimation was obtained in vitro by the Doppler technique, but considerable variation occurred in patients studied during coronary artery bypass surgery. In conclusion, intraoperative Doppler ultrasound provides a qualitative assessment of phasic flow in coronary artery bypass grafts but is less accurate in quantifying absolute flow in these patients.

Adult↗
PubMed1988

A comparison of the long-term effects of sotalol and atenolol on QT interval and arrhythmias after myocardial infarction.

In order to dissociate the Class III effects of sotalol on QT interval and arrhythmias from those of chronic beta-receptor blockade, we compared the effects of sotalol 160 mg b.d. and atenolol 50 mg b.d. in a double-blind crossover study of 103 patients followed for one year after discharge following acute myocardial infarction. Sotalol caused a highly significant lengthening of the absolute and corrected QT (QTc) interval over atenolol which was apparent by day 6 and persisted unchanged throughout the follow-up period. The increase in QT interval averaged 43 ms (9%). Sotalol blunted the increase in ventricular premature beat frequency on ambulatory monitoring which occurred with atenolol, although direct comparison of arrhythmia frequency between the groups receiving atenolol and sotalol revealed no significant difference. Marked lengthening of QTc interval (greater than 500 ms) was observed on 29 occasions in patients receiving sotalol, most commonly at day 6, but no episodes of polymorphic ventricular tachycardia were recorded. The Class III action of sotalol persists over and above any response to beta-blockade during a one-year follow-up period. In a population with a low incidence of spontaneous arrhythmias, however, there was only a modest difference in antiarrhythmic efficacy between atenolol and sotalol. Episodes of marked lengthening of QT interval induced by sotalol in the absence of other adverse factors need not be arrhythmogenic.

Adult↗
PubMed1987

Misuse of intravenous verapamil in patients with ventricular tachycardia.

Intravenous verapamil is effective in the acute termination of supraventricular tachycardia but is also used for broad-complex tachycardia when the diagnosis is uncertain. This study analysed the responses to verapamil in 57 episodes of ventricular tachycardia, incorrectly diagnosed as supraventricular tachycardia, in 32 patients. Diagnostic electrocardiographic features of ventricular tachycardia were present in 81% of episodes. Intravenous verapamil (mean dose 9.8 mg) failed to terminate the tachycardia in 45 episodes (79%). 2 patients sustained cardiac arrest after verapamil (1 ventricular fibrillation, 1 asystole), and in 22 episodes severe hypotension occurred. At least one serious adverse effect occurred in 19 patients (59%). Sinus rhythm was restored after verapamil on 10 occasions in 6 patients. Verapamil is ineffective and potentially hazardous in most patients with ventricular tachycardia. It should not be used to treat broad-complex tachycardia unless a supraventricular origin has been established.

Adult↗
PubMed1987

Clinical usefulness of the Vaughan Williams classification system.

The clinical usefulness of the Vaughan Williams classification scheme is limited by the complexity of the mechanisms of arrhythmia formation in man, which offer multiple potential sites for intervention. The properties of antiarrhythmic drugs may be considerably altered in abnormal myocardium. Despite these limitations, however, the classification provides a valuable conceptual framework for the understanding of the clinical electrophysiological properties of antiarrhythmic drugs and for their use.

Anti-Arrhythmia Agents↗