the main
about the project
Medicine news
To authors
Licensed books on medicine
<< Ahead Next >>

Advanced atrioventricular block of the second degree and blockade of the third degree of type A1

1 According to the classification of the authors, type A denotes a variant of AV-blockade with the normal form of the QRS complex, and type B - a variant of AV-blockade with an extended QRS complex. - Note. translator.

The term “advanced AV block II degree” is used in cases when more than two consecutive supraventricular impulses are blocked [9]. Although it is difficult to distinguish this variant of the blockade from AV-blockade of the III degree (if available), still with the blockade of the III degree most of the ventricular complexes are a consequence of impulses arising in the secondary source of automatism, whereas with the advanced blockade of the II degree the activation of the ventricles is controlled mostly unlocked supraventricular pulses. The type of conduction in which one sinus impulse is conducted into the ventricles and followed by two blocked impulses is called 3: 1 conduction, whereas successful conduction of only one of the four atrial impulses is defined as 4: 1 conduction. A few examples of this type of blockade are discussed below.

In fig. 1.13 shows the experimental registration of transmembrane action potentials in the field of the AV node, as well as an electrocardiogram and ladder diagram for the analysis of the activation sequence [9]. In the initial part of fig. 1.13 there are several periods of AV-conduction 2: 1, in which the AV-interval detects an alternation of short and long cycles of 202, 138, 190 and 150 ms. Violation of conduction always occurs above the NH fiber, while the conduction time in the His-Purkinje system (or sub-node time) remains constant and almost corresponds to the norm. Judging by the ventricular complex on the ECG, intraventricular conduction disorders are absent. Thus, there appears to be only one block level. However, fluctuations in the amplitude of local responses of NH fibers suggest that the alternation of AV-conduction time is due to the difference in the depth of penetration of blocked atrial impulses into the AV node. For example, the second and sixth waves of atrial excitation (low-amplitude biphasic oscillations on the electrocardiogram) are hardly accompanied by any changes in the membrane potential of the rest of the NH fiber, while the fourth atrial impulse causes some change in potential (local response), indicating a somewhat deeper penetration arousal. This increases the time of AV-conduction of the fifth atrial impulse compared with other non-blocked impulses - the effect of latent conduction. As noted above, a 2: 1 AV-holding period is followed by a 4: 1 holding period. During 4: 1, the second of three consecutive blocked pulses causes a slightly larger change in potential, which implies a deeper penetration of this pulse into the node. A similar phenomenon is usually observed when 4: 1 is performed.

Fig. 1.13. Advanced AV-blockade of the II degree with a variable depth of penetration of the atrial impulse into the AV-node (AVU).

Presented in Fig. 1.13, B record received 3 minutes after the registration shown in Fig. 1.13, A, three periods of AV-holding 2: 1 followed by answers 3: 1 and 4: 1. Registration of the transmembrane potential in the N-region of the AV-node during 2: 1 again demonstrates fluctuations in the level of conduction disturbance, causing the alternation of AV-conduction time periods. When a blocked pulse penetrates deeper into the AV node, the subsequent action potential of the fiber detects a decrease in the rate of rise of the front when the zero phase is smeared or notched. Obtaining such data suggests the presence of either decrement or uneven.
Based on the sequence of alternation of the degree of penetration of excitation - during periods of 2: 1, one would expect that the sixth atrial impulse would block somewhere in the proximal part of the AV node, but it seems to penetrate deeper, judging by the amplitude of the corresponding local response. Intra-node blocking of the subsequent (seventh) atrial impulse and the occurrence of a 3: 1 ratio is most likely due to this deeper latent conduction. Thus, with advanced AV-blockade II, variations in the depth of penetration of the excitation, apparently, are the rule, even if a violation of the conduction always occurs in the AV-node tissue.

The development of AV-blockade is promoted by other mechanisms, such as latent excitation circulation [9].

When conditions similar to atrial flutter are created experimentally by increasing the frequency of atrial stimulation in an isolated rabbit heart, AV-conduction 2: 1 is usually observed with a sufficiently high frequency of stimulation. In such cases, every second atrial impulse is blocked inside the AV node, although phenomena similar to those shown in Fig. 1.12, also sometimes observed.

In AV-blockade of III (or high) degree, activation of the ventricles is controlled mainly by the secondary pacemaker, and sinus or atrial impulses are rarely conducted to the ventricles. It is obvious that the classification of types I and II of the AV block II degree is not applicable for this variant of the blockade.

In the example of AV-blockade of III degree, presented in Fig. 1.14, And, sinus bradycardia with moderate sinus arrhythmia is observed. However, the P teeth and QRS complexes are independent of each other with a constant ventricular rhythm of 30 beats / min. The width of the QRS complex is within the normal range (0.07 s); therefore, automatic focus is most likely located above the His bundle bifurcation. This implies localization of the block above the secondary pacemaker, probably inside the AV node [17,30,33].

In fig. 1.14, B small waves at the level of the isoline indicate atrial fibrillation, while ventricular complexes appear quite regularly at a frequency of 40 beats / min. Thus, the presence of a secondary pacemaker is quite obvious [15-17]. In order for such an escape mechanism (escape) of the rhythm to retain its activity, it is necessary to postulate a very high degree of disturbance with the blocking of the majority of impulses emanating from the flickering atria. The normal width of the QRS complexes in this case implies the localization of the conduction block in the atrioventricular junction, most likely in the AV node. With the introduction of high doses of cardiac glycosides and the presence of a violation of conduct should be suspected primarily digitalis intoxication as a mechanism for such violations. On the other hand, if the ventricular cycles against the background of atrial fibrillation are not completely regular, as in this case, and many R — R intervals are the same, one can assume the frequent occurrence of escape pulses as a result of AV degree II blockade. However, in the absence of clear criteria for estimating the percentage of identical R – R intervals (assuming the rhythm escapes in any lengthy fragment of the record), blockade of the II degree should be suspected. Thus, the diagnosis in such cases may be subjective rather than empirical, in contrast to the cases of grade III blockade presented in fig. 1.14, B. Nevertheless, in such situations the clinician should not forget about the possible influence of digitalis preparations.

