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Biomedical subjects

H Swanton

Publications and source records attributed to H Swanton.

29 records · Page 2Linked to original sources
PubMed1987

Effects of nifedipine on coronary perfusion; recent assessment by parametric digital subtraction.

The effects of nifedipine on myocardial perfusion abnormalities were investigated in 6 patients with left coronary artery disease using a digital angiographic method. Selective left coronary angiograms were digitized on-line into a 256 x 256 pixel matrix, approximately 20 ECG-gated end-diastolic frames being acquired during each coronary injection. After background subtraction, parametric analysis was undertaken, measuring sequential changes in contrast opacification against time. Isochrone maps were derived showing the distribution of times to attainment of peak contrast density throughout the left ventricle (the Tmax image) reflecting myocardial perfusion, and of times to arrival of half peak opacification (the T1/2max image) as an index of coronary flow. At basal heart rate (fixed by pacing) mean Tmax was attained in well supplied myocardium at the 7th cardiac cycle, and at the 9th cardiac cycle in the least perfused territory. Overdrive pacing reduced arrival times by 2-3 cycles, but inhomogeneity persisted. After sublingual nifedipine, contrast arrival was significantly accelerated by a mean of two cardiac cycles in poorly perfused regions, and by one cardiac cycle elsewhere. After nifedipine, overdrive pacing shortened Tmax and T1/2max most markedly in the least supplied territory. Results with this new technique indicate that nifedipine has beneficial effects on regional malperfusion in coronary disease.

Aged↗
PubMed1986

Use of monophasic action potential recordings during routine coronary-artery bypass surgery as an index of localised myocardial ischaemia.

In 8 patients undergoing routine coronary-artery bypass surgery, monophasic action potentials (MAPs) were measured by means of a hand-held pressure contact electrode to provide an index of local ischaemic changes. 4 patients received left internal mammary anastomoses (LIMA), and there were a total of 27 saphenous vein grafts (SVG). After completion of all grafts blood-flow to the myocardium was reduced for 90 s by means of different permutations of SVG and LIMA occlusion, either on or off bypass. In all patients MAPs indicated typical ischaemic changes. The high sensitivity of the method enables the study to be completed quickly and without hazard to the patient. The technique provides a new means to assess local ischaemia, the viability of specific areas of myocardium, and the efficiency of individual grafts during surgery.

Action Potentials↗
PubMed1984

Effect of nitroglycerin on the electrical changes of early or subendocardial ischaemia evaluated by monophasic action potential recordings.

Intracavitary recording of monophasic action potentials (MAP) is a sensitive means of detecting the electrophysiological effects of early or subendocardial ischaemia. The effects of nitroglycerin (NTG) on the MAP was evaluated during pacing-induced angina in seven patients with localised, reversible ischaemia. Recordings from the ischaemic zone demonstrated a decrease in MAP amplitude and an abnormal rate-corrected shortening of MAP repolarisation. The "control" right ventricular MAP showed only the expected rate-dependent decrease in duration throughout the pacing stress test. The ischaemic MAP were unchanged following the intracoronary administration of NTG (100 micrograms). In contrast, intravenous NTG (200 to 300 micrograms) produced a normalisation of MAP amplitude and duration in spite of continuous pacing at the angina-provoking rate. These changes were preceded by a fall in aortic pressure (from mean 123/84 to 96/62) and subsequent lowering of the rate-pressure product. The major beneficial effects of NTG on the early electrical changes of pacing-induced ischaemia are thus related to decreased oxygen demand due to reduction in cardiac preload.

Action Potentials↗
PubMed1983

Intracardiac electrode detection of early ischaemia in man.

We have evaluated an intracardiac technique for the study of the electrophysiological patterns of early or subendocardial ischaemia in man. Simultaneous recordings of the paced endocardial evoked response and monophasic action potentials were obtained during pacing stress testing in 10 patients with reversible myocardial ischaemia. Early patterns of change occurred in both these recordings in response to regional ischaemia. Abnormal rate corrected shortening of the local repolarisation time in the paced endocardial evoked response from the left ventricular ischaemic zone diverging from control non-ischaemic values by a mean of 10.6% was paralleled by decreases in the simultaneous paced monophasic action potentials duration. A differential delay in the local activation time and conduction was also documented by the paced endocardial evoked response and monophasic action potential electrodes. Non-ischaemic control zones showed no changes in the pattern of activation and repolarisation. Disparate repolarisation times and asynchronous activation within the myocardium were thus consistently demonstrated during regional ischaemia. These changes in the endocardial paced evoked response and monophasic action potentials always preceded the appearance and regression of the clinical ischaemia. Intracavitary recordings may thus provide earlier and more sensitive detection of regional ischaemia during cardiac catheterisation or coronary artery surgery. The study of the patterns of activation and response could permit the assessment of interventions on the early electrical changes of ischaemia, and may bridge the gap between in vitro studies and the electrophysiological studies performed upon the intact heart.

Action Potentials↗
PubMed1983

The role of nitrates on regional subendocardial ischaemia--studies with endocardial monophasic action potentials during pacing-induced angina.

Intracavitary recording of monophasic action potentials (MAP) is a sensitive means of detecting the electrophysiological effects of early or subendocardial ischaemia. The effect of nitroglycerin on the MAP was evaluated during pacing-induced angina in seven patients with localized, reversible ischaemia. Recordings from the ischaemic zone demonstrated a decrease in MAP amplitude and an abnormal rate-corrected shortening of MAP repolarization. The "control" right ventricular MAP showed only the expected rate-dependent decrease in duration throughout the pacing stress test. The ischaemic MAP were unchanged following the intracoronary administration of 100 micrograms nitroglycerin. In contrast, 200-300 micrograms intravenous nitroglycerin produced a normalization of MAP amplitude and duration in spite of continuous pacing at the angina-provoking rate. These changes were preceded by a fall in aortic pressure (from mean 123/84 to 96/62) and subsequent lowering of the rate-pressure product. The major beneficial effects of nitroglycerin on the early electrical changes of pacing-induced ischaemia are thus related to decreased oxygen demand due to cardiac unloading.

Action Potentials↗
PubMedDate not supplied

Amiodarone.

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Amiodarone↗