Anatomic studies of the cardiac conducting system in acute myocardial infarction

The Primary Alteration of Ventricular Myocardium Conduction: The Significant Determinant of Left Bundle Branch Block Pattern

Intraventricular conduction disturbances (IVCD) are currently generally accepted as ECG diagnostic categories. They are characterized by defined QRS complex patterns that reflect the abnormalities in the intraventricular sequence of activation that can be caused by pathology in the His-Purkinje conduction system (HP) or ventricular myocardium. However, the current understanding of the IVCD's underlying mechanism is mostly attributed to HP structural or functional alterations. The involvement of the working ventricular myocardium is only marginally mentioned or not considered. This opinion paper is focused on the alterations of the ventricular working myocardium leading to the most frequent IVCD pattern-the left bundle branch block pattern (LBBB). Recognizing the underlying mechanisms of the LBBB patterns and the involvement of the ventricular working myocardium is of utmost clinical importance, considering a patient's prognosis and indication for cardiac resynchronization therapy.

Association between new-onset right bundle branch block and primary or secondary ventricular fibrillation in ST-segment elevation myocardial infarction

AIMS

New-onset right bundle branch block (RBBB) in myocardial infarction (MI) is often associated with ventricular fibrillation (VF) but the nature of this relationship has not been determined.

METHODS AND RESULTS

Between 1998 and 2014, among other data, incidence and duration of RBBB and VF occurrence were prospectively collected in 5301 patients with ST-segment elevation MI (STEMI) admitted to two University Hospitals in Murcia (Spain). Multinomial adjusted logistic regression analyses were used to examine the association between RBBB, attending to its duration, and VF according to its primary VF (PVF) or secondary VF (SVF) character. Among 284 (5.4%) patients with new-onset RBBB, 158 were transient and 126 permanent. VF occurred in 339 (6.4%) patients, 201 PVF and 138 SVF, documented within the first 2 h of symptoms-onset in 78% and 60%, respectively. New-onset RBBB was more frequent in PVF (11.4%) and SVF (20.3%), than in non-VF (4.7%). Transient RBBB incidence was higher in PVF (9.0%) and SVF (9.4) than in non-VF (2.6%), whereas permanent RBBB was higher in SVF (10.9%) than PVF (2.5%) and non-VF (2.1%). New-onset RBBB 1.83 [95% confidence interval (CI): 1.07-3.11] and new-onset transient RBBB 2.39 (95% CI: 1.32-4.32) were independently associated with PVF. New-onset 3.03 (95% CI: 1.83-5.02), transient 2.40 (95% CI: 1.27-4.55), and permanent 2.99 (95% CI: 1.52-5.86) RBBB were independently associated with SVF.

CONCLUSION

New-onset RBBB and VF in STEMI are independently associated and show particularities based on the duration of the conduction disturbance and/or the primary or secondary character of the arrhythmia.

New or presumed new left bundle branch block in patients with suspected ST-elevation myocardial infarction

AIMS

Using a comprehensive large prospective regional ST-elevation myocardial infarction (STEMI) system database, we evaluated the prevalence, clinical and angiographic characteristics, and outcomes in patients with ischemic symptoms and new or presumed new left bundle branch block (LBBB). We then tested a new hierarchical diagnosis and triage algorithm to identify more accurately new LBBB patients with an acute culprit lesion.

METHODS AND RESULTS

From March 2003 to June 2013, 3903 consecutive STEMI patients were treated using the Minneapolis Heart Institute regional STEMI protocol including 131 patients (3.3%) with new LBBB. These patients had fewer culprit arteries (54.2% vs. 86.4%; P<0.001), were older, more commonly women, with a lower ejection fraction, and more frequently presented with cardiac arrest or heart failure than those without new LBBB. At 1 year follow-up, all-cause mortality accounting for baseline differences was higher in patients with new LBBB (hazard ratio 1.73, 95% confidence interval 1.17-2.58; P=0.007). The new algorithm yielded high sensitivity (97%) and negative predictive value (94%) for identification of a culprit lesion. Using the definition of new LBBB with either hemodynamically unstable features or Sgarbossa concordance criteria on electrocardiogram (ECG), 45% of new LBBB patients would have been treated as 'STEMI equivalent'.

CONCLUSION

Patients with acute ischemic symptoms and new LBBB represent a high-risk population with unique clinical challenges. If validated in an independent dataset, the new algorithm may improve the diagnostic accuracy regarding reperfusion therapy for new LBBB patients.

The left bundle-branch block puzzle in the 2013 ST-elevation myocardial infarction guideline: from falsely declaring emergency to denying reperfusion in a high-risk population. Are the Sgarbossa Criteria ready for prime time?

Prompt and accurate identification of ST-elevation myocardial infarction (STEMI) in the presence of left bundle-branch block (LBBB) remains difficult. The 2004 STEMI guideline recommended emergent reperfusion therapy to patients with suspected ischemia and new or presumably new LBBB. These recommendations have led to frequent false catheterization laboratory activation and inappropriate fibrinolytic therapy because most patients with suspected ischemia and new or presumably new LBBB do not have acute coronary artery occlusion on angiography. The new 2013 STEMI guideline makes a drastic change by removing previous recommendations. Therefore, patients with suspected ischemia and new or presumably new LBBB would no longer be treated as STEMI equivalent. The new guideline fails to recognize that some patients with suspected ischemia and LBBB do have STEMI, and denying reperfusion therapy could be fatal. The Sgarbossa electrocardiography criteria are the most validated tool to aid in the diagnosis of STEMI in the presence of LBBB. A Sgarbossa score of ≥3 has a superb specificity (98%) and positive predictive value for acute myocardial infarction and angiography-confirmed acute coronary occlusion. Thus, we propose a diagnosis and triage algorithm incorporating the Sgarbossa criteria to quickly and accurately identify, among patients presenting with chest pain and new or presumably new LBBB, those with acute coronary artery occlusion. This is a high-risk population in which reperfusion therapy would be denied by the 2013 STEMI guideline. Our algorithm will also significantly reduce false catheterization laboratory activation and inappropriate fibrinolytic therapy, the inevitable consequence of the 2004 STEMI guideline.

