Based on results of electrophysiology studies, ablation therapy may be used to eliminate an accessory pathway in the electrical system of the heart. When this circuit is eliminated, fast heart rates should not occur. For this procedure, a specially designed catheter is positioned next to the extra pathway. A form of energy (radio frequency waves) is then delivered into the catheter, heating the heart tissue under the catheter tip and causing the normal cells to no longer function, thus resulting in elimination of the pathway. Much of the success of this approach depends on the pathway location. If the path is on the left side of the heart, the success rate is 90% to 95%. If the pathway is in the center or on the right side of the heart, the success rate is 85% to 90%. In approximately 5% to 10% of patients, even though the extra pathway appears to have been successfully eliminated, the pathway function may return later, requiring a repeat procedure.

Heart muscle cells and nerve cells share many things in common, one of which is the fact that they are both capable of rapidly reversing their resting membrane potential from negative to slightly positive values. This is known as the “action potential” and is brought on by a change in membrane permeability by certain ions. The cardiac action potential, which is associated with contraction, has five distinct phases (numbered 0–4) as described below.

Phase 0: Rapid depolarization (sodium in)

On depolarization, the cell becomes permeable to sodium through “fast” channels, and sodium, previously outside the cell, rushes inside. This causes the initial rapid upstroke of
the curve and a reversal of potential (resting cell was negative on the inside and becomes positive on the inside when depolarized).

Phase 1: Initial repolarization (sodium stops, chloride in)

The brief, rapid start of repolarization is believed to be due to the inactivation of the inbound sodium as well as a secondary influx of chloride.

Phase 2: Repolarization plateau (calcium in, potassium out)

The repolarization slows as a result of a complex interaction between a slow influx of calcium entering the cell and a slow exiting of potassium. Phases 1 and 2 are periods of absolute refractoriness.

Phase 3: Repolarization Continues (calcium stops, potassium out)

The influx of calcium ceases, whereas the outward flow of potassium continues. Phase 3 is a period of relative refractoriness.

Phase 4: Resting (sodium/potassium pump)

Most cardiac cells are -70 to -90 mV at rest. The net negative electrical charge is restored by a sodium/potassium exchange across the membrane. The slow diastolic depolarization is caused by a time-dependent fall in outbound potassium. This, combined with an increase in the sodium influx, causes the threshold to be reached.

Acute coronary syndrome is an umbrella term used to cover a group of three clinical entities:

The initial diagnosis of ACS is based on the patient’s clinical history (including risk factors), on clinical presentation, and changes on serial ECG tracings. The following table summarizes the similarities and differences of each diagnosis.

Allen’s test is a quick bedside procedure performed specifically to assess ulnar arterial circulation to the hand and evaluate the patency of the ulnar artery prior to radial arterial puncture. Elevate patient’s hand with fist clenched while both radial and ulnar arteries are compressed to occlude arterial blood flow. Pressure is then released over only the ulnar artery. Color should return to the hand within 6 seconds, indicating a patent ulnar artery and adequate collateral blood flow to the hand.

An aortic aneurysm is an abnormal dilation of a weakened aorta arterial wall that expands the diameter of the vessel >1½ times normal. (Normal aorta diameter range = 1.4–3 cm.)

Development: At first, pressure increases from the aneurysm cause the aorta lumen to widen and blood flow to slow. An aneurysm typically expands on an average of 0.3 to 0.4 cm per year, with larger aneurysms expanding faster. As the growth progresses, hemodynamic compromise ensues, creating pulsatile stresses on the weakened wall and resulting in the aorta becoming bowed and torturous. Without surgical intervention, the aneurysm may ultimately rupture or tear suddenly and cause possible death.

Sites: The abdominal aorta is the most common site for aortic aneurysms, with 80% developing below the bifurcation of the renal arteries.

Signs/Symptoms: Most aneurysms do not cause any symptoms and are usually discovered incidentally. Unfortunately, asymptomatic aneurysms have a higher risk for rupture. When symptoms do occur, they typically include flank pain (because of the pressure placed on other organs by the expanding size of the aneurysm) or back pain (between the shoulder blades and chest), bradycardia, different pressures in the right and left arms, bruit, jugular venous distention, and unequal carotid and radial pulses. An aneurysm must be at least 5 cm in diameter to be detected on a routine physical exam, and is definitively diagnosed by ultrasound, MRI, or CT.

