Approach Considerations
Lyme disease is diagnosed by its clinical picture and serologic confirmation. Serologic test findings may be negative during the first several weeks, but most patients have a positive antibody response to B burgdorferi by enzyme-linked immunoabsorbent assay (ELISA). In addition, B burgdorferi may be cultured from skin lesions during the acute phase or from skin lavage as it has been recently described.
Diagnosis of acute Chagas disease is made by microscopic examination of fresh anticoagulated blood to visualize the parasites. Whenever this technique is unsuccessful, xenodiagnosis can yield positive test results in virtually all patients with acute Chagas disease and in half of those with chronic disease. In this technique, uninfected reduviids feed on the patient's blood and, 30 days later, their intestinal contents are examined for the presence of parasites. In case of chronic Chagas disease, serologic tests to detect antibodies against T cruzi antigens, such as complement fixation and ELISA, are used.
The diagnosis of Reiter syndrome is mainly clinical, because no specific laboratory tests are used for this entity. However, nonspecific findings include elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), elevated immunoglobulin A (IgA), mild normochromic and normocytic anemia, and absent rheumatoid factor (RF) and antinuclear antibodies (ANAs).
Definitive diagnosis of diphtheria is made by isolation of C diphtheriae from local lesions.
Perform laboratory testing for lymphoma, amyloidosis, sarcoidosis, and digoxin as indicated.
Antenatal diagnosis of third-degree AV block requires careful maternal-fetal management and monitoring with ultrasonography and echocardiography. [29] Delivery is recommended at a tertiary care center with a multidisciplinary team that includes perinatal care and an association with a pediatric cardiology center. [29]
Electrophysiologic Studies
Intracardiac electrophysiologic (EP) studies are usually not necessary for most patients with AV block; however, when performed, the EP results can be used to determine whether the AV block is above, within, or below the bundle of His.
EP studies are not required for patients with complete AV block and symptoms such as dizziness, syncope, or congestive heart failure. These patients require permanent pacemaker therapy. Indications for pacing are outlined in detail in the ACC/AHA/HRS consensus document.
Infra-His AV block
Patients with infra-His atrioventricular (AV) block typically have a much slower ventricular rate (ie, heart rate) and require permanent pacemaker therapy to avoid asystole, ventricular arrhythmia, syncope, or symptoms.
The block is located in the AV node above the His bundle when the ventricular depolarization is preceded by a His depolarization, which, in turn, is not coupled to the atrial depolarization.
The block is within the His bundle if the His bundle depolarization is preceded by an atrial depolarization, and a second His bundle depolarization precedes a ventricular depolarization.
The block is below the His bundle when the His depolarization follows an atrial depolarization but does not precede a ventricular depolarization.
Junctional/ventricular pacing
Adequacy of the junctional or ventricular pacemaker can be evaluated by pacing the ventricles at different rates for 30-60 seconds, stopping abruptly, and measuring their recovery time (ie, from the last paced ventricular beat to the first spontaneous ventricular beat). A junctional or ventricular recovery time exceeding 3 seconds in children is abnormal and has been associated with risk for sudden death.
See the following examples of intracardiac EP studies.
This is an example of a normal finding on intracardiac electrophysiologic (EP) study. The surface electrocardiogram (ECG) is represented in different colors, with its corresponding intervals (ie, PR, QT) on top. A catheter with several electrodes is placed inside the heart, close to the superior vena cava–right atrial junction. This catheter records the sinoatrial node (SN) activity and is depicted here as the high-right atrial (HRA) deflection. Beneath the HRA intracardiac electrogram is the His-bundle intracardiac electrogram, which is recorded by the electrodes of a second catheter placed across the posterior aspect of the tricuspid valve. The His-bundle electrogram provides the most information about atrioventricular (AV) conduction. Three main deflections are present, with 2 intervals: (1) the A deflection corresponds to the activation of the low-right atrium, (2) the H deflection corresponds to the activation of the His-bundle before its branching into the Purkinje system, and (3) the V deflection corresponds to the activation of the proximal portion of the right ventricle. The atrium-His (A-H) interval represents the conduction time through the AV node. It shows the time elapsed between the activation of the low-right atrium (A) and the activation of the His-bundle (H), ranging normally from 50-120 milliseconds. The His-ventricle (H-V) interval is measured from the beginning of the H deflection to the beginning of the V deflection and represents the conduction time through the His-Purkinje system (normally 35-55 ms). Disease in the AV node prolongs the A-H interval, whereas disease in the distal conducting system prolongs the H-V interval.
This is a Mobitz type II second-degree atrioventricular (AV) block. The surface electrocardiograph (ECG) shows normal PR intervals and a P wave that is not followed by a QRS (in this graphic, the first P wave does not conduct through the AV node). The intracardiac electrogram shows no His deflection (H) after the blocked A deflection. In this case, the escape rhythm originates higher in the AV node at a rate of 40-50 beats per minute and is fairly reliable. However, patients may report symptoms of bradycardia such as dizziness, fatigue, and syncope. Because this type of AV block may progress to complete or third-degree AV block, patients should be monitored regularly even in the absence of symptoms.
This is a Mobitz type II second-degree atrioventricular (AV) block that may likely progress to a third-degree, or complete, AV block. The difference from the previous image is that, in this case, a His (H) deflection is present after the A deflection (the atrium-His [A-H] interval is maintained); however, no ventricle (V) deflection is present after the first H deflection. Therefore, in this case, the escape rhythm is slower than in the intracardiac electrophysiologic study of the patient in the previous image (< 40/min) and less reliable. This patient is more likely to receive a pacemaker because of the higher incidence of sudden death secondary to prolonged asystole.
-
This is an example of a normal finding on intracardiac electrophysiologic (EP) study. The surface electrocardiogram (ECG) is represented in different colors, with its corresponding intervals (ie, PR, QT) on top. A catheter with several electrodes is placed inside the heart, close to the superior vena cava–right atrial junction. This catheter records the sinoatrial node (SN) activity and is depicted here as the high-right atrial (HRA) deflection. Beneath the HRA intracardiac electrogram is the His-bundle intracardiac electrogram, which is recorded by the electrodes of a second catheter placed across the posterior aspect of the tricuspid valve. The His-bundle electrogram provides the most information about atrioventricular (AV) conduction. Three main deflections are present, with 2 intervals: (1) the A deflection corresponds to the activation of the low-right atrium, (2) the H deflection corresponds to the activation of the His-bundle before its branching into the Purkinje system, and (3) the V deflection corresponds to the activation of the proximal portion of the right ventricle. The atrium-His (A-H) interval represents the conduction time through the AV node. It shows the time elapsed between the activation of the low-right atrium (A) and the activation of the His-bundle (H), ranging normally from 50-120 milliseconds. The His-ventricle (H-V) interval is measured from the beginning of the H deflection to the beginning of the V deflection and represents the conduction time through the His-Purkinje system (normally 35-55 ms). Disease in the AV node prolongs the A-H interval, whereas disease in the distal conducting system prolongs the H-V interval.
-
This is a Mobitz type II second-degree atrioventricular (AV) block. The surface electrocardiograph (ECG) shows normal PR intervals and a P wave that is not followed by a QRS (in this graphic, the first P wave does not conduct through the AV node). The intracardiac electrogram shows no His deflection (H) after the blocked A deflection. In this case, the escape rhythm originates higher in the AV node at a rate of 40-50 beats per minute and is fairly reliable. However, patients may report symptoms of bradycardia such as dizziness, fatigue, and syncope. Because this type of AV block may progress to complete or third-degree AV block, patients should be monitored regularly even in the absence of symptoms.
-
This is a Mobitz type II second-degree atrioventricular (AV) block that may likely progress to a third-degree, or complete, AV block. The difference from the previous image is that, in this case, a His (H) deflection is present after the A deflection (the atrium-His [A-H] interval is maintained); however, no ventricle (V) deflection is present after the first H deflection. Therefore, in this case, the escape rhythm is slower than in the intracardiac electrophysiologic study of the patient in the previous image (< 40/min) and less reliable. This patient is more likely to receive a pacemaker because of the higher incidence of sudden death secondary to prolonged asystole.
-
This is a 12-lead electrocardiograph (ECG) of a 2-year-old girl with first-degree atrioventricular (AV) block that progressed to a complete, or third-degree, AV block (which is shown here). Her mother brought her to the clinic with described symptoms of easy tiredness and refusal to walk more than 1 block, which was a dramatic change for this girl. A normal sinus rhythm is present (shown by upward P waves in leads I, II, and aVF) at a rate of 135 per minute, which is completely dissociated from the QRS at a rate of 67 per minute. The QRS is narrow at 100 milliseconds with a frontal axis of 62°. No ventricular hypertrophy is present by voltage criteria. Because of the narrow QRS and its escape rate, this ECG is interpreted as complete AV block with junctional escape rhythm.
-
This is a 12-lead electrocardiograph (ECG) of a 2-year-old girl with first-degree atrioventricular (AV) block that progressed to a complete, or third-degree, AV block (see the previous image). This ECG was taken after dual chamber (DDD-R) pacemaker placement. Sinus P waves are present at a rate of 90 per minute, followed by a pacemaker spike that produces a wide QRS of 128 milliseconds. No spike occurs before each P wave, because this type of pacemaker senses the patient's own P waves and stimulates the ventricle afterward. Therefore, the patient's ventricular rate follows her physiologic needs by tracking the patient's own atrial rate. With a DDD-R pacemaker, if the patient develops sinus bradycardia, the pacemaker takes over and paces the right atrium at the programmed rate, which is followed by the ventricular stimulation, maintaining AV synchrony.