Spontaneous recovery of complete atrioventricular block complicating acute anterior wall ST elevation myocardial infarction

BACKGROUND

Complete atrioventricular block complicating acute anterior wall ST elevation myocardial infarction (MI) is classically considered one of the worst prognostic indicators.

METHODS

We present the case of a gentleman who developed complete atrioventricular block during the course of acute anterior wall ST elevation MI, and had spontaneous resolution of the same. Mechanisms of spontaneous resolution of complete atrioventricular block in the setting of acute MI are discussed. Attention is drawn to a subgroup of patients, albeit a minority, who have a better prognosis owing to reversible causes than classically expected and seen.

RESULTS

Clinical features suggested that this patient had reocclusion of the infarct-related artery after thrombolysis on presentation and spontaneous reperfusion.

CONCLUSION

Coronary angiography provides invaluable information for decision making in such clinical scenarios. Complete atrioventricular block due to reversible ischaemia produced by reocclusion of an infarct-related artery should be reversible by percutaneous coronary angioplasty of the infarct-related artery. We suggest that reversible causes be considered before attributing atrioventricular block to irreversible damage, which would require a permanent pacemaker implantation. This would be more significant in most of the developing world, where resources are scarce.

Compromised atrial coronary anatomy is associated with atrial arrhythmias and atrioventricular block complicating acute myocardial infarction

BACKGROUND

The relevance of the atrial coronary anatomy in the pathogenesis of atrial arrhythmias and atrioventricular (AV) block complicating acute myocardial infarction (AMI) remains unclear.

OBJECTIVES

We evaluated the location of the infarct-related coronary lesion relative to the principal atrial branches (ie, sinoatrial nodal, AV nodal, left atrial circumflex) in 454 patients with ST-elevation AMI in the CAPTORS II trial.

METHODS

Patients underwent systematic 60-minute postfibrinolytic angiograms, and coronary anatomy was correlated with evidence of atrial arrhythmias and AV block on sequential electrocardiograms.

RESULTS

Patients with either sinoatrial nodal or left atrial circumflex compromise (n = 34) had a higher incidence of "early" (ie, up to 90 minutes postfibrinolysis) atrial arrhythmias vs those without (23.5% vs 7.1%; P = .004). Patients with AV nodal compromise (n = 207) had a higher incidence of "early" AV block vs those without (12.1% vs 3.6%; P = .001).

CONCLUSION

These findings support the etiological role of acute atrial ischemia in the development of early atrial arrhythmias and AV block complicating AMI.

[Prognostic significance of advanced atrioventricular block in patients with acute myocardial infarction]

BACKGROUND

Advanced atrioventricular block (AB) during acute myocardial infarction (AMI), characterizes a high-risk subgroup of patients. Our aim was to determine the prognostic significance of AB and its possible peculiarities in relation to infarction localization and/or the thrombolytic therapy.

PATIENTS AND METHODS

The prospective study involved 1,239 patients with AMI. We studied clinical characteristics, as well as indexes of infarct size, short and long-term complications.

RESULTS

AB was present in 85 (6.8%) patients and was more often associated with: previous treatment with diuretics, diabetes, inferior localisation, higher number of ECG leads with elevated ST segment, and higher peak of CK. The AB was associated with a higher mortality: in-hospital (27% vs 10.6%; p < 0.01)) and after one-year (31.7% vs 19.4%; p < 0.05). Patients with AB had a different in-hospital mortality depending on anterior or inferior infarct localization (66% vs 18.5%; p < 0.001, respectively). In patients receiving thrombolytic treatment (n = 681), the duration of AB was shorter and in-hospital mortality was lower (13.7% vs 47%, p < 0.11) than that occurred in patients without this treatment (n = 558). AB had independent value for predicting in-hospital mortality (OR: 3.56; 95% CI: 1.84-6.90) and one-year mortality (OR: 2.77; 95% CI: 1.52-5.04).

CONCLUSIONS

AB is associated with larger infarcts and higher incidence of complications. The prognosis is especially poor when it is presented associated with anterior infarction and/or in patients without thrombolytic treatment. AB is a variable with independent prognostic value on the mortality.

Complete atrioventricular block complicating acute myocardial infarction in the thrombolytic era. SPRINT Study Group and the Israeli Thrombolytic Survey Group. Secondary Prevention Reinfarction Israeli Nifedipine Trial

OBJECTIVES

We assessed the incidence, associated clinical parameters and prognostic significance of complete atrioventricular block (CAVB) complicating acute myocardial infarction (AMI) in the thrombolytic era and compared them to data from the prethrombolytic era.

BACKGROUND

The introduction of new therapeutic modalities to treat AMI, aimed to enhance coronary reperfusion and to limit myocardial necrosis, was expected to decrease the incidence of CAVB and to improve prognosis. However, there are only limited data regarding the incidence and the prognosis of AMI patients with CAVB in the thrombolytic era.

METHODS

Data from 3,300 patients from the Israeli Thrombolytic Surveys (prospective, nationwide surveys of consecutive patients with AMI in all 25 coronary-care units in Israel in 1992 and 1996) were analyzed and compared with data from 5,788 patients included in the SPRINT (Secondary Prevention Reinfarction Israeli Nifedipine Trial) Registry (1981 to 1983).

RESULTS

During the 1990s, the incidence of CAVB was 3.7% compared with 5.3% in the 1980s, p = 0.0007. In the 1990s, mortality of patients with CAVB was significantly higher than in those without CAVB at 7 days (odds ratio [OR] = 4.05 95% CI [confidence interval] 2.34 to 6.82, 30 days OR = 3.98 [95% CI 2.44 to 6.43] and one-year hazard ratio [HR] = 2.36, [95% CI 1.68 to 3.30]) and similar in thrombolysis-treated and not-treated patients. Mortality of patients with CAVB has not changed significantly between the two periods; seven-day OR = 0.82 (95% CI 0.46 to 1.43); 30-day OR = 0.78 (95% CI 0.45 to 1.33) and one-year HR = 0.79 (95% CI 0.54 to 1.56), respectively, in the 1990s as compared to a decade earlier.