Treatment: Elective surgical repair is considered for aneurysms that exceed 5.5 cm in diameter, or when small aneurysms increase 0.5 cm within a 6-month period.

Postoperative care focuses on strict blood pressure control in the first 24 to 48 hours to prevent bleeding, tearing of suture lines, and formation of a pseudoaneurysm.

Dissection: This occurs when there is a progressive tear in the aorta, allowing blood to collect and form a hematoma between the intimal and medial layers of the aortic wall.
Dissections are classified according to location and severity and defined by two systems; see table below.

Treatment of dissection is based on the extent and location of the dissecting segment. Daily Type A and DeBakey Type I or II are treated as surgical emergencies, and the dissecting segment is replaced with a synthetic graft or endovascular placement of a stent. Daily Type B and DeBakey Type III are generally treated medically unless hemorrhage is suspected, although grafting is an option.

Coronary angiography, also called an angiogram, a heart catheterization, or a ventriculogram, is the main diagnostic test used to pinpoint where obstructions are in the coronary arteries and to determine their severity. Conscious sedation is administered, and access is accomplished via the femoral artery. A catheter is then threaded through the entry site, up the artery, through the aorta, and into the openings of the left and right coronary arteries. Contrast dye is injected, and under x-ray, the coronary arteries are viewed in motion, making it possible to visualize plaques. After visualizing the coronary arteries (sometimes before then), another catheter is threaded into the heart’s left ventricle, which allows visualization of the wall motion, wall thickness, chamber size, and determination of ejection fraction. (This is known as a ventriculogram.) Throughout the procedure, heart pressures are monitored to determine if any pressure gradients exist. Because there are no nerve endings in the arteries, the patient is unaware that the test is being done (except for a warm sensation following injection of the contrast dye). (See Schematics on next page.)

Coronary angioplasty is accomplished using a balloon-tipped catheter inserted through the femoral or brachial artery (and threaded to the coronary artery) to widen a vessel that is narrowed due to stenosis or occlusion. Also known as percutaneous transluminal coronary angioplasty (PTCA), if successful, can alleviate myocardial ischemia, relieve angina, and prevent myocardial necrosis. The indications for PTCA have expanded with the advent of improved equipment and techniques; however, the procedure is generally reserved for patients with at least a 50% narrowing of vessels. There are a number of different balloons that can be used; a discussion of the most common follows.

The ankle-brachial index is a noninvasive examination that provides baseline data regarding circulation in the lower limbs. A blood pressure cuff is put around the ankle above the malleolus. When the dorsalis pedis pulse has been located via Doppler, the cuff is inflated
in the usual manner until the Doppler signal is no longer heard. As the cuff is slowly deflated, the systolic pressure is recorded when the signal returns. The same procedure is done by using a Doppler on the posterior tibial pulse. The higher pressure of the two pressures is used for the calculation of the index. The brachial systolic pressure is then measured in the same manner and is divided into the ankle systolic pressure. The lower of the two numbers (right vs. left) results in the overall ABI.

An annulus is a ring of tissue around the opening of a valve. When the annulus is dilated, it allows blood to leak back through the valve after it has closed. Most commonly used on the mitral valve, the implantation of an annuloplasty ring (either rigid or flexible) will bring the annulus back to a more normal position, facilitate the meeting of the valve leaflets, and aid in eliminating the regurgitant blood flow.

Aortic regurgitation/insufficiency is a condition in which there is a weakening or ballooning of the aortic heart valve, causing the valve to fail to close tightly, leading to backflow of blood into the ventricle. This reduces the amount of blood available to perfuse the coronary artery and leads to myocardial ischemia. Over time, it also causes dilatation and hypertrophy of left ventricle.

Aortic stenosis is a narrowing or constriction of the opening of the aortic valve, which results in a decrease in the outflow of blood from the left ventricle to the aorta. This causes a pressure overload in the left ventricle, an increase in left ventricular systolic pressure, and hypertrophy. As the left ventricular pressure continues to increase, the pulmonary system becomes congested, and the right side of the heart begins to fail. Stenosis reduces stroke volume, and without a compensatory increase in heart rate, cardiac output falls and perfusion of the coronary arteries is reduced.

