Cardiac safety of conducted electrical devices in pigs and their effect on pacemaker function.

OBJECTIVE: The aims of this study are to evaluate the cardiac safety of the Stinger S-200 Conducted Energy Weapon Device (CED) (Stinger Systems, Tampa, Fla) on a human-sized pig model and to test the effect of various commercially available CEDs, specifically the Stinger S-200, TASER M26 (Taser International, Scottsdale, Ariz), and TASER X26 on pacemaker function. METHODS: Two groups of pigs, divided based on weight as group 1 (n = 3, 67.3 ± 4.7 kg) and group 2 (n = 3, 89.3 ± 1.2 kg), were used. In protocol 1, the Stinger S-200 was applied in multiple different orientations to simulate possible field scenarios across the heart. In protocol 2, a single-chamber bipolar lead connected to a pacemaker was placed in the right ventricle of the pig, and different CEDs were applied to test the pacemaker function during CED application. RESULTS: In protocol 1, the S-200 was applied a total of 216 times in the 6 pigs, and neither episodes of ventricular fibrillation nor episodes of sustained ventricular tachycardia were noted. In protocol 2, the CED discharges (1) were recognized by the pulse generator and sensed as either high-rate atrial or ventricular activity, (2) did not affect the native rhythm, (3) did not conduct down the lead systems to cause any extra systoles, and (4) had no effect on paced rhythm. CONCLUSIONS: In this model, the application of the S-200 in various orientations across the heart did not result in any sustained abnormal cardiac rhythms. None of the tested CEDs adversely affected the functioning of the tested pacemaker. Stinger Systems has now replaced the S-200 with the S-200T with a different output.

Cocaine and aortic dissection.

Aortic dissection is a rare, potentially catastrophic vascular emergency. Early recognition of the clinical manifestations, rapid confirmation using imaging modalities, urgent administration of appropriate medication and expedient selection of definitive long-term therapy are key to preserving life and reducing morbidity. In recent years it has become increasingly clear that there is a relation between cocaine and aortic dissection. Cocaine serves as both a predisposing factor to aortic dissection due to its effect on aortic connective tissue and as a precipitating factor due to its propensity to produce abrupt and severe hypertension. While similarities exist in the clinical features and diagnostic methods between cocaine-related aortic dissection and aortic dissection unrelated to cocaine use, there are important differences in management between these two syndromes which are rooted in the pharmacology and physiology of cocaine. An understanding of these differences is key to effective early and long-term management of cocaine-related aortic dissection.

Spontaneous baroreflex measures are unable to detect age-related impairments in cardiac baroreflex function during dynamic exercise in humans.

The dynamic relationship between 'spontaneous' fluctuations in arterial blood pressure (BP) and heart rate (HR) is increasingly being used to provide an estimate of resting cardiac baroreflex sensitivity. Given the ease of use and clinical utility, spontaneous methods are now also being used to examine cardiac baroreflex sensitivity in distinct subject groups during various laboratory stressors and tasks encountered during daily life, such as physical activity. However, the utility of such spontaneous measures to estimate cardiac baroreflex function during exercise remains unclear, particularly when comparing groups. Therefore, we tested the ability of spontaneous indices to detect age-related differences in cardiac baroreflex function during dynamic exercise. Beat-to-beat HR and BP were measured in eighteen healthy young subjects (24 +/- 1 years) and sixteen healthy middle-aged subjects (59 +/- 1 years) at rest and during steady-state leg cycling. Estimates of spontaneous cardiac baroreflex sensitivity using the sequence technique (G(SEQ)) and low-frequency transfer function gain (G(TF)) were compared with the operating point (G(OP)) and maximal gain (G(MAX)) of the full carotid-cardiac baroreflex function curve. At rest G(SEQ), G(TF), G(OP) and G(MAX) were all significantly lower in older subjects. During moderate-intensity steady-state exercise no differences were observed in G(SEQ) and G(TF) (older 0.26 +/- 0.03 beats min(-1) mmHg(-1) versus younger 0.32 +/- 0.04 beats min(-1) mmHg(-1); P > 0.05), whereas G(OP) and G(MAX) (older -0.21 +/- 0.02 beats min(-1) mmHg(-1) versus younger -0.39 +/- 0.03 beats min(-1) mmHg(-1); P < 0.05) remained lower in older subjects. These data indicate that spontaneous measures of cardiac baroreflex sensitivity alone provide limited information when comparing age-groups during exercise, which makes genuine differences in baroreflex function difficult to identify.

