Manganese Ions Individually Alter the Reverse Transcription Signature of Modified Ribonucleosides

Reverse transcription of RNA templates containing modified ribonucleosides transfers modification-related information as misincorporations, arrest or nucleotide skipping events to the newly synthesized cDNA strand. The frequency and proportion of these events, merged from all sequenced cDNAs, yield a so-called RT signature, characteristic for the respective RNA modification and reverse transcriptase (RT). While known for DNA polymerases in so-called error-prone PCR, testing of four different RTs by replacing Mg²⁺ with Mn²⁺ in reaction buffer revealed the immense influence of manganese chloride on derived RT signatures, with arrest rates on m¹A positions dropping from 82% down to 24%. Additionally, we observed a vast increase in nucleotide skipping events, with single positions rising from 4% to 49%, thus implying an enhanced read-through capability as an effect of Mn²⁺ on the reverse transcriptase, by promoting nucleotide skipping over synthesis abortion. While modifications such as m¹A, m²₂G, m¹G and m³C showed a clear influence of manganese ions on their RT signature, this effect was individual to the polymerase used. In summary, the results imply a supporting effect of Mn²⁺ on reverse transcription, thus overcoming blockades in the Watson-Crick face of modified ribonucleosides and improving both read-through rate and signal intensity in RT signature analysis.

Regional wall stress predicts ventricular remodeling after anteroseptal myocardial infarction in the Healing and Early Afterload Reducing Trial (HEART): an echocardiography-based structural analysis

BACKGROUND

Increased left ventricular (LV) wall stress after myocardial infarction (MI) has been implicated in LV remodeling. However, the relationship between LV wall stress and LV remodeling is incompletely defined.

METHOD

We prospectively studied the relationship between regional wall stress and LV remodeling by application of the finite element method to end-systolic LV models from patients enrolled in the Healing and Early Afterload Reducing Therapy (HEART) Trial. Individual LV models were constructed from orthogonal apical echocardiographic views obtained at day 14 after anteroseptal MI in 64 patients. Of these, 31 patients received low-dose (0.625 mg) ramipril and 33 patients received full-dose (10 mg) ramipril. LV wall stress was calculated by the finite element method and correlated with change in LV volume from day 14 to day 90 after MI.

RESULTS

Among all patients, increases in apical regional wall stress were associated with LV volume changes (P -trend =.015). The relationship between apical regional wall stress and change in LV volume was strongest in the low-dose ramipril group (r = 0.53, P =.002) and remained significant after adjustment for end-diastolic volume, infarct size, ejection fraction, and systolic blood pressure yet was attenuated in the full-dose ramipril group.

CONCLUSIONS

Apical regional wall stress is an independent predictor of subsequent LV remodeling after MI. The relationship between increased apical wall stress and LV dilatation appears to be attenuated by full-dose angiotensin-converting enzyme inhibition.

Intraoperative echocardiography

Intraoperative echocardiography has emerged as a new technique by which the cardiac surgeon can more precisely define the operative anatomy and physiology, immediately evaluate the results, and more accurately monitor left ventricular function in the operating room. This review summarizes the current applications of intraoperative two-dimensional and Doppler echocardiography in both the epicardial and transesophageal forms, and discusses the advantages and possible limitations of these methods in the practice of clinical cardiac surgery.

Pericardial pseudotumor. Echocardiographic observation of juxtacardiac pulmonary collapse

Despite its value in the diagnosis of pericardial disease, two-dimensional echocardiography also is known to produce confounding results. Ten patients had juxtacardiac masses simulating pericardial tumor implants on echocardiographic examination ("pericardial pseudotumor") caused by juxtacardiac pulmonary atelectasis or lobar collapse. The atelectatic nature of these masses was based on echocardiographic delineation of pericardial and pleural anatomy, combined with ancillary radiographic and CT studies. Drainage of pleural fluid also led to disappearance of the masses on echocardiographic examination, suggesting that the masses were an ultrasonic manifestation of pulmonary atelectasis resulting from surrounding compressive effusive fluid. Finally, clinical follow-up failed to show development of malignant disease in any patient. The possibility of pericardial pseudotumor should be considered when ultrasound studies show juxtacardiac masses within large collections of pleural fluid, especially in the clinical absence of malignant disease.

Right ventricular tardokinesis in cardiac contusion: a new observation on phase images

The usefulness of gated blood pool (GBP) scintigraphy in evaluating cardiac contusion among trauma patients was examined. In ten of 62 patients who sustained blunt chest trauma, phase images of GBP studies demonstrated delayed onset of right ventricular (RV) contractions (RV tardokinesis). Clinical charts of these ten patients were reviewed to determine the significance of this finding. Only one had no supportive evidence of cardiac injury. Four patients were determined to have clinically significant cardiac contusion on the basis of the occurrence of arrhythmias of cardiac failure during their hospital course. These patients had ventricular histogram widths greater than 30 degrees of the entire cardiac cycle at half maximum height and had a bifid peak in their ventricular contraction histograms. Of the 52 patients who did not have RV tardokinesis, only one had a clinically significant cardiac contusion, resulting in a false-negative rate of 2% for the test. This new observation of RV tardokinesis may be clinically useful in establishing the difficult diagnosis of cardiac contusion.