CONCLUSIONS

The incidence of CAVB complicating AMI is lower in the thrombolytic era than in the prethrombolytic era. Mortality among patients with CAVB is still high and has not declined within the last decade. The AMI patients who develop CAVB in the thrombolytic era have significantly worse prognosis than do patients without CAVB.

Acute myocardial infarction and complete bundle branch block at hospital admission: clinical characteristics and outcome in the thrombolytic era. GUSTO-I Investigators. Global Utilization of Streptokinase and t-PA [tissue-type plasminogen activator] for Occluded Coronary Arteries

OBJECTIVES

We sought to assess the outcome of patients with acute myocardial infarction (MI) and bundle branch block in the thrombolytic era.

BACKGROUND

Studies of patients with acute MI and bundle branch block have reported high mortality rates and poor overall prognosis.

METHODS

The North American population with acute MI and bundle branch block enrolled in the Global Utilization of Streptokinase and t-PA [tissue-type plasminogen activator] for Occluded Coronary Arteries (GUSTO-I) trial was matched by age and Killip class with an equal number of GUSTO-I patients without conduction defects.

RESULTS

Of all 26,003 North American patients in GUSTO-I, 420 (1.6%) had left (n = 131) or right (n = 289) bundle branch block. These patients had higher 30-day mortality rates than matched control subjects (18% vs. 11%, p = 0.003, odds ratio [OR] 1.8) and were more likely to experience cardiogenic shock (19% vs. 11%, p = 0.008, OR 1.78) or atrioventricular block/asystole (30% vs. 19%, p < 0.012, OR 1.57) and to require ventricular pacing (18% vs. 11%, p = 0.006, OR 1.73). Bundle branch block also carried an independent 53% higher risk for 30-day mortality. Thirty-day mortality rates for patients with complete, partial and no reversion of the bundle branch block were 8%, 12% and 20%, respectively (two-tailed chi-square test for trend 5.61, p = 0.02, OR 0.34 for complete reversion, OR 0.55 for partial reversion).

CONCLUSIONS

Bundle branch block at hospital admission in patients with acute MI predicts in-hospital complications and poor short-term survival.

Changes in R wave amplitude: ECG differentiation between episodes of reocclusion and reperfusion associated with ST-segment elevation

This study assesses the electrocardiographic (ECG) differences between episodes of increased ST-segment amplitude induced by coronary artery occlusion and by reperfusion in the open-chest rabbit model. Nine anesthetized open-chest male New Zealand White rabbits were subjected to four episodes of 5 minutes of coronary artery occlusion followed by 5 minutes of reperfusion. The ST-segment and R wave amplitudes were measured from an ECG lead attached to the pericardium overlying the ischemic myocardium. In 10 out of 35 (29%) of the episodes, reperfusion resulted in a transient increase in ST-segment amplitude. While episodes of coronary artery occlusion were associated with increase in R wave amplitude (69% and 97% of the episodes after 1 and 5 minutes, respectively), all reperfusion episodes were associated with prompt decrease in R wave amplitude. There was no difference between the repeated episodes in the occurrence of ST-segment elevation during reperfusion. However, ST-segment elevation during reperfusion could be distinguished from the ischemic episodes by the prompt decline in the R wave amplitude in the former compared with no change or increase in the latter.

Anatomy, histology, and pathology of the cardiac conduction system--Part V

Although morphologic findings in many of the cardiac arrhythmias of acute and chronic disease have been elusive, the correlates of heart block (particularly atrioventricular block) are abundant. Pathologic features of sinoatrial, atrioventricular, and bundle-branch block are reviewed. Lev and Lenegre diseases (idiopathic bilateral bundle-branch fibrosis) are also reviewed.

Rapid resolution of new right bundle branch block in acute anterior myocardial infarction patients after thrombolytic therapy

The objectives of this retrospective study are to describe the effect of thrombolytic treatment on the clinical course of patients with acute anterior myocardial infarction complicated by acute right bundle branch block. Patients admitted to the intensive cardiac care unit within < 4 hours from onset of symptoms, and demonstrating an acute right bundle branch block with, or without left axis deviation, on the qualifying ECG were included. All were given intravenous thrombolytic treatment consisting of: streptokinase (1,500,000 IU/40 min) or recombinant tissue type plasminogen activator (120 mg/6 hours). Following admission, patients were continuously monitored and a 12-lead ECG was recorded during each of the first 3 hours and then every 3 hours over the next 21 hours. Eight patients were included (8/211 = 3.8%). Their mean age was 62 +/- 7 years and time elapse from onset to treatment was 122 +/- 26 minutes. Complete resolution of the right bundle branch block occurred within < 3 hours in all and left axis deviation normalized in two patients. Mean peak creatine kinase was 1214 +/- 604 IU and global left ventricular ejection fraction, measured by isotope ventriculography within 24 hours from admission, was 39% +/- 15%. Only one patient was prophylactically paced. In the others, rapid normalization of the conduction block with reperfusion exceeded the logistics required for the transvenous pacemaker implantation procedure. Coronary angiography performed in six patients during 72 hours from admission revealed high grade stenoses in the proximal portion of the left anterior descending coronary artery in five patients and complete occlusion in one.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative histopathological study of right bundle branch block complicating acute anteroseptal myocardial infarction

The aim of the present study was to evaluate whether necrosis of the right bundle branch is responsible for development of right bundle branch block in acute myocardial infarction. Twenty patients with acute anteroseptal myocardial infarction were studied--10 with right bundle branch block (group A) and 10 without (group B)--to evaluate by serial sectioning the pathological extent of myocardial infarction surrounding the right bundle branch and also that of right bundle branch necrosis. Myocardial infarction reached the right bundle branch more than 8 mm above the moderator band in all of group A, whereas myocardial infarction reached the right bundle branch less than 3 mm above the moderator band in only three patients in group B. Nine hearts in group A showed significant necrosis of the right bundle branch. In group B and in one case with transient right bundle branch block no necrosis was found. The occurrence of right bundle branch block was almost entirely explained by necrosis of the right bundle branch, but transient right bundle branch block did develop without necrosis of the right bundle branch.

