Electrocardiographic Diagnosis of Myocardial Infarction and Ischemia during Cardiac Pacing

Diagnosis of myocardial infarction and ischemia in the setting of bundle branch block and cardiac pacing

The diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) or during ventricular pacing (VP) is challenging because of inherent changes in the sequence of ventricular depolarization and repolarization associated with both conditions. Although LBBB and right ventricular (RV) pacing may both produce abnormalities in the ECG, it is often possible to diagnose an acute MI (AMI) or an old MI based on selected morphologic changes. Primary ST-segment changes scoring 3 points or greater according to the Sgarbossa criteria are highly predictive of an AMI in patients with LBBB or RV pacing. The modified Sgarbossa criteria are useful for the diagnosis of AMI in patients with LBBB; however, these criteria have not yet been studied in the setting of RV pacing. Although changes of the QRS complex are not particularly sensitive for the diagnosis of an old MI in the setting of LBBB or RV pacing, the qR complex and Cabrera sign are highly specific for the presence of an old infarct. Diagnosing AMI in the setting of biventricular (BiV) pacing is challenging. To date there is minimal evidence suggesting that the traditional electrocardiographic criteria for diagnosis of AMI in bundle branch block may be applicable to patients with BiV pacing and positive QRS complexes on their ECG in lead V1. This report is a careful review of the electrocardiographic criteria facilitating the diagnosis of acute and remote MI in patients with LBBB and/or VP.

A Case Series of Acute Myocardial Infarction in Left Ventricular Assist Device-Supported Patients

Acute myocardial infarction (AMI) is an underrecognized phenomenon in patients with continuous-flow left ventricular assist devices (CF-LVAD). Previously, there has been an optimistic expectation of a benign clinical course; however, AMI in LVAD-supported patients can result in profound consequences and management remains controversial. We describe a case series of AMI in four CF-LVAD patients, each with a different presentation, clinical course, treatment, and outcome. The clinical variability and mixed outcomes of these patients highlights the unique challenges in diagnosis and management of AMI in this population, particularly the uncertain role of percutaneous intervention (PCI), and underscores the potentially poor prognosis of this entity. Several key points emerge from this review. First, LVAD-supported patients frequently have underlying abnormalities on the electrocardiogram (ECG) that obscure the diagnosis of AMI. Second, clinicians should have a high degree of suspicion for AMI in the presence of suggestive clinical features, elevated cardiac biomarkers, or new-onset ventricular arrhythmias. Third, the decision to proceed with PCI requires careful evaluation of the risk of hemorrhage, and strong consideration should be given to the use of bleeding avoidance strategies during and after PCI.

Electrocardiographic identification of prior myocardial infarction during right ventricular pacing--effect of septal versus apical pacing

BACKGROUND

Electrocardiographic (ECG) identification of prior myocardial infarction (MI) during right ventricular (RV) pacing is of clinical importance. Proposed ECG criteria have been evaluated only during apical pacing. We evaluated the effect of pacing site on the predictive performance of ECG signs of prior MI.

METHODS

The present study is a secondary analysis of a prospective, multicenter study which randomized recipients of an implantable cardioverter defibrillator to an apical versus septal RV lead positioning. ECGs of patients with or without prior MI were analyzed for the presence of the following criteria: Cabrera sign, Chapman sign, QR pattern in leads I, aVL, V5 or V6, QR in inferior leads and notching in the descending slope of the QRS complex in inferior leads.

RESULTS

The MI group included 89 patients (55.1% apically paced), while 99 patients had no prior MI (50.5% apically paced). In the total population, the Cabrera sign presented the highest specificity (97%) and diagnostic accuracy (62.2%), with a sensitivity of 23.6%. The Cabrera sign was the only significant predictor of a prior MI [OR=9.9, (95%CI:2.8-34.5), p<0.001], among all ECG markers. Pacing site did not significantly influence the sensitivity and specificity of the Cabrera sign for detection of prior MI.

CONCLUSIONS

In our study, the Cabrera sign was the only ECG marker that predicted the presence of prior MI during ventricular paced rhythm. Septal RV lead positioning did not affect the predictive performance of the Cabrera sign.

Electrocardiographic abnormalities of takotsubo cardiomyopathy in a patient with paced ventricular rhythm

Takotsubo cardiomyopathy (TCM) is a unique cardiomyopathy characterized by chest pain, ECG, and regional wall motion abnormalities closely mimicking acute myocardial infarction, in the absence of significant coronary artery disease. Classic ECG changes of TCM include ST elevation or T wave inversion. However, ECG abnormalities of TCM in patients with paced ventricular rhythms have not been well characterized. Herein, we report the case of an 85-year-old pacemaker dependant female who was diagnosed with TCM four weeks following the demise of her husband. Abnormal negative T wave concordance in precordial leads and QT interval prolongation were the only new ECG findings and these reverted back to baseline on followup.

Value of the 12-lead resting electrocardiogram for the diagnosis of previous myocardial infarction in paced patients

AIM

This study was conducted to assess the clinical value of the 12-lead electrocardiogram (ECG) for the diagnosis of previous myocardial infarction (MI) in permanently paced patients.

METHODS

A total of 107 unselected patients with permanent pacemakers were retrospectively studied and divided into 3 groups: group 1 (control group): 38 patients without a history of MI (mean age, 67 +/- 16 years; 20 men; ejection fraction 63% +/- 8%); group 2: 44 patients (mean age, 72 +/- 11 years; 41 men) with documented previous MI (21 anterior, 23 inferior; ejection fraction 38% +/- 13%; P < .0001 vs group 1); group 3: 25 patients (mean age, 71 +/- 14 years; 24 men) with biventricular pacing for severe heart failure (16 ischemic, 9 nonischemic; ejection fraction 28% +/- 8%; P = .001 vs group 2, P < .0001 vs group 1). A surface 12-lead ECG with full ventricular capture was used for analysis. Comparing group 1 and group 2, the sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of 5 criteria was calculated: (1) Cabrera's sign (notching in the ascending limb of the S wave in lead V(3), V(4), or V(5)); (2) Chapman's sign (notching of the R wave in lead I, aVL, or V(6)); (3) presence of a qR in lead I, aVL, or V(6); (4) notching of QRS in lead II, III, or aVF; (5) presence of a qR in lead II, III, or aVF.

RESULTS

To detect prior MI, sensitivity was moderate for Cabrera's sign (63.6%) and poor for all other ECG criteria ranging from 9.1% to 40.9%. Specificity was relatively high for all ECG criteria ranging from 81.6% to 100%. Combining all 5 ECG signs increased sensitivity to 86.4%, with a specificity of 65.8% and an overall accuracy of 76.8% for the diagnosis of previous MI. None of the 5 criteria was particularly useful to assess the site of prior MI. In patients with biventricular pacing, the accuracy of the 5 ECG criteria was poor and the presence of a qR wave in lead I, aVL, or V6 appears nonspecific and related to pacing site.

CONCLUSION

The ECG diagnosis of previous MI in paced patients remains a difficult challenge but the presence of 1 or more of the aforementioned ECG criteria may be clinically useful to detect previous MI, suggesting that these ECG signs should be widely taught during medical training. However, in patients with biventricular pacing, these ECG signs are of no value.