Atrial Fibrillation Post Coronary Artery Bypass Grafting Surgery Incidence and Risk factors

DISCUSSION

Around one-third of patients who undergo cardiac surgery develop atrial fibrillation, which is associated with an increase in adverse events across all quantitative outcomes of care, as well as an increase in hospital resource use and, as a result, the cost of care.¹Postoperative atrial fibrillation is the most prevalent arrhythmia post cardiac surgery. This arrhythmia is becoming more frequent as a result of an increase in the number of older people receiving cardiac surgery. It's uncertain how often POAF is after heart surgery. The reported incidences range from 10% to 65%. Due to the fact that the studies assessing AF following CABG varied in terms of baseline patient characteristics, AF criteria, operation types, and detection methods, the range is wide. POAF is estimated to occur in roughly 30% of patients following pure CABG surgery, 40% following valve replacement or repair, and approximately 50% following combined CABG and valvular surgeries.¹⁴

In our study, the rate of POAF was 22.22 percent, with 50 patients out of 225 underwent isolated CABG operations over the course of two years. The incidence of POAF was 22.22 percent in this investigation, which matched the findings. According to the most recent STS data report¹⁵, 24.9 percent of patients who underwent coronary artery surgery developed new onset of atrial fibrillation. The factors underlying the AF onset following heart surgery are still unknown. Pericardial inflammation, transcellular fluid and electrolyte shifts, metabolic abnormalities, catecholamine elevation, autonomic discord, and atrial stretch are all believed to play a role in causing atrial fibrillation either alone or in concert. The atrial refractory period is shortened as a result of these circumstances, which slows atrial conduction. The atrioventricular node is excited as a result of the re-entry wavelets, causing fast and irregular ventricular contractions.¹⁶

POAF has been linked to increased risk of ICU readmission, longer intensive care unit stay, longer hospital stay, and higher hospital expenses in studies.

Detecting a population who are at increased risk of POAF allows for more targeted preventive and therapeutic measures that would decrease the overall cost.

In our study, we targeted 50 cases who developed new-onset atrial fibrillation post coronary artery surgeries.

In the current study, atrial fibrillation peak incidence was in the second day postoperative then the third day postoperative. Similar results were obtained in a study POAF most commonly occurs in the 2^nd and 3^rd days postop, respectively.¹⁷ In another study, before the end of postoperative days 4 and 6, 70 percent and 94 percent of CABG patients developed POAF, respectively.¹⁸

In our study, we found that old age was an extremely important risk factor for POAF. Elderly patients (esp. above 55years) were more likely to develop POAF than younger ages with a significant p-value (0.01). Also, males were more susceptible to develop POAF than females in our study. According to Aranki et al., old age and male gender were risk factors for atrial fibrillation following CABG. ¹⁸

Also, Leitch et al. found that age represents the most important independent prognosticator of atrial fibrillation.¹⁹ Per decade of advanced age, the incidence increases by at least 50%.¹⁹In the general population, older age also predicts atrial fibrillation, probably due to greater atrial fibrosis and dilatation.²⁰Men tend to be more prone than women to develop atrial fibrillation after CABG.²¹

The incidence of POAF was just 0.8 percent in patients under the age of 50 who received CABG (which made up 8.7% of our sample). OPCAB was found to be linked to a lower risk of POAF among men and in patients younger than 65 years.²²

According to one study, there is a 75 percent rise in the risk of having AF for every ten years of age. After 50 years, we discovered a considerable increase in the occurrence of POAF with each passing decade: 1.8 percent in patients under the age of 50, 10.79 percent in those between the ages of 50 and 59, 19.25 percent in those between the ages of 60 and 69, 28.22 percent in those between the ages of 70 and 79, and 50 percent in those over the age of 80.⁵

The onset of POAF is linked to a number of risk factors classified as: preoperative, intraoperative, and postoperative. An increased risk of atrial fibrillation was associated with advanced age, smoking, left ventricular enlargement, and renal impairment in preoperative patients.²³

In our study, 24% of patients who experienced POAF were smokers, which represents a significant finding. Because these smokers may have COPD, they frequently have ventilation-perfusion (V/Q) mismatch, resulting in arterial hypoxemia. Poor ventilating mechanics and atelectasis of the lungs can increase the V/Q mismatch following surgery.²³

In our study, there is a great relationship between hypertension and POAF. More than 75% of POAF cases were hypertensive. In a study by Patel et al., it showed that history of hypertension is predictive for POAF, hypertensive heart commonly associated with left ventricular hypertrophy and myocardial fibrosis, which can provide a proper substrate for generation of POAF²⁴, which can be related to the concomitant fibrosis and dispersion of atrial refractoriness⁶

Patients who had a history of diabetes mellitus showed an insignificant difference in the development of postoperative atrial fibrillation.²³ However, Echahidi et al. reported that diabetes mellitus and metabolic syndrome are associated with POAF²⁵, the study reported by Tsai et al. revealed that diabetes mellitus is a significant risk factor fopostoperative atrial fibrillation.²⁶

Some studies revealed preoperative renal dysfunction as a predictor opostoperative atrial fibrillation because of ischemia, atheroembolism, and systemic inflammation²⁷. This was similar to the result of Tsai and colleague.²⁶However, in our study, preoperative renal impairment is not a significant risk factor for developing POAF.

