7: Ventricular Blocks

Ventricular Blocks


7.1.  General Concepts


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Figure 7.1  Scheme of intraventricular conduction system: RB = right bundle; LB = Leith bundle trunk; SA and IP = superoanterior and inferoposterior division; FM = middle fibers.

For more information regarding the diagnosis of the association of bundle branch block with ventricular enlargement, acute ischemia, or necrosis, consult Bayés de Luna (2012a).


7.2.  Right Bundle Branch Block (RBBB)


7.2.1.  Advanced RBBB (Third-Degree)


We speak of advanced, and not of complete RBBB, and also of advanced, and not of complete LBBB (Section 7.3), because it is difficult to know whether the conduction of the stimulus through the affected branch would be possible, if transeptal depolarization from the other ventricle does not exist.


7.2.1.1  Mechanisms of ECG Changes (Fig. 7.2)


The activation (depolarization + repolarization) of the right ventricle occurs transseptally producing, due to a small number of Purkinje fibers in the septum, a QRS with longer duration. The transeptal activation originates the delayed 3 and 4 vectors of depolarization of the septum and RV, and the formation of a characteristic QRS loop.

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Figure 7.2  Left: QRS and T vectors and loops in advanced (third-degree) RBBB. Right: projection of the loops on the two planes and the resultant morphologies most often encountered in clinical practice.

Figure 7.2 shows the correlation of these vectors and the corresponding loop with the hemifield of each lead, all of which explain the morphologies observed. [B]


Figure 7.3 shows how the morphology of ST-T changes seen in advanced RBBB are explained by septal repolarization, which dominates over that of the LV wall. The septal repolarization dipole begins in the left side of the septum, and thus the head (positivity) of the repolarization vector always faces the left side and is recorded as negative in V1 and positive in V6.

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Figure 7.3  Diagrams of the formation of the dipole and vector of depolarization and repolarization in advanced RBBB. The T wave is negative in V1 and positive in V6, because the vector of septal repolarization dominates and has the head (positive charge) facing the left side, although the sense of phenomenon (←∼∼∼) is going from left to right.

Figure 7.4 compares the QRS loop and morphologies in the FP and HP under normal conditions and in advanced RBBB.

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Figure 7.4  Frontal (FP) and horizontal (HP) plane loops in a normal patient and in a patient with advanced RBBB. Observe how this type of block does not modify the general loop direction in the FP, but it is somewhat more anterior in the HP.

7.2.1.2.  Diagnostic Criteria in Advanced RBBB (Third-Degree) [C]


The diagnostic criteria for advanced RBBB are as follows (Sodi et al., 1967; Bayés de Luna, 2012a):



  1. QRS ≥ 0.12 s with variable ÂQRS.
  2. Horizontal plane: rsR’ in V1 and in general V2 with slurrings in R’, and in general slightly depressed ST in V1 and an asymmetrical negative T wave in V1–V2 and occasionally in V3. qRs in V5–V6 with slurrings in the ‘s’ wave.
  3. Frontal plane: QR in VR with slurrings in R, and negative T wave and qRs in I and usually VL with slurrings in S wave. ÂQRS may be located in the normal range in the absence of RBBB. More to the right or left according to the rotation of the heart and/or presence of right or left ventricular enlargement.

Figure 7.5 shows a typical example of advanced RBBB in a normal heart without rotations.

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Figure 7.5  ECG and VCG of a healthy 75-year-old woman with no heart disease (M.B.V). For more than 15 years, the ECG was unchanged. This is a case of advanced RBBB in a normal heart with no apparent rotations (ÂQRS in the first half of QRS = +30° and there is a qRs morphology in V5). FPa: frontal plane amplified; HPa: horizontal amplified. See the final part of QRS depolarization that produces R‘ in VR and V1 (see Fig. 7.2).

The key leads for diagnosis are V1, V6 and VR.


