This study is the first observational study to address the clinical and genetic markers affecting the response to prophylactic beta-blockers required for the prevention of POAF after CABG in the Egyptian population.

In this study, POAF was reported in 20.8% of the patients despite the use of beta-blockers for POAF prophylaxis after CABG which is close to that reported by Kertai et al. in their discovery cohort (19.7%) and in their replication cohort (17.1%) [10].

We found that increasing age was the most prominent clinical risk factor for POAF despite prophylaxis with beta-blockers. Notably, aging causes cardiac fiber loss, increased fibrosis, and collagen deposition in the atria, mainly at the sinoatrial node, altering atrial electrical characteristics [2, 14].

In addition, our results showed that the presence of GRK5 SNP rs2230345 T-allele, known as GRK5-Leu41, was independently associated with higher POAF occurrence compared with homozygous Gln41 in CABG patients receiving prophylactic beta-blockers; thus, GRK5 Gln41Leu different genotypes could be used as a genetic marker for the prediction of the response to beta-blockers in POAF prophylaxis. The frequency of the rs2230345 T-allele in Egyptians was found to be 10% which is close to the frequency of south Asians (8%) but lower than Africans (30%) and higher than Europeans (1%) and Eastern Asians (2%).

G protein-coupled receptor kinase 5 is highly expressed in the normal human heart and is encoded by the GRK5 gene. GRK5 regulates catecholamines, which bind and activate adrenergic receptors [15]. The genetic polymorphism in GRK5 SNP rs2230345 (GRK5 122 A > T; Gln41Leu) in which Leucine (Leu) is substituted for glutamine (Gln) causes a gain-of-function for the G-protein receptor kinase. Thus, it leads to enhanced loss-of-function (desensitization) of beta-1 adrenergic receptor (β1AR) during persistent agonist exposure [16, 17] mimicking the effect of beta-blockers in genetic mouse models [17]. The effect of this polymorphism has not been studied before in association with the response to beta-blockers required for POAF prophylaxis in patients undergoing CABG. Nevertheless, studies on patients with heart failure or hypertension yielded conflicting results [11, 18, 19]. In accordance with our findings, a prospective cohort study that included Caucasian and African American heart failure patients reported a detrimental effect on survival in GRK5-Leu41 carriers treated with beta-blockers in Caucasians and among the whole cohort. However, in African American patients, there was no association between GRK5-Gln41Leu polymorphism genotypes and heart failure outcomes [11]. In another cohort of hypertensive patients on beta-blockers, there was no significant difference in the cardiac adverse outcomes (first occurrence of death, nonfatal MI, or stroke) between patients with homozygote Gln-41 or Leu-41 variant. The lack of pharmacogenetic interaction in that study was supported by blood pressure response data, which showed that both Leu41-carriers and Gln41-homozygote-carriers had similar responses to atenolol [18]. In contrast to our findings, a study by Ramalingam et al. on Indian heart failure patients found that patients carrying GRK5 Leu41 variants and receiving beta-blocker therapy showed better ejection fraction and increased hospitalization-free survival compared with patients with wild-type genotype on beta-blockers [19]. The discrepancy between our results and those of Ramalingam et al. [19] could be attributed to several reasons. First, Ramalingham et al. reported a significant reduction in the beta-blocker (carvedilol) dose in the GRK5 Leu41 carriers from the initial dose to the final one. Yet, there was no change in the doses of the GRK4 Gln-41 carriers from baseline to the end of the study. Second, the authors did not clarify the other medications administered by the GRK5 Leu41 and GRK5 Gln41 carriers specifically and whether they were similar or not. Hence, this could raise the doubt if the beneficial effects observed in the GRK5 Leu-41 carriers were all attributed to the effect of beta-blockers or other medications as well.

In the current study, another genetic polymorphism in the GRK5 gene (rs3740563; A > C) was studied in association with the development of POAF. Our results revealed that patients with AC or AA variants had a higher risk for the development of POAF despite prophylactic beta-blockers; however, this SNP had a limited role in predicting the response to beta-blockers in POAF prophylaxis. The frequency of the A-allele in Egyptians was 10% which is almost similar to Europeans (9%) but lower than the other populations. Similarly, Kertai et al. found that the risk allele “A” of rs3740563 was significantly associated with a higher risk of POAF despite perioperative beta-blocker prophylaxis. Even though the potential mechanism of action of this SNP was not studied by Kertai et al., the authors postulated that it might be mediated via DNA transcription regulation [10]. Although Li et al. did not study the effect of this SNP on the response to beta-blockers, they found that each additional copy of minor allele A in Asian patients was associated with a 1.31-fold increased risk of development of POAF in the discovery cohort (OR = 1.31; 95% CI: 1.09–1.58, p-value = 0.005) but it was replicated in the validation cohort without significance [20].

The third GRK5 SNP evaluated was rs10787959 (A > G). The frequency of the rs10787959 A-allele in Egyptians was 31% which is almost similar to Europeans (28%) but lower than the other populations. In the current study, there was no association between this SNP and POAF development in beta-blockers-users. In alignment with our study, Liu et al. could not find an association between this SNP and POAF development in the validation study that was done on Asians regardless of beta-blocker use [20]. In contrast to our results, Kertai et al. found a significant association between the A-variant of the rs10787959 SNP and POAF despite perioperative beta-blocker use [10]. The variation between these two studies could be attributed to difference in sample sizes, patient’s comorbidities, and medications administered between the studies.

It is worth mentioning that only one published study so far has studied the effect of ADRB1 rs1801253 (Arg389Gly) polymorphism on the development of POAF following cardiac surgeries. Jeff et al. found that those with the ADRB1 Gly389Gly variant had a higher incidence of POAF following cardiac surgery compared to patients with the wild homozygous genotype (Arg389Arg). In contrast, they discovered that the link between the Gly389Gly variation and the risk of postoperative AF was no longer apparent in a subgroup of patients receiving perioperative beta-blockers, demonstrating that the risk of POAF was modulated by beta-blockers [21]. Results of the current study were in agreement with the aforementioned study as we could not find an association between Arg389Gly polymorphism and POAF in patients receiving perioperative beta-blockers for POAF prophylaxis. Our data revealed that the frequency of the rs1801253 G-allele in Egyptians was 41% which is similar to Africans (43%), lower than Europeans (32%) but higher than Eastern Asians (21%), and Southern Asians (27%).

This study has some limitations. Our cohort study consisted only of Egyptians. Thus, replication of our study to include different ethnic populations is recommended. In addition, further studies will be required to identify other clinical or genetic factors that may affect the response to beta-blockers. Machine learning techniques could be applied in future studies to identify novel genetic variants giving further predictive insights.

The current study has concluded that genetic polymorphism in GRK5 gene has an impact on the response to prophylactic beta-blockers in patients undergoing CABG. The use of prophylactic beta-blockers in GRK5-Leu41 variant allele carriers who are undergoing CABG is of no benefit; hence, other prophylactic medications with different mechanistic bases could be of more benefit in this specific population.