Doppler color flow mapping of epicardial coronary arteries: initial observations

A new noninvasive method for assessing mild coronary atherosclerosis: transthoracic convergent color Doppler after heart rate reduction. Validation vs. intracoronary ultrasound

BACKGROUND

A more sensitive transthoracic color Doppler technology (convergent color Doppler), along with a heart rate (HR) reduction and new tomographic planes, can greatly improve coronary blood flow velocity (BFV) recordings in the left main (LMCA) and left anterior descending (LAD) coronary arteries, allowing the detection of even a slight acceleration of BFV due to mild coronary stenosis.

METHODS

A group of 26 patients underwent convergent color Doppler transthoracic echocardiography (CC-Doppler TTE) in the LMCA and in the LAD coronary arteries before and after HR lowering. A second group of 71 patients scheduled for intravascular ultrasound, expanded to 96 with 25 more patients with normal LAD (by angiography/low likelihood of disease), underwent BFV Doppler recordings by CC-Doppler TTE of the whole LAD (specifically the proximal, mid and distal segments) to detect a localized increase in BFV, after attaining maximal and reference BFV in each segment.

RESULTS

In the first group, HR reduction dramatically improved the detection of optimal flow in the LMCA and LAD, from 4 to 54% and from 6 to 94% of the segments, respectively (P < 0.001). In the second group intravascular ultrasonography (IVUS) showed mild stenoses in 60 patients. The maximum velocity was higher in the diseased segment than normal segments (49 ± 24 vs. 33 ± 11 cm/s; P < 0.001) and as the reference velocity was similar (32 ± 9 vs. 33 ± 11 cm/s; P = ns), the % increase was also higher (52 ± 52 vs. 0.7 ± 3%; P < 0.001). Using a >21% increase in velocity as a cutoff value, the sensitivity and specificity of CC-Doppler TTE in detecting at least one LAD plaque were 87% (52/60 patients [pts]) and 100% (36/36 pts), respectively.

CONCLUSION

CC-Doppler TTE evaluation of LAD BFV is greatly improved after reducing HR, allowing accurate noninvasive assessment of mild LAD stenosis with no radiation exposure.

Coronary Flow and Reserve by Enhanced Transthoracic Doppler Trumps Coronary Anatomy by Computed Tomography in Assessing Coronary Artery Stenosis

We report the case of a 71-year-old patient with many risk factors for coronary atherosclerosis, who underwent computed coronary angiography (CTA), in accordance with the guidelines, for recent onset atypical chest pain. CTA revealed critical (>50% lumen diameter narrowing) stenosis of the proximal anterior descending coronary, and the patient was scheduled for invasive coronary angiography (ICA). Before ICA he underwent enhanced transthoracic echo-Doppler (E-Doppler TTE) for coronary flow detection by color-guided pulsed-wave Doppler recording of the left main (LMCA) and whole left anterior descending coronary artery (LAD,) along with coronary flow reserve (CFR) in the distal LAD calculated as the ratio, of peak flow velocity during i.v. adenosine (140 mcg/Kg/m) to resting flow velocity. E-Doppler TTE mapping revealed only mild stenosis (28% area narrowing) of the mid LAD and a CFR of 3.20, in perfect agreement with the color mapping showing no flow limiting stenosis in the LMCA and LAD. ICA revealed only a very mild stenosis in the mid LAD and mild atherosclerosis in the other coronaries (intimal irregularities). Thus, coronary stenosis was better predicted by E-Doppler TTE than by CTA. Coronary flow and reserve as assessed by E-Doppler TTE trumps coronary anatomy as assessed by CTA, without exposing the patient to harmful radiation and iodinated contrast medium.

Directional Doppler in Cardiology: A 50-Year Journey

In 1968, while cardiologists were focused on cardiac structures imaged by ultrasound, Daniel Kalmanson in Paris, France, devised a new ultrasonic modality, directional continuous-wave Doppler, enabling him to record instantaneous cardiovascular blood flow velocities with recognition of their direction (relative to the transducer) in vessels. An innovative presentation of Doppler data also made velocity traces physiologically understandable. Following the noninvasive study of the arterial and venous beds, flow velocity in the right (1969) and left (1970) cardiac chambers was studied by means of a directional Doppler catheter. The curtain was then raised for the renewal of our pathophysiologic understanding of cardiac dynamics and the adoption of a new methodology. Technological evolution paved the way for clever researchers to pioneer important advances, diversifying the technique. Guided by the early principles, which are still valid in 2018, directional Doppler finally gained acceptance from the entire scientific community.

Hemodynamic changes in left anterior descending coronary artery and anterior interventricular vein during right ventricular apical pacing: a doppler ultrasound study in open chest beagles

Objective

The aim of this study was to quantify the effects of right ventricular apical pacing (RVAP) on hemodynamics in left anterior descending coronary artery (LAD) and anterior interventricular vein (AIV) contrast to baseline condition in open chest beagles using Doppler ultrasound imaging.

Methods

In 6 anesthetized open chest beagles, the spectral Doppler waveforms of the middle segmental LAD and the AIV were acquired with a 5 MHz linear array transducer at baseline condition and during RVAP. The aortic pressure-time curves were recorded synchronously. The Doppler hemodynamic parameters of the LAD and AIV at both states were derived and compared.

Results

The spectral Doppler waveforms of the LAD had a principal diastolic positive wave (Dp), which heelled by a momentary negative wave and a positive wave during early systole at baseline condition. During RVAP, an additional negative wave appeared in the LAD at late systole. The duration of the Dp shortened (227.83±12.16 ms vs 188.50±8.97 ms, P<0.001), and the acceleration of the Dp decreased (11.85±2.22 m/s² vs 3.54±0.42 m/s², P<0.001). The spectral Doppler waveforms of the AIV only had a principal positive wave (Sp) at baseline condition, but an additional diastolic negative wave appeared during RVAP. The duration of the Sp shortened (242.99±7.98 ms vs 215.38±15.44 ms, P<0.001), and the acceleration of the Sp decreased (9.61±1.93 m/s² vs 1.01±0.11 m/s², P<0.001).

Conclusions

Obvious hemodynamic changes in the LAD and AIV during RVAP were observed, and these abnormal flow patterns in epicardial coronary arteries and vena coronaria may be sensitive and important hints of the disturbed cardiac electrical and mechanical activity sequences.

Physiologic Assessment of Coronary Artery Stenosis without Stress Tests: Noninvasive Analysis of Phasic Flow Characteristics by Transthoracic Doppler Echocardiography

We evaluated the significance of the diastolic-to-systolic blood flow velocity ratio (DSVR) determined by transthoracic Doppler echocardiography, for a physiologic assessment of the severity of coronary stenosis without stress tests, as compared with thallium 201 single photon emission computed tomography. In 95 patients undergoing thallium