Patients with POAF have a large left atrium diameter as compared with patients without POAF in the present study. Similar to the previous report, Echahidi et al. showed that enlarged left atrium represents a risk factor for developing POAF²⁵, which was similar to the findings of Mostafa and colleague²⁸, as POAF risk has been linked to atrial hypertrophy prior to surgery. POAF following CABG was also predicted by preoperative refractoriness dispersion and a large PR delay. Uncontrolled ventricular rate and congestive heart failure have been linked to atrial stretch, apoptosis, and myolysis, resulting in atrial structural abnormalities.

Benjamin et al. demonstrated that congestive heart failure predisposes to atrial fibrillation.²⁹ This is consistent with our findings that patients having lower ejection fractions were predisposed to POAF more than patients with higher ejection fractions. Mostafa et al. demonstrated that a history of heart failure is a preoperative risk factor for POAF development.²⁸ Also, Sanders et al. found that those with congestive heart failure are more vulnerable to AF because they have a longer p-wave, a longer sinus node recovery time, and a longer refractory period at the right atrial wall. As a result, prolonged conduction time is connected to significantly disrupted substrates, as is in the case of longer iso-electric intervals and a higher percentage of double potentials. Chronic dilated atria, a result of congestive heart failure, appear to be the cause of these pro-arrhythmic alterations.³⁰ 

Some studies³⁰ demonstrated that Patients with previous ischemic insults or a history of myocardial infarction were more vulnerable to develop POAF than other ones, and this may be related to poor left ventricular function, dilated dimensions, and myocardial ischemia.

Prolonged cross-clamp time and prolonged cardiopulmonary bypass time were two intraoperative variables linked to POAF. Cardiopulmonary bypass restricts blood flow to the heart, which can lead to atrial ischemia-reperfusion damage and POAF. Prolonged procedure times were linked to an increased risk postoperative atrial fibrillation in certain studies. Also cross-clamp time has been related to POAF.³¹POAF was also discovered to be more common in patients who had extended bypass and cross-clamp periods. Due to prolonged periods of ischemia and insufficient atrial protection with current cardioplegia procedures, it was hypothesized that atrial ischemia was most likely the cause of AF in vulnerable patients. Several studies back this notion, showing that extended cardiopulmonary bypass and cross-clamp periods are independent predictors of atrial fibrillation.³²

These results agreed with that postoperative atrial fibrillation is the outcome of repeated re-entry wavelets caused by "atrial refractoriness dispersion." An atrial structural substrate is required for dispersion of atrial refractoriness. Old age, obesity, diabetes, hypertension, left atrial enlargement could all have a role. During and after surgery, surgical atrial damage and atrial ischemia may also lead to the formation of the structural substrate. Inflammation, oxidative stress, and hereditary factors are all thought to play a role. Once these conditions are present, an activating event, such as a premature atrial contraction, electrolyte imbalance, and/or increased adrenergic or vagal activation, will induce postoperative atrial fibrillation.³³

Hypokalemia is a risk factor for postoperative arrhythmia³⁴. In the current study, hypokalemia was a significant risk factor in patients who experienced POAF. Serum potassium levels in patients with POAF was (3.47±0.58).

In the study reported by Hashemzadeh and colleagues, inotropic use was an important risk factor for developing postoperative atrial fibrillation.²³

ECG early postoperative showing ischemic changes, e.g., ST-segment elevation and hyperacute T-wave, is also a predictor for POAF. This may be attributed to atrial ischemia that affects atrial refractoriness and conduction.

Intensive care unit (ICU) stay duration was increased with patients who experienced POAF in our study. This finding is supported by several studies.²³ This is caused to a circulatory standstill in the left atrium, which causes an embolus to occur.³⁴

Ventilation hours in ICU and Intra-aortic balloon pumps are factors that didn't much affect the risk of POAF, as shown in our study.

Patients who developed atrial fibrillation following surgery were much less likely to be on beta-blockers than those who did not develop AF. According to the findings of this study, preoperative beta-blockers that are taken throughout the pre-and postoperative periods decrease postoperative atrial fibrillation.

CONCLUSION

Atrial fibrillation is the most prevalent arrhythmic consequence following heart surgery.  About 10% to 60% of patients who undergo coronary artery bypass graft and valvular surgery experience new-onset atrial fibrillation. Although it is a benign complication, it can increase mortality, morbidity, duration of ICU stays, and hospital costs.

In our study, we found that low ejection fraction, dilated left atrium, hypertension, smoking, old age, male gender, prolonged bypass time, prolonged cross-clamping time, renal impairment, previous myocardial infarction, low temperatures on bypass, early ischemic changes postoperative, hypokalemia, use of adrenaline and noradrenaline, all of these factors were found to be significant predictors for developing atrial fibrillation after cardiac surgery.

To lower the incidence of postoperative AF, the well-known preoperative risk factors can be treated before surgery