Relation of silent myocardial ischemia to ventricular arrhythmias and sudden death

High Prevalence and Clinical Implication of Myocardial Bridging in Patients with Early Repolarization

PURPOSE

Recent evidence suggests that early repolarization (ER) is related with myocardial ischemia. Compression of coronary artery by a myocardial bridging (MB) can be associated with clinical manifestations of myocardial ischemia. This study aimed to evaluate the associations of MB in patients with ER.

MATERIALS AND METHODS

In consecutive patients (n=1303, age, 61±12 years) who had undergone coronary angiography, we assessed the prevalence and prognostic implication of MB in those with ER (n=142) and those without ER (n=1161).

RESULTS

MB was observed in 54 (38%) and 196 (17%) patients in ER and no-ER groups (p<0.001). In multivariate analysis, MB was independently associated with ER (odd ratio: 2.9, 95% confidence interval: 1.98-4.24, p<0.001). Notched type ER was more frequently observed in MB involving the mid portion of left anterior descending coronary artery (LAD) (69.8% vs. 30.2%, p=0.03). Cardiac event was observed in nine (6.3%) and 22 (1.9%) subjects with and without ER, respectively. MB was more frequently observed in sudden death patients with ER (2 out of 9, 22%) than in those without ER (0 out of 22).

CONCLUSION

MB was independently associated with ER in patients without out structural heart disease who underwent coronary angiography. Notched type ER was closely related with MB involving the mid portion of the LAD. Among patients who had experienced cardiac events, a higher prevalence of MB was observed in patients with ER than those without ER. Further prospective studies on the prognosis of MB in ER patients are required.

Coronary microvascular dysfunction is associated with baseline QTc prolongation amongst patients with chest pain and non-obstructive coronary artery disease

BACKGROUND

Coronary microvascular dysfunction (CMD) causes ischemia and is linked to adverse cardiovascular events. Acute transmural ischemia is associated with QT prolongation, but whether CMD affects repolarization is unknown. The aim of this study was to determine if CMD is associated with prolongation of resting heart rate corrected QT interval (QTc).

METHODS

In patients presenting to the catheterization laboratory with chest pain and non-obstructive coronary artery disease (CAD) at angiography, coronary flow reserve (CFR) in response to intracoronary adenosine was measured and compared to baseline to give a CFR ratio. The Bazett's-derived QTc was manually derived from patients' 12-lead ECG obtained prior to the procedure. QTc was compared between patients with normal and abnormal (CFR ratio≤2.5) coronary microvascular function.

RESULTS

Of the 926 patients included in this study, 281 patients (30%) had CMD (mean age 53.2 years [SD 12.7], 25% male). QTc was significantly longer in those with an abnormal CFR response to adenosine (median [Q1, Q3] ms: 420 [409, 438] vs. 416 [405, 432]; p value<0.001) and patients in the lowest quartile of CFR had a significantly longer QTc compared to those in the highest quartile (median [Q1, Q3] ms: 420 [409, 439] vs. 413 [402, 426]; p<0.001). In a linear regression model adjusting for age and sex, CMD was associated with an increase in QTc of 3.09 ms (p=0.055).

CONCLUSION

Our data suggest that CMD may be associated with an increase in baseline QTc, however the precise clinical relevance of this finding needs to be better investigated in larger clinical studies.

Early repolarization and myocardial scar predict poorest prognosis in patients with coronary artery disease

PURPOSE

Recent studies show positive association of early repolarization (ER) with the risk of life-threatening arrhythmias in patients with coronary artery disease (CAD). This study was to investigate the relationships of ER with myocardial scarring and prognosis in patients with CAD.

MATERIALS AND METHODS

Of 570 consecutive CAD patients, patients with and without ER were assigned to ER group (n=139) and no ER group (n=431), respectively. Myocardial scar was evaluated using cardiac single-photon emission computed tomography.

RESULTS

ER group had previous history of myocardial infarction (33% vs. 15%, p<0.001) and lower left ventricular ejection fraction (57±13% vs. 62±13%, p<0.001) more frequently than no-ER group. While 74 (53%) patients in ER group had myocardial scar, only 121 (28%) patients had in no-ER group (p<0.001). During follow up, 9 (7%) and 4 (0.9%) patients had cardiac events in ER and no-ER group, respectively (p=0.001). All patients with cardiac events had ER in inferior leads and horizontal/descending ST-segment. Patients with both ER in inferior leads and horizontal/descending ST variant and scar had an increased adjusted hazard ratio of cardiac events (hazard ratio 16.0; 95% confidence interval: 4.1 to 55.8; p<0.001).

