T-vector direction differentiates postpacing from ischemic T-wave inversion in precordial leads

The Heart Remembers: A Case of Cardiac Memory

An 80-year-old male with a history of atrial fibrillation and a single-chamber ventricular pacemaker presented to the hospital for an elective colonoscopy. He experienced a transient episode of unresponsiveness with seizure-like activity before the procedure. This prompted him to get an EKG showing deep T-wave inversions (TWIs) in the precordial leads on a background of paced beats. Such findings were concerning for an acute and potentially life-threatening process such as myocardial infarction (MI) or intracranial insult. After ruling out any severe conditions, the EKG findings were attributed to cardiac memory, an underdiagnosed cause of deep TWIs in patients with a pacemaker.

Pediatric T-wave memory after accessory pathway ablation in Wolff-Parkinson-White syndrome

BACKGROUND

Altered ventricular depolarization due to manifest accessory pathway conduction (ie, Wolff-Parkinson-White syndrome) leads to repolarization abnormalities that persist after pathway ablation. The term T-wave memory (TWM) has been applied to these changes, as the postablation T-wave vector "remembers" the pre-excited QRS vector. In adults, these abnormalities can be misinterpreted as ischemia leading to unnecessary interventions. To date, no comprehensive studies have evaluated this phenomenon in the pediatric population.

OBJECTIVE

The purpose of this study was to define TWM in the pediatric population, identify preablation risk factors, and delineate the timeline of recovery.

METHODS

Pre- and postablation electrocardiograms (ECGs) in patients ≤25 years were analyzed over a 5-year period. Frontal plane QTc interval, T-wave axis, QRST angle, and T-wave inversions were used to identify patients with TWM. Univariate analysis was performed to determine the association of preablation ECG features with the outcome of TWM.

RESULTS

TWM was present in 42% of pediatric patients, with resolution occurring within 3 months of ablation. Preablation QRS axis <0° was a strong predictor of TWM (odds ratio [OR] 15.2; 95% confidence interval [CI] 5.7-40), followed by posteroseptal pathway location (right posteroseptal-OR 8.9; 95% CI 4.2-18.8; left posteroseptal-OR 6.1; 95% CI 1.7-22.3). The degree of pre-excitation had a modest association with the development of TWM. No adverse events were observed.

CONCLUSION

TWM is less common in children compared to adults, and normalization occurred within 3 months postablation. The most predictive features for the development of TWM include a leftward pre-excited QRS axis and posteroseptal pathway location.

Worth Remembering: Cardiac Memory Presenting as Deep Anterior T-Wave Inversions Explained by Intermittent Left Bundle Branch Block

Cardiac memory is a common cause of deep T-wave inversions (TWI) in the anterior precordial leads and can be difficult to distinguish from alternative causes of TWI such as myocardial ischemia. Cardiac memory is generally a benign condition except in the setting of prolonged QT when it can contribute to the precipitation of torsades de pointes. Herein, we describe the presentation and clinical course of a case of cardiac memory due to intermittent left bundle branch block (LBBB) that presented asymptomatically to our outpatient cardiology clinic with deep anterior TWI. We discuss common causes of and mechanisms underlying cardiac memory and how to distinguish it from alternative causes of TWI based on 12-lead electrocardiogram. In conclusion, intermittent LBBB is an under-recognized cause of cardiac memory that can present as deep anterior TWI mimicking cardiac ischemia, and awareness of this clinical entity may help prevent unnecessary invasive and expensive testing on otherwise healthy patients.

Clinical Dilemma - Cardiac Memory vs Myocardial Ischemia

Cardiac memory (CM) is a commonly unrecognized entity in which electrocardiograph (EKG) changes demonstrate T wave inversions (TWI) that appear consistent with ischemia. Inability to recognize and distinguish CM from actual ischemia can be a burden for both patients and hospitals, leading to unnecessary hospital admission, cardiac testing, and cardiac catheterization. Simple EKG analysis and meticulous interpretation of T-wave axis and morphology can help differentiate between the two. We present a case with such a dilemma, and an overview literature and physiology behind this entity.