Prinzmetal angina. Multifocal ischemia, recurrent AV block, and bradycardia with patent coronary arteries responsive to verapamil

Coronary vasospasm may result in recurrent angina pectoris and cause acute myocardial infarction. The extent to which the "sudden death syndrome" occurs is unknown. The case described herein is unique in that the clinical features, including hypotension, AV block, and ventricular arrhythmias, were similar to those seen in myocardial infarction with a poor prognosis, yet infarction was not documented. In subsequent, long-term follow-up evaluation, chest pain has been recurrent, but despite close observation, no further major cardiac complications have been documented. Long-term use of verapamil has contributed to better control of clinical symptomatology.

Complete atrioventricular block complicating inferior wall acute myocardial infarction treated with reperfusion therapy. TAMI Study Group

Previous studies report larger myocardial infarcts and increased in-hospital mortality rates in patients with inferior wall acute myocardial infarction (AMI) and complete atrioventricular block (AV), but the clinical implications of these complications in patients treated with reperfusion therapy have not been addressed. The clinical course of 373 patients--50 (13%) of whom developed complete AV block--admitted with inferior wall AMI and given thrombolytic therapy within 6 hours of symptom onset was studied. Acute patency rates of the infarct artery after thrombolytic therapy were similar in patients with or without AV block. Ventricular function measured at baseline and before discharge in patients with complete AV block showed a decrement in median ejection fraction (-3.5 vs -0.4%, p = 0.03) and in median regional wall motion (-0.14 vs +0.24 standard deviations/chord, p = 0.05). The reocclusion rate was higher in patients with complete AV block (29 vs 16%, p = 0.03). Patients with complete AV block had more episodes of ventricular fibrillation or tachycardia (36 vs 14%, p less than 0.001), sustained hypotension (36 vs 10%, p less than 0.001), pulmonary edema (12 vs 4%, p = 0.02) and a higher in-hospital mortality rate (20 vs 4%, p less than 0.001), although the mortality rate after hospital discharge was identical (2%) in the 2 groups. Multivariable logistic regression analysis revealed that complete AV block was a strong independent predictor of in-hospital mortality (p = 0.0006). Thus, despite initial successful reperfusion, patients with inferior wall AMI and complete AV block have higher rates of in-hospital complications and mortality.

Factors associated with late onset of advanced atrioventricular block in acute Q wave inferior infarction

To elucidate the clinical characteristics associated with advanced atrioventricular (AV) block that appears relatively late (more than 24 hours) after the onset of myocardial infarction (MI), 101 patients with acute Q wave inferior MI were studied. Fourteen patients had late-onset advanced AV block, and 87 patients were free of AV block. The hospital mortality rate was 11%. Multivariate analysis was performed to determine the important variables associated with the occurrence of late advanced AV block and hospital mortality rates based on 12 clinical variables. Colloid osmotic pressure, right atrial pressure, serum potassium level, and number of segments with advanced asynergy were the significant factors associated with the occurrence of late advanced AV block, whereas advanced asynergic segments and alveolar arterial oxygen difference were important in the consideration of hospital mortality rates. Therefore not only the extent of myocardial ischemia but also the increases in the extracellular potassium level and interstitial fluid are some of the factors that are associated with the occurrence of late advanced AV block in acute inferior MI. Late advanced AV block, in itself, has no significant influence on hospital mortality rates.

Conduction defects in acute myocardial infarction in the Chinese in Hong Kong

In order to delineate the conduction defects complicating acute myocardial infarction in the Chinese, 636 Chinese patients admitted into one of the three medical units of a general hospital in Hong Kong in the period 1973-80 were reviewed. A relatively high incidence of conduction defects was observed, including atrioventricular block (11.3%), right bundle branch block (12.7%) and left bundle branch block (3.3%). Right bundle branch block (whether isolated or combined with left fascicular block) and atrioventricular block complicating anterior Q-wave infarction were ominous, with a high incidence of pump failure, cardiogenic shock and cardiac arrhythmias. These are markers of massive infarction. Atrioventricular and bundle branch blocks complicating inferior Q-wave infarction were benign. Left bundle branch block appeared to be a more chronic lesion, with moderate mortality, and isolated left anterior hemiblock did not adversely affect the short-term outcome. These results conform well to the patterns seen in Western series. The high incidence of conduction defects, in particular right bundle branch block and atrioventricular block complicating anteroseptal infarction, indicates a more serious clinical spectrum of acute myocardial infarction in the Chinese, and could have contributed to a higher hospital mortality in the Chinese series.

The tall R wave in lead V1 in posterior myocardial infarction: a reciprocal sign or a His-Purkinje conduction disturbance?

The significance of the tall R wave in lead V1 with an R/S ratio greater than or equal to 1 in posterior myocardial infarction (PMI) was investigated in 28 patients during programmed electrical stimulation. The patients had been admitted with acute PMI documented by electrocardiogram and proven by enzymatic increase. Electrophysiological study was performed 3 weeks after acute PMI. In 17 of the 28 patients (group 1), the tall R wave in V1 disappeared during stimulation: In 13 of them a premature atrial extrastimulus was responsible for an abrupt normalization of QRS complex in V1 related to an increase in AH or HV interval. In the 4 remaining patients the disappearance of the tall R wave in V1 was related to a sinus pause. In 14 patients of group 1, a different prematurity in atrial stimulation induced a right or left bundle branch block (BBB). In 11 of the 28 patients (group 2) the tall R wave in V1 was unchanged but a premature atrial extrastimulus induced a right BBB in 5 patients and a left BBB in 6. In conclusion, the normalization of QRS complex in lead V1 during atrial stimulation or alterations in cycle length suggests that the tall R wave in V1 in PMI is not a simple reciprocal sign of leads V8 V9. Its association with different varieties of BBB and changes in AH or HV intervals could suggest a relationship with a His-Purkinje conduction disturbance in some patients.

