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Biomedical subjects

K M Fox

Publications and source records attributed to K M Fox.

At least 181 records · Page 10Linked to original sources
PubMed1984

Effect of partial agonist activity in beta blockers in severe angina pectoris: a double blind comparison of pindolol and atenolol.

The use of beta adrenoceptor blockade in the treatment of rest angina is controversial, and the effects on severe angina of partial agonist activity in beta blockers are unknown. Eight patients with effort angina and seven with effort and nocturnal angina and severe coronary artery disease were studied initially when they were not taking any antianginal drugs. Pindolol 5 mg thrice daily (with partial agonist activity) and atenolol 100 mg daily (without partial agonist activity) were given for five days each in a double blind randomised manner. Diaries of angina were kept and treadmill exercise testing and ambulatory ST monitoring performed during the last 48 hours of each period of treatment. Daytime and nocturnal resting heart rates and the frequency of angina were significantly reduced by atenolol compared with pindolol (p less than 0.01). The duration of exercise was significantly increased and the frequency, duration, and magnitude of daytime and nocturnal episodes of ST segment depression on ambulatory monitoring were reduced by atenolol. Reduction in resting heart rate is important in the treatment of both effort and nocturnal angina. Partial agonist activity in beta adrenoceptor antagonists may be deleterious in patients with severe angina pectoris.

Adrenergic beta-Agonists↗
PubMed1984

Diagnosis of broad complex tachycardias with ambulatory monitoring of atrial electrography.

Simultaneous 24 hour ambulatory monitoring of the surface electrocardiogram and the intra-atrial electrocardiogram was evaluated in eight patients with broad complex tachycardia. The technique using a J shaped atrial pacing wire permitted a distinction between ventricular tachycardia and supraventricular tachycardia in all eight patients. Formal electrophysiological testing would still be required, however, in patients in whom diagnostic doubt remained.

Electrocardiography↗
PubMed1984

Mechanisms of nocturnal angina pectoris: importance of increased myocardial oxygen demand in patients with severe coronary artery disease.

Changes in heart rate before and throughout episodes of ST-segment depression were recorded during ambulatory electrocardiographic monitoring in five patients with daytime and nocturnal resting angina and six patients with daytime angina only, who all had severe obstructive coronary disease. In 16 of 17 nocturnal episodes and in all the daytime episodes the heart rate increased before the onset of ST-segment depression. There were no significant differences in the sequence and magnitude of changes in daytime, nocturnal, painful, or painless episodes. The maximum heart rate during individual episodes preceded the maximum ST-segment depression by a mean 80.7 s and in the majority of episodes the heart rate returned to baseline before the ST segment. Thus, in severe coronary artery disease the mechanisms producing nocturnal resting ischaemia were apparently similar to those during daytime exertion; increased myocardial oxygen demand not coronary spasm seemed responsible for most of the episodes of nocturnal ischaemia.

Aged↗
PubMed1984

Inability of the ST segment/heart rate slope to predict accurately the severity of coronary artery disease.

Analysis of the ST segment/heart rate slope during exercise testing has been suggested as a method of accurately predicting the presence and severity of coronary artery disease. Exercise tests were performed in 78 patients presenting with the chest pain to determine the maximum ST segment/heart rate slope. In 21 (27%) patients the ST segment/heart rate slope could not be calculated in any electrocardiographic lead. In the remaining 57 (73%) patients the maximum ST segment/heart rate slope accurately predicted the presence or absence of coronary disease in 44 patients (sensitivity 90%, specificity 40%). In addition, the extent of coronary disease was accurately predicted in 24 patients (sensitivity 42%). Thus the maximum ST segment/heart rate slope did not perfectly predict either the presence or the severity of significant coronary artery disease.

Adult↗
PubMed1983

Variable susceptibility to dynamic coronary obstruction: an elusive link between coronary atherosclerosis and angina pectoris.