7.2.2.  Partial RBBB (First-Degree)


In this case the transseptal activation is more (B) or less (A) important (grey area) depending on the degree of stimulus delay in the right bundle branch (Fig. 7.6). Consequently, a greater or lesser part of the RV is depolarized with a delay (striped area). [D]

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Figure 7.6  Diagram of ventricular depolarization in global but partial (first-degree) RBBB of proximal origin, less intense in (A) and more intense in (B). In this type of RBBB (see text), one part of the right septum (dotted area) depolarizes transseptally because when the impulse reaches the right septum from the left side, the impulse from the right bundle branch has still not arrived. The longer this impulse takes to reach the right septum, the larger the portion of it that depolarizes transseptally (B). This delay in the arrival of the impulse to the right ventricle means that a proportionate part of the right ventricle depolarizes later than the left ventricle (lined area), originating a final ventricular depolarization vector (3) directed upwards and to the front. It must be remembered that under normal circumstances a small portion of the right ventricle is the last to depolarize, and it produces a vector directed upward and backward. In partial RBBB, the final vector of QRS is directed upward and a little forward, and it usually falls at least a little in the positive hemifield of V1 and VR. It is also somewhat delayed. Therefore, an rSr’ or rsR’ morphology in V1 and a final r’ in VR that is wider than normal but with QRS <0.12 s is produced. However, as seen in Fig. 7.8, the first change of QRS morphology may be from rS to RS pattern (see text).

For this reason, the ECG of first-degree RBBB is characterized by the following (Fig. 7.7):



  1. QRS measures <120 ms.
  2. rSr’ in V1. The r’ is not wide and may have a voltage more or less evident. It may be seen in the initial phases as an RS morphology, because the first part of QRS loop goes a little forwards before the last part presents the forward slurrings. This explains the RS pattern in V1 (Fig. 7.8). However, to avoid overdiagnosis, we can give the diagnosis of partial RBBB in the presence of r’ in V1.
  3. Terminal with ‘r’ that is not wide is also found in VR, and ‘s’ in I and V6.
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Figure 7.7  Typical example of partial RBBB. To compare with morphologies of normal conduction advanced RBBB and other morphologies of partial RBBB see Figure 7.8.
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Figure 7.8  VR, V1, and V6 morphologies in a normal case and in third- and first-degree RBBB. Note that in partial (first degree) RBBB three ECG patterns corresponding to three consecutives bigger grades of first degree RBBB may be seen.

7.2.3.  RBBB: Comparative Morphologies (Fig. 7.8)


See the different morphologies in VR, V1, and V6 in the case of normal activation and in first-degree and third-degree RBBB. In V1 the morphology may be from ‘rs’ to ‘rsR’, with QRS ≥120 ms.


7.2.4.  Second-Degree RBBB (Fig. 7.9) [E]


In this case a pattern of transient first- or third-degree RBBB appears in the same tracing (see legend and Chapter 11, ventricular aberrancy).

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Figure 7.9  V1. Continuous recording. A 55-year-old patient with first-degree RBBB morphology (the first four complexes) who abruptly presented with advanced RBBB morphology (third-degree) for four complexes, with minimal changes in the RR interval. After five first-degree RBBB complexes, there were five advanced RBBB complexes. This is an example of second-degree RBBB (some impulses are completely blocked in the right bundle branch), although it stems from a first-degree RBBB morphology. The appearance of advanced RBBB coincides with slow decreases of heart rate (see Section 7.4).

7.2.5.  Differential Diagnosis of RBBB Morphology



  • The differential diagnosis of RBBB must be made with all processes that present a prominent R or r’ in V1, including pre-excitation, right or biventricular enlargement, athletes, pectus excavatum, and Brugada syndrome, among others (Table 6.1 and Chapter 16).
  • A mistakenly high placement of the electrodes of V1 and V2 and other variants on the normal ECG must also be ruled out. In cases of high placement in V1–V2, the P wave is negative (Fig. 7.10). A negative P wave in V1 with the electrode located in the correct place, is a common finding in pectus excavatum. See differential diagnosis of r’ in V1 in Table 6.1. [F]
  • Naturally, the differential diagnosis is more difficult in partial RBBB because the sole presence of QRS ≥120 ms indicates, once pre-excitation is ruled out based on normal PR, advanced RBBB.
  • For more information on the diagnosis of advanced RBBB associated with necrosis, ischemic heart disease, or pre-excitation, and on the diagnosis of peripheral right bundle branch block (which as we have said may present SI SII SIII pattern similar to RVE and variant of normality [Fig. 6.8]), consult Bayés de Luna (2012a).
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Figure 7.10  A very slim 15-year-old patient without heart disease. The rSr’ morphology is due to a misplaced V1 electrode in the second right intercostal space (see negative P wave) and disappears when the electrode is properly positioned (fourth right intercostal space).

