Association between red blood cell parameters & atrial fibrillation after acute myocardial infarction

Sir,

We read with interest the study by Distelmaier and colleagues1. They analyzed the association between the blood parameters and new-onset atrial fibrillation (AF) after acute myocardial infarction (MI), as diagnosed with coronary angiography. The patient group with the occurrence of AF after AMI had a significantly higher level of haemoglobin and higher red blood cell counts compared with the group without. The odds ratios of haemoglobin and the red blood cell count for the occurrence of AF were significantly high. The occurrence of AF is multifactorial, and the parameters predictive of AF remain to be explored; therefore, identifying such parameters would be helpful to prevent the development of subsequent adverse complications and mortality in the management of MI patients. The findings of this study are thus valuable, although the authors did not fully seem to state a hypothesis and perspectives for the reported epiphenomenon.

In another recent study conducted by Oda et al2, a higher level of haemoglobin was reported to be associated with AF. Both studies12 appear to have found similar results, which indicate that it is necessary to think about the meaning of red blood cell parameters.

In our clinical experience, a good parameter for the occurrence of AF is ageing, which is referred to as an oxidative condition3. We have paid special attention to the relevance of oxidative stress in cardiometabolic pathologies. Notably, oxidative stress conditions are involved in the pathogenesis of AF34. Thus, we wonder if some patients had a relatively high red blood cell level (even though it was not at the level of polycytemia), which could have led to oxidative stress. For instance, information obtained from patients with pathologies related to hypoxia, including sleep apnoea syndrome, and measurement of oxidative stress markers should be included in future studies. Additional information about abdominal obesity and the smoking status (which are also associated with oxidative stress) should also be included. Distelmaier group study did not offer such data1.

In the Oda group study2, erythropoiesis, a factor associated with increased red blood cell parameters, was discussed in terms of the occurrence of AF. This seems to be an important point, considering that hypoxia can also stimulate erythropoiesis. Measuring the erythropoietin level may be of interest in future work. Linked to erythropoiesis, iron metabolism is another point to debate regarding the association between the red cell biology and heart pathophysiology. Ferritin has already been reported to be associated with an increased cardiovascular risk5. Measurement of the iron metabolism, therefore, needs to be simultaneously considered.

Hyperhaemodynamic states (accompanied with hyperviscosity)2 and impaired rheological properties6 caused by increased red blood cell parameters would be additional points, because these can enhance oxidative stress. Also, a relative decrease in the plasma volume (even if it is not at the level of obvious dehydration) leads to increased red blood cell parameters. Although this cannot be thought to contribute directly to the occurrence of AF, it may provide a potential basis for AF if overlapping some conditions (e.g. sympathetic nerve activation and oxidative stress) are also present7.

The fact that the haematocrit level did not show a similar impact on the occurrence of AF in a manner proportional to the haemoglobin and red blood cell counts in this study1 is seemingly confusing. This implies that subsequent investigation is necessary, while it may also lead to a hint of hypothesis about the association between red blood cell parameters and AF. For more sophisticated future research based on this study1, a detailed analysis of the heart rates and blood pressure levels at admission and prior to the onset of AF, as well as unification of the timing of data collection (blood and electrocardiogram examinations), clarification of the underlying diseases (i.e. valvular heart diseases)8, and therapeutic situations (including fluid therapy) should be included. Although we outlined an aspect of cardiometabolic pathologies from the viewpoint of oxidative stress, further studies with hypotheses from a wide range of research fields are called for, because these will be useful to identify predictors of the onset of AF during the post-MI management.