Surface ECG criteria can discriminate post-septal pacing cardiac memory from ischemic T wave inversions

Cardiac memory (CM) refers to transient T wave changes that appear after cessation of a period of abnormal ventricular activation, such as right ventricular (RV) pacing. ECG criteria for differentiating post-pacing CM from ischemia-induced T wave changes were previously published only for apical, but not for septal RV pacing.

AIM

To find ECG criteria for discriminating post-septal pacing CM from ischemic T wave inversions.

METHODS

ECGs were analyzed in 2 groups: CM (n = 23) and ischemia (n = 26). CM was induced by 2 weeks of DDD pacing with a short AV delay. Ischemic patients were grouped by culprit vessel: left anterior descending (LAD), circumflex (Cx), right coronary artery (RCA).

RESULTS

CM was visible on the ECG after 1 week of ventricular pacing, started to disappear in <1 week after pacing cessation and was completely reversible within 4 weeks of pacing cessation. T wave axis differed between CM (75.8 ± 18.5°) and Cx (-25.2 ± 25.5°, p < 0.01) and RCA (-18.3 ± 18.9°, p < 0.01) groups, but not compared to LAD group (96.4 ± 65.0°, p = 0.17). The combination of (1) positive T wave in aVF; and (2) (i) T wave amplitude in aVF ≥ the absolute value of the most negative precordial T wave, or (ii) positive T wave in V5 and positive or isoelectric T wave in lead I identified CM from all ischemia with a sensitivity of 91% and a specificity of 92%.

CONCLUSION

ECG criteria can discriminate post-septal RV pacing CM from ischemic changes with high sensitivity and specificity.

[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.

Cardiac memory: an under-recognised cause of deep T wave inversion in a patient presenting with chest pain

T wave inversion (TWI) has many differential diagnoses with acute myocardial ischaemia being the highest on the list of potential causes. Cardiac T wave memory is a benign, under-recognised and clinically important phenomenon seen after periods of altered ventricular conduction. After normal ventricular conduction is restored, the T wave 'remembers' and mirrors the direction of the wide QRS complex. Therefore, negative T waves are seen in leads that had negative wide QRS complexes. We describe the case of a 60-year-old truck driver with chest pain, deep TWI and traditional cardiovascular risk factors. After ruling out significant myocardial ischaemia, it was crucial to determine the cause of his T wave changes to provide reassurance and provide commercial license medical clearance. While it is currently a diagnosis of exclusion, it remains an important clinical entity for clinicians to recognise to provide an explanation for certain T wave changes to avoid future unnecessary cardiac testing.

Rate-related left bundle branch block and cardiac memory in a patient with bradycardia: Case report and literature review

Rate-related left bundle branch block (LBBB) is a well-studied phenomenon. Cardiac memory is another physiologic phenomenon in which T-wave abnormalities occur in the absence of ischemia. The association between these 2 phenomena has been described in several case reports. A literature review was performed through Ovid and PubMed, where at total of 93 cases of rate-related LBBB were identified. Cases were reviewed, and data were collected on rates of appearance and disappearance as well as the presence or absence of cardiac memory. There is some overlap in the rate at which LBBB appears. Cardiac memory is associated with rate-related LBBB in several cases, but its true prevalence is unknown. Cardiac memory is a phenomenon that is well described in the literature but is often underrecognized in clinical practice. As a consequence of overlooking this phenomenon and not including cardiac memory in the differential when T-wave abnormalities are observed, patients may be subjected to unnecessary invasive diagnostic testing.

Mark E Josephson: Clinical Investigator

Mark E Josephson entered the world of clinical cardiac electrophysiology (EP) almost at its inception (1972); with so much to learn and so many directions one could take, he dived into the field with unbridled enthusiasm and an uncommon - perhaps almost unique - aptitude for asking questions and finding ways to answer them. Few aspects of EP escaped his indelible influence. In this short paper, I will attempt to touch on some of the high points of his astounding career as a clinical investigator.

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.

Intermittent left bundle branch block: an overlooked cause of electrocardiographic changes that mimic high-grade stenosis of the left anterior descending coronary artery

CONTEXT

The electrocardiographic (ECG) pattern of high-grade stenosis of the left anterior descending coronary artery (LAD) is important clinically because of the high risk of myocardial infarction and cardiac death if the pattern is not recognized. Although the recognition of this pattern is currently widespread, false-positive ECG changes that mimic this pattern are infrequently reported.