7.3.  Left Bundle Branch Block (LBBB)


7.3.1.  Advanced LBBB (Third-Degree)


7.3.1.1.  Mechanisms of ECG Changes (Fig. 7.11) [G]


The activation of the entire left ventricle takes place transseptally, as also happens in advanced RBBB. This explains the slowness in forming QRS, because transseptal depolarization is slow due to the few number of Purkinje fibers that exist in the septum. Transseptal and left ventricle activation originate four vectors (Fig. 7.11) that explain the formation of a QRS loop and a wide QRS complex, the morphologies of which can be explained by the loop–hemifield correlation (Fig. 7.11).

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Figure 7.11  Left: QRS vectors and loops in advanced LBBB (third-degree). Right: projection of the loops on the two planes with formation of the respective loops and ECG morphologies most often seen in clinical practice.

The morphology of ST-T in the case of advanced LBBB is explained because the repolarization of the septum dominates over that of the LV wall (Fig. 7.12). The repolarization dipole that begins on the right side of the septum is directed from right to left, and thus the repolarization vector also moves from right to left with the head (positivity) always facing V1. As a result, the T wave is positive in V1 and negative in V6.

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Figure 7.12  Diagram of formation of dipole and the depolarization and repolarization vector in advanced LBBB. The T wave is positive in V1 and negative in V6, because it dominates the septal repolarization vector that is always from left to right (V1 faces positivity and V6 faces negativity), although the sense of phenomenon is going from right to left.

7.3.1.2.  Diagnostic Criteria for Advanced LBBB (Third-Degree) (Fig. 7.13)


The classic diagnostic criteria (Sodi, 1967; Willems et al., 1985; Bayés de Luna, 2012a) include the following:



  1. QRS ≥120 ms. Recent studies suggest that in cases of heart failure, the preferred wideness of QRS for the placement of resynchronization pacemakers has to be ≥130 ms in women and ≥140 ms in men (Strauss, 2011; Gettes and Kligfield, 2012; Zareba, 2013) (see before).
  2. The presence of notches or slurrings in the middle third of QRS in at least two of the following leads: V1, V2, V5, V6, I, and VL, with a prolongation at the delayed peak in R in V5-V6 to >60 ms.
  3. Generally, the ST segment is slightly opposed to the QRS polarity, especially when it is ≥140 ms and it is rapidly followed by an asymmetrical T wave of opposed polarity. [H]
  4. Horizontal plane: QS or rS in V1 with small ‘r’ with ST slightly elevated and positive asymmetrical T wave, and unique R in V6 with negative asymmetric T wave. When the QRS is <140 ms, the T wave in V6 may be even positive.
  5. Frontal plane: R exclusively in I and VL often with a negative asymmetrical T wave and slightly ST depression, and usually QS in VR with positive T wave. In cases with advanced heart failure and great dilation of right cavities, there is a delay of depolarization of RV that explains the final R in VR (QR pattern) (Van Bommel et al., 2011).
  6. The ÂQRS is variable. It may be rightwards in patients with RVE and/or congestive heart failure (Fig. 7.14), and leftwards in case of associated superoanterior hemiblock, deleted CM, etc. (Fig. 7.15).
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Figure 7.13  ECG and VCG of a healthy 68-year-old man with advanced LBBB and no apparent heart disease. QRS >0.12 s. Its morphology is consistent with those in Figure 7.11.
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Figure 7.14  ECG of a patient with congestive heart failure and a morphology of advanced LBBB with right deviated ÂQRS, low voltage in FP and QS pattern till V4.
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Figure 7.15  (A) ECG of a patient with idiopathic dilated cardiomyopathy with very low ejection fraction and LBBB with left ÂQRS. The ECG is similar to (B) that corresponds to an elderly patient with chronic obstructive pulmonary disease, but without evident heart failure with the same LBBB at least in the last 20 years. The only difference is that in the first case there is a QR pattern in VR that is explained by late activation of right ventricle due to its dilation (see text).

