Sepsis and Tachycardia – Aetiologic Factors

During sepsis, the sympathetic nervous system plays a key role in maintaining cardiac output and blood pressure. This is achieved through changes in heart rate, contractility, and vascular tone. The proper function of the baroreflex system is important for maintaining haemodynamic homeostasis. Tachycardia (increased heart rate) in the early phases of sepsis becomes a crucial mechanism for compensating the decrease in stroke volume (SV) and indicates the efficacy of baroreflex activity. Adequate volume resuscitation often decreases heart rate due to the compensatory origin of tachycardia (Morelli et al. 2016).

Tachycardia is very common in septic patients in the ICU. In septic shock, the baroreflex response is often impaired due to high levels of catecholamines, leading to a hyper-adrenergic state. This results in persistent tachycardia even after adequate fluid resuscitation in many septic shock patients, which is a sign of excessive sympathetic stimulation (Baygin and Kararmaz 2018).

Patients who were tachycardic 24 hours after starting norepinephrine infusion have a three-time higher risk of death than those without tachycardia. This may be due to an exhausted compensatory reflex mechanism. Persistent tachycardia can harm the heart by increasing oxygen demand, reducing diastolic filling, and causing direct cardiotoxicity (Domizi et al. 2020).

Studies report that the incidence of atrial fibrillation (AF) in septic patients is nearly 25.5%. This number increases to 31.6% for those in the ICU. Patients who have AF during sepsis have a higher five-year risk of hospitalisation for heart failure, ischaemic stroke and death compared to those without AF (Vélez-Gimón 2021). Heart failure (low left ventricular ejection fraction) and sepsis, independently, increase the risk of arrhythmias. AF is a common supraventricular arrhythmia in sepsis, accounting for up to 70% of cases. Rate control is the preferred treatment in ICU patients, as the majority will convert back to normal sinus rhythm once their acute illness has been resolved. A study of critically ill patients with AF showed that 81% returned to normal sinus rhythm via rate control alone (Jones et al. 2021).