Factors associated with persistent and transient fascicular blocks in anterior wall acute myocardial infarction

To determine the factors associated with persistent and transient fascicular blocks, 144 patients with Q-wave anterior wall acute myocardial infarction (AMI) were studied. Thirty-three patients had new onset of fascicular block considered to be a consequence of AMI. Multivariate analysis using 16 clinical variables revealed that the number of asynergic segments, serum potassium level and pericardial rub were significant factors related to the occurrence of fascicular block. Among the 33 patients with fascicular block, 18 had persistent (group 1) and 15 had transient (group 2) fascicular blocks. When the 2 groups with fascicular block were compared, group 1 had significantly more asynergic segments than group 2 (4.7 +/- 1.2 vs 3.7 +/- 1.6, respectively), whereas pericardial rubs were observed significantly more in group 2 (67%) than in group 1 (28%). Therefore, the inflammatory process of AMI was 1 of the mechanisms related to the occurrence of a transient fascicular block and a more extensive myocardial necrosis was associated with a persistent fascicular block.

Transient alterations of the QRS complex and ST segment during percutaneous transluminal balloon angioplasty of the left anterior descending coronary artery

Using continuous 3-lead electrocardiographic (ECG) recordings in 19 patients undergoing elective percutaneous transluminal coronary artery angioplasty (PTCA) of the left anterior descending (LAD) artery, this study described the dynamic changes of the ST segment and the R- and S-wave amplitudes that occur during transient myocardial ischemia. The waveforms from lead V2 were quantified at 10-second intervals during the length of the balloon inflation that produced the greatest extent of ST-segment deviation. The simultaneous changes that occurred in leads aVF and V5 were also observed, but not quantified. Measurements of R- and S-wave amplitudes were performed during maximal ischemia from both the PR- and the J-ST-segment baselines to determine which of these most nearly maintained its control position during ischemia. The results indicate that the R-wave amplitude is best determined from the PR-segment baseline (p = 0.0007), while the S wave is best determined from the J-ST-segment baseline (p = 0.03). However, only a portion of the QRS changes observed during PTCA could be accounted for by the baseline shift. There were additional QRS changes during ischemia in 11 of the patients (58%) suggestive of conduction disturbances in 3 endocardial sites: left septal, right septal and left anterosuperior. It is hypothesized that these changes may represent ischemia-induced delay in conduction ("periischemic block") previously thought to occur only with myocardial infarction.

Ischemic blocks during early phase of anterior myocardial infarction: correlation with ST-segment shift

Of 760 consecutive cases with anterior acute myocardial infarction (AMI), 55 developed acute bundle-branch block (BBB), fascicular block, or high-degree atrioventricular block during the hyperacute ECG stage of AMI. According to the direction of the ST segment during the acute ischemic episode, patients were divided into two groups. Group A consisted of 32 patients who developed BBB during ST-segment elevation, positive T wave, and absent or minimal Q wave. Group B consisted of 23 patients who developed BBB during ST-segment depression and evolved into anterior AMI. Group A was characterized by a higher incidence of right BBB and left anterior hemiblock [91% vs. 26% and 56% vs. 13%, respectively (p less than 0.005)]. Group B was characterized by a higher incidence of left BBB and left posterior hemiblock [57% vs. 9% and 26% vs. 12%, respectively (p less than 0.001)]. The BBB was transient (disappearing within hours to one day) in 14 patients in Group A and in 5 patients in Group B. The incidence of progression to high-degree atrioventricular block was almost equal in the two groups (25% and 26%). The mortality rate was very high in both groups, but higher in Group B [74% vs. 59% (p = NS)] especially in those with LBBB (85%). Most patients died on the day of occurrence of BBB [Group A, 50% vs. Group B, 70% (p = NS)]. The causes of death in both groups were cardiogenic shock and/or electromechanical dissociation.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrioventricular block in posterior acute myocardial infarction: a clinicopathologic correlation

The specialized conducting systems of 44 hearts with posterior-inferior acute myocardial infarction were studied to clarify the anatomic basis of atrioventricular (AV) block. The results showed a lack of correlation between the block and the lesional pathology of the specialized conducting system. On the other hand, an evaluation of the atrial prenodal myocardium revealed strong clinicopathologic correlation between the block and the necrotic damage to these fibers. Twenty-nine or 97% of patients with AV block showed acute necrosis of the prenodal atrial myocardium. Considering the conducting prenodal septal atrial myocardium as a suprahisian structure, the necrosis at this level would provide an anatomic basis of the block in posterior-inferior acute myocardial infarction. Analysis of the behavior of the AV block after pharmacologic treatment further established a relationship between the block and acute lesions in the central conduction system.

Advanced early and late atrioventricular block in acute inferior wall myocardial infarction

Seventy-six patients with acute inferior acute myocardial infarction (AMI) and advanced atrioventricular (AV) block are described. According to pre-established ECG criteria and time of appearance of the advanced AV block, patients were divided into two groups. The early block group consisted of 31 patients who developed advanced AV block during the hyperacute ECG stage of AMI. Advanced AV block in these patients was characterized by early appearance, short duration, third-degree type block, poor response to atropine, and increased need for pacemaker therapy. The late block group consisted of 45 patients who developed advanced AV block during subsequent ECG stages of AMI. Advanced AV block in these patients was characterized by late appearance, longer duration, second-degree type block, positive response to atropine, and diminished need for pacemaker therapy. Morbidity and mortality also differed between both groups. Patients with early block had more syncope (32% vs 2%, p less than 0.0001), more left heart failure (36 vs 7%, p less than 0.005), and more cardiogenic shock (39% vs 2%, p less than 0.001) than patients with late block. The mortality rate in the early block group was high (23%) and similar to that reported in the literature, whereas the mortality rate in the late block group was low (7%, p less than 0.05) and similar to the mortality rate reported for acute inferior AMI without advanced AV block. These data identify a subgroup of patients with acute inferior AMI and advanced AV block, which accounts for the high mortality rate reported in this group of patients.