Figure 7.13 shows a typical example of advanced LBBB, and in Figures 7.14 and 7.15 two examples of advanced LBBB with associated pathology are shown (see legends). The association with IHD is briefly explained in Chapter 9 (see Section 9.6).


7.3.2.  Partial Left Bundle Branch Block (First-Degree)


In this case, the stimulus passes slowly down the left bundle branch. This explains that some part of the left ventricle is depolarized transseptally and some part is depolarized by a normal pathway (more in B than A in Fig. 7.16). [I]

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Figure 7.16  Diagram of ventricular depolarization in first-degree LBBB. If the delay is mild (A), there is small transseptal depolarization by the right bundle branch and the only ECG repercussion is the disappearance of the first vector due to the fact that the delay in its inscription causes it to cancel out the right forces. The T wave may be positive or negative when there is associated disease. If the delay is greater (B), there is more anomalous septal depolarization, resembling more advanced LBBB, but the QRS does not reach 0.12 s in duration and the T wave is positive or negative–positive in I, VL, and/or V5 and V6 depending on the associated heart disease.

Because the start of septal depolarization occurs from right to left, the septal q wave is not originated and thus a unique R is seen in V6, I, and VL. Initial r is not found in V1 either, or it is very small, due to RV depolarization by the stimulus that passes down the right bundle branch.


The ECG of a .first-degree LBBB is characterized by:



  1. QRS <120 ms, with a unique R in I, VL, and V6.
  2. Repolarization in V6 may be positive or flat/negative according to the accompanying pathology and degree of transseptal depolarization (Fig. 7.17).
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Figure 7.17  One example of partial LBBB. A 75-year-old patient without clinical heart disease.

7.3.3.  Comparative Morphologies


In Figure 7.18 may be seen the different morphologies in the VR, V1, and V6 in cases of normal activation and first- and third-degree LBBB.

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Figure 7.18  Comparative morphologies in partial (first degree) and advanced (third degree) LBBB.

7.3.4.  Second-Degree LBBB (Fig. 7.19) [J]


As in second-degree RBBB, a pattern of transient first or third degree LBBB appears in the same tracing (see legend and Chapter 11, Ventricular Aberrancy).

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Figure 7.19  Intermittent LBBB. The third and sixth complexes manifest a LBBB morphology. The same occurs from the eighth complex to the seventeenth complex, after which rhythm becomes bradycardic and LBBB disappears (see Section 7.4).

7.4.  Hemiblocks or Fascicular Blocks


See Rosenbaum et al., 1968; Elizari & Chiale, 2012.


In 1968, Rosenbaum and Elizari defined the ECG criteria of superoanterior and inferoposterior fascicular block of the left branch from a clinical and experimental point of view, calling it hemiblock. Many cases exist of superoanterior hemiblock (SAH) and few of inferoposterior hemiblocks (IPH).


7.4.1.  Superoanterior Hemiblock (SAH)


Figure 7.20 shows how ventricular activation occurs in a case of block in this fascicle. [K]

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Figure 7.20  Diagram of the activation in superoanterior hemiblock. On the left are two vectors responsible for ventricular depolarization and the global QRS loop. The three stars represent the three entrances of the electric impulse in the left ventricle. On the right is the projection of the two vectors on the frontal and horizontal planes, with formation of the respective loops and the most common morphologies observed in clinical practice according to the loop–hemifield correlation. The dotted line above lead I represents what is probably the most exact situation of the positive part of lead I. As such, the entire last part of the loop would be in the positive hemifield of I, justifying the absence of S in I, which normally occurs (a line perpendicular to the true I has been added to the sketch, delimiting the positive and negative hemifields of this lead and illustrating this point).

