An AV Block is when the electrical signals from the top chambers of your heart (atria) slow down or get blocked on their way to the bottom chambers (ventricles). Think of it like a traffic jam in your heart’s electrical system.
There are different types — from mild (like first-degree, where things are just a little delayed) to more serious ones (like second-degree or third-degree, where some signals get dropped or completely blocked).
Sounds scary, but it’s usually not! First-degree heart block just means the signal telling your heart to beat is taking a little longer than normal to travel from the top chambers (atria) to the bottom chambers (ventricles).
Most people don’t feel any symptoms, and it’s often only discovered by accident during an ECG. It’s usually harmless and doesn’t need treatment — just something to keep an eye on. (Read: What First-Degree AV Block Looks Like on Your Watch ECG)
Supraventricular Tachycardia (SVT) happens when your heart suddenly races — often shooting up to 150–220 beats per minute — because the electrical signal starts from the wrong spot in the upper chambers (atria).
On your ECG, SVT usually shows:
Sometimes SVT is short (non-sustained), sometimes it lasts longer (sustained). It can feel like fluttering, dizziness, or even anxiety. (Read: What Supraventricular Tachycardia (SVT) Looks Like on Your Watch ECG)
EKG (Electrocardiogram) is a simple test that records the electrical signals from your heart to check how fast and steady it’s beating. It’s used to spot problems like irregular heart rhythms (arrhythmias). EKG and ECG mean the same thing — EKG comes from the German word “Elektrokardiogramm.” :)
A 1-lead ECG (Electrocardiogram) is a simple heart test that uses just one electrical pathway (or “lead”) to check your heart’s rhythm. It’s called “1-lead” because it looks at your heart from one angle only. Devices like the Apple Watch, Samsung Watch, Fitbit, and Kardia use this method to easily detect irregular heartbeats, like AFib, anytime and anywhere. It’s quick
The baseline, or the isoelectric line, is the line between the T wave and the next P wave. It's a line on the ECG paper where there are no positive or negative charges of electricity from your heart to create deflections (waves). Deflections above the baseline are positive, and deflections below are negative.
The baseline is a key reference point when determining your heart's rhythm. Sometimes, when your ECG has a lot of noise, your baseline can be distorted. These wavy baselines are usually caused by movement or breathing, making the review of an ECG more difficult.
The third wave you see immediately after the QRS complex is the T wave. It represents the relaxation of the bottom chambers in your heart, called the ventricles. A normal T wave is a smooth transition from the ST segment and is slightly asymmetric with a steeper downslope.
The isolated ectopic beat is a fancy way of saying that your ECG has a single occurrence of an ectopic beat, like a PVC or a PAC.
An ectopic beat is basically an early heartbeat that shows up before your heart expects it. Think of it as your heart “jumping the gun.” It often feels like a flutter, a skipped beat, or a sudden jolt in your chest.
Ectopic beats come from spots in the heart other than your usual pacemaker (called the sinus node). That’s why they’re called “ectopic” — meaning “out of place.”
There are two common types:
This is when your ECG shows jumpy lines because of movement. If you move, shake, cough, or bump the device while recording, the ECG line can wiggle in ways not related to your heart. For example, if you talk or move your arm during a watch ECG, you'll see messy lines - and your device might say the reading is "poor quality." Apple even tells users to put their arms on a table and stay still during an ECG to avoid this problem. Remember: these jumpy lines are just noise. They don't mean you have a heart problem - they just show that movement disrupted your recording.
“Inconclusive” on a device ECG means the app was unable to classify the recording. This often happens if the heart rate is out of the range the device can analyze or if the signal quality is poor. For instance, if your heart rate is very low (say, 40s) on the watch ECG, it might show “Inconclusive” because it can’t decide between normal or AFib . Essentially, the result isn’t saying something is wrong, just that the device couldn’t get a clear reading. (Related: What “Inconclusive” Means on Your Apple Watch ECG)
"Unclassified” is a term used by some ECG devices (for example, KardiaMobile or others) when the recording doesn’t fit any of the known categories like normal, AFib, bradycardia, etc. It means the rhythm didn’t match the device’s criteria for a specific diagnosis. You might see “Unclassified” if you have an unusual rhythm that’s not AFib, or multiple extra beats, for example. It’s a prompt that the device detected a heart rhythm but couldn’t label it. (Read: What Unclassified EKG Means on Your KardiaMobile)
If you see messages like “Poor recording,” “Noisy signal,” or “Try again” on an ECG app, it means the device picked up too much interference (artifact) to interpret the ECG. Artifact can come from moving, talking, or loose contact while recording – the tracing will look messy or irregular, not due to heart beats but due to noise. For the patient, this just means the ECG wasn’t clear. The solution is usually to stay still, ensure good skin contact with sensors, and repeat the recording. (Read: What Poor Recording ECG Means on Your Apple Watch)
A portable ECG recorder that you wear continuously, typically for 24 to 48 hours . It involves small sticky electrode patches on your chest connected to a lightweight recording device (often worn on a belt or shoulder strap). The Holter monitor tracks every heartbeat during the day(s) you wear it, allowing doctors to catch irregular heart rhythms that might come and go. It’s essentially an extended ECG test you carry with you in your normal daily life. You might be asked to keep a diary of activities or symptoms while wearing it, so the doctor can match any irregularities on the recording with what you were doing or feeling at the time.
