Heart block
The heartbeat does not start on its own. Each contraction begins with an electrical signal that arises in the upper chambers and travels down dedicated…
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The heartbeat does not start on its own. Each contraction begins with an electrical signal that arises in the upper chambers and travels down dedicated pathways to the lower ones. Heart block is a delay or a break in that signal on its way down. The muscle itself may be perfectly healthy and the arteries perfectly clear. The name misleads people: they hear "block" and picture a clogged artery, but this is about the wiring, not the plumbing. Hence the complaints — a slow pulse, sluggishness, vision fading out and, sometimes, a sudden faint.
What actually fails in the wiring
The impulse starts in the sinus node, a cluster of specialised cells in the right atrium. From there it spreads across the atria, reaches the atrioventricular node — the only legitimate crossing between the top and bottom of the heart — and travels on through the bundle of His and its branches into the ventricles. A hold-up at that crossing is what is called atrioventricular block, by far the commonest kind.
A small delay at the atrioventricular node is actually useful: it gives the atria time to finish filling the ventricles before they eject blood. Trouble begins when the delay grows, when individual impulses stop getting through, or when the connection fails altogether. The ventricles then fall back on a rhythm of their own — slow, around thirty to forty beats a minute, and, more importantly, unreliable, because it can drop out for several seconds.
Bundle branch blocks are a separate matter. They happen within the ventricles themselves, do not slow the pulse and often cause no sensation at all. A left bundle branch block appearing for the first time alongside crushing chest pain, however, is a finding cardiologists look at urgently.
What it feels like
The symptoms depend far less on the label of the degree than on how slow the pulse has become and whether the brain is still getting enough blood:
- sluggishness and tiring quickly for no obvious reason;
- breathlessness on exertion that used to be easy;
- dizziness, particularly on standing up or walking uphill;
- vision greying out, a sense that the room is drifting away;
- fainting with no warning at all — the person sinks to the floor on level ground and comes round within seconds;
- a slow pulse that can be felt at the wrist;
- chest pain or heaviness;
- in older people, confusion, unexplained falls and worsening memory.
A good share of heart block causes nothing whatsoever and turns up by chance: on a tracing taken before surgery, at a workplace check, or when a fitness certificate is being issued. That does not mean the finding can be forgotten. It needs an explanation, even if it does not always need treatment.
When it cannot wait until morning
Call an ambulance (in Spain, Italy, Portugal, Poland and Ukraine the single European number 112 applies) if:
- someone has lost consciousness and is not coming round;
- the faint has happened more than once, or caused an injury on the way down;
- there is pressure or burning in the chest, pain spreading to the arm, neck or jaw, with cold sweat and nausea;
- breathing is hard at rest and there is not enough air for a few words in a row;
- the pulse is around forty or below and the person is pale, drowsy and clammy;
- there were convulsive movements during the loss of consciousness.
Driving yourself in that state is a bad idea: the episode can recur on the way. If the trouble started after a new medicine or a dose change, take the packets along — it saves the doctor time.
One point deserves its own line. A faint at rest, a faint during exertion and a faint in someone with known heart disease never belong in the "just overtired" category. They are looked into the same day, even if the person has fully recovered.
Three degrees, and they do not weigh the same
Grading is not a formality: it decides directly whether to watch or to act.
- First degree. Every impulse gets through, just late. As a rule nothing is felt and nothing is treated. It is worth hunting for a cause, though: medicines, electrolytes, a high vagal tone.
- Second degree. Some impulses are lost. Two very different situations hide under this one label. In the first, the delay lengthens beat by beat until one beat drops; this turns up in trained athletes and during sleep and is usually harmless. In the second, beats drop abruptly with no warning at all — that variant tends to progress to complete block and is taken seriously.
- Third degree, or complete block. The link is severed: the atria beat to their own rhythm, the ventricles to a slow one of theirs. This is where fainting mostly happens, and where a pacemaker almost always comes into the conversation.
Where it comes from
The commonest cause is gradual scarring of the conduction system itself with age. Next come coronary artery disease and previous heart attack (especially of the inferior wall), cardiomyopathies, valve disease, and the aftermath of heart surgery or catheter ablation.
A very frequent and entirely reversible cause is medication. Beta blockers, some calcium channel blockers, digoxin and several antiarrhythmic drugs slow conduction, and their levels climb when someone becomes dehydrated or kidney function drops. In the same group belong a high blood potassium and an underactive thyroid.
Some rare causes are worth knowing about, because they are treated at the root rather than with a device:
- Lyme disease — carditis following a tick bite; the block can be complete and still clear up entirely on antibiotics;
- cardiac sarcoidosis and amyloidosis, which produce block in comparatively young people;
- myocarditis, including viral;
- congenital complete block in a newborn, linked to autoimmune antibodies in the mother.
Advanced block in a young person with no obvious explanation is not something to shrug off; it is a reason to go looking for one of these.
How it is confirmed
The basic test is an ordinary electrocardiogram, which takes a couple of minutes. The snag is that block can come and go, and a short recording may miss it. Hence continuous monitoring over one or several days and, when faints are widely spaced, recorders worn for weeks or a tiny device placed under the skin that logs the rhythm for months.
Then comes the search for the underlying ground: an echocardiogram shows the muscle and the valves, an exercise test shows how conduction behaves under load, and blood tests cover potassium, thyroid function and markers of inflammation. If there has been a tick bite, serology is added; if the picture is unclear in a young patient, cardiac imaging follows. And the full list of medicines is always reviewed — including beta blocker eye drops, which patients almost never think to mention.
What happens next
If the block causes no symptoms and sits on a quiet rung, management amounts to observation and dealing with the cause. Medication comes first: some drugs are stopped or the dose adjusted, always together with the doctor, because stopping heart medicines on your own is no safer than the block itself.
When advanced block is persistent, when there are faints, or when the rhythm is simply too slow, a pacemaker is implanted. It is a small device placed under the skin below the collarbone, with leads running into the heart; it watches the rhythm and supplies an impulse whenever the heart's own fails to arrive. The procedure is done under local anaesthetic, usually with one night in hospital. Where the cause is temporary — drug toxicity or the acute phase of a heart attack — pacing is set up on a temporary basis instead.
Life with a device is ordinary. Household appliances and mobile phones do not interfere, though strong magnetic fields, industrial machinery and security arches call for some care: it is handy to carry the device card. Many current models are compatible with magnetic resonance scanning, but the team needs to be told in advance. Devices are checked at scheduled appointments and the battery lasts for years. Rules on driving after a faint or after an implant differ from country to country, so check yours with your own doctor.
Online consultation
In an online consultation an Oladoctor doctor goes through your situation: asks about the circumstances of the dizziness and the faints, looks at the tracings and reports you send, checks your medicine list for anything that slows conduction, and explains what the wording on the report actually means.
The format suits making sense of an electrocardiogram finding, deciding whether a twenty-four-hour recording is needed, preparing for a cardiology appointment, and sorting out questions after a pacemaker implant. For a faint, chest pain or a very slow pulse with a person feeling unwell, an online appointment is the wrong route — that needs urgent care in person.
This material is for information only and does not replace medical advice.
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