Outcomes in patients with abnormal myocardial perfusion imaging and normal coronary angiogram.

A subset of subjects undergoing myocardial perfusion imaging has perfusion abnormalities that are subsequently labeled false positive based on coronary angiography. We evaluated the long-term prevalence of cardiovascular events in these patients. We retrospectively identified 48 patients who had reversible perfusion abnormalities with myocardial perfusion imaging and normal coronary angiography. Patients with known coronary artery disease, left ventricular dysfunction, valvular disease, and cardiomyopathy were excluded. Patient follow-up, conducted for at least 3 (mean interval, 7.4) years from the index myocardial perfusion imaging, was accomplished by a review of medical records and telephone interviews. Study endpoints were cardiovascular events defined as sudden cardiac death, myocardial infarction, percutaneous coronary revascularization, coronary artery bypass grafting, and cerebrovascular or peripheral revascularization. Thirty-one percent (15 of 48) of the patients had cardiovascular events. Six of the 48 patients had coronary events. These patients had abnormal myocardial perfusion imaging and normal coronary angiogram. The time between myocardial perfusion imaging and coronary event was 0.5 to 8.67 years. There was a strong correlation between the regions of original perfusion abnormality and the ultimate coronary ischemia or revascularization. Abnormal findings on myocardial perfusion imaging may predict a higher prevalence of coronary and peripheral vascular events than suggested by a normal coronary angiogram.

A case of aortic dissection in a cocaine abuser: a case report and review of literature.

BACKGROUND: Prompt diagnosis and management of aortic dissection are key to reduce patient morbidity and mortality; hence the need to a have a high index of suspicion for this condition. We believe it's important to report this case because it underscores the relationship between cocaine abuse and aortic dissection. In addition it strongly emphasizes basic principles in medicine: patients should not be profiled, and chronic complaints may need reassessment. CASE PRESENTATION: We are presenting a case of Stanford type A aortic dissection in a 46 year old patient with history of cocaine abuse. The aortic dissection presented as worsening of chronic upper abdominal pains he has had for years. He presented to us hours after using crack cocaine. CONCLUSION: Aortic dissection associated with cocaine abuse develops at a younger age. Therefore it's crucial to have high index of suspicion for aortic dissection in this subset of patients. Furthermore as this case illustrates, serious diseases can masquerade in old complaints. Patients should never be profiled, and chronic complaints should always be revisited.

Syncope with a twist.

Left atrial ball thrombus is an uncommon entity, seen more commonly in the presence of mitral valve disease. We present here a case of a large left atrial thrombus presenting as sudden cardiac death.

Bachmann's bundle: does it play a role in atrial fibrillation?

BACKGROUND: Cardiac anatomists have known the presence of a group of specialized fibers connecting the right and left atrium for years. However, only recently have clinical cardiologists come to recognize the potential importance of this specialized conduction system. Anatomical and microscopic studies have shown that the Bachmann's bundle (BB) represents a distinct structure similar to the atrio-ventricular node and the His-Purkinje conduction system but without any insulating tissue. RESULTS: BB cells have specialized electrophysiological properties like supernormal excitability and faster longitudinal conduction that can facilitate more rapid impulse transmission compared to the normal atrial tissue. Experimental blockage of this pathway causes prolongation and widening of the P wave, which is associated with an increased incidence of atrial fibrillation. Atrial pacing is effective in reducing the incidence of atrial fibrillation by preventing bradycardia, synchronizing the atria, limiting anisotropy and reducing the dispersion of refractoriness. Various animal and human studies have shown pacing near the right atrial insertion of BB to have a beneficial effect in patients with interatrial conduction delay and atrial tachyarrhythmias. This mode of atrial septal pacing is convenient, safe, reliable, and clinically as effective as multisite pacing. CONCLUSION: This article is an effort to define the special properties of BB and its possible role in prevention of atrial fibrillation by permanent pacemakers.