The set of three waves (Q, R, and S) that appear as one big spike on the ECG. The QRS complex reflects the electrical impulse spreading through the ventricles (the lower chambers), causing them to contract and pump blood out to the body. It’s usually the tallest, most obvious part of the heartbeat on the ECG. Doctors often look at the width of the QRS spike – a narrow QRS means the ventricles are activated quickly and normally, whereas a wide QRS means the impulse is traveling more slowly or through an abnormal pathway. (A wide QRS can happen, for example, in a bundle branch block, where one side of the heart’s conduction highway is slowed.)
The time delay between the start of the P wave and the start of the QRS complex. In other words, it measures how long it takes for the electrical impulse to travel from the atria to the ventricles. This interval corresponds to the brief pause as the signal goes through the AV node (the “bridge” between upper and lower chambers). In a healthy heart the PR interval is about 0.12 to 0.20 seconds (120–200 milliseconds) – just a fraction of a second. If the PR interval is longer than normal, it means the signal is moving slower than usual (for instance, a consistently long PR can indicate a first-degree AV block, which is essentially a mild delay in conduction) . If it’s too short, the signal might be taking a shortcut to the ventricles (s happens in certain conditions like Wolff-Parkinson-White syndrome).
The first small bump in the heart’s ECG wave. It shows the electrical signal spreading across the atria (the heart’s upper chambers), causing them to contract (squeeze) and push blood into the ventricles. In a normal rhythm (sinus rhythm), every heartbeat has a P wave before the big spike (QRS).
For example, in atrial fibrillation (an irregular rhythm), there are no clear P waves on the tracing because the atria aren’t beating in a coordinated way.
Atrial fibrillation is an irregular heart rhythm where the upper chambers of the heart (atria) beat in a chaotic, uncoordinated way. Instead of one steady beat, the atria quiver, causing an irregular and often rapid pulse. AFib can cause symptoms like palpitations, shortness of breath, or fatigue, and it increases the risk of stroke if not managed. In simple terms: Your heart's top chambers shake instead of pump, making your heartbeat irregular and raising stroke risk. (Read: What Atrial Fibrillation (Afib) Looks Like on Your Watch ECG)
Trigeminy is a heart rhythm pattern where every third heartbeat comes too early. The pattern goes: normal beat, normal beat, early beat - and then repeats over and over. This early beat can start from the upper chambers of the heart (called PACs) or from the lower chambers (called PVCs).
Many people feel this as an uneven or jumpy heartbeat because of these regular early beats happening throughout the day.
Think of it like this: bump-bump-EXTRA, bump-bump-EXTRA, bump-bump-EXTRA, in an ongoing pattern. (Read: What Atrial Trigeminy Looks Like on Your Watch ECG)
Bigeminy is a heart rhythm pattern in which every normal heartbeat is followed by a premature beat . In other words, the beats come in pairs – one regular beat and then one extra beat. This can happen with extra beats from the atria (atrial bigeminy) or from the ventricles (ventricular bigeminy). People with bigeminy might feel palpitations because of the frequent extra beats. (Read: What Ventricular Bigeminy Looks Like on Your Watch ECG)
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A couplet refers to two premature beats occurring back-to-back, in a row . For example, two PVCs in succession would be called a “ventricular couplet.” Noticing couplets on an ECG is important because runs of consecutive premature beats may suggest the heart is more irritable.
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A PJC is an early heartbeat originating around the AV node (the “junction” between the atria and ventricles) instead of from the atria. It’s basically a premature beat from the middle of the heart’s electrical system. PJCs are less common than PACs or PVCs, but like other premature beats, they can cause a brief sensation of a skipped beat. (Read: What Premature Junctional Contraction (PJC) Looks Like on Your Watch ECG)
A PVC is an extra heartbeat that begins in one of the heart’s lower chambers (ventricles), occurring before the normal heartbeat is due . A PVC can cause the feeling of a stronger or “skipped” beat. Occasional PVCs are common and often not harmful. (Read: What Premature Atrial Contraction (PAC) Looks Like on Your Watch ECG)
The normal, regular heartbeat rhythm is controlled by the sinus node (the heart’s natural pacemaker). In sinus rhythm, electrical signals start at the top of the heart and produce a steady rate (about 60–100 beats per minute at rest). This is the result your ECG shows when everything is functioning normally. (Related: What Sinus Rhythm Looks Like on Your Watch ECG)
The normal, regular heartbeat rhythm is controlled by the sinus node (the heart’s natural pacemaker). In sinus rhythm, electrical signals start at the top of the heart and produce a steady rate (about 60–100 beats per minute at rest). This is the result your ECG shows when everything is functioning normally. (Related: What Sinus Rhythm Looks Like on Your Watch ECG)
Tachycardia means a heart rate that is faster than normal (typically over 100 beats per minute at rest) . This can happen due to exercise, stress, or illness, but if it’s very fast at rest, it might indicate an arrhythmia. (Read: What Sinus Tachycardia Looks Like on Your Watch ECG)
Bradycardia refers to a heart rate that is slower than normal (usually below about 60 beats per minute at rest). In many cases it’s harmless (for example, in athletes or during sleep), but if it’s too slow, it can cause dizziness or fatigue. (Read: What Sinus Bradycardia Looks Like on Your Watch ECG)
Palpitations are the sensation of feeling your own heartbeat when it’s skipping, fluttering, or racing. You might feel like your heart is pounding or flip-flopping in your chest. (Read: What Heart Palpitations and Irregular Heartbeats Look Like on Your Watch ECG)
An arrhythmia is an abnormal or irregular heartbeat – the heart may beat too fast, too slow, or with an uneven rhythm. In simple terms, it means the heart isn’t beating in the normal pattern.
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