OBJECTIVE

To demonstrate that ECG changes from intermittent left bundle branch block (LBBB) and cardiac memory can mimic anterior ischemia.

METHODS

Medical record review of cardiology patients in whom ECG tracings showed intermittent LBBB and anterior T-wave changes during normal QRS conduction. Patients were included if ECG changes suggestive of high-grade LAD stenosis in leads V2 and V3 met the following criteria: (1) the QRS conduction was essentially normal during periods of absent LBBB; (2) the ST segment took off from an isoelectric point or only slightly elevated from baseline; and (3) the ST segment sloped up gradually with an abrupt and sharp down stroke leading to terminal T-wave inversion. Additional criteria were little or no ST segment elevation, no loss of precordial R waves, and ECG changes suggestive of high-grade LAD stenosis demonstrated in precordial leads V2 and V3. All patients demonstrated intermittent LBBB, and patients were excluded if a ventricular pacemaker was present. The case series began in 2003 and continued until 2011.

RESULTS

Sixteen patients (3 male) with intermittent LBBB were identified with ST- and T-wave changes during normal ventricular conduction that matched the pattern described by Hein J.J. Wellens, MD. Of these patients, none had evidence of clinically substantial coronary artery disease. Eleven patients had stress testing with myocardial perfusion imaging, and 5 patients underwent cardiac catheterization. In 1 patient whose ECG pattern showed high-grade LAD stenosis but normal coronary arteries at catheterization, a stress test was later performed, which provoked LBBB. All other patients had spontaneous, intermittent periods of LBBB and normal conduction.

CONCLUSION

The ECG pattern of high-grade LAD stenosis has proven to be an important marker of high-risk patients with chest pain. This pattern may also be seen in patients with a right ventricular pacemaker on resumption of native QRS conduction. Intermittent LBBB is a less obvious cause of a similar ECG pattern that may mimic anterior ischemia due to high-grade stenosis.

Cardiac memory during rather than after termination of left bundle branch block

An 83-year-old woman with chronic left bundle branch block and remote history of pacemaker implantation for intermittent AV block was hospitalized for fatigue and leg swelling. She had no cardiac complaints. Routine 12-lead electrocardiogram showed sinus rhythm with left bundle branch block. There were diffuse negative T waves in the inferior and anterolateral leads that were concordant with the QRS complexes. Echocardiogram was normal and nuclear perfusion heart scan showed no abnormality. It was noted that the negative T waves during left bundle branch block were in the exact same leads as were the deep negative QRS complexes during ventricular pacing. The electrocardiographic changes were consistent with cardiac memory. This case is unique because cardiac memory in patients with intermittent left bundle branch block typically occurs when the QRS complexes normalize and not during left bundle branch block itself. Our findings indicate that memory Ts can develop not only after normalization of wide complex rhythms but also with alternating wide complex rhythms as in the presented case where a ventricular paced rhythm was replaced by left bundle branch block.

Difficult ECGs in STEMI: lessons learned from serial sampling of pre- and in-hospital ECGs

Prehospital interpretation of electrocardiograms (ECGs) is crucial to ensure early diagnosis and optimal treatment of patients with ST elevation myocardial infarction (STEMI). Recognition of ST-segment elevations (STE) by qualified personnel in the prehospital phase has successfully reduced the delay from the first medical contact to reperfusion. A few other ECG patterns without true STE, referred to as "STEMI equivalents", bear the same prognostic significance, reflect imminent or ongoing transmural ischemia, but are less easily identified. Hyperacute T waves, de Winter ST-T complex, Wellens' syndrome, and posterior STEMI, as well as myocardial infarction in the presence of left bundle branch block, paced rhythm or left ventricular hypertrophy, among others are diagnostic challenges. This article reviews some critical examples of ischemic ECG patterns that may be ephemeral, misinterpreted by medical staff or not identified by automated ECG algorithms, and it emphasizes the importance of serial ECG acquisition.

Don't forget the memory: Contribution of the T wave vector in localizing the site of origin of a monomorphic idiopathic ventricular tachycardia

We report a case of cardiac memory following recurrent episodes of monomorphic idiopathic ventricular tachycardia and explain how it could be helpful in localizing the site of origin of the arrhythmia.