Effects of left ventricular venting and distention during heterogenous distribution of cardioplegic solution

The effects of left ventricular venting and distention on myocardial protection during heterogenous distribution of cardioplegic solution remain undefined. This study was undertaken to determine if left ventricular venting enhances and distention impairs myocardial cooling and recovery of global and regional left ventricular function. Twenty-one pigs were placed on cardiopulmonary bypass and subjected to 80 minutes of ischemic arrest with the mid-left anterior descending artery occluded. Hearts were protected with multidose potassium (25 mEq/L) crystalloid cardioplegic solution supplemented with topical (4 degrees C) and systemic (28 degrees C) hypothermia. During arrest, the left ventricle was vented in seven pigs, seven pigs were not vented, and seven others had systemic pump blood infused into the left ventricle to maintain an end-diastolic pressure of 15 mm Hg. Parameters measured included left ventricular temperature, stroke work index, compliance (end-diastolic pressure-end-diastolic volume curves) and wall motion scores (two-dimensional echocardiography). Distended hearts had the lowest mean left ventricular temperature beyond the left anterior descending arterial occlusion (10.1 degrees +/- 1.8 degrees C distended [p less than 0.025 from vented and nonvented groups] versus 14.2 degrees +/- 0.7 degrees C vented versus 15.5 degrees +/- 1.2 degrees C nonvented), the highest postischemic stroke work index (0.78 +/- 0.09 gm-m/kg distended versus 0.62 +/- 0.07 gm-m/kg vented versus 0.66 +/- 0.07 gm-m/kg nonvented at end-diastolic pressure = 10 mm Hg), and the best wall motion scores (0.7 +/- 0.04 distended [p less than 0.025 from vented and nonvented groups] versus 5.5 +/- 1.80 vented versus 4.8 +/- 1.20 nonvented). Postischemic end-diastolic pressure-end-diastolic volume curves were unchanged from preischemic values in each group. We conclude that during heterogenous cardioplegic arrest, left ventricular venting offers no additional myocardial protection and may negate the beneficial effects of moderate (end-diastolic pressure = 15 mm Hg) left ventricular distention.

Rotational artifact in phase imaging of cardiac scans: potential pitfalls in diagnosis

In the past few years, we have occasionally observed linear bands in the phase images of gated cardiac blood-pool scans along the interventricular septum region among patients with normal septal motions. Our retrospective study investigated the cause of out-of-phase bands of 12 patients. We documented through review of cines, computer analysis of gated cardiac blood-pool scintigraphy data, and correlation with echocardiograms that this phenomenon was artifact introduced by rotational movements of the heart. It is important for nuclear physicians to recognize this rotational artifact on the phase analysis image in order to avoid the erroneous misdiagnosis of wall motion abnormalities of the septum.

Echocardiographically determined left ventricular structural and functional correlates of complex or frequent ventricular arrhythmias on one-hour ambulatory electrocardiographic monitoring

The associations between 6 echocardiographic measurements and ventricular arrhythmias on 1-hour ambulatory electrocardiograms were evaluated in 3,348 subjects of the Framingham Heart Study who were free of symptomatic coronary artery disease, congestive heart failure and valvular heart disease and were not receiving diuretic drugs or other blood pressure or cardiac medications. Age-adjusted estimates of association between echocardiographic measurements of left ventricular (LV) structure and function and complex or frequent (Lown grade 2 or greater) ventricular arrhythmia were computed using logistic regression. In this bivariate model only LV internal diameter (systolic and diastolic) and fractional shortening were associated with arrhythmia in both sexes (p less than 0.01). When all variables were entered into a multivariate model, only age and systolic LV internal diameter remained independently associated with arrhythmia (p less than 0.001). Thus, LV chamber size and function are important predictors of risk for ventricular arrhythmia. Systolic LV internal diameter, which reflects both functional and structural information, is the only measurement independently predictive of arrhythmia risk in persons free of apparent heart disease.

Embolization of a left ventricular mural thrombus: verification by two-dimensional echocardiography

A two-dimensional (2-D) echocardiogram in a 69-year-old man disclosed a septal-apical left ventricular thrombus six days after an acute anterior wall myocardial infarction. On the ninth hospital day, he suddenly experienced left-sided weakness and a left-sided field cut consistent with the diagnosis of a cerebrovascular accident (CVA). A repeated 2-D echocardiogram showed that the original mural thrombus had completely disappeared, which strongly supported an embolic event as the cause of the CVA. Two-dimensional echocardiography helped to verify the cause of this patient's neurologic problem. The mechanism and predisposing factors that led to a systemic embolism are discussed.