CONCLUSION

ER in inferior leads with a horizontal/descending ST variant was associated with increased risk of cardiac events. These findings suggest that ER in patients with CAD may be related to myocardial scar rather than pure ion channel problem.

Arrhythmic cardiac arrest due to isolated coronary artery spasm: long-term outcome of seven resuscitated patients

OBJECTIVES

Our aim was to look at the clinical features and long-term follow-up of seven patients without coronary artery disease, who had a history of life-threatening ventricular arrhythmias due to coronary spasm.

BACKGROUND

Arrhythmic cardiac arrest due to isolated coronary spasm is rare, and there is limited information on the patients affected by this entity alone.

METHODS

The seven patients were recruited retrospectively from a cohort of survivors of cardiac arrest. None had a history of angina pectoris, structural heart disease or significantly narrowed coronary segments. All had a positive ergonovine provocation test result.

RESULTS

The patients' mean age was 44 years; three were male and four female. All were habitual cigarette smokers. No arrhythmias were induced on programmed ventricular stimulation; corrected QT interval (QTc) and corrected JT interval (JTc) dispersion were within normal ranges. After the ergonovine provocation test, treatment with calcium channel blocking agents (diltiazem, verapamil, nifedipine or amlodipine) was initiated at a dose determined by titration until a negative test result was obtained. At a mean follow-up interval of 58 months for the total group, six patients remained free of symptoms, whereas the one patient who did not stop smoking had a new cardiac arrest despite treatment for coronary spasm.

CONCLUSIONS

A favorable long-term outcome may be expected in survivors of cardiac arrest due to coronary spasm, in the absence of significant coronary artery disease. Calcium channel blockers are the most appropriate therapy in these patients. These observations provide further evidence for the role of silent ischemia in cardiovascular death.

Incidence of implantable defibrillator discharges after coronary revascularization in survivors of ischemic sudden cardiac death

Coronary revascularization has been suggested as sole therapy for secondary prevention of sudden cardiac arrest associated with ischemia. The use of implantable defibrillators (ICD) in combination with coronary revascularization for this patient population is unclear. Among 412 consecutive patients receiving an ICD, 23 (6%) were identified as sudden cardiac arrest survivors who were noninducible with programmed stimulation and had unstable angina or ischemia on a functional study; they underwent successful coronary revascularization. During a follow-up of 34 +/- 18 months, 10 (43%) of the 23 patients received ICD shocks (8 +/- 8 per patient, range 1 to 22 shocks), and nine of the 10 patients had syncope/presyncope associated with at least one ICD discharge. Patients with ICD discharges were compared with those without ICD discharges, and no clinical characteristics were statistically different between the two groups. In conclusion, revascularization alone may be inadequate therapy for survivors of sudden cardiac arrest associated with ischemia who are noninducible with programmed stimulation, and clinical variables cannot predict which patients are likely to have recurrent malignant ventricular arrhythmias.

Silent ischemia after uncomplicated myocardial infarction: lack of incremental clinical significance

To determine the potential utility of the detection of silent myocardial ischemia after acute myocardial infarction for clinical decision making, we investigated the hypothesis that the occurrence of silent myocardial ischemia on ambulatory electrocardiographic (EGG) monitoring after acute myocardial infarction is independently predictive of adverse outcome in patients in whom conventional clinical and investigative parameters indicate favourable prognosis on medical therapy. Among 465 consecutive patients admitted to our Coronary Care Unit with acute myocardial infarction, 42 patients (39% of those eligible) were randomly selected for study. Twenty-four hour ambulatory ECG monitoring was carried out 13 +/- 10 (standard deviation) days post-acute myocardial infarction. Ninety-eight percent of patients were receiving prophylactic anti-ischemic medications and 81% on aspirin. Silent myocardial ischemia was detected in 14%. During the follow-up period of 16 +/- 3 months, acute ischemic events occurred in 33% of those with silent myocardial ischemia and 19% of those without previous silent myocardial ischemia (P = 0.59). The sensitivity of the test for prediction of future acute ischemic events was 22% (95% confidence interval: 3-60%), specificity 87% (95% confidence interval: 72-97%), positive predictive value 33% (95% confidence interval: 4-78%) and negative predictive value 81% (95% confidence interval: 64-92%). Therefore the detection of ambulatory silent myocardial ischemia after acute myocardial infarction is not of sufficient incremental value as a predictor of the occurrence of adverse cardiac events to justify its routine clinical use in this subgroup of patients.