Apheresis is a process using the Liposorber system, indicated for use in removing LDL cholesterol from the plasma of the following high-risk patient populations for whom diet has been ineffective and maximum drug therapy has either been ineffective or not tolerated:

The patient’s blood is withdrawn via a venous access and is pumped to a plasma separator, where it is separated and pumped into one of the two LDL absorption columns. As the plasma passes through the column, LDL, Lp(a), and VLDL are selectively absorbed by dextran sulfate cellulose beads within the column. There is minimal effect on other plasma components such as HDL and albumin. The LDL-depleted plasma leaves the column and is recombined with the blood cells exiting the separator, all of which are returned to the patient via a second venous access. When the first column has completed absorbing the LDL, the computer-regulated machine automatically switches the plasma flow to the second column. The plasma remaining in the first column is returned to the patient. The column is then regenerated, eluting the LDL, Lp(a), and VLDL to the waste lines. After elution, the column is reprimed completely and is ready for the next cycle of absorption, allowing continuous treatment. A typical treatment takes about 2 to 4 hours to complete and may be repeated every 2 to 3 weeks.

Ashman’s theory states that aberrant conduction is more likely to complicate atrial fibrillation when a longer cycle is succeeded by a shorter one.

The phenomenon may also occur when sinus bradycardia is complicated by a premature atrial contraction (PAC). The cycle of sinus bradycardia is long, but PAC
shortens cycle and is conducted aberrantly (usually in right bundle branch [RBB] pattern, rsR′):

Therefore, according to Ashman, the beat that follows a long/short cycle favors aberrancy. This, however, is not a hard-and-fast rule, because by the rule of bigeminy, a longer cycle also tends to produce a ventricular ectopic beat equally as many times.

Atherectomy is indicated in conditions not well treated by standard angioplasty, such as when the plaque in the coronary arteries is too large or the plaque is hardened to a degree that it is no longer possible to flatten it. Atherectomy creates a smoother surface by debulking the vessel and is sometimes followed by angioplasty or stent placement. In theory, the process permits a more controlled vascular injury and minimizes the degree of arterial stretch.

Potential complications in both procedures include perforation of the coronary artery, abrupt closure, embolization distal to the lesion site, and myocardial infarction. The rate of restenosis and other complications is comparable to that of angioplasty.

An automatic implantable cardiac defibrillator is a device implanted transvenously with local anesthetic, using a simple surgical procedure (the patient is usually able to be discharged with 24 hours) to treat ventricular arrhythmias with pacing and shock therapy. Current versions also have the capability to treat and suppress atrial arrhythmias, resynchronize the ventricles to manage heart failure symptoms, or pace the heart with all the features of a dual-chamber pacemaker. Originally indicated for patients who have survived two cardiac arrests, the devices have recently been shown to improve survival in all patients with prior myocardial infarction and an ejection fraction of 30% or less (identifying them as high risk for sudden death).

The axis is the mean direction (vector) in which electrical activity spreads across the heart. The strength of the vector is indicated by recording a small deflection for a weak vector and a large deflection for a strong vector.

Normal axis is described by some authors to be in the narrow bounds of +30° to +60° and by others to be between 0° and +90°. Using the range from -30° to +110° allows easier definition of hemiblock.

Many technologies are currently under investigation for the treatment and prevention of restenosis following angioplasty and stenting, but the most promising appears to be brachytherapy. This technique, approved by the FDA in 2002, delivers either beta or gamma radiation to the blocked site (via a catheter, postangioplasty) utilizing a miniaturized x-ray emitter. Once delivered, the radiation “beads” remain in place from 3 to 20 minutes before being withdrawn. No radioactive material is left in the body. The radiation is not felt, and the normal healing process is unaffected. The procedure works on the principle that the radiation interacts with vessel walls, destroying their capability for cell division and regrowth.

Brugada syndrome is a condition associated with sudden cardiac death, idiopathic ventricular fibrillation, or self-terminating polymorphic ventricular tachycardia in an otherwise structurally normal heart. Characterized by a right bundle branch block pattern and ST segment elevations in leads V₁ to V₃, the syndrome is seen more frequently in males than in females and primarily in a mean age group of 35 to 40 years. It is consistent with a chromosomal mutation and predisposes individuals to a lifetime risk of sudden cardiac death. There is no effective pharmacologic treatment, and genetic counseling is advised.

