Right bundle branch conduction block is divided into complete right bundle branch conduction block and incomplete right bundle branch conduction block according to the degree of block. Complete right bundle branch block means that the right bundle branch that transmits to the right ventricle is faulty and the bioelectrical signal cannot be transmitted directly to the right ventricle, but it does not matter, the electrical signal can be transmitted from the left ventricle, only the contraction of the right ventricle is slightly delayed. Complete right bundle branch block does not necessarily have extensive myocardial damage, and is often not significant if it is not associated with other organic heart disease. If you have no organic heart disease on further medical examination, incomplete right bundle branch block is usually of no pathologic significance. Since there is no pathological significance, i.e., a normal healthy lifestyle will not have an effect on it.
Right bundle branch conduction block examination mainly relies on electrocardiography for diagnosis.
1.Complete right bundle branch conduction block
(1) Typical electrocardiographic features of complete right bundle branch conduction block.
(1) QRS waves in V1 and V2 leads (or V3R and V4R leads) of the right chest are rsR′, rSR′ type, rsr′ type or M type, and their R′ waves are usually higher than r waves; a few of them show wide and tangential R waves.
②S waves in V5 and V6 leads were significantly broad, with a time limit of ≥0.04s, but not deep. Ⅲ, aVR leads showed qR wave, the R wave was mostly broadened but not high, while Ⅰ, aVL and Ⅱ leads were mostly wide and not deep S waves.
③ QRS time limit ≥ 0.12s.
The R-wave peak time (ventricular wall excitation time) is >0.05s in V1 and V2 leads, while the R-wave peak time is normal in V5 and V6 leads.
⑤ ST-T changes in the direction opposite to that of the QRS wave end vector, i.e. ST segment depression and T wave inversion in V1 and V2 leads, while ST segment elevation and T wave upright in V5 and V6 leads.
(2) Detailed description of the typical ECG of complete right bundle branch block.
(1) QRS time limit ≥ 0.12s, usually not more than 0.14s.
The frontal QRS axis is usually measured using the unblocked part of the QRS wave, i.e., the first 1/2 of the QRS wave voltage. The frontal QRS axis is often within the normal range. If the electrical axis shows significant deviation, combined branch conduction block should be considered.
The terminal part of QRS wave in aVR lead is always upright, and the terminal part of QRS wave in aVL lead is always downward, while the terminal part of QRS wave in II, III and aVF leads can be upright or inverted.
④ST-T changes are generally not used as diagnostic criteria for complete right bundle branch block.
2.Incomplete right bundlebranch block (IRBBB)
(1) Typical electrocardiographic features of incomplete right bundle branch block.
(1) Typical ECG features of incomplete right bundle branch block: (1) The QRS waves in V1 and V2 leads of right thoracic leads are rsR′ type, rsr′ type, rSR′ type or M type. The R′ wave is usually higher than the r wave.
②The S waves in V5, V6 and Ⅰ leads are widened but not deep.
(③QRS time limit <0.12s.
(2) Detailed description of the typical ECG features of incomplete right bundle branch block.
(①It can be accompanied by secondary ST-T changes, but it is usually not used as a diagnostic criterion for incomplete right bundle branch block.
②In practice, it can often be encountered that only the rsr’ wave group with a time limit of much less than 0 or 12 s appears in the right anterior thoracic leads, while the corresponding changes in other leads are not obvious, such as the left thoracic leads do not have coarse and blunt S waves, or the V1 leads are of Rsr′ type with r′
③Normal variation is mostly related to physiological delayed depolarization of the right ventricular outflow tract, and the R′ wave is often
④Another ECG alteration of the normal variant is the appearance of r′ waves in leads V1 and aVL; and S waves in leads Ⅰ, Ⅱ, Ⅲ, and V6. This S Ⅰ, S Ⅱ, S Ⅲ pattern is seen in those without heart disease and is associated with delayed distal depolarization of the supraventricular crest.