ST-segment instability preceding simultaneous cardiac arrest and AMI in a patient undergoing continuous 12-lead ECG monitoring

Little data exist concerning the actual onset time (time zero) in sudden death (SD) and acute myocardial infarction (AMI). Most studies have focused on describing the warning arrhythmias that occur before SD and AMI and have relied on retrospective analyses of fortuitous data obtained from patients who experience these adverse outcomes while undergoing routine ambulatory holter monitoring. Because of the limitations of holter monitoring, little information is known concerning the actual incidence of ST-segment changes preceding SD and AMI. The first case of simultaneous onset of silent SD and AMI occurring in a patient undergoing continuous 12-lead electrocardiograph (ECG) monitoring during his initial emergency department evaluation is reported. Analyses of the serial 12-lead electrocardiographs showed extensive transient silent ST-segment elevations and depressions preceding cardiac arrest and AMI and provided insight in the pathogenesis of SD and AMI. Continuous 12-lead ECG monitoring can identify patients at high risk for SD and AMI and allow physicians to intervene before the development of life-threatening conditions.

Exercise-induced ventricular arrhythmias in patients with healed myocardial infarction

BACKGROUND

Controversy exists about the clinical and prognostic significance of exercise-induced ventricular arrhythmias late after myocardial infarction. The aim of the study was to identify the main clinical and prognostic features of exercise-induced ventricular arrhythmias in out-patients with healed Q-wave myocardial infarction.

METHODS

The study population was 777 consecutive patients who underwent a symptom-limited (Bruce protocol) treadmill test from May 1988 to January 1991 after myocardial infarction (at least 1 year). Clinical and exercise data were prospectively entered in a computerized database and retrospectively two different groups were selected: (1) 228 patients with exercise-induced ventricular arrhythmias; (2) 549 patients without. Incidence and morphology of exercise-induced ventricular arrhythmias, various exercise parameters and a follow-up were evaluated.

RESULTS

Patients with exercise-induced ventricular arrhythmias were older (P < 0.001), had higher blood pressure (P < 0.03) and peak exercise rate pressure product (P < 0.00) than the others. No difference was found in the incidence of exercise-ischaemia: either symptomatic or not. When simple (< or = 2 Lown) versus complex (> or = 3 Lown) exercise-induced ventricular arrhythmias were considered, the latter were more frequent in patients with anterior myocardial infarction, shorter exercise duration (P < 0.001) and lower exercise rate pressure product, lower ejection fraction and lower incidence of exercise-induced ischaemia. In the follow-up (mean 24 +/- 13 month) there were 24 deaths: five (2.2%) in patients with exercise-induced ventricular arrhythmias and 19 (3.4%) in patients without. Cardiac event rate was similar in both groups.

CONCLUSIONS

We conclude that in out-patients with healed myocardial infarction exercise-induced ventricular arrhythmias are quite frequent, but they are not associated with exercise-induced ischaemia, either symptomatic or not. Exercise-induced ventricular arrhythmias seem to be related to age or peak workload. Moreover patients with these arrhythmias have no adjunctive negative risk on prognosis.

Sudden cardiac death. Support for a role of triggering in causation

Epidemiological studies have identified associations between time of day and risk of sudden cardiac death. The marked peak in the occurrence of sudden cardiac death after awakening suggests that the disease is triggered by changes that occur during this time period. Increased sympathetic stimulation is a likely cause of such triggering. In the light of the circadian variation of sudden cardiac death and the evidence linking physical activity or mental stress (both associated with activation of the sympathetic nervous system) to the disease, the role of potential triggering events should be investigated. Controlled studies are needed to determine the relative risk of activities that may trigger sudden cardiac death. Since such studies must rely on witnesses (or resuscitated patients), data quality must be closely scrutinized, and studies using case-control and case-crossover designs are needed. The epidemiological and pathophysiological data reviewed in the present article suggest a number of pathways through which activities may trigger sudden cardiac death. Different extrinsic stimuli may cause similar physiological changes that subsequently lead to acute pathological events, a decrease in the ventricular fibrillation threshold through a direct myocardial effect, or a harmful effect on the conduction system. Myocardial ischemia induced by plaque rupture and thrombosis may lead directly to myocardial electric instability. The presence of chronic structural abnormalities of the myocardial tissue or the conduction system may further lower the threshold for electric instability and ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Life-threatening ventricular arrhythmias in patients with silent myocardial ischemia due to coronary-artery spasm

BACKGROUND

Silent myocardial ischemia in patients with coronary atherosclerosis is associated with an increased risk of adverse cardiac events, including sudden death. The relation between silent ischemia and the initiation of potentially fatal ventricular arrhythmias has not been defined, however.

