Efficacy of cardiac resynchronization in acutely infarcted canine hearts with electromechanical dyssynchrony

BACKGROUND

Patients with acute myocardial infarction (MI), left bundle branch block (LBBB), and marked left ventricular (LV) decompensation suffer from nearly 50% early mortality. Whether cardiac resynchronization therapy (CRT) improves hemodynamic status in this condition is unknown. We tested CRT in this setting by using a canine model of delayed lateral wall (LW) activation combined with 2 hours of coronary artery occlusion-reperfusion.

OBJECTIVE

This study aimed to evaluate the acute hemodynamic effects of CRT during and immediately after MI.

METHODS

Adult dogs (n = 8) underwent open-chest 2-hour mid-left anterior descending artery occlusion followed by 1-hour reperfusion. Four pacing modes were compared: right atrial pacing, pseudo-left bundle block (right ventricular pacing), and CRT with the LV lead positioned at either the LW (LW-CRT) or the peri-infarct zone (peri-infarct zone-CRT). Continuous LV pressure-volume data, regional segment length, and proximal left anterior descending flow rates were recorded.

RESULTS

At baseline, both right ventricular pacing and peri-infarct zone CRT reduced anterior wall regional work by ~50% (vs right atrial pacing). During coronary occlusion, this territory became dyskinetic, and dyskinesis rose further with both CRT modes as compared to pseudo-LBBB. Global cardiac output, stroke work, and ejection fraction all still improved by 11%-23%. After reperfusion, both CRT modes elevated infarct zone regional work and blood flow by ~10% as compared to pseudo-LBBB, as well as improved global function.

CONCLUSION

CRT improves global chamber systolic function in left ventricles with delayed LW activation during and after sustained coronary occlusion. It does so while modestly augmenting infarct zone dyskinesis during occlusion and improving regional function and blood flow after reperfusion. These findings support CRT in the setting of early post-MI dyssynchronous heart failure.

Prevalence and prognostic significance of exercise-induced nonsustained ventricular tachycardia in asymptomatic volunteers: BLSA (Baltimore Longitudinal Study of Aging)

OBJECTIVES

This study sought to determine the clinical predictors and prognostic significance of exercise-induced nonsustained ventricular tachycardia (NSVT) in a large population of asymptomatic volunteers.

BACKGROUND

Prior studies have reported variable risk associated with exercise-induced ventricular arrhythmia.

METHODS

Subjects in the BLSA (Baltimore Longitudinal Study of Aging) free of known cardiovascular disease who completed at least 1 symptom-limited exercise treadmill test between 1977 and 2001 were included. NSVT episodes were characterized by QRS morphology, duration, and rate. Subjects underwent follow-up clinical evaluation every 2 years.

RESULTS

The 2,099 subjects (mean age: 52 years; 52.2% male) underwent a mean of 2.7 exercise tests, in which 79 (3.7%) developed NSVT with exercise on at least 1 test. The median duration of NSVT was 3 beats (≤5 beats in 84%), and the median rate was 175 beats/min. Subjects with (vs. without) NSVT were older (67 ± 12 years vs. 51 ± 17 years, p < 0.0001) and more likely to be male (80% vs. 51%, p < 0.0001) and to have baseline electrocardiographic abnormalities (50% vs. 17%, p < 0.0001) or ischemic ST-segment changes with exercise (20% vs. 10%, p = 0.004). Over a mean follow-up of 13.5 ± 7.7 years, 518 deaths (24.6%) occurred. After multivariable adjustment for age, sex, and coronary risk factors, exercise-induced NSVT was not significantly associated with total mortality (hazard ratio: 1.30; 95% confidence interval: 0.89 to 1.90; p = 0.17).

CONCLUSIONS

Exercise-induced NSVT occurred in nearly 4% of this asymptomatic adult cohort. This finding increased with age and was more common in men. After adjustment for clinical variables, exercise-induced NSVT did not independently increase the risk of total mortality.

Epidemiology of arrhythmias and conduction disorders in older adults

Normal aging is associated with a multitude of changes in the cardiovascular system, including decreased compliance of blood vessels, mild concentric left ventricular hypertrophy, an increased contribution of atrial contraction to left ventricular filling, and a higher incidence of many cardiac arrhythmias, both bradyarrhythmias and tachyarrhythmias. Conduction disorders also become more common with age, and may either be asymptomatic, or cause hemodynamic changes requiring treatment. The epidemiology of common arrhythmias and conduction disorders in the elderly is reviewed.

Cardiac amyloidosis presenting with prolonged QT interval and recurrent polymorphic ventricular tachycardia

Cardiac amyloidosis results in severely symptomatic heart failure that has a poor prognosis because of the development of a restrictive cardiomyopathy. The diagnosis of cardiac amyloidosis is often delayed because of nonspecific signs and symptoms. We report the case of a 66-year-old woman who had been diagnosed with sick sinus syndrome and presented 5 months later with a long QT interval and recurrent polymorphic ventricular tachycardia. The diagnosis of cardiac amyloidosis was confirmed upon analysis of endomyocardial biopsy results. The patient was subsequently diagnosed with and treated for underlying plasma cell myeloma and later died of cardiac arrest. This atypical presentation of cardiac amyloidosis underscores the need to consider it in the differential diagnosis of patients who have ventricular arrhythmias. To our knowledge, the combination of long QT interval and polymorphic ventricular tachycardia has not been previously reported in association with amyloid heart disease.

