ECG Report Explained: Sinus Rhythm, T Wave Changes and Borderline ECG
What common ECG phrases mean, from normal sinus rhythm to non-specific ST-T changes and borderline ECG, which are usually harmless, and why a normal ECG is not proof.
Key takeaways
- Normal sinus rhythm means the heart is beating in its normal pattern, at 60 to 100 beats a minute.
- The computer-printed interpretation at the top of an ECG is often wrong or over-cautious. A doctor's reading is what counts.
- Phrases such as non-specific ST-T changes, borderline ECG, incomplete RBBB and early repolarisation are frequently harmless in people without symptoms.
- A normal resting ECG does not rule out blocked arteries. Chest pain with exertion needs further tests even with a normal ECG.
An ECG is quick, inexpensive and done in almost every Indian health check and emergency department. It is also the test most likely to frighten people with its printed text, because the machine’s software flags anything near a cut-off: “borderline ECG”, “abnormal ECG”, “non-specific T wave abnormality”. Most of these phrases mean far less than they sound. A few mean a great deal. This guide explains which.
Quick answer
Normal sinus rhythm means the heart is beating in its normal pattern at 60 to 100 beats a minute. The computer interpretation printed on top is often over-cautious; a doctor’s reading is what matters. Non-specific ST-T changes, borderline ECG and incomplete RBBB are frequently harmless without symptoms. A normal resting ECG does not rule out blocked arteries.
What an ECG records
Small stickers on the chest, arms and legs pick up the electrical signal that triggers each heartbeat. The tracing shows the rate, the rhythm, how the signal spreads, and clues to strain, enlargement, or reduced blood supply. It is a ten-second snapshot at rest, which is both its strength and its limit.
Common phrases and what they usually mean
| Report phrase | What it usually means | Usually concerning? |
|---|---|---|
| Normal sinus rhythm | Normal heartbeat, 60 to 100 per minute | No |
| Sinus bradycardia | Normal rhythm below 60, common in fit people and in sleep | Not if no symptoms |
| Sinus tachycardia | Normal rhythm above 100; fever, anxiety, anaemia, dehydration | Treat the cause |
| Sinus arrhythmia | Rate varies with breathing; normal in the young | No |
| Borderline ECG | Software flag near a cut-off | Usually not |
| Non-specific ST-T changes | Small, non-diagnostic changes | Not without symptoms; compare with old ECG |
| Incomplete right bundle branch block | Slight delay on the right side | Usually a normal variant |
| Early repolarisation | Common pattern in young, fit people | Usually benign |
| Left axis deviation | Signal points more to the left | Sometimes normal; doctor decides |
| Left ventricular hypertrophy (LVH) | Signs of a thickened heart muscle | Check blood pressure; echo may follow |
| T wave inversion | Inverted waves in some leads | Normal in some leads; concerning if new |
| Prolonged QTc | Longer recovery time between beats | Review medicines and electrolytes |
| Atrial fibrillation | Irregular rhythm from the upper chambers | Yes, needs medical review |
| ST elevation with chest pain | Possible heart attack | Emergency |
Why the computer interpretation misleads
ECG machines measure intervals and amplitudes and apply fixed rules. They over-call minor variations, especially in slim, young, athletic or anxious people and in women, and they occasionally miss real problems. The text at the top is a prompt for a doctor, not a diagnosis. Always have the tracing itself reviewed, and keep earlier ECGs, since a change from a previous tracing is often more meaningful than any single finding.
A normal ECG is not a clean bill of heart health
Do not let a normal ECG reassure you about these
Chest pain or tightness that comes on with exertion and eases with rest. Breathlessness on exertion that is new or worsening. Fainting during exercise. These need further tests, such as a stress test, echocardiogram or CT coronary angiogram, even if the resting ECG is normal.
During a heart attack the ECG usually changes, but early on it can be normal, which is why emergency departments repeat it and check troponin blood tests. The chest pain vs acidity guide explains which chest pain needs an ECG today.
When to see a doctor
Get an ECG reviewed promptly for any palpitations, fainting, chest pain, breathlessness or a report mentioning atrial fibrillation, heart block, a prolonged QTc or ischaemic changes. Chest pain with sweating, breathlessness or pain spreading to the arm or jaw is an emergency: call 108 or 112. For the numbers that predict heart risk years in advance, see the lipid profile guide and the blood pressure guide.
Frequently asked questions
What does normal sinus rhythm mean?
It means each heartbeat starts from the heart's natural pacemaker, the sinus node, and travels through the heart normally, at a rate of 60 to 100 beats a minute. It is the expected, healthy pattern.
What does 'borderline ECG' mean?
It is a phrase generated by the ECG machine's software when a measurement is close to a cut-off. It does not mean heart disease. Many borderline ECGs are normal on a doctor's review, especially in young, fit or slim people.
Are non-specific ST-T changes dangerous?
Usually not, in someone without symptoms. They are small changes that can come from posture, breathing, electrolyte levels, anxiety, medicines or normal variation. They become important if they are new, appear with chest pain, or change between ECGs, which is why a previous ECG is useful to bring.
Is sinus tachycardia a heart problem?
Sinus tachycardia means the normal rhythm is running faster than 100 beats a minute. It is usually a response to something, such as anxiety, fever, pain, dehydration, anaemia, caffeine or an overactive thyroid, rather than a heart disease. Treating the cause usually settles it.
Can an ECG detect a blocked artery?
Only sometimes. During a heart attack the ECG often changes, but at rest, between symptoms, an ECG can be completely normal even when arteries are significantly narrowed. Exertional chest pain is investigated with a stress test, echocardiogram or CT coronary angiogram as the doctor decides.
Sources
Dr. Garima Panse is a medical doctor who writes plain-language guides for Indian readers on skin health, heart health, brain and nerves, medical imaging and everyday medicine. Every guide lists its sources, shows the date it was last reviewed, and says when to see a doctor in person.
This guide is for general education and reflects the evidence available on the last reviewed date. It is not a diagnosis, a prescription or a substitute for seeing a doctor who can examine you. If you have symptoms that worry you, or the guide tells you to see someone, please do. Full disclaimer.