Negative concordant T waves during paced ventricular rhythm: An honest enemy is better than a false friend

[Cardiac memory following pacemaker implantation]

BACKGROUND

Although T wave inversions due to cardiac memory were described already 50 years ago, little is known about the prevalence and about clinical predictors of this phenomenon.

METHODS

After exclusion of 238 patients due to bundle branch block or pacemaker dependency, a total of 325 consecutive patients were enrolled in this study during routine outpatient control of their pacemaker. A 12-lead standard ECG was obtained in all patients during transient inhibition of pacing therapy.

RESULTS

Cardiac memory could be documented in 115 of 325 patients (35%) and showed a strong association with the amount of ventricular stimulation. The prevalence of cardiac memory was 9% in patients with ≤25% ventricular stimulation and 86% in patients with ≥75% ventricular stimulation.

DISCUSSION

Cardiac memory was observed in one third of patients following pacemaker implantation. The prevalence of cardiac memory in the ECG with intrinsic rhythm is above 80% in patients with frequent ventricular stimulation. Cardiac memory due to ventricular stimulation is benign and should not be confused with similar T wave inversions due to acute coronary syndrome, severe left ventricular hypertrophy, or myocarditis.

Cardiac Memory: A Case Report and Review of the Literature

BACKGROUND

A variety of clinical syndromes can cause T-wave inversion (TWI), ranging from life-threatening events to benign conditions. One benign cause of TWI is cardiac memory, which is characterized by the transient inversion of T-waves following abnormal activation of the ventricles, commonly due to intermittent left bundle branch block (LBBB), tachydysrhythmias, electrical pacing, or ventricular pre-excitation.

CASE REPORT

A 72-year-old man presented to the emergency department with chest pain, nausea, vomiting, and headache. Upon arrival, his electrocardiogram (ECG) showed new-onset LBBB with appropriate secondary ST-T wave changes. A subsequent ECG showed disappearance of LBBB and newly inverted T-waves in precordial leads V1-V5, followed by a repeat ECG that again showed LBBB. Serial troponin testing was unremarkable. During hospitalization, echocardiogram and nuclear perfusion stress test were normal. The transient TWIs in this patient were believed to be due to cardiac memory. We performed a literature review and identified 39 published cases of cardiac memory. The most common etiology for cardiac memory was after cardiac pacemaker placement, followed by intermittent LBBB (as was seen in our patient), and post-tachydysrhythmia. Patient ages ranged from 21 to 88 years, with an equal number of cases reported in men and women. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Cardiac memory is a poorly understood, rarely observed phenomenon that can occur in the setting of intermittent LBBB. Testing for acute cardiac ischemia and underlying coronary artery disease is still recommended, as the diagnosis of cardiac memory can only be made after negative workup.