Reversal of primary and pseudo-primary T wave abnormalities by ventricular pacing. A novel manifestation of cardiac memory

AIMS

"Cardiac memory" refers to abnormal T waves (TW) appearing after transient periods of altered ventricular depolarization. The aim of the study was to test the hypothesis that in the presence of abnormal TW, short periods of tailored ventricular pacing (VP) can be followed by normalization of ventricular repolarization.

METHODS

Ten patients with normal TW (control group) and 18 patients with abnormal TW (study group) underwent 15 min of VP at a cycle length of 500 ms. In the control group, VP was performed from the right ventricular apex, and in the study group from right or left ventricular sites that resulted in paced QRS complexes of opposite polarity to that of the abnormal TW. Before and after VP, atrial pacing was maintained at a stable cycle length. Simultaneous 12-lead electrocardiography (ECG) was recorded before, during, and following VP to assess changes in TW polarity, amplitude, electrical axis, QTc interval, and QTc interval dispersion.

RESULTS

As expected, VP was followed by memory-induced changes in TW in eight of ten patients in the control group. Mean T wave axis shifted from +60 degrees + or - 21.2 degrees to +23.5 degrees + or - 50.7 degrees (p = 0.01) in the frontal plane. In the study group, complete or partial normalization of TW occurred in 17 of 18 patients. Mean T wave axis shifted from -23.7 degrees + or - 22.9 degrees to +19.7 degrees + or - 34.7 degrees (p < 0.0002) in the frontal plane when paced from right ventricular outflow tract. The QTc interval shortened after VP both in the control group (424 + or - 25 vs. 399 + or - 27 ms; p = 0.007) and in the study group (446 + or - 26 vs. 421 + or - 22 ms; p < 0.0002). No significant changes were found in QTc interval dispersion.

CONCLUSIONS

Transient changes in the sequence of ventricular activation may either induce or normalize abnormal TW. The background of preceding ventricular depolarization needs to be taken into account before determining the clinical significance of a given pattern of ventricular repolarization.

Why T waves change: a reminiscence and essay

The following article is a personal reflection on my study of a subject which has long interested me. The subject is the T wave, and especially the T wave changes occurring as a marker of cardiac memory. My interest evolved over coffees that Mauricio Rosenbaum and I used to share at the Hotel Algonquin during his frequent trips from Buenos Aires to New York. There is something about the Algonquin, whose scarred wooden tabletops carry the imprints of Robert Benchley, Dorothy Parker, and the 1920's New York literati, and there was something about Mauricio-clinician-scientist, friend, and raconteur extraordinaire-that made his repeated challenges to me to "look at cardiac memory before you begin losing your own" irresistible. So began my personal voyage into trying to understand the T wave. My guideposts were the experiments of Wilson and Finch,(1) the astute observations of a host of investigators who followed, and Mauricio's iconoclastic insights. The story is far from over...I doubt I'll see the end of it in my lifetime. But if the beauty of discovery is in the voyage, then it has been - for me - a memorable trip.

Tako-tsubo cardiomyopathy in a patient with pacemaker syndrome

We report the case of a 71-year-old woman, with a dual chamber pacemaker (PM), in whom a PM syndrome, due to loss of atrial sensing and pacing, was associated with a tako-tsubo cardiomyopathy (TTC). The repositioning of the atrial lead immediately improved symptoms, whereas complete regression of left ventricular wall motion abnormalities occurred after 1 month. We hypothesize that haemodynamic and hormonal responses associated with a PM syndrome, such as increased levels of catecholamines, may account for TTC in our patient.

[Cardiac memory of the ECG following ventricular pacing]

During abnormal pacemaker depolarization, abnormal repolarization occurs and persists in normal QRS beats often seen in alternation with paced beats. The T-wave direction of normal beats is typically similar to the direction of the QRS complex during pacing, hence the term cardiac memory. The normal nonpaced beats have shown a sensitivity of 92% and a specificity of 100% for cardiac memory in the presence of T-wave inversions (TWI) in the precordial and inferior (II, III and aVF) leads with a positive T wave in aVL, a positive or isoelectric T wave in lead I, and the maximal precordial TWI being greater than the TWI of lead III, discriminating it from ischemic precordial TWI. In the latter, TWI are also seen in leads aVL and I.

