Slow Heart Rate

Slow heart rate is also known as bradycardia. Under normal circumstances, heart beats from 60 to 90 times per minute. Herat contractions are perceived as palpable pulse waves in peripheral arteries. Under certain circumstances, heart rate may drop below 60 beats per minute and in this case we speak of slow heart rate. By some people it is absolutely normal, by others it may be a pathological symptom.

Causes

Slow heart rate by sporting people

Professional athletes and sporting people in general tend to have more trained cardiovascular system that is able to work efficiently even by slower heart contractions frequency. Therefore it is not surprising by athletes; we can find pulse frequency around 50 per minute without any clinical importance. This bradycardia is usually diagnosed incidentally, is it natural and means no restriction for its bearer. Therefore we do not treat it.

Drug-induced slow heart rate

Heart rate may be influenced by medication and this is probably one of the most common causes of bradycardia. Overdose by drugs known as beta-blockers is typical. Beta-blockers are often prescribed by heart disorders. They have a wide range of effects – they lower high blood pressure (antihypertensive agents), they reduce risk of fatal heart arrhythmias and also slow the heartbeat. Slower heart rate has some advantages as it is less exhausting. A big dose of beta-blockers can, however, drop heart rate too strongly. The status is usually solved relatively simple by dose reduction or discontinuation of beta–blockers usage. The risk of side effects of beta-blockers worsens when combined with certain drugs from calcium channel blockers group.

Hypothyroidism

Decreased function of thyroid gland causes lower levels of thyroid hormones. That situation has a complex suppressive effect on human body metabolism and that includes slower heartbeat.

Sick sinus syndrome (SSS)

This is a disease occurring mainly by elderly. It is a disruption of so-called SA node (sinoatrial node). SA node is an important part of the cardiac conduction system. It is the place where, in healthy heart, electrical impulses emerge. Impulses generated in SA node spread from heart atria to the ventricles causing coordinated heart muscle contraction. In sick sinus syndrome, SA node works incorrectly that causes episodes of slow heart rate often alternating with episodes of rapid atrial fibrillation. The actual cause of SA node failure is probably its degeneration by the elderly.

Atrium-ventricle conduction disorders

A mentioned above electric impulses causing heart contractions emerge in atrium in so-called SA node. The conduction from atria to ventricles is possible in only one place called AV node (atrioventricular node). When this area is unable to transmit the impulses, the heart adapts and heart ventricles start to generate own impulses to maintain ventricle contractions. Heart ventricle cells are however unable to generate these impulses in sufficient frequency and heart rate drops to about 40 beats per minute.

Electrolyte imbalance

Bradycardia often occurs by elevated potassium concentration in blood (so called hyperkalemia).

Symptoms

Slow heart rate may be completely asymptomatic, otherwise it manifests as heart failure with insufficient cardiac output. It is logical – slowly pumping heart muscle doesn’t manage to supply tissue with blood, including brain. These symptoms are for example shortness of breath, dizziness, weakness, fainting, etc.

Diagnosis

During physical examination we check pulse by touch (typically in wrist area) and listen to heartbeat with a stethoscope in chest. A suspicion of slow heart rate is easily confirmed by ECG that can even reveal some pathologic causes. When bradycardia is diagnosed, it is necessary to know patient’s actual medication.

Treatment

Treatment of bradycardia is often challenging. We can discontinue usage of causative drugs, or treat hypothyroidism. However, when slow heart rate is caused by disorders of heart conduction system, our options are limited. If a patient experiencing acute bradycardia becomes unstable, we can administer medications to accelerate heart rate (atropine, epinephrine) as a short-term solution.

 

The only definitive solution is a pacemaker implantation. Pacemaker is a device that is placed under the skin not far from heart (typically in the area above collarbone). Pacemaker’s electrodes extend to the heart and by emitting electric impulses they cause heart contractions in desired frequency. The pacemaker has a built-in long-lasting battery that must be changed every few years of its function.