METHODS

As part of a long-term study of sudden cardiac death, data on arrhythmias, coronary anatomy, and responses to ergonovine testing to provoke coronary-artery spasm were collected prospectively among survivors of out-of-hospital cardiac arrest who had no flow-limiting coronary-artery lesions, prior myocardial infarctions, or other structural causes of cardiac arrest and no angina pectoris. Associations between silent myocardial ischemia due to coronary-artery spasm and the occurrence and characteristics of life-threatening ventricular arrhythmias were studied by both invasive and noninvasive techniques.

RESULTS

Silent ischemic events were associated with the initiation of life-threatening ventricular arrhythmias in five patients with induced or spontaneous focal coronary-artery spasm (or both). These patients were identified among a group of 356 survivors of out-of-hospital cardiac arrest who were evaluated between 1980 and 1991. In two of the five patients reperfusion, rather than ischemia itself, correlated with the onset of the ventricular arrhythmia. Only one of the five had an inducible arrhythmia during electrophysiologic testing. Titration of the dose of a calcium-entry-blocking agent (verapamil, diltiazem, or nifedipine) against the ability of ergonovine to provoke spasm was successful in preventing both the provocation of spasm and arrhythmias in all four patients who were tested.

CONCLUSIONS

Silent myocardial ischemia due to coronary-artery spasm can initiate potentially fatal arrhythmias in patients without flow-limiting structural coronary-artery lesions. The role of silent ischemia, reperfusion, or both in the initiation of fatal arrhythmias in larger groups of patients with advanced coronary-artery lesions remains to be defined.

Efficacy of three-channel ambulatory electrocardiographic monitoring for the detection of myocardial ischemia

The recognition of silent myocardial ischemia (SMI) has been demonstrated to have important clinical relevance. Two-channel ambulatory (Holter) electrocardiographic recording is a commonly utilized method for detecting transient electrocardiographic ST segment changes representative of SMI. It has been suggested that the analysis of two channels alone may not adequately detect SMI. We therefore evaluated the diagnostic yield of three channels using a three-channel electrocardiographic monitoring device in 46 consecutive patients (age 61 +/- 9 years) undergoing percutaneous transluminal coronary angioplasty of an isolated single-vessel stenosis. Modified bipolar chest leads V2, V5, and AVF (CM-V2, CM-V5, and CS-AVF) were utilized for analysis. The percent detection of ST segment changes from various combinations of two-lead recordings were compared to the total three leads, and an absolute transient ST segment shift (STSS) of greater than or equal to 1 mm during balloon inflation was considered as evidence of myocardial ischemia. One patient was excluded because of the need for ventricular pacing during balloon inflation. A total of 33 of 45 patients had STSS in all three leads (percent detection = 73%), while 32 (71%) had STSS in the two-lead grouping with the highest diagnostic yield (CM-V2/CM-V5; p = ns). Of the various two-lead combinations studied, leads CM-V2 and CM-V5 provided the best lead set overall for the detection of ischemic STSS. Three-channel ambulatory electrocardiographic recording only marginally improves upon the detection of ischemia when compared with standard (CM-V2/CM-V5 or CM-V5/CS-AVF) two-channel ambulatory electrocardiographic recordings.

Silent ischaemia in the 1990s

Silent myocardial ischaemia (significant ST depression without chest pain) is a common occurrence in most forms of coronary heart disease and can be associated with permanent changes in myocardial structure. The haemodynamic and ECG manifestations of silent episodes are similar to those observed in painful ischaemia. Exercise testing is the most appropriate method for assessing the severity of coronary artery disease; increased sensitivity can be obtained by combining it with radionuclide scintigraphy or ventriculography. Ambulatory ECG monitoring may fail to detect ischaemic changes revealed by exercise provocation. The treatment approach should depend on the degree of ischaemia. Numerous clinical investigations in stable and unstable angina and in patients with a previous myocardial infarction indicate that the prognosis of patients with myocardial ischaemia does not depend on whether the ischaemia is silent or symptomatic. Silent and symptomatic episodes alone represent the same degree of coronary disease. Moreover, it appears that ischaemic episodes are a more powerful adverse prognostic influence than left ventricular function or the extent of coronary artery disease. All anti-ischaemic agents, such as beta-blockers, calcium antagonists and nitrates, and interventions such as coronary balloon angioplasty or coronary bypass surgery, are very effective treatments for myocardial ischaemia. All efforts should be made to prevent ischaemic episodes, whether silent or symptomatic, since the severity of disease rather than the presence or absence of symptoms more accurately reflects the need for intervention.