Vectorcardiographic determinants of cardiac memory during normal ventricular activation and continuous ventricular pacing

BACKGROUND

Cardiac memory (CM) refers to persistent T-wave changes on resumption of normal conduction after a period of abnormal ventricular activation. Traditionally, to observe CM, normal ventricular activation had to be restored, limiting the exploration of this phenomenon in clinical practice.

OBJECTIVE

This study sought to prove that CM can be detected during continuous aberrant activation and to establish factors affecting its magnitude using a vectorcardiographic technique.

METHODS

Sixteen nonpacemaker-dependent patients (11 male, age 72 +/- 8 years, mean +/- SD) undergoing pacemaker/internal cardioverter-defibrillator implantation were paced in DDD mode with a short atrioventricular (AV) delay for 7 days to induce CM. Electrocardiograms were acquired during AAI and DDD pacing at a constant rate before and after CM induction. Dower transform-derived vectorcardiograms were reconstructed and analyzed.

RESULTS

T vector during AAI pacing changed in both magnitude (baseline, 0.26 +/- 0.10 mV; Day 7, 0.39 +/- 0.13 mV, P < .01) and direction aligning with the paced QRS vector (baseline DDD QRS - AAI T angle 125 degrees +/- 36 degrees; Day 7, 39 degrees +/- 21 degrees, P < .01). During DDD pacing, there was no change in T-vector direction, but T amplitude decreased (baseline, 1.06 +/- 0.32 mV; Day 7, 0.71 +/- 0.26 mV, P < .01). CM measured as T-vector peak displacement (TPD) was identical in AAI and DDD mode (TPD 0.46 +/- .0.17 mV and 0.46 +/- 0.17 mV, respectively). Individual CM magnitude correlated with QRS/T-vector amplitude ratio during DDD pacing at baseline (r = 0.90).

CONCLUSION

CM can be reliably shown during continuous ventricular pacing, expanding its application to situations in which abnormal ventricular activation persists. Its magnitude is determined by the QRS/T-amplitude ratio of the ventricular paced beat.

Cardiac memory: a work in progress

Cardiac memory is a form of electrophysiological remodeling generally considered benign, although it shares transduction pathways with factors that may be pathological, such as angiotensin II and reactive oxygen species. When induced by electrical pacing, memory provides a window into the mechanisms engaged during cardiac device therapy. Emphasis is placed on the complexity of signaling processes occurring downstream to the simple intervention of cardiac pacing and the relationship of resultant ion channel changes to their expression in action potentials and body surface recordings.

Effect of sodium and calcium channel blockers on short-term cardiac memory in humans

BACKGROUND

Cardiac memory (CM) can be induced by both short and long period of pacing from the right ventricle. Although several mechanisms have been proposed in animal studies, mechanisms of CM in humans are not well studied.

METHODS

A total of 46 patients (20 females; mean age 46+/-13 years) with paroxysmal supraventricular tachycardia referred for catheter ablation were enrolled. After catheter ablation, CM was induced by 20 min of pacing from right ventricular apex (RVA). The CM was quantified as the difference of T wave area in each lead between baseline and after RVA pacing. After complete recovery from the induced CM, verapamil (1.5 mg/kg; 0.005 mg/kg/min), lidocaine (1 mg/kg; 2 mg/min), procainamide (10 mg/kg; 4 mg/min), and nitroglycerine (0.6 mg sublingually; 5 microg/min), were given in 14, 10, 12, and 10 patients respectively. The pacing procedure was repeated and the degrees of CM were compared before and after each drug administered.

RESULTS

The short-term CM was demonstrated by changes in T wave area after RVA pacing in all patients. The degrees of CM were suppressed in patients after verapamil and lidocaine. In contrast, procainamide and nitroglycerin had no significant effect on the degrees of CM expression.

CONCLUSIONS

The expression of short-term CM can be suppressed by verapamil and lidocaine but not by procainamide and nitroglycerin. The results may suggest that short-term CM in humans can be modulated by calcium dependent process and the functional alternations of sodium and potassium channels.