The block in the superoanterior division originates a change in the start of activation that is then made through a small septal vector (vector 1) that moves downward, forward, and to the right, and then depolarizes the rest of the left ventricle upwards and backwards (vector 2).


The loop generated by this activation when projected on the positive and negative hemifields of each lead of the FP and HP explain the different QRS morphologies found in each case.


7.4.1.1.  Diagnostic Criteria for SAH [L]


See Rosenbaum et al., 1968; Elizari & Chiale, 2012. The diagnosis of SAH may be made based on the presence of the following electrocardiographic criteria:



  1. Leftwards ÂQRS between −45° and −75°. ÂQRS between −30° and −45° may correspond to non-advanced degrees of SAH.
  2. FP morphology: qR in D1 and VL; rS in II, III, and VF, with SIII > SII and RII > RIII, and sometimes with terminal r in VR.
  3. HP morphology: S until V6 with intrinsicoid deflection time (IDT) in V6 < IDT in VL and with IDT in VL ≥50 ms. Some changes occur if the precordial electrodes are located above the normal site: in V1-V3 small q waves may appear, simulating a previous septal myocardial infarction, and in V2 an r’ wave may also appear. In V5-V6 the ‘S’ wave may be reduced and a small q may appear.
  4. QRS duration <120 ms. However, in isolated cases the QRS may not surpass 100 ms. A QRS between 100 ms and 120 ms usually indicates associated LVE.
  5. In advanced cases, mid-terminal slurrings are present in I and VL.

Figure 7.21 shows a typical example of SAH.

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Figure 7.21  ECG–VCG of a patient with typical isolated superoanterior hemiblock. The morphology is that corresponding to Figure 7.20.

7.4.1.2.  Partial SAH


It is not easy to diagnose the presence of partial SAH. Leftwards ÂQRS starting at −30° may correspond to partial SAH if this pattern evolves into AQRS at −45° or more over time, as shown in Figure 7.22.

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Figure 7.22  Evolution in time in a case of superoanterior hemiblock (SAH). Different drawings of QRS recording in lead II. In D and E, SAH is evident, but there must also be a certain degree of SAH in A and B, and especially in C.

7.4.2.  Inferoposterior Hemiblock (IPH)


Figure 7.23 shows how ventricular activation is carried out in cases of block in this fascicle. As seen in the figure, activation occurs inversely to that observed in SAH (see before). [M]

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Figure 7.23  Diagram of activation in inferoposterior hemiblock. On the left are the two vectors that account for ventricular depolarization and the global QRS loop, and on the right, the projection of these vectors on the frontal and horizontal planes, with formation of the respective loops and the most common morphologies seen in practice according the loop–hemifield correlation.

The diagnosis of hemiblock in the inferoposterior division (IPH), a process that is much less common than SAH because this fascicle is larger and narrower, may only be made in the absence of RVE and very vertical heart. According to some authors, a pathology on the left ventricle must also be present.


7.4.2.1.  Diagnostic Criteria for IPH [N]


The diagnostic criteria of inferoposterior hemiblock are listed below.



  1. ÂQRS greatly deviated to the right (between +90° and +140°).
  2. RS or Rs in I and VL, and qR in II, III, and VF. With regard to precordial leads, the most common morphologies are seen in Figure 7.21.
  3. QRS <120 ms.
  4. TDI = >50 ms in VF and V6, with TDI <50 ms in VL.
  5. Mid-terminal slurrings in II, III, and VF in advanced cases.

Figure 7.24 shows the appearance of an IPH morphology. Very often it appears in association with RBBB.

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Figure 7.24  (A) ECG of a 55-year-old patient with arterial hypertension and coronary heart disease. (B) Without any clinical change, a month later the patient presented a striking ECG change: ÂQRS went from left to right, in VF Rs passed to qR with IDT = 0.06 s, and in V6 qR changed to Rs. All this may be explained by the appearance of inferoposterior hemiblock.