Possible role of a ventricular conduction disturbance in the electrogenesis of the ECG-VCG signs of myocardial infarction

The typical QRS patterns of myocardial infarction (MI-QRS) are commonly attributed to myocardial cellular death. However, observation of a transient appearance of MI-QRS during coronary insufficiency, the disappearance of MI-QRS after coronary by-pass surgery and the appearance of MI-QRS after intracranial hemorrhage suggest that a different electrophysiological mechanism may be at work. There is a single convincing explanation for all these observations. It seems possible, at least theoretically, that a localized conduction disturbance can generate or contribute to the generation of the MI-QRS. The results obtained in nine out of 194 cases studied by means of premature right atrial stimulation (PRAS) in our laboratory seem to confirm this hypothesis. In five of them we observed typical MI-QRS in the aberrant beats which were absent in the basal tracings. In the other four cases, MI-QRS which were present in basal tracings disappeared in the aberrant beats. In three of these a reduction in the duration of QRS was also observed, while in the fourth the duration of QRS did not change. In no case could the alterations of QRS (induction or disappearance of MI-QRS) be explained by a classical conduction disturbance, preexcitation or by a premature ventricular beat. While the induction of MI-QRS was clearly due to an aberrant conduction in the supraventricular beats, the disappearance of basal MI-QRS changes in premature supraventricular beats is more difficult to explain. One possible electrophysiological mechanism could be a supernormal phase conduction. If this is the case, the basal MI-QRS could be due to a ventricular conduction disturbance. In conclusion, our results suggest that MI-QRS can be generated, at least in our cases, by a localized conduction disturbance.

Isolated and complicated left anterior fascicular block: a review of suggested electrocardiographic criteria

The electrocardiographic criteria for isolated left anterior fascicular block are reviewed and illustrated. Left anterior fascicular block decreases the voltage in the chest leads and increases the voltage in the limb leads. The usual voltage criteria of left ventricular hypertrophy must be modified appropriately. Changes in repolarization include a decrease in the T wave of leads I and AVL and an increase in leads II, III, AVF, V5 and V6. Small Q waves in V2 may simulate an anteroseptal myocardial infarction. Three criteria for the possible diagnosis of superimposed inferior myocardial infarction have been suggested. Both inferior and anterior myocardial infarctions may be masked by R waves replacing Q waves. In the presence of a recent anterior infarction, right bundle branch block may also be masked. Thus, left anterior fascicular block may mask or mimic infarction and left ventricular hypertrophy and mask right bundle branch block in the setting of an acute anterior myocardial infarction.

Anatomic effects of cryoablation of the atrioventricular conduction system

Because of the value of cryoablation of the atrioventricular (AV) conduction system in treatment of refractory cardiac rhythm disorders, the anatomic effects of cryoablation on the cardiac conduction system must be defined. In this report we summarize studies done on four patients who had intractable recurrent supraventricular tachyarrhythmias or or refractory atrial flutter-fibrillation. They were treated by cryoablation of the AV conduction system and died 8-360 days postoperatively. Serial sections of the AV conduction system were studied. Cryoablation produced lesions that completely destroyed most of the AV node in three cases, the penetrating portion of the His bundle in all four cases, and the branching portion of the His bundle in two cases. The right bundle branch was not involved markedly in any case. The lesions were discrete and sharply delimited; the patient who died 8 days postoperatively had hemorrhage, necrosis and slight inflammatory infiltrate; patients who survived for 49-360 days showed collagen deposition. The AV nodal artery and its branches showed slight to marked intimal thickening in three cases. Small, partly organized thrombi were present just behind the tricuspid valve in two patients. We conclude that cryoablation of the AV conduction system produced discrete cardiac lesions that did not markedly damage the tricuspid valve or aorta.

His-bundle electrogram in the convalescent stage of inferior myocardial infarction complicated with complete A-V block

Twelve patients with inferior wall myocardial infarction complicated with complete atrioventricular block during the acute stage were studied. The His-bundle electrogram was studied in the convalescent stage at an average of 6 months after the acute attack. The age of the patients was 62 +/- 16 years. The width of the QRS complex was within the normal range and the PR interval was less than 200 msec. AH time was 74 +/- 18 msec (mean +/- SD). No split H activity was observed. HV time however, was significantly prolonged in the 12 patients; 54 +/- 12 msec vs. 42 +/- 9 msec in the control group (p less than 0.02). Five patients had HV time equal to or more than 60 msec. Intra-His block was suggested to exist in a high frequency in the patients who had previous complete AV block during the acute stage of myocardial infarction of the inferior wall.

Correlation of the width of the QRS complex with the pathologic anatomy of the cardiac conduction system in patients with chronic complete atrioventricular block

A study correlating the electrocardiographic findings and the histology of the atrioventricular (AV) conduction system was carried out in 14 cases with chronic complete AV block and in 13 cases without chronic complete AV block. Patients with chronic complete AV block were divided into two groups, based on the width of the QRS complex. The QRS complexes were narrow (less than 0.12 second) in four cases (group 1) and wide (greater than or equal to 0.12 second) in 10 cases (group 2). In group 1, the main lesion was located in the penetrating portion of His bundle (Hisp) in one heart, in the branching portion of the His bundle (Hisb) in another and in the combined regions of Hisb and the left bundle branch in two. Three of the four cases in group 1 had idiopathic fibrosis of the conduction system and one had calcific nodules in the central fibrous body. In group 2, the main lesion was located in Hisb in two cases, in the combined regions of Hisb and the right bundle branch in one, in the Hisb and in the bilateral bundle branches in two, and in the bilateral bundle branches in five. All cases in group 2 were of the idiopathic type, except case 5, which had calcific aortic stenosis. In 13 cases without chronic complete AV block the AV conduction system was histologically normal, except for slight-to-moderate aging changes in the His bundle or the bundle branches. Lesions of the Hisb, which is believed to be the "distal His" electrophysiologically, may induce complete AV block with narrow or wide QRS complexes, depending upon the severity of the lesions in Hisb or adjacent bundle branches.

