Practical Electrophysiology
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TODD J. COHEN, MD

The History of Electrophysiology

In the years since Willem Einthoven described the 12-lead electrocardiogram (ECG), little has changed regarding how to record a surface electrocardiogram. This has been the acceptable standard. However, with respect to intracardiac electrograms (direct recordings of electrical signals from within the heart), a lot has changed since the first recording of the His bundle. During the past half-century we have witnessed the development of cardiopulmonary resuscitation, transthoracic cardioversion and defibrillation, and the advent of implantable devices (pacemakers, defibrillators, loop recorders, biventricular devices). Innovations in catheter ablation have resulted in a very high success rate for most reentrant and focal supraventricular tachycardias and certain ventricular tachycardias. Even atrial fibrillation can be successfully managed in many circumstances via pulmonary vein isolation procedures and left atrial ablations. These procedures can be performed percutaneously with an ablation catheter.

In 1884, the first graphic documentation of ventricular fibrillation was performed by M. Hoffa. Shortly thereafter, in 1888, Augustus Desiré Waller introduced his findings on electromotive properties of the human heart. Waller presented his dog with each paw in a pan of saline, from which the electrical potentials were recorded, and termed these electrical currents “electrograms.” John A. McWilliam published his findings, “Electrical Stimulation of the Heart in Man,” in 1889; in them he stated that “in certain forms of cardiac arrest there appears to be a possibility of restoring by artificial means the rhythmic beat.”

Cardiac Anatomy and the Electrical Conduction System

Extending throughout the human body is a complex circulatory system comprised of veins and arteries, which circulates blood in order to replenish tissues and vital organs with oxygen and nutrients. The main component of this system is the heart (or myocardium), which functions as the circulatory engine pumping blood (composed of red blood cells containing hemoglobin to carry oxygen, white blood cells to fight infections and platelets to help with clotting) throughout the body. The heart has many components that must work effectively in order to optimize cardiovascular performance.

The sac surrounding the heart is called the pericardium. The parietal pericardium is the outermost layer. It is secured in the thoracic cavity between the lungs and fused to the diaphragm’s central tendon. It is also attached to the back of the sternum, or breastbone, by the superior and inferior sternopericardiac ligaments. The visceral pericardium is the innermost layer of the pericardium. It is a layer of tissue that is closely adhered to the heart. The pericardial space is the middle layer between the parietal and visceral pericardia. It is composed of a fluid that serves as a lubricant so that the heart can move without friction. Figure 2.1 shows the layers of the heart.

The myocardium is the muscle layer of the heart. It is composed of cardiac muscle cells (myocytes), which are one-third smaller than somatic muscle cells and are not as striated. Within the heart there are at least two types of myocardial muscle fibers: those of the atria (upper chambers) and those of the ventricles (lower chambers). The innermost layer of the heart is called the endocardium. The endocardium is a tissue layer made of closely packed endothelial cells that provide a smooth surface for blood flow.

Radiation Protection

 Radiation protection in electrophysiology is essential to all patients and personnel in order to minimize the cumulative effects to the bone marrow and other radiation-sensitive tissue as well as the possible risk of cancer. The electrophysiology laboratory (including all associated operating rooms) should strive for the ALARA principle, which stands for radiation exposure should be "As Low as Reasonably Achievable."

In order to minimize radiation exposure, there are three factors that need to be considered: 1) time, 2) distance, and 3) shielding. The amount of radiation exposure is directly related to the exposure time of the procedure. In particular, the current needed to generate x-rays, mAs (milliampere seconds), should be maintained as low as possible. The image intensifier to object (patient) distance must be kept to a minimum at all times to reduce exposure from scattered radiation to both the operator and assisting personnel. The further the image intensifier is from the patient, the greater the radiation required to produce a diagnostic image with subsequent increase of scatter and radiation exposure to the staff. All non-essential personnel should be at least six feet from the source of the scattered radiation, the patient, during fluoroscopy. In addition, the duration of fluoroscopy exposure for long and complex electrophysiology procedures (catheter ablations and biventricular implants) should be less than 60 minutes in order to minimize the potential for a radiation burn to the patient’s skin.

Pharmacotherapy and Electrophysiology

The most widely used classification system for antiarrhythmic drugs is a modification of the system proposed by Vaughan Williams (table 10.1). It classifies drugs according to their effects on action potentials in individual cells. Class I drugs block sodium channels responsible for the fast response in atrial, ventricular, and Purkinje tissues, thus depressing conduction velocity. Class II drugs are beta-adrenergic receptor antagonists (or beta blockers). Class III drugs prolong cardiac repolarization, predominantly by blocking potassium channels during phases 2 and 3 of the action potential, thereby increasing tissue refractoriness. Class IV drugs block calcium channels (calcium channel blockers), depressing the slow response in sinus nodal and AV nodal cells, and perhaps in other cells as well.

This classification system is an oversimplification, however, and does not account for many other effects. Additionally, it does not account for the multiple effects a drug may have on cardiac cells. For example, sotalol has beta-blocking activity (Class II), but it also significantly prolongs the action potential duration (Class III). Another drug, amiodarone, has been shown to have Class I, II, III, and IV effects and perhaps others as well. Furthermore, many drugs undergo metabolism to electrophysiologically active metabolites, which may have electrophysiologic effects that differ from those of the parent compound.