3. Special types of right bundle branch conduction block ECG
(1) Intermittent right bundle branch block (intermitent RBBB)
(1) Heart rate independent intermittent right bundle branch block: This type of intermittent right bundle branch block has nothing to do with the fast or slow heart rate. The right bundle branch block (complete or incomplete block) can be seen on continuous ECG recordings, appearing and disappearing from time to time, independent of heart rate. The R-R interval of the right bundle branch block pattern is equal or nearly equal to the R-R interval of a normal QRS-T wave group, and the ventricular rate is mostly in the normal range. This type of intermittent right bundle branch block is actually a second degree type II right bundle branch block.
(2) Frequency-dependent intermittent right bundle branch block: including fast frequency, slow frequency and mixed frequency-dependent right bundle branch block.
(2) Wen’s phenomenon of right bundle-branch conduction block
That is, second degree type I right bundle branch conduction block ECG diagnostic criteria are
① very regular sinus (or other supraventricular) rhythm.
(ii) Very regular atrioventricular conduction time (P-R interval).
(iii) The presence of QRS waves with a relatively normal appearance of the cycle.
(iv) If successive QRS waves show progressive worsening of bundle branch conduction block, a diagnosis of direct display ventromedial phenomenon is made.
⑤ If all beats except the first one show a complete bundle branch block pattern, it is presumed to be an incomplete occult ventromedial phenomenon.
The left and right bundle-branch Ven’s phenomenon can be divided into the following three categories.
(1) Directly displayed left or right bundle-branch intraventricular phenomenon: It is manifested by a group of QRS waves widening beat by beat to complete bundle-branch block pattern.
(2) Incomplete insidious bundle branch intraventricular phenomenon: The first QRS wave in a group of heartbeats is normal, but the rest are complete bundle branch block pattern.
(3) Complete anaphylactic intra-bundle-branch Wen’s phenomenon: This possibility is suspected only when the heart rate is slowed down enough to form a direct display or incomplete anaphylactic phenomenon.
(3) Second degree type II (Mohs type II) right bundle branch conduction block
The electrocardiogram shows a certain percentage of non-right bundle branch block patterns intermittently or alternately with complete right bundle branch block patterns. For example, in a 2:1 second degree type II right bundle branch block, the ECG shows a QRS wave without right bundle branch block alternating with a QRS wave with complete right bundle branch block. For example, in 4:3 second degree type II right bundle branch block, the ECG shows 3 QRS waves without right bundle branch block alternating with 1 QRS wave with complete right bundle branch block.
(4) Occult right bundle branch block.
It refers to the absence of right bundle branch block pattern on the body electrocardiogram, and the right bundle branch block pattern can be shown only after the application of manual methods, which are.
① Right bundle branch block pattern appears due to accelerated heart rate by exercise or action test. There are two reasons for this: one is that the myocardium is not ischemic, but only due to the early appearance of excitation in the already prolonged pathological nonresponse period, which is fast frequency-dependent intermittent right bundle branch block. The right bundle branch conduction block pattern disappears after the heart rate is slowed down: the second factor is a combination of myocardial ischemia caused by exercise or aggravated by damage and increased heart rate.
②Drug: Atropine or isoproterenol can stimulate the appearance of right bundle branch block pattern.
(3) The compensatory interval after the precontraction and the application of propranolol slow down the heart rate, which can make the original right bundle branch block pattern disappear and turn into occult right bundle branch block.
(5) Postural right bundle branch block.
The right bundle branch block pattern appears in both standing and prone position. The right bundle branch block in the prone position is related to the predominance of vagal excitation, and there is no organic heart disease. When changed to sitting position, sympathetic excitability increases, heart rate is accelerated, and the expiration period is shortened, which improves conduction function and restores normal conduction of the right bundle branch.
(6) Complete right bundle branch conduction block combined with right ventricular hypertrophy
It is difficult to diagnose right ventricular hypertrophy by electrocardiogram alone. Right bundle branch block combined with right ventricular hypertrophy ECG features are: ① incomplete right bundle branch block, R′V1>1,0 mV; complete right bundle branch block, R′V1>1,5 mV; ② right-sided electrical axis, often ≥ 110?②; ③ SV5, V6 often exceed RV5, V6, Huang Wan et al. In addition to the increased voltage of R′V1 and SV5, if there is a significant rightward deviation of the cardiac axis, more than 90% of the cases can be correctly diagnosed as right bundle branch block combined with right ventricular hypertrophy.