A morphologic study on human conduction system of heart considering influences of some disorders of individuals

The authors have investigated the aging changes of the human AV node, AV bundle, and bundle branches considering the influences of various disorders of individuals upon these conduction tissues. These conduction tissues began to develop gradually from the infant stage and the development was completed by young adult stage. Aging changes of the conduction tissues were fat infiltration, fibrosis and elastosis, disappearance of muscle fiber, and general atrophy of the conduction tissues. They were thought to occur not only by aging but also by the influences of various disorders particularly of long-standing chronic diseases. Changes of the conduction tissues seem to be related with thickening and luminal narrowing of the AV nodal artery and superior ventricular septal arteries. Marked elastosis or atrophy was noted in the cases suffering from some long-standing disorder regardless of the sort of disorders. In the cases which were diagnosed as complete heart block clinically, destruction of the conduction tissues was extremely severe including those of the SA node.

Transient QRS changes simulating acute myocardial infarction

The purpose of this study was to determine the characteristics and incidence of abrupt occurrence of abnormal initial QRS forces that cannot be explained by acute myocardial infarction or left or right ventricular overload. Computerized data from 3175 patients with suspected acute infarction were reviewed to identify those in whom the ECGs revealed QRS complexes considered to be diagnostic (Q wave or markedly diminished R wave) in the presence of persistently normal profiles of both creatine kinase and lactic dehydrogenase isoenzymes. Lead misplacement had been minimized by obtaining multispace tracings and vectorcardiograms. Eight patients (0.25%) were identified. The abnormal forces were confined to leads V 1-3 in six, V 4-6 in one, and involved all precordial leads in the last. These QRS changes resolved completely within 6 days in all eight patients, which suggests that they did not have an acute infarction. This theory was supported by postmortem examination in one patient. An extremely low incidence (0.25%) has been documented for a syndrome characterized by transient loss of initial anterior forces with persistently normal isoenzyme profiles. Although no etiology could be determined, a transient conduction block of the septal fascicle of the left bundle could have been the cause in seven of the eight patients.

Occurrence and significance of coagulative myocytolysis in the specialized conduction system: clinicopathologic observations

In 5 of 18 selected human hearts (15 from patients with early myocardial infarction and severe coronary arterial obstruction), coagulative myocytolysis (myofibrillar degeneration with contraction bands) was demonstrated in the specialized conduction tissue. Its morphologic peculiarities, apparently inherent in the number and arrangement of the affected myofibrils in each type of specific myocell, are described. In nine cases the ordinary cardiac muscle was also involved; in all hearts concomitant changes were present. The debated toxic catecholamine and anoxic aspects of coagulative myocytolysis are briefly reviewed in light of the finding that specialized tissue seems to withstand myocytolytic damage (or any ischemic-anoxic injury) better than ordinary myocardium. This may also explain why coagulative myocytolysis is observed less frequently and evidently in specific rather than in ordinary myocells. Clinicopathologic comparisons focused on arrhythmias, although hampered by inadequacies in routine electrocardiographic documentation, suggest that coagulative myocytolysis of the conduction system may be relevant to life-threatening disturbances in impulse formation and conduction. These data, with their bearing on important current problems in cardiologic emergencies, deserve better morphopathophysiologic assessment.

Left anterior hemiblock obscuring the diagnosis of right bundle branch block in acute myocardial infarction

Thirty cases in which transient left anterior hemiblock (LAHB) obscured the diagnosis of right bundle branch block (RBBB) appearing during the first days of an acute myocardial infarction (AMI) are presented. Twenty-eight of the patients with AMI had a clear septal wall involvement, while the remaining two had an anterolateral and lateral wall AMI, respectively. These intraventricular conduction defects developed 2-120 hours (mean 64.9 +/- 26 hours) after the acute event, and persisted for 24 hours to 7 days (mean 63.1 +/- 35 hours). The ECG was characterized by a pure LAHB with wide QRS complexes and the presence of RBBB was shown by recording high V1 and right-sided chest leads. The vectorcardiogram was also useful in several cases. The clinical course of this type of bifascicular block was transient and benign, with an in-hospital mortality of 6.7%. No patient developed trifascicular or complete atrioventricular block and, therefore, we conclude that prophylactic installation of a temporary pacemaker is not indicated in this type of bifascicular block. The possible role of extracellular potassium released during acute myocardial necrosis in the pathophysiological mechanism of these blocks is discussed.

Bundle-branch block in the setting of acute anteroseptal myocardial infarction. Clinicopathological correlation

Images

Electrophysiologic effects of anterior septal arterial occlusion

The effect of reduction in anterior septal arterial flow on the conduction system was studied in seven anesthetized dogs. After 2 hours of occlusion P-Q, A-H, and H-V intervals as well as atrioventricular nodal effective and functional refractory periods were significantly prolonged, sinoatrial conduction time was prolonged and the heart rate was decreased. The duration of the His bundle electrogram was significantly prolonged and the configuration altered. However, QRS duration did not prolong significantly. Fifteen minutes after reperfusion, A-H interval, duration of the His bundle electrogram, effective refractory period and functional refractory period returned toward control values. However, the H-V and QRS intervals as well as sinoatrial conduction time were unchanged after reperfusion. Thus, reduction of anterior septal arterial flow influences not only the distal but also the proximal portion of the conduction system; the most vulnerable part is probably the His bundle. The distal portion of the conduction system is directly influenced by ischemia itself, whereas the proximal portion is influenced through other mechanisms induced by reduction of anterior septal arterial flow.

Intra-His bundle block in acute myocardial infarction. Report of two cases

Two patients with acute intra-His bundle block, both secondary to myocardial infarction, are described. The diagnosis of the block was proved by means of His bundle recordings during the phase of complete atrio-ventricular (A-V) block. Two His bundle potentials, one (H) following each A wave and the other (H') preceding each QRS complex, were detected. In both cases, as well as in the few cases reported in the literature, the site of the infarction was in the inferior wall, an occurrence which shows the functional importance of the posterior blood supply to the His bundle. In both cases the block developed into a chronic form, requiring the implantation of a transvenous pacemaker in one case. This evolution suggests that the post-infarction intra-His bundle block may be due to irreversible anatomic damage.