Antiarrhythmic drugs are generally considered potential cardiac toxins and must be used with caution. Almost all antiarrhythmic drugs have the potential for producing proarrhythmia (figure 10.1). Proarrhythmia is the potentiation of life-threatening ventricular tachycardia and/or ventricular fibrillation (including torsades des pointes, a polymorphic ventricular tachycardia that twists upon an axis) and is often (but not necessarily) associated with QT prolongation.


Programmed Electrical Stimulation

To induce arrhythmias, a technique known as programmed electrical stimulation is performed. Programmed electrical stimulation uses standard pacing of the atrium or the ventricle at a predetermined heart rate or cycle length with the placement of premature extra stimuli. The premature extra stimuli start at a preset interval and get progressively more premature.

Generally, programmed stimulation starts at a drive cycle length faster than the sinus cycle length. Standard pacing typically occurs at a drive cycle length of 8 beats to 10 beats at 600 msec, 500 msec, or 400 msec. This drive cycle length is followed by a single premature stimulus that is often 100 msec to 200 msec shorter than the drive cycle length.

The interval between the last drive cycle length and the first premature beat is called the coupling interval. This coupling interval is shortened by intervals of 10 msec to 20 msec until the paced stimulus fails to capture the myocardium. Subsequently a second stimulus can be added. The cycle length of the first stimulus should be increased by 30 msec or 40 msec from the refractory period, and the second stimulus could be the same as or slightly less than the coupling interval of the first stimulus.

Congestive Heart Failure

Congestive heart failure (CHF) has become one of the most common diseases in the United States. Nearly 5 million people are living with CHF, and approximately 500,000 new cases are diagnosed each year in the United States alone. While this disease is associated with significant morbidity and mortality, with appropriate lifestyle modifications and medical and device-based therapy, quality of life and survival may be improved.

CHF occurs with impaired myocardial filling and/or contraction. This results in either the heart’s inability to pump a sufficient amount of oxygenated blood and nutrients to meet the body’s needs or the heart’s ability to pump blood effectively only by elevating the filling pressures. A manifestation of acute CHF is pulmonary edema, the backup of blood from the left heart into the lungs. Heart failure may be due to myocardial damage (ischemia, long-standing hypertension, the effects of alcohol, health risks of obesity, etc.). Table 23.1 shows the etiology of congestive heart failure.

CHF is the result of an imbalance in the degree of end-diastolic fiber stretch proportional to the systolic mechanical work achieved. This imbalance can produce a malfunction between mechanisms that keep the interstitium and the alveoli dry and the competing forces that result in fluid transfer to the interstitium. The mechanisms that keep the interstitium and the alveoli dry are the maintenance of plasma oncotic pressure higher than pulmonary capillary pressure, maintenance of connective tissue and cellular barriers relatively impermeable to plasma proteins, and maintenance of a vast lymphatic system.


Chapter 27 - Intravenous Drug Administration/Preoperative Checklist

The responsibility for the administration of intravenous (IV) drugs in the EP lab lies with the nurse, under the direction of the physician. Because IV medications are delivered directly into the bloodstream, their dispensation requires more knowledge and greater precautions than do other methods of drug administration. Drug serum levels reach higher concentrations, and adverse reactions occur more rapidly and are usually more severe with the use of IV medications. Therefore, it is important to recognize the problems associated with IV drug administration and to impose caution when dispensing drugs by IV push.

IV administration ensures prompt onset of action and reduces ambiguity allied with the incompleteness of drug absorption by other routes. IV administration requires regular monitoring by a nurse, because this route increases the risk of side effects or toxicity.

It is important for the EP nurse to display an understanding of the drug to be administered by exhibiting knowledge regarding the rationale for the use of a specific drug in a particular patient, the rate of the drug administration, the drug’s possible side effects, the drug’s normal dosage range, and the compatibilities and incompatibilities of the drug with other IV drugs and fluids.



Chapter 28 - Members of the EP Team

The electrophysiology team is made up of a diverse group of individuals who work together to perform a single service: arrhythmia management. This group consists of administrators, transporters/orderlies, nurses, practitioners (physician assistants/nurse practitioners), vendors (selling catheters and other devices), technicians (Ph.D.s, radiologic technologists, EP technicians), secretaries, physicians, and physicians-in-training. All these individuals must integrate into the facility in which they operate, regardless of whether the facility is an inhospital

institution (as most EP centers are) or a freestanding facility. A hierarchy among the EP team is important to ensure continuity of care. Figure 28.1 shows a possible hierarchy in which there is a director as well as a coordinator who helps supervise and organize a large fleet of staff and their activities on a day-by-day basis.

Besides the team members, many other individuals contribute to the success of the EP center. The hospital administration must believe in and be committed to the service in order to provide the adequate space, facility, and equipment. Substantial capital is necessary to equip and maintain such an EP laboratory, which continuously requires disposable and implantable equipment. Acommitment to the overall success of the program means that the facility, the staff, and the volume of equipment must grow commensurate with the growth of the program.
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