(7) Right bundle branch block combined with left ventricular hypertrophy
Since the two do not affect each other, both right bundle branch block and left ventricular hypertrophy are diagnosed on the ECG. The T-loop may be located anteriorly to the left or running in a clockwise direction.
(8) Right bundle branch block combined with myocardial infarction
The ECG shows both myocardial infarction and right bundle branch block, which can clearly diagnose myocardial infarction. The initial depolarization vector in right bundle branch block is the same as normal, but there is a change in the posterior part of the vector loop: in myocardial infarction, the vector change of QRS is in the initial 0,03-0,04s, so both can be shown separately.
In anterior wall myocardial infarction without septal involvement, right precordial leads, such as V3R, V1, and V2 leads, still showed right bundle branch block patterns with rsR′-type waves, but in each precordial lead from the left of V3 lead, there were wide Q waves reflecting abnormal initial 0, 03 to 0, 04s vectors. Therefore, both sets of graphs showed that the diagnosis of anterior wall myocardial infarction could still be made definitively.
In anterior wall myocardial infarction combined with right bundle branch block, the majority of the ventricular septum will be involved. In this case, the normal left-to-right initial septal depolarization vector disappears, and the r waves in leads V3R, V1, and V2 of the ECG also disappear, and a wide qR wave appears; there are abnormal Q waves and reduced R waves in the left precordial leads. Due to the right bundle branch block, the R wave was still followed by a broad S wave. the changes of ST segment and T wave were the same as those of general myocardial infarction.
In inferior wall myocardial infarction combined with right bundle branch block, leads II, III, and aVF have the manifestations of myocardial infarction, and precordial leads still show right bundle branch block pattern. the ST segment T wave changes are consistent with the manifestations in myocardial infarction.
(9) Masked right bundle branch block
When right bundle branch block is combined with left anterior branch block, left bundle branch block and left ventricular hypertrophy, the right bundle branch block pattern on the ECG is atypical, for example, the right bundle branch block pattern in the precordial leads, but the right bundle branch block pattern in the standard leads disappears, showing a similar right bundle branch block pattern; or the right bundle branch block pattern in the precordial leads disappears; or the right bundle branch block pattern in the right chest leads and the left bundle branch block pattern in the left chest leads The left thoracic lead shows a left bundle branch block pattern, etc. The above features are called masked right bundle branch block.
A. Left anterior branch block obscures the right bundle branch block pattern in standard leads: the limb leads show similar to left bundle branch block, and the thoracic leads show typical right bundle branch block pattern. Principle of generation: The left anterior branch block masks the right bundle branch block. In fact, it is an atypical type of right bundle branch block with left anterior branch block. It is caused by a strong leftward vector that is delayed and partially or completely cancels out the rightward terminal vector of the right bundle branch block that is generated simultaneously or almost simultaneously. The more pronounced the block, the stronger the leftward vector and the greater the leftward bias of the electrical axis. ECG features: right bundle branch block in thoracic leads; deep SⅡ and SⅢ in left anterior branch block, no R′ wave in lead III, small or absent SⅠ, QⅠ may or may not appear; frontal QRS electric axis in -75?~60?
B. Left anterior branch conduction block obscures the right bundle branch conduction block pattern in thoracic leads: at this time, lead Ⅰ and leads V5 and V6, both without terminal S waves, have patterns similar to left bundle branch conduction block. The right thoracic leads show a right bundle branch block pattern. However, sometimes the R′ wave in the right thoracic lead is also absent. However, raising 1 intercostal tracing V1, V3R or V4R will still show the R′ wave. The rationale for this is the same as that for left anterior branch block, which obscures the pattern of right bundle branch block in the standard leads. This may be due to the generation of a strong posterior leftward terminal vector that completely cancels out the anterior rightward terminal vector (R′) of the right bundle branch block. Sometimes, but less frequently, the pattern of right bundle branch block can be masked in both the standard and thoracic leads. In persistent left anterior branch block masking right bundle branch block, the left anterior branch block is accompanied by widening of the QRS time; the right thoracic lead has an rsR′ pattern, similar to right bundle branch block; and the left thoracic and limb leads have an R pattern, similar to left bundle branch block. The left anterior branch block pattern can present a complete left bundle branch block pattern in the limb leads.
