One of the unique property of the cardiac muscle cell is its ability to contract and transmit electricity at random given enough oxygen and nutrients.

The heart has four chambers, the right and left Atrium on top and the right and left Ventricle below. The basic electrical conduction starts at the Sinus Node which is located at the right atrium. The electricity is then distributed to both the right and left atria and down to what’s called the Atrio-Ventricular Node or AV Node. The Sinus and AV Node serve as the control stations in which the speed and direction of electrical conduction is regulated. From the AV Node the electricity is then carried down the ventricular septum and spreads to the right and left ventricle through bundle branches. This basic conduction has to occur in the fraction of a second before the heart contracts and pumps the blood to the appropriate chambers and supplies the whole body. What we also know is that the myocardium or heart muscle is filled with electrical networks and collateral pathways which may be used as natural escape-way or occur in a pathological state or a disease state. We have seen evidence of such in the various cardiac arrhythmias. The example of the natural escape-way mechanism is Atrial Fibrillation in the elderly. When the Sinus Node ages, degenerates and fails to respond to the normal electrical signal from the brain and other neuro-humoral effects, the heart contraction slows down and the function of other organ system could be in jeopardy. It is interesting to note that the incidence of Atrial Fibrillation is quite common after age 70, likewise is the Sinus Nodal disease. Atrial Fibrillation is thought to form by multiple smaller electrical circuitries or networks firing electrical charges at the same time trying their best to transmit signals to the AV Node so that the cardiac contraction does not slow down. In the aging heart, often times the AV Node is also diseased and we have a ‘heart block’ situation in which the heart rate or pulse slows down significantly with occasions of pauses and the person effected may have episodes of faintings or even passed out. When Atrial Fibrillation occurs in the younger individual with a healthy AV Node, it would result in the rapid heart rate called Tachyarrhythmia and this is a pathological state. Various bundle branch conduction blocks are also caused by Coronary artery disease which causes damage to the conduction tissue due to myocardial ischemia or infarcts. Others due to Cardiomyopathy in which the cardiac muscle and conduction tissue is unhealthy, weakened or damage due to acute and chronic inflammation.

Pacemaker therapy in its classical sense encompasses the detection or sensing of the basic conduction through the Sinus and AV Nodes and pacing on demand at the preset low and high rate limits. Various pacing modes and the mode switching capability allow detection and automatic adjustment of the rate and pacing mode in cases of arrhythmia. Technically speaking, the pacemaker implantation involves a mild sedation and a local anesthesia. There are usually two pacing leads, an Atrial and a Ventricular leads, inserted via the central venous system to the right atrium and right ventricle respectively. The leads are then connected to the pulse generator which is placed under the skin outside the rib cage. Follow up in the pacemaker clinic and via telephone is mandated to ensure appropriate settings and thresholds for diagnostics, sensing and pacing therapy.

The newest area of interest in the pacemaker therapy involves an additional lead inserted in the cardiac vein and paces the lateral wall of the left ventricle. This has been studied in the population with Congestive heart failure due to myocardial infarction. The use is recommended as an adjunct in the treatment of moderate to severe heart failure. The theory is that a severely damaged heart is no longer contracting optimally due to the remodeling and loss of cardiac synchrony. By effectively pacing the septum and lateral wall of the left ventricle at the adjustable and controlled setting, the cardiac synchrony is improved. Several indicators for timing of implantation have been recommended and remain to be refined and updated as we learn more. We expect improvement in the functional status and reduction in the cardiac chamber size. We encourage the community and our patients to inquire more about the cardiac resynchronization therapy ( CRT ). It is an adjunct that will help people with moderate to severe heart failure to have an improved quality of life.

Signs and symptoms of Sinus and/or AV Nodal disease commonly include somnolence or ‘sleepiness’, fatigue, dizziness, fainting spells, and Syncope or passing out episodes. In the presence of coronary heart disease or other major organ system deficiency, it could result in an acute morbidity and even mortality. Early detection of Sinus and/or AV Nodal disease is pivotal to the success in the prevention and treatment of this cardiac arrhythmia. If you or your loved ones show any signs and symptoms above, please talk to your doctor.

Pacemaker therapy is a relatively simple and safe procedure with great and almost immediate benefits to the patient.

Courtesy of Dr. Budi Bahureksa
Board Certified in Cardiovascular and Internal Medicine