Growing evidence suggests that dynamic coronary obstructions play an important but elusive role in the genesis of ischemic events. Dynamic coronary obstructions can develop during certain phases of coronary disease as a result of a variable combination of vasoconstriction, arterial wall lesions, and increased thrombotic tendency. In a certain phase of their disease some patients develop dynamic coronary obstruction, while others with a similar degree of fixed atherosclerotic obstruction do not.

Angina Pectoris↗
PubMed1983

Safety and effectiveness of a portable external automatic defibrillator-pacemaker.

Sudden cardiac death in the community can be reduced by early resuscitation. The commonest arrhythmia encountered in this setting is ventricular fibrillation. A portable external automatic defibrillator-pacing machine for use by emergency services and laymen after basic training, has recently been introduced. This device has a tongue-abdominal pathway for sensing the electrocardiogram and respiration, as well as delivery of current. In its automatic mode, the machine cannot defibrillate unless the patient's breathing and gag reflex are virtually absent. The decision-making characteristics of the machine were defined in isolation from the patient using simulated ECG signals and recordings of arrhythmias obtained during cardiac surgery and during electrophysiological studies. The pathway was evaluated separately by attaching it to a conventional defibrillator and using it in the elective cardioversion of 15 patients. Electrode sites were examined and creatine phosphokinase (CPK) and creatinine phosphokinase isoenzyme (CPKMB) release determined following conversion. Repeated playback of the same 34 minutes of selected recordings showed that decisions were consistent 95% of the time. Automatic pacing always occurred with asystole. ECG signals less than 0.35 mV in amplitude were not recognized, but a manual override switch could be operated in those circumstances where there was failure to act upon fine ventricular fibrillation. Defibrillation of 50% of the recordings of supraventricular and ventricular tachycardia did occur, but this could not have happened in practice unless the patient was unconscious, and in addition, the operator failed to countermand this decision. The tongue-abdominal pathway yielded good recordings of the ECG.(ABSTRACT TRUNCATED AT 250 WORDS)

Creatine Kinase↗
PubMed1983

Precordial electrocardiographic mapping in the identification of patients with left main stem narrowing.

This study was designed to determine if exercise testing using 16-lead precordial mapping can be used to identify patients with left main stem narrowing. In a group of 235 consecutive patients undergoing coronary angiography there were 35 patients with left main stem narrowing. The patients with left main stem disease differed from the others in that not only did they develop extensive S-T segment depression, but more specifically these changes occupied a characteristic position high on the precordium above the usual site of the precordial leads of the 12-lead electrocardiogram. This finding was then tested prospectively in a second group of 100 patients. Fourteen of the 100 patients had left main stem narrowing; the sensitivity and specificity of S- T segment changes high on the precordium in identifying patients with left main stem disease were 82 and 84% respectively. Thus precordial mapping and exercise testing is valuable in the diagnosis of patients with left main stem narrowing. The technique is simple and inexpensive and provides data not available using the conventional precordial leads of the 12-lead electrocardiogram.

Adult↗
PubMed1983

Significance of exercise induced ST segment elevation in patients with previous myocardial infarction.

In order to determine the significance of exercise induced ST segment elevation in patients with previous myocardial infarction, we have studied 156 patients, 26 months (mean) after myocardial infarction. Each patient underwent 16 lead precordial electrocardiographic mapping before, during, and after exercise and in addition coronary arteriography was performed. There was no significant difference in the extent of coronary disease or abnormalities of left ventricular function between patients with exercise induced ST segment elevation that was noted to occur in leads with Q waves and those with ST segment elevation plus depression or those with ST segment depression alone. Patients without exercise induced ST segment changes had fewer coronary arteries involved than those who developed ST segment changes. Nineteen patients with exercise induced ST segment elevation alone underwent coronary artery bypass surgery; in 11 this resulted in complete abolition of the exercise induced ST segment elevation and was associated with symptomatic relief and patent grafts without alteration of left ventricular function. Thus, exercise induced ST segment elevation in patients with previous myocardial infarction should be considered as important as ST segment depression in terms of underlying myocardial ischaemia, coronary anatomy, and left ventricular function.