In cases of IPH due to progressive conduction aberrancy of atrial extrasystoles or extrastimulus, it has been observed that cases of partial inferoposterior hemiblock may only be diagnosed by comparative study.


7.5.  Bifascicular Block


The most typical cases are due to RBBB associated with SAH or IPH.


A.  RBBB + SAH [O]


See the wide QRS (>120 ms), the rsR’ pattern in V1, and the very left ÂQRS with rS pattern in II, III and VF (Fig. 7.25A).

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Figure 7.25  (A) A 70-year-old patient with no apparent heart disease with a typical advanced RBBB + SAH morphology. (B) An example of masked bifascicular block (see text).

When exists an important delay of LV activation, the final vectors of activation may be directed forwards (R in V1 due to RBBB), but to the left instead of to the right. Due to this, there is no S in I and VL. Thus the HP looks like RBBB and the FP like LBBB. This type of bifascicular block is named ‘masked bifascicular block’ (Bayés de Luna, 2012a) (Fig. 7.25B).


B.  RBBB + IPH (Fig. 7.26)


See the wide QRS (>120 ms), the rsR’ pattern in V1, and the right ÂQRS with qR pattern in II, III, and VF to assure the diagnosis, the ECG has to be taken from a patient with no right heart disease or a very vertical heart.

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Figure 7.26  A 76-year-old patient with ischemic heart disease and arterial hypertension, and with no right heart disease or vertical heart, who presented with a morphology typical of advanced RBBB + IPH (see text). The ST segment is depressed in the left precordial leads because of the underlying disease.

See Bayés de Luna (2012a) for more explanation of the clinical implications of these types of block.


7.6.  Trifascicular Block (Fig. 7.27)


In this case a block in three fascicles is present. [P]

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Figure 7.27  Typical example of trifascicular block. (A) RBBB + SAH. (B) The next day the frontal ÂQRS passed from −60° to +130°, indicating the appearance of an inferoposterior hemiblock substituting the superoanterior hemiblock.

The most typical case presents a morphology of RBBB alternating with SAH and IPH.


See (Fig. 7.27) how in the presence of a wide QRS and a pattern of RBBB in the two ECGs, an abrupt change in ÂQRS occurs in the frontal plane from −70° in A to +130° in B. These patients may present syncopes when trifascicular block coincides, because an abrupt advanced AV block occurs (Rosembaum–Elizari syndrome). These situations require the urgent implantation of a pacemaker.


The presence of LBBB alternating with RBB + SAH has the same clinical considerations as the previous case.


The cases of bifascicular block with a long PR interval may be explained by first degree block in the His bundle. Therefore they cannot be considered due to trifascicular block.


7.7.  Block in the Middle Fibers of the Left Branch [Q]


The presence of block in the middle fibers (MF), also known as the septal fascicle (SF), probably originate some ECG changes. At present the following two criteria are the most used to describe this type of block: (1) lack of septal q (lack of q in leads V5-v6 and I) and (2) the presence of a prominent R in V1-V2. The Brazilian school supports more this last criterion.


The presence of these patterns (missing septal q wave in I, V5-V6, or presence of R/S in V1–V2) if transient, confirm that they are due to some type of intraventricular conduction disturbance, although the location of the conduction delay is not certain. The lack of septal q wave in V6, I, may be also explained by first-degree LBBB, and the presence of RS in V1-V2 may occur in case of MF/SF block or partial right bundle branch block (Fig. 7.8) or both. Many other processes may also present prominent R or r’ in V1 (see Table 6.1) (Bayés de Luna et al., 2012d).


Self-assessment




A.  What types of block exist at the ventricular level?

Related posts:

  1. II: Morphological Abnormalities in the ECG
  2. 5: Atrial Abnormalities
  3. 16: The ECG in Genetically Induced Heart Diseases and Other ECG Patterns with Poor Prognosis
  4. 9: Myocardial Ischemia and Necrosis

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Aug 29, 2016 | Posted by in CARDIOLOGY | Comments Off on 7: Ventricular Blocks

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