Conduction system in a patient with Prinzmetal's angina and transient atrioventricular block

His bundle recordings obtained during and between attacks of Prinzmetal's variant angina and transient atrioventricular (A-V) block were followed by a comprehensive serial section study of the conduction system in a 33 year old woman. Recordings between attacks showed normal A-H and H-V intervals. During an attack there was block proximal to the His bundle recording site. Pathologic studies revealed severe narrowing of the right coronary artery. Arteriolosclerosis of the heart was diffuse. Insignificant changes were found in the approaches to the A-V node and the A-V node itself. Major changes found in the left bundle branch had no counterpart in the electrocardiogram; the discordance in these findings is discussed.

Histopathology of conducting system in left anterior hemiblock

In 8 cases of left anterior hemiblock, combined with right bundle-branch block in 7, serial sections of the conducting system of the heart were examined histologically. In all cases there were pathological changes in the left bundle-branch but the anterior part of it was predominantly affected in only 2 cases. Acute changes were found in 6 cases of early myocardial infarction, and fibrosis in 2 cases of chronic heart disease. Reversible lesions may have a pathogenetic role in acute hemiblocks. The right bundle-branch was disrupted by fibrosis in 6 of the 7 cases with right bundle-branch block, and minor changes in the AV node were observed in 1. The widespread damage to the left bundle-branch in the majority of the present cases does not seem to be consistent with the limited clinicopathological correlation implied by the terms anterior fascicular block or hemiblock. Other cardiac lesions within the left bundle-branch and outside it may contribute to this electrocardiographic pattern.

Structural basis of ventricular arrhythmias in human myocardial infarction: a hypothesis

The present study was undertaken using light and electron microscopic techniques to determine whether Purkinje fibers survive in the subendocardial region of anteroseptal infarcts in humans. Tissue was obtained for this purpose from 11 patients with 12 documented infarctions at the time of autopsy; six patients died within 72 hours of the infarction and five had healed infarcts. Seven of the 11 patients had ventricular arrhythmias. Light microscopic study indicated that intact cells with a normal appearance remained on the subendocardial surface, although the underlying ventricular muscle either was necrotic or was replaced by fibrous tissue. Electron microscopy demonstrated that these intact surviving cells over the surface of the infarct had few randomly oriented myofibrils, abundant glycogen, and other characteristics of Purkinje fibers. These cells could be readily distinguished from normal or infarcted ventricular muscle cells. Purkinje fibers, the most peripheral part of the conduction system, survive in extensive anteroseptal infarcts and may be the site of origin of ventricular arrhythmias.

Conduction disturbances of the bundle branches produced by lesions in the nonbranching portion of His bundle

The present experiments were conducted on isolated dog hearts to demonstrate that conduction disturbances can be induced in the bundle branches by transection of about 50 per cent of the cross-sectional area of the His bundle on the right or left side. The His bundle, the posterior and anterior divisions of left bundle, and the right bundle were exposed by careful dissection, and microelectrode techniques were used to record action potentials from the three bundle branches. Pacing stimuli were applied to the nonbranching portion of His bundle proximal and then distal to the site of transection to study the effect of such lesions on impulse conduction to the bundle branches. It was demonstrated that conduction to the bundle branches was not affected by such lesions in the His bundle at pacing rates slower than 100 per minute; however, conduction disturbances were rate-dependent and manifested at faster pacing rates. In nine out of all 16 experiments, partial or complete block occurred in all three bundle branches regardless of the side of the lesion. In the remaining seven experiments, they were observed in the bundle branch on the same side as the lesion. It was assumed that conduction disturbances of the bilateral bundle branches resulted from decremental conduction in the uncut portion of His at the level of lesion, and those of the ipsilateral branch from the functional failure of transverse crossover connections between the longitudinal His bundle fibers. The results indicate that localized lesions in the nonbranching portion of His bundle can indeed produce the pattern of bundle branch block under certain conditions.

Left posterior hemiblock in acute myocardial infarction

Fifteen cases of left posterior hemiblock associated with acute myocardial infaction were studied. In 5 cases the left posterior hemiblock was the only intraventricular conduction defect, while in the other 10 cases it was associated with complete right bundle-branch block. Left posterior hemiblock proved to be an early complication, appearing within a few hours from the onset of the acute episode, and an ominous sign, since hospital mortality rate was 87 per cent. Cause of death was mainly pump failure. In most of these cases ther was electrocardiographic evidence of infarction involving both anterior and inferior ventricular walls. Infarction of most or all of the ventricular septum was a common finding in the cases examined anatomically. Histologically, acute changes involving mainly the posterior septal and midseptal fibres were observed in 6 of the 8 cases studied. On the basis of these findings and of other published findings an alternative physiopathological mechanism for so-called left posterior hemiblock is proposed.

Histopathology of the conduction system in sudden death from coronary heart disease

Sudden cardiac death (SCD) has been attributed to the development of lethal dysrhythmias in coronary heart disease victims, and several recent autopsy surveys showed that 10 to 50% of SCD patients had unsuspected acute myocardial infarction (AMI). The present study concerned histopathological findings of the conduction system in 49 SCD (within six hours of the onset of acute symptoms) patients; 39 with established AMI (group A) and ten without (group B). Both groups showed high incidence of cardiomegaly, significant coronary artery disease affecting one or more vessels, and acute myocardial ischemia detectable by specific histological criteria. Stenosis of nutrient vessels of the conduction system was present in about 50% of the atrioventricular (A-V) node arteries and about 25% of the sinoatrial (SA) node arteries in both groups of SCD patients. Nonspecific "degenerative" changes (fibrosis, fatty infiltration, or both) of the conduction tissue, which might or might not represent results of old ischemic injury, also occurred with similar frequencies. Acute changes (infarction, hemorrhage) of the A-V node and bundle branches were found only in two group A patients, both had massive septal infarction. Thus, the conduction tissue appeared more resistant to ischemic injury and was overtly damaged only on rare occasions in fatal AMI. The scarcity of acute lesions in the conduction system itself suggested that lethal dysrhythmia in SCD was probably due to electrical instability of the acutely ischemic contractile myocardium rather than a direct injury to the specialized tissue of the heart.