The clinical significance of left anterior branch block masking right bundle branch block is the same as that of left anterior branch block with right bundle branch block, but it should be noted that it may be misdiagnosed as pure left anterior branch block or alternating left anterior branch block with right bundle branch block and the possibility of double bundle branch block is overlooked. In addition, the possibility of significant left ventricular hypertrophy or limited left ventricular lateral wall block (infarction or myocardial fibrosis) is suggested, so it should be well differentiated.
A, Right bundle branch conduction block is completely counteracted by symmetric conduction block in the left bundle branch. In this case, the degree, type, atrioventricular ratio, length of conduction time, and simultaneity of conduction onset of left bundle branch conduction block are completely identical to those of right bundle branch conduction block. The electrocardiogram shows normal QRS-T waves, and the P-R interval may be prolonged to different degrees depending on the conduction time of the left or right bundle branch. If there is conduction interruption in both the left and right bundle branches (bundle branch leak), a ventricular leak may result.
B, The right bundle branch block is completely masked by the relatively heavy asymmetry of the left bundle branch conduction block and presents a left bundle branch block pattern. In this case, the length of the P-R interval depends on the conduction time of the right bundle branch and may be normal or prolonged. If both right and left bundle branch conduction is interrupted, then a missed ventricular beat may occur.
The electrocardiogram has the following manifestations due to the different degrees of both.
A. Left ventricular hypertrophy masking QRS-T abnormalities of right bundle branch conduction block: The ECG manifestation of left ventricular hypertrophy at this time is: the S wave in V1 lead is very deep, so that the rsR′ pattern of right bundle branch is transformed into rsr′ pattern. At this point, pseudo right bundle branch block due to depolarization of the pulmonary cone should be excluded. r wave >2,5mV in V5 leads. st segment in V5 and V6 leads is not elevated, but decreases, and T wave is flat or inverted; ventricular wall excitation time in V5 leads >0,05s; ST segment in V1 leads does not decrease, and T wave is upright; R II R III >2,5mV: the electrocardiographic axis is close to left deviation, at around 0?
B. Left ventricular hypertrophy is masked and only the right bundle branch block pattern appears: Since the QRS ring area produced in right bundle branch block is larger, the left ventricular hypertrophy must be quite significant in order for the ECG to partially mask each other. For example, in right bundle branch block, ST-segment depression and T-wave inversion in lead V1, ST-segment elevation and T-wave upright in leads V5 and V6, while in left ventricular hypertrophy, ST-segment elevation and T-wave upright in lead V1, ST-segment depression and T-wave inversion in leads V5 and V6, which cancel each other out. However, the main abnormality in right bundle branch block is that the additional loop of the terminal vector (i.e., the third vector of ventricular depolarization) points anteriorly to the right; whereas the main abnormality in left ventricular hypertrophy is that the major vector increases to the left (i.e., the second vector of ventricular depolarization). When right bundle branch block is combined with left ventricular hypertrophy, the initial QRS vector is normal and the major QRS loop vector, especially after 0 and 06 s, is more significantly biased to the left posterior and superior than in right bundle branch block alone, with the terminal vector being an additional loop to the right. the ST-T vector may be near normal or slightly biased to the left or right due to the opposite changes in right bundle branch block and left ventricular hypertrophy offsetting each other. Usually, when left ventricular hypertrophy is combined with right bundle branch block, the deep S waves in lead V1 and high R waves in lead V5 presented by left ventricular hypertrophy are sometimes preserved.
Type B preexcitation syndrome can completely mask right bundle branch block or make right bundle branch conduction block atypical.
4. Hirschsprung’s bundle electrogram characteristics of right bundle branch conduction block.
(1) The time of V wave is ≥0,12s, which indicates prolonged ventricular depolarization time.
(2) Normal A-H and H-V times indicate that the conduction time from AV node → Hirschsprung’s bundle → left bundle branch is normal. If the H-V time is prolonged, it indicates that the downward transmission via the left bundle branch is also delayed.
(3) Trans-left ventricular recording of left bundle branch potentials and simultaneous recording of right bundle branch potentials via the Hitchcock bundle electrode can confirm right bundle branch conduction block.