Second-degree heart block, Mobitz type I (Wenckebach): symptoms, tests and treatment

Every heartbeat starts as an electrical impulse. The British Heart Foundation explains that these impulses move through the heart and make it beat, and that a heart block happens when they are blocked or delayed. In an atrioventricular (AV) block, the delay or block happens as the signal travels between the atria, the top chambers, and the ventricles, the bottom chambers.

AV block is described in three degrees. First-degree block is a delay in which every signal still gets through. Third-degree, or complete, block is when no signals get through. Second-degree block sits in between: some signals reach the ventricles and some do not. Within second-degree block there are two main patterns, usually called Mobitz type I and Mobitz type II, and they are treated differently because they behave differently.

In Mobitz type I, which is also known as the Wenckebach phenomenon, the delay lengthens a little with each beat until one signal fails to get through and a beat is dropped. After the dropped beat the delay resets and the pattern starts again. GPnotebook says the level of the block is generally at the AV node and the QRS complexes on the ECG are of normal duration.

The NHS says heart block may cause dizziness, fainting or feeling as if you are about to faint, chest pain, tiredness and shortness of breath, and that these can range from mild to severe depending on the type of heart block. It also says you may have no symptoms at all. The BHF says first-degree block does not usually cause symptoms, while second and third-degree blocks can.

Whether a particular ECG pattern is a concern depends on the individual person, so symptoms should not be ignored just because the pattern is Mobitz type I. The BHF notes that AV heart blocks can sometimes turn into higher-degree blocks if they are left untreated, which is part of why an unexplained change should be assessed.

• Feeling faint or dizzy, or actually fainting.

• Unusual tiredness, and sometimes feeling confused (listed by the BHF).

• Chest pressure or pain.

• Shortness of breath, especially if it is getting worse with normal activity or when lying down (the NHS lists this under symptoms that need NHS 111 advice).

• A very low heart rate, which the BHF says some people with heart block have.

The NHS advises getting help from NHS 111 if you feel dizzy all the time or it keeps coming back, if you have fainted, or if you have shortness of breath that gets worse when you do normal activities or lie down. It adds that you are not wasting anyone's time by getting it checked.

The NHS says to call 999 if you have been diagnosed with heart block and have chest pain, severe difficulty breathing (gasping, choking or unable to get words out), or feel sweaty, sick or lightheaded, or if someone faints and is not breathing or cannot be woken within 1 minute. It says not to drive yourself to A&E. The BHF similarly says that if you have severe or sudden symptoms you should call 999 for an ambulance.

GPnotebook points out that in a healthy person the Wenckebach pattern is often due to increased vagal tone, which is the activity of the nerve that slows the heart. In that situation it is described as being abolished by exercise and atropine. It can also result from other causes, listed as inferior myocardial ischaemia, Lyme disease, cardiac surgery, hyperkalaemia (a raised blood potassium) and medication toxicity, for example from beta-blockers and calcium channel blockers.

The NHS says heart block is most often caused by a heart condition such as coronary heart disease or a heart attack, and lists some types of medicine, infection and inflammation of the heart, and having heart surgery as other possible causes of AV heart block. The BHF adds congenital heart disease, cardiomyopathy, ageing of the electrical pathways and thickening of the heart muscle, and notes that heart block can also happen naturally in people with a normal heart. Sometimes, according to the NHS, there is no obvious cause.

Because several causes are reversible, a review of your medicines and a blood test for electrolytes such as potassium is a usual early step. The BHF says that if heart block is due to medications or electrolyte imbalances, people are monitored closely in hospital and given treatment to reverse the medications or correct the imbalance.

The main test is an electrocardiogram (ECG), which the NHS says measures the electrical activity of the heart and usually takes only a few minutes. The BHF says the ECG can show the type of heart block you have. A pattern of lengthening PR intervals followed by a dropped beat is what identifies Mobitz type I.

Because the dropped beats can come and go, you may be asked to wear a portable ECG for a day or two. The NHS says other tests that may help include an echocardiogram or MRI scan to get a picture of the heart and nearby blood vessels, exercise tests that check the heart while you use a bike or treadmill, and blood tests. The BHF notes that unless you have symptoms, heart block is often noticed during routine tests for other conditions.

The NHS says treatment depends on what is causing the heart block and whether you have symptoms, and that if it is not causing symptoms you will not usually need treatment. For Mobitz type I specifically, GPnotebook says treatment is often not necessary, and that guidance suggests permanent pacing is only indicated if the AV block causes symptoms or if the conduction delay occurs below the bundle of His.

If a pacemaker is needed, the NHS says it is a small device put under the skin of the chest that sends a small electrical signal to help control the heartbeat. It describes a standard fitting as taking about an hour under local anaesthetic, with an overnight stay, and says recovery involves not driving for at least the first week and avoiding heavy lifting and vigorous exercise for 4 to 6 weeks. You must tell the DVLA and your insurer that you have a pacemaker. The BHF says that when heart block follows a heart attack you may need only a temporary pacemaker in hospital.

If the cause is a medicine, the first step may be a change or stop of that medicine under medical supervision. Do not stop a heart medicine on your own because you have read about heart block; speak to your GP, pharmacist or cardiology team first.

Many people with Mobitz type I are found incidentally, for example on an ECG done for another reason, and are simply monitored. In the NHS the first contact is usually the GP, who can arrange an ECG and refer to cardiology. Cardiology teams and pacemaker clinics provide longer-term follow-up if a device is fitted; the NHS says that after a pacemaker you will have a check at about 6 weeks, another at 3 to 6 months, and then at least every 12 months, and that a pacemaker battery usually lasts 6 to 7 years.

Private cardiology services can offer ECGs, ambulatory monitoring and specialist opinions, and the clinical approach is the same as in the NHS. Whichever route you use, you should be given a clear plan for what symptoms should prompt a call back, and what to do about driving and exercise while the cause is being worked out.

The BHF runs a heart helpline staffed by cardiac nurses and offers a free booklet on heart block, which some people find useful for putting questions together before an appointment.