Adult↗
PubMed1983

Factors influencing R wave amplitude in patients with ischaemic heart disease.

R wave amplitude changes during exercise have been ascribed to alteration in left ventricular volume and their measurement advocated for the improved diagnosis of coronary disease. The reproducibility of exercise QRS changes and their relation to ST segment depression, respiratory pattern, and left ventricular volume during ischaemia were studied in 10 patients with angina and coronary disease. QRS amplitude was measured in a 16 lead precordial map during three identical exercise tests in each patient and left ventricular volume assessed continuously using gated blood pool imaging with a single scintillation probe during manoeuvres to provoke ischaemia. During exercise, QRS amplitude increased or remained unchanged in four patients and fell in six patients in a consistent manner for each patient. R wave amplitude was not affected by changes in respiratory pattern. R wave amplitude did not alter in 33 of 39 episodes of left ventricular volume increase (mean 32%) or decrease (mean 36%) in end-diastolic counts. These findings suggest that precordial R wave changes during ischaemia are not determined primarily by alteration in left ventricular volume or the respiratory pattern. Though reproducible in each patient and following a definite relation to ST segment depression, the variable directional response during exercise suggest that R wave amplitude changes have little diagnostic value.

Adult↗
PubMed1982

Effects of platelet inhibition on myocardial ischaemia.

Ticlopidine, a potent inhibitor of platelet aggregation, was found to have no direct effects on coronary resistance or coronary flow in 5 dogs. To determine whether platelets can be implicated in the pathogenesis of myocardial ischaemia the effects of this drug were studied in 10 patients with proven coronary-artery disease and daily angina pectoris. Each underwent three single-blind treatments: (a) placebo for 2 weeks; (b) ticlopidine 500 mg for 4 weeks; and (c) placebo for 2 weeks. For 4 days after the end of each treatment ambulatory S-T segments were monitored and a record was kept of the reported frequency of chest pain. 4 weeks' treatment with ticlopidine resulted in a significant fall in both the reported frequency of chest pain and the number of episodes of S-T segment depression. This effect was most striking in those episodes of S-T segment depression that occurred without increase in heart rate and in the middle of the night. Thus, although the exact mechanisms remain to be clarified this study suggests that platelets may play an important part in the pathogenesis of myocardial ischaemia.

Angina Pectoris↗
PubMed1982

Facial swelling: a complication of transvenous pacing.

A case of progressive venous thrombosis involving the superior vena cava is reported following implantation of a permanent transvenous pacemaker. Acute symptoms in the arm appeared after 18 months, but the symptoms of superior vena caval obstruction developed gradually, three years after pacemaker insertion. The diagnosis was confirmed by cavography and symptoms resolved with heparin therapy. Long-term anticoagulation is indicated when thrombosis is responsible for this uncommon but important complication of transvenous pacing.

Aged↗
PubMed1982

Measurement of serum C-reactive protein concentration in myocardial ischaemia and infarction.

Serum C-reactive protein (CRP) and creatine kinase (CK) MB levels were measured prospectively in patients with definite myocardial infarction, patients with spontaneous or exercise-induced angina, subjects undergoing coronary arteriography, and patients with non-cardiac chest pain. All individuals with infarction developed raised CRP levels and there was a significant correlation between the peak CRP and CK MB values. The CRP, however, peaked around 50 hours after the onset of pain at a time when the CK MB, which peaked after about 15 hours, had already returned to normal. In 20 patients who recovered uneventfully, CRP levels fell, returning to normal about seven days after infarction in four cases who were followed to this point. In eight complicated cases, including four who died within the first 10 days, the CRP level remained high. Angina alone or coronary arteriography did not cause a rise in the CRP or CK MB concentrations. Increased CRP production is a non-specific response to tissue injury and raised CRP levels in cases of chest pain with a normal CK MB indicated a pathological process other than myocardial infarction. Regular monitoring of CRP levels may also assist in early recognition of intercurrent complications occurring after myocardial infarction.

Angina Pectoris↗