Sinus tachycardia is a heart rate >100 beats per minute originating from the sinoatrial (SA) node. While it can be a physiological response to stress, in the post-cardiac surgery setting, it often signals an underlying problem requiring prompt evaluation.
After procedures such as coronary artery bypass grafting (CABG), valve replacement, or congenital heart repair, the body undergoes significant physiological changes. Factors like surgical trauma, anesthesia effects, blood loss, pain, and postoperative complications can trigger sinus tachycardia.
Persistent sinus tachycardia post-surgery is not just a benign finding — it may indicate hypovolemia, inadequate oxygen delivery, infection, or myocardial dysfunction.
A simple, memorable way to recall the main causes in this context is the ACTIVE MOM mnemonic.
Mnemonic – ACTIVE MOM
| Letter | Cause | Typical Clinical Scenario |
|---|---|---|
| A | Anaemia | Post-op blood loss, hemodilution |
| C | Cardiogenic shock | LV dysfunction post-surgery |
| T | Temperature ↑ | Postoperative fever from infection or inflammation |
| I | Inotropes | Dobutamine, adrenaline side effects |
| V | Volume deficit | Hypovolemia due to bleeding or fluid loss |
| E | Emotions & Pain | Anxiety, inadequate analgesia |
| M | Massive bleeding | Surgical site bleeding, chest drain output |
| O | Oxygenation poor | Hypoxia from atelectasis, pneumonia |
| M | Malignant hyperthermia | Rare anesthesia-related emergency |
A – Anaemia
Why It Happens Post-Surgery
- Blood loss during surgery and from postoperative drains.
- Hemodilution from cardiopulmonary bypass priming solutions.
- Reduced red blood cell mass decreases oxygen-carrying capacity.
Pathophysiology
The heart compensates for reduced oxygen delivery by increasing rate to maintain oxygen supply to tissues.
Clinical Signs
- Pallor, fatigue
- Low hemoglobin/hematocrit on labs
- Orthostatic symptoms
Management
- Identify bleeding sources
- Blood transfusion when Hb <7–8 g/dL (individualized for cardiac patients)
- Iron supplementation if chronic anemia present
C – Cardiogenic Shock
Definition
Inadequate cardiac output due to myocardial dysfunction, often after valve surgery or CABG.
Causes After Heart Surgery
- Myocardial stunning from cardiopulmonary bypass.
- Intraoperative myocardial infarction.
- Valve malfunction.
Signs
- Hypotension, low urine output, cool extremities
- Elevated filling pressures (PA catheter)
Management
- Optimize preload and afterload
- Use inotropes cautiously (may worsen tachycardia)
- Consider mechanical circulatory support (IABP, ECMO)
T – Temperature ↑
Causes
- Infective: Surgical site infection, pneumonia, catheter-related sepsis.
- Non-infective: Postpericardiotomy syndrome, blood transfusion reaction.
Mechanism
Fever increases metabolic rate, causing a compensatory rise in heart rate.
Management
- Identify source (blood cultures, chest X-ray)
- Initiate antibiotics if infection confirmed
- Antipyretics for comfort
I – Inotropes
Why They Cause Tachycardia
- Drugs like dobutamine, dopamine, adrenaline directly stimulate beta-adrenergic receptors.
- Increase myocardial oxygen demand.
Approach
- Use lowest effective dose
- Consider switching to agents with less chronotropic effect (e.g., milrinone)
V – Volume Deficit
Causes Post-Surgery
- Third spacing after CPB
- Inadequate fluid replacement
- Postoperative diuresis
Impact
Hypovolemia triggers sympathetic activation → increased heart rate to maintain cardiac output.
Correction
- Fluid resuscitation guided by hemodynamic monitoring
- Avoid overloading (risk of pulmonary edema)
E – Emotions & Pain
Mechanism
Pain and anxiety increase catecholamine release → elevated heart rate.
Signs
- Restlessness, grimacing
- Elevated BP with tachycardia
Management
- Adequate multimodal analgesia
- Psychological reassurance and anxiolytics if needed
M – Massive Bleeding
Identification
- Chest tube output >150 mL/hour for >2 hours.
- Rapid drop in Hb and hemodynamic instability.
Urgency
Massive bleeding is a surgical emergency. Persistent tachycardia may be an early warning sign before overt hypotension.
Management
- Immediate surgical review
- Blood products per massive transfusion protocol
O – Oxygenation Poor
Postoperative Causes
- Atelectasis (common after thoracic surgery)
- Pulmonary embolism
- Pneumonia
- ARDS
Effect
Hypoxia stimulates chemoreceptors → sympathetic activation → tachycardia.
Treatment
- Oxygen therapy
- Recruitment maneuvers and incentive spirometry
- Treat underlying respiratory pathology
M – Malignant Hyperthermia
Overview
A rare, life-threatening hypermetabolic crisis triggered by certain anesthetics (e.g., succinylcholine, volatile agents).
Postoperative Clues
- Rapid rise in temperature
- Muscle rigidity
- Metabolic acidosis, hyperkalemia
Management
- Immediate administration of dantrolene
- Stop triggering agents
- Aggressive cooling and supportive measures
Clinical Approach to Sinus Tachycardia After Heart Surgery
- Immediate assessment – Rule out life-threatening causes (massive bleeding, cardiogenic shock, malignant hyperthermia).
- Focused history & exam – Pain score, drain output, signs of infection.
- Monitoring – ECG, arterial blood gases, central venous pressure.
- Investigations – CBC, electrolytes, chest X-ray, echocardiography if cardiac cause suspected.
- Treat underlying cause – Tachycardia is a symptom, not the disease.
Quick Reference Table – ACTIVE MOM
| Letter | Cause | Key Notes |
|---|---|---|
| A | Anaemia | Low Hb post-op, transfuse if needed |
| C | Cardiogenic shock | LV dysfunction, low BP, cool extremities |
| T | Temperature ↑ | Infection, inflammation |
| I | Inotropes | Dose-related, beta-stimulation |
| V | Volume deficit | Hypovolemia, third spacing |
| E | Emotions & Pain | Increased catecholamines |
| M | Massive bleeding | Surgical site hemorrhage |
| O | Oxygenation poor | Hypoxia from pulmonary causes |
| M | Malignant hyperthermia | Rare anesthesia emergency |
FAQs
1. Is sinus tachycardia always dangerous after heart surgery?
Not always — mild tachycardia can be a normal physiological response. Persistent or severe tachycardia, however, often indicates a complication.
2. How fast should we act on postoperative tachycardia?
Rapidly — because in surgical patients, it may be the earliest sign of hemorrhage, infection, or low cardiac output.
3. Which cause is most common immediately after surgery?
Hypovolemia and pain are the leading early causes; infection becomes more common later.
4. Can beta-blockers be used?
Yes, but only after ruling out reversible causes and ensuring adequate cardiac output.
5. Why is malignant hyperthermia rare but critical?
It has a high mortality rate if not recognized and treated immediately with dantrolene.