Cardiac index = cardiac output ÷ body surface area Normal: 2.5 to 4.5 L/min/m²

Cardiac output = stroke volume × heart rate Normal: 4 to 8 L/min

Cardiomyopathy is an irreversible primary disease of the heart muscle, most commonly affecting the myocardial layer but occasionally affecting the endocardial, subendocardial, and/or pericardial layers of the heart. Cardiomyopathies are divided into the following three types:

Electrical cardioversion (also known as direct current, or DC cardioversion) is the delivery of a synchronized electrical shock through the chest wall to the heart via conducting pads. Its purpose is to suddenly and simultaneously interrupt the abnormal electrical circuit(s) in the heart, and restore a normal electrical rhythm. Most cardioversions (synchronized shocks) are performed to treat rhythms such as atrial fibrillation, atrial flutter, ventricular tachycardia with a pulse, or any other perfusing rhythm that is undesirable due to complications or symptoms.

Cardioversion differs from defibrillation in that the shock is synchronized, meaning it is timed to deliver current during the safest point of the cardiac cycle (the R wave phase). A defibrillator placed in the synchronized mode will actually delay delivery of the shock, waiting instead until it senses an R wave before firing. This avoids the delivery of energy during the electrically vulnerable downslope of the T wave, and prevents possible R on T phenomenon, where a perfusing rhythm can deteriorate to a chaotic, pulseless one.

Closure devices assist in achieving hemostasis postfemoral artery puncture and have proven to be an efficient alternative/adjunct to manual compression. They can be divided into four categories:

The number of devices available on the market is numerous and continues to expand. A short discussion of only the more “classic” models follows. In general, the principles for all devices in the same category are similar, and some universal rules apply:

Aortic constriction, usually distal to the left subclavian artery, stresses the left ventricle and causes an increase in afterload.

Treatment: Usually corrected by surgery or by nonsurgical balloon dilation.

Cor pulmonale is a right ventricular enlargement secondary to a lung disorder that produces pulmonary artery hypertension (i.e., pulmonary embolism, COPD, loss of lung tissue related to surgery or trauma). The following hallmarks indicate that the right ventricle is feeling strain:

Defibrillation is the discharge of energy (joules) in the form of a nonsynchronized shock, generally delivered to the heart via transthoracic paddles or pads for the purpose of re­establishing normal electric conduction in the presence of VF or pulseless V-tach.

The Dor procedure, also known as left ventricular reconstructive surgery, or EVCPP (endoventricular circular patch plasty), is a surgical approach that is sometimes used after an aneurysm forms following a heart attack. By restoring the normal elliptical geometry of the left ventricle, the ability of the ventricle to contract is improved, resulting in improved heart function.

The heart is placed on heart-lung bypass, and a small incision is made into the left ventricle to find the exact location of the scarred tissue. Two or more rows of circular stitches are then placed around the border of the dead tissue to separate it from healthy muscle tissue and then are pulled together like a purse string to permanently separate the dead tissue from the rest of the heart. (Sometimes an area of scar tissue is removed first before the stitches are pulled together, of if there is a lot of dead tissue to remove and the stitches are not enough to isolate the area, a patch must be placed.) Lastly, the outside of the ventricle is closed and reinforced with another row of stitches. Often, other surgeries, such as CABG or valve surgery, are often done at the same time.

A pronounced form of pericarditis that develops in some patients weeks or months after an MI, characterized by pleuritic chest pain, fever, pericardial friction rub, and mild to moderate pleural effusion, Dressler’s syndrome is rarely serious, although it often recurs several times before finally resolving spontaneously.

Pitting >1 inch = 4+

Pitting ½ to 1 inch = 3+

Pitting ¼ to ½ inch = 2+

Pitting <¼ inch = 1+

First-pass angiocardiography is used to show end-diastolic and end-systolic images, shunts, and details of heart wall motion. From these values, an ejection fraction (EF) can be determined, indicating the percentage of ventricular chamber emptying. It is determined by this formula:

Normal ejection fraction is 60% to 65% (±8%); lower values indicate ventricular dysfunction, whereas an ejection fraction of <35% indicates serious ventricular problems.

Fusion beats occur when two opposing electrical currents meet and collide within the same chamber at the same time. The ensuing EKG complex is often narrower and of lesser amplitude than an ectopic beat alone.

Depending on the monitoring system, the number of EKG electrodes (wires) positioned on the patient will differ. But remember: One electrode (wire) cannot be a “lead.” Leads are pictures, so this means that a group of electrodes is required to capture a specific view. (For example, to obtain a 12-lead EKG, there are six “chest” electrodes, and four “limb” electrodes. This is only 10 wires, but the different combinations of the wires yield 12 different views.)