Fig. 1.14. Grade III AV blockade with narrow QRS complexes with sinus rhythm (A) and atrial fibrillation (B).
<< Ahead Next >>
= Go to tutorial content =

Advanced atrioventricular block of the second degree and blockade of the third degree of type A1

  1. Advanced atrioventricular block of the second degree and blockade of the third degree of type B
    Advanced Grade II blockade and Grade III blockade can also be determined in the presence of wide QRS complexes [33]. The experimental recording 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)
  2. Atrioventricular block second degree
    AV degree II blockade is usually divided into two types: Wenckebach I (Mobitz I) and Wenckebach II (Mobitz II) [35, 36]. A high degree of AV blockade with a higher holding ratio (2: 1, 3: 1) may be a blockade of type I or II. Wenckebach I (Mobitz I) block. Classical blockade of type I is characterized by a progressive increase in the interval P — R until wave P is blocked (Fig. 2.3).
  3. Second degree atrioventricular block with advanced QRS complexes
    AV degree II blockade, combined with delayed intraventricular conduction (QRS ^ 0.12 s), usually proceeds as Mobitz II and has a less favorable prognosis than AV blockade with normal QRS complexes. Therefore, it is important that the features and principles of diagnosis of this type of blockade are fully “understood [6,7,9,32,33]. A typical example of AV degree II blockade (type II) is shown in Fig. 1.7;
  4. Second degree atrioventricular block with normal QRS complexes
    In fig. 1.2 in the middle part of the lead, three contractions are seen 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 P (P5) wave, which is conducted into the ventricles (again with a shorter P — R interval). Since three of the four sinus impulses are transmitted to the ventricles, this is called the
  5. Spontaneous atrioventricular block Atrioventricular block of the first degree
    AV degree I blockade (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) [27]. In 79% of our patients with an extended P – R interval, the delay in conduction occurred in two (or more) sites, although the dominant place of delay was the AV node (in 83% of patients). Delay in only one place was observed in 21% of patients: in 11%
  6. The degree of atrioventricular block
    From the point of view of the severity of the blockade, it is considered complete if on the ECG there are no signs of conduction in the ventricles anywhere. It should be noted, however, that on very large rhythmogram fragments and with 24-hour Holter monitoring, random non-blocked excitations are often detected in patients suspected of having a “complete” AV block. This situation should be distinguished from so
  7. Atrioventricular block of the first degree
    Since the normal range of atrioventricular conduction time (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 AV degree I blockade. This criterion can only be used if there is a regular sinus (or atrial) rhythm. When the atrial extrasystole is carried out to ventricles with an interval P - R
  8. Atrioventricular block of the 2nd degree - incomplete
    For the 2nd degree atrioventricular block, it is characteristic that part of the impulses that have left the sinus node do not pass the atrioventricular connection and do not reach the ventricles. Therefore, this part of the sinus impulses blocked by the atrioventricular junction cannot cause ventricular stimulation. Therefore, on the electrocardiogram after the P wave (atrial excitation) of the ventricular
  9. Atrioventricular block of the 3rd degree - complete
    With complete atrioventricular block, the atria are excited from the primary pacemaker, from the sinus node. Therefore, an P wave will be present on the electrocardiogram, recorded with a certain constant frequency (for example, 90 per minute), and P — P intervals measured on different parts of the ECG tape will be the same (in our example, 0.67 s). And what will be the pacemaker for
  10. Second-degree atrioventricular block
    ICD-10 cipher I44.1 Diagnostics When making a diagnosis Mandatory Level of consciousness, frequency and effectiveness of respiration, heart rate, pulse, blood pressure, ECG, history possible Mg, Ca, Cl), blood glucose, leukocytes, blood formula, enzymes CK, ALT, AsAT In the process of treatment Monitoring
  11. Anterograde AV blockade of the I degree, or incomplete AV blockade with lengthening of the AV time
    This form of blockade was described at the end of the 19th century. K. Wenckebach (1899), who showed that as AV conduction deteriorates, the a — c interval lengthens on the curve of the jugular venous pulse. The same phenomenon on an ECG (more in the second lead) is reflected by a lengthening of the interval P — R (Q), and each P wave is followed by a QRS complex associated with it. Total AV blockade I degree
  12. Anterograd AV blockade of III degree, or complete AV blockade
    The loss of connection between the excitation of the atria and ventricles is the most important feature of the transverse heart block. The atrial rhythm (P teeth) is more often ventricular (QRS complexes), unlike AV dissociation, in which the independent ventricular rhythm exceeds or is equal to the atrial rhythm. Electrocardiographic and clinical signs of complete AV blockade largely depend on the level
  13. Anterograde II degree blockade, or incomplete AV blockade with the absence of one or several consecutive sinus (atrial) impulses
    In 1894, T. Engelman reported that he had observed on the frog's heart a progressive increase in conductivity from the atria to the ventricles, ending with the disappearance of one contraction. After 5 years, K. Wenckebach (1899) described the same phenomenon in humans and called it Luciani periods by the name of a researcher who, as far back as 1872, pointed out a similar phenomenon. In 1906, J. Hay discovered that with
Medical portal "MedguideBook" © 2014-2016