In some patients, the heart beats too slowly. The electrical signals may follow the normal conduction system of the heart beginning at sinus node and traveling to the ventricles, but the frequency of the signals (beats per minute) produced at the sinus node is too low. This condition is called sinus bradycardia. Sometimes, the signals of the heart are produced at the sinus node in the normal frequency, but only a proportion of all signals reaches the ventricles. This condition is called AV block or heart block.
The commonest reason for a slow heart rhythm is the normal aging of the heart and its conduction system. However, some medications, e.g. beta-blockers or several heart conditions (e.g. a heart muscle disease, a myocardial infarction or some genetic conditions) can also cause a slow heart rhythm, that requires treatment. In some cases, the abnormal heart rhythm can be treated by addressing the underlying condition (e.g. by stopping the responsible medication). When this is not possible or not enough, a cardiac device called a pacemaker may be needed.
When the heart beats weakly
In heart failure, the heart muscle often pumps weakly, and is unable to pump enough blood to the lungs or to the rest of the body. This can worsen when the muscle in the ventricles is uncoordinated as a result of electrical conduction problems through the heart muscle (left bundle branch block). This condition is called cardiac or ventricular dyssynchrony.
The medications used for heart failure can reduce symptoms and improve the heart function, but in some severe cases, the implantation of a cardiac device, called cardiac resynchronization therapy (CRT) or biventricular pacemaker may be needed.