Dyslipidemia Management for Secondary Prevention in Women with Cardiovascular Disease: What Can We Expect From Non-pharmacologic Strategies?

Cardiovascular disease is the leading cause of death in women and the treatment of dyslipidemia is a cornerstone of secondary prevention. Pharmacologic therapy with statins can lower LDL-C by 30-50% and reduce the risk of recurrent coronary heart disease in both men and women. While significant reductions in LDL-C can be achieved with statin therapy, diet and lifestyle modification remain an essential part of the treatment regimen for cardiovascular disease. Moreover, a large proportion of the U.S. population is sedentary, overweight, and does not consume a heart-healthy diet. Non-pharmacologic treatment strategies also improve other cardiovascular risk factors and are generally easily accessible. In this review, we examine the effect of non-pharmacologic therapy on lipids as part of the secondary prevention strategy of cardiovascular disease in women.

Laughter-induced left bundle branch block

We present the case of a patient with ischemic heart disease and intermittent left bundle branch block, reproducibly induced by laughter. Following treatment of ischemia with successful deployment of a drug-eluting stent, no further episodes of inducible LBBB were seen. Transient ischemia, exacerbated by elevated intrathoracic pressure during laughter, may have contributed to onset of this phenomenon.

Rallying the troops: a four-step guide to preparing a residency program for short-term weather emergencies

BACKGROUND

Weather emergencies present a multifaceted challenge to residents and residency programs. Both the individual trainee and program may be pushed to the limits of physical and mental strain, potentially jeopardizing core competencies of patient care and professionalism. Although daunting, the task of preparing for these events should be a methodical process integrated into every residency training program.

SUMMARY

The core elements of emergency preparation with regard to inpatient services include identifying and staffing critical positions, motivating residents to consider the needs of the group over those of the individual, providing for basic needs, and planning activities in order to preserve team morale and facilitate recovery. The authors outline a four-step process in preparing a residency program for an anticipated short-term weather emergency. An example worksheet for emergency planning is included.

CONCLUSION

With adequate preparation, residency training programs can maintain the highest levels of patient care, professionalism, and esprit de corps during weather emergencies. When managed effectively, emergencies may present an opportunity for professional growth and a sense of unity for those involved.

Heart failure with transient left bundle branch block in the setting of left coronary fistula

Coronary arterial fistulas are rare communications between vessels or chambers of the heart. Although cardiac symptoms associated with fistulas are well described, fistulas are seldom considered in the differential diagnosis of acute myocardial ischemia. We describe the case of a 64-year-old man who presented with left shoulder pain, signs of heart failure, and a new left bundle branch block (LBBB). Cardiac catheterization revealed a small left anterior descending (LAD)-to-pulmonary artery (PA) fistula. Diuresis led to subjective improvement of the patient's symptoms and within several days the LBBB resolved. We hypothesize that the coronary fistula in this patient contributed to transient ischemia of the LAD territory through a coronary steal mechanism. We elected to observe rather than repair the fistula, as his symptoms and ECG changes resolved with treatment of his heart failure.

Prognostic significance of cardiac troponin I levels in hospitalized patients presenting with supraventricular tachycardia

Although cardiac troponin I (cTnI) elevation in patients presenting to the hospital with supraventricular tachycardia (SVT) is well recognized, the prevalence, predictors, and prognostic significance of cTnI elevation associated with SVT presentation are not known. We screened records of all patients presenting to 2 hospitals over a 4-year period with the diagnosis of SVT confirmed by 12-lead electrocardiogram, and who had at least 1 measured cTnI level and at least 1 year of follow-up after discharge. The primary endpoint was the occurrence of 1 of the following outcomes: death, myocardial infarction, or cardiovascular rehospitalization. Seventy-eight patients met the study criteria (54% female; mean age, 62.2 +/- 15.8 yr), and 29 patients (37.2%) had an elevated cTnI level of > or =0.06 ng/mL (range, 0.06-7.78 ng/mL). Univariate predictors of elevated cTnI included left ventricular ejection fraction (LVEF) <50%, renal dysfunction, ST-segment depression or left bundle branch block on the electrocardiogram, and moderate or severe regurgitation of any cardiac valve. Predictors of elevated cTnI after multivariate analysis included peak heart rate during SVT (per 15 bpm) (odds ratio [OR], 1.58; 95% confidence interval [CI], 1.01-2.46; p = 0.04) and LVEF <50% (OR, 6.12; 95% CI, 1.40-26.7; p = 0.02). After multivariable adjustment, the presence of elevated cTnI with SVT was associated with increased risk of the primary endpoint of death, myocardial infarction, or cardiovascular rehospitalization (hazard ratio [HR], 3.67; 95% CI, 1.22-11.1; p = 0.02). Mild elevation of cTnI is common in patients presenting to the hospital with SVT, and is associated with increased risk of future cardiovascular events. Further study is needed to determine the mechanisms of SVT-related cTnI elevation and its association with elevated cardiovascular risk.