The effect on the heart of hypoxaemia in patients with severe coronary artery disease

Abstract

SummaryThe aim of the study was to examine the effect of Key wordsHypoxia. Heart; ischaemia, coronary occlusion.Smokers and overweight patients may have ischaemic heart disease and following upper abdominal or thoracic surgery such patients usually have prolonged and profound postoperative hypoxaemia [ 11. The worst hypoxaemia is often on the second and third nights but can be maximal on the fourth. In these circumstances, profound oxygen desaturation (Sao? < 80%) can occur without being noticed and may last for several hours, almost invariably when the patient falls asleep. Clinical practice does not normally include the administration of oxygen beyond the first 24 h postoperatively and this raises the question about the significance of episodic hypoxaemia in patients with ischaemic heart disease. The effect of hypoxaemia on the heart has been discussed in a number of recent editorials [ 2 4 ] but surprisingly little is known about the effects of hypoxaemia on the diseased heart, although it is suggested that sleep-related hypoxaemia may precipitate potentially serious arrhythmias [2]. The role of hypoxaemia in precipitating myocardial ischaemia and infarction is controversial. It has been proposed that in susceptible patients some episodes of postoperative myocardial infarction and cardiac failure are caused by hypoxaemia and that oxygen therapy would therefore be beneficial [3]. However, an editorial in the Lancet [4] claimed that there is insufficient evidence that postoperative oxygen therapy either reduces the amount of ischaemia in patients with coronary artery disease or improves outcome.In an extensive review of peri-operative morbidity, Mangano [5] pointed out that the incidence of postoperative myocardial infarction in the general population is low (0.1-0.7%). However, the risk of postoperative myocardial infarction increases for those who have suffered a previous infarct (1.9-7.7%) and the rate is very much higher, up to 37%, in those who have had an infarction within the previous 3 months. The mortality from postoperative myocardial infarction is considerable (36-70%) [5]. Knorring [6] showed that 87% of the postoperative infarctions occurred during the first 3 postoperative days with a peak incidence on the second day. In another study by Rao et al. [7], 89-100% of reinfarctions occurred within the first 3 postoperative days, with a peak incidence on the third postoperative day, 50% of these being silent infarctions. It is tempting to speculate that this temporal relationship between myocardial infarction and hypoxaemia may indicate that postoperative hypoxaemia is a causative factor.Factors associated with significantly increased postoperative reinfarction rates include: pre-operative hypertension, intra-operative hypotensive episodes and non-cardiac thoracic or upper abdominal operations of more than 3 h H

Routine use of oxygen in the treatment of myocardial infarction: systematic review

“…The secondary outcomes of ventricular tachycardia occurrence and use of opiates were not different between the two groups, despite a higher prevalence of severe hypoxaemia in the group receiving air. These findings are consistent with previous studies that reported no relationship between hypoxia and ischaemia in coronary artery disease,36 37 but contrasted with another study that demonstrated a temporal relationship between nocturnal hypoxaemia and both ST-segment depression and arrhythmia after a MI 38…”

Effect of acute changes in oxygen tension on flow-mediated dilation. Relation to cardiovascular risk

“…A myocardial infarction or decompensated heart failure may be accompanied by local and generalized hypoxia and spontaneous nocturnal hypoxia with desaturation for hours is a frequent phenomenon in patients with severe coronary artery disease (11). Patients with coronary artery disease also respond differently to high altitudes than healthy persons.…”

Influence of oxygen tension on myocardial performance. Evaluation by tissue Doppler imaging

“…Spontaneous nocturnal hypoxia with desaturation for hours is a frequent phenomenon in patients with severe coronary artery disease [2]. Left atrial, left ventricular (LV), and right ventricular (RV) end-systolic diameter fall during simulated extreme altitude [3] and during moderate altitude exposure [4].…”