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Advanced atrioventricular block of the second degree and block of the third degree of type B
Advanced AV block II degree and AV block III degree can also be determined in the presence of wide QRS complexes .
The experimental record shown in Fig. 1.15 was obtained a few minutes after the recording shown in Fig. 1.12. In fig. 1.15 registration of transmembrane potentials in the atrial fiber adjacent to the AV node (II), as well as in the NH region of the AV node (NH), is presented together with electrograms of the region of the sinus node (SU) and ventricles (G). In the initial part of this figure, two consecutive atrial pulses completely depolarize the NH fiber and pass into the ventricles, but the conduction time (both intranodal and in the His-Purkinje system) increases with a second contraction. The third atrial impulse causes incomplete depolarization of the NH fiber (shown by the arrow in Fig. 1.15) and is unable to activate the ventricles. Consequently, the conduct of 3: 2 with the Wenckebach periodical is determined. Further, two atrial impulses again cause a normal action potential in the NH fiber, which indicates successful intra-nodal conduction. However, only the first impulse penetrates the ventricles, while the second is blocked below the NH region, most likely in the His-Purkinje system. Violation of the third impulse occurs above the NH fiber, as in the initial Wenckebach cycle, as a result of which a 3: 1 response is observed. Please note that the presence of two levels of the block (inside and below the AV node) is combined with a violation of intraventricular conduction, as evidenced by the expansion of QRS complexes and an increase in conduction time in the His-Purkinje system. In contrast to the intra-nodal holding relationship 4; 3 observed in Fig. 1.12, the ratio 3: 2 in Fig. 1.15 may well reflect the further suppression of intra-nodal conduction. And indeed, some time after the registration presented in Fig. 1.15, an intra-nodal blockade of 2: 1 developed. It is possible that when violations of the intraventricular conduction are pronounced enough to cause AV blockade, the underlying pathophysiological mechanisms often include the region of the AV node.
In fig. 1.15, the second of two atrial impulses that successfully pass through the AV node activates the ventricles once, and is blocked for the second time in the His-Purkinje system, although the ratio of conducting 3: 2 remains at the level of the AV node. A brief discussion of this mechanism seems to us necessary. First, it is possible that the conductivity of the His – Purkinje system exhibits temporary oscillations [9, 32]; thus, some improvement in conductivity will trigger a 3: 2 response. Whereas its deterioration will determine the ratio of holding 3: 1 (as seen in the right half of Fig. 1.15). On the other hand, blocking the third atrial impulse inside the AV node in the presence of a 3: 2 ratio will lead to a decrease in the frequency of excitations in the His-Purkinje system. Therefore, the first excited excitation after such a pause will be accompanied by a noticeable increase in the duration of the action potential and the refractory period of the Purkinje fibers. Due to increased refractoriness, the atrial impulse second after a pause may be blocked at the level of the His-Purkinje system (a mechanism often referred to as a block during phase 3). In the case under consideration, for the action of this mechanism, it must be assumed that the duration of the action potential of the Purkinje fibers exceeds 500 ms. Although this duration seems rather long, similar action potentials for Purkinje fibers are often observed under various experimental conditions.
1.15. Two levels of the block in the heart of the rabbit (in the AV node and the Gis-Purkinje system), which determine the AV conduct of 3: 2 and 3: 1. SU - sinus node; P - atria; F - ventricles.
Fig. 1.16 illustrates the case of grade III AV block with wide QRS complexes (compare with QRS in Fig. 1.19) [30.33]. On the upper two fragments of the recording made on June 21 (Fig. 1.16), the sinus P waves, as well as several ectopic P waves, do not have a constant connection with ventricular excitations and QRS complexes follow regularly with a frequency of 44 beats / min. Wide QRS complexes with signs of blockade of the right leg indicate the localization of the secondary pacemaker in the system of the left leg of the bundle (or near it). The diagnosis of grade III AV block is straightforward. At the bottom of fig. 1.16 presents an electrocardiogram obtained two days later: a regular ventricular rhythm is maintained despite the presence of atrial fibrillation, determined by shallow waves at the level of the contour. The ventricular rhythm is somewhat accelerated (49 beats / min). The fact that the configuration of the QRS complex has not changed is evident in leads aVF and V1; this indicates ventricular control from the same secondary focus that was observed two days earlier. The third contraction in the aVp lead and the second contraction in the aVF lead (the shape of the latter is distorted due to the imposition of a 1 mV calibration pulse) are ventricular extrasystoles. Since the interval between the QRS extrasystolic complex and the next QRS complex of the escape rhythm is either equal to the remaining R – R intervals (in the aVp lead), or slightly larger than them (in the aVF lead), we can assume the premature discharge of the additional pacemaker during retrograde conduct of extrasystolic impulses and the restoration of its automatism . In this case, the site of the conduction disturbance is most likely located below the bis of the bundle of His.
Fig. 1.16. High degree AV block with an escape rhythm that occurs in the left leg of the bundle of His, both with a sinus rhythm (above) and with atrial fibrillation (below).
However, it should be noted that when a high degree of AV block is observed against the background of atrial fibrillation, the likelihood of intra-nodal conduction disturbances (in addition to the subnodal block) is much higher than in cases of sinus rhythm with a high degree of AV block. The reason for this is as follows: since the atrial excitation waves during atrial fibrillation are very irregular and less effective as stimuli of the AV node [53–56], the intranodal block develops much more easily than with the sinus rhythm. Therefore, if there is only an electrocardiogram similar to that presented at the bottom of Fig. 1.16, especially in the case of taking digitalis, before diagnosing a high degree blockade at the level of the His-Purkinje system, it is necessary to suspect the development of grade III AV block at the level of the AV node in addition to the previous block of the bundle leg. In differential diagnosis, a comparative analysis of similar ECGs and a temporary discontinuation of digitalis preparations are advisable, however, for a definitive diagnosis, in certain cases, electrodes of the His bundle may be required.
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Advanced atrioventricular block of the second degree and block of the third degree of type B
- Advanced atrioventricular block of the second degree and block of the third degree of type A1
1 According to the authors' classification, type A denotes a variant of AV blockade with a normal form of the QRS complex, and type B indicates a variant of AV blockade with an expanded QRS complex. - Note. translator. The term “advanced grade II AV block” is used when more than two consecutive supraventricular impulses are blocked . Although to distinguish this option from the blockade of the AV blockade III degree
- Atrioventricular block of the second degree
Grade II AV block is usually divided into two types: Wenckebach I (Mobitz I) and Wenckebach II (Mobitz II) [35, 36]. A high degree AV block with a higher conduction ratio (2: 1, 3: 1) may be a block of type I or II. Block type Wenckebach I (Mobitz I). Classical blockade of type I is characterized by a progressive increase in the P – R interval until the P wave is blocked (Fig. 2.3).
- Atrioventricular block of the second degree with expanded QRS complexes
Grade II AV block, combined with delayed intraventricular conduction (QRS ^ 0.12 s), usually proceeds like Mobitz II and has a less favorable prognosis than AV block with normal QRS complexes. Therefore, it is important that the features and principles of the diagnosis of this type of blockade are fully understood [6,7,9,32,33]. A typical example of grade II AV block (type II) is shown in Fig. 1.7;
- Atrioventricular block of the second degree with normal QRS complexes
In fig. 1.2 in the middle part of the II lead three contractions are visible with a progressive increase in the P – R interval; the fourth P-wave (P4) cannot pass into the ventricles, which causes a long pause. The pause ends with a wave P (P5), which is carried out in the ventricles (again with a shorter interval P — R). Since three of the four sinus impulses are transmitted to the ventricles, this is called the “holding ratio
- Spontaneous atrioventricular block Atrioventricular block of the first degree
Grade I AV block (P — R> 0.21 s) may be the result of delayed conduction in the atrium, AV node, His bundle or in its legs (Fig. 2.2) . In 79% of our patients with an increased P – R interval, delayed conduction occurred in two (or more) places, although the AV node was the dominant place of delay (in 83% of patients). Delay in only one place was noted in 21% of patients: in 11%
- The degree of atrioventricular block
From the point of view of the severity of the blockade, it is considered complete if signs of excitation in the ventricles are not found anywhere on the ECG. It should be noted, however, that in very large fragments of the rhythmogram and with 24-hour Holter monitoring, random unblocked excitations are often detected in patients presumably having a “complete” AV block. This situation should be distinguished from
- Atrioventricular block of the first degree
Since the normal time range of atrioventricular conduction (P – R interval) in adults is believed to be 0.12–0.21 s, the determination of P – R intervals exceeding 0.22 s indicates degree I AV block. This criterion can only be used if there is a regular sinus (or atrial) rhythm. When atrial extrasystole is administered to the ventricles at intervals of R — R
- 2nd degree atrioventricular block - incomplete
For atrioventricular blockade of the 2nd degree it is characteristic that part of the impulses emerging from the sinus node do not pass the atrioventricular connection and do not enter the ventricles. Therefore, this part of the sinus impulses blocked by the atrioventricular connection cannot cause ventricular excitation. Therefore, on the electrocardiogram after the P wave (atrial excitation) of the ventricular
- 3rd degree atrioventricular block - complete
With complete atrioventricular block, the atria are excited from the main driver of the heart rhythm - from the sinus node. Therefore, a P wave recorded at a certain constant frequency (for example, 90 per minute) will take place on the electrocardiogram, and the P – P intervals measured on different sections of the ECG tape will be the same (in our example, 0.67 s). And what will be the pacemaker for
- Atrial ventricular block of the second degree
ICD-10 code I44.1 Diagnostics Diagnosis Mandatory Level of consciousness, respiratory rate and effectiveness, heart rate, pulse, blood pressure, ECG, history if possible Laboratory tests: hemoglobin, blood gases, CBS, electrolytes (K, Na, Mg, Ca, Cl), blood glucose, white blood cells, blood counts, KFK, AlAT, AsAT enzymes During treatment Monitoring
- Anterograde AV blockade of the I degree, or incomplete AV blockade with lengthening of time of AV carrying out
This form of blockade was described at the end of the 19th century. K. Wenckebach (1899), who showed that when AV conductivity worsens, the a – c interval elongates on the jugular venous pulse curve. The same phenomenon on the ECG (more in the II lead) is reflected in the lengthening of the P – R (Q) interval, with each P wave followed by a QRS complex associated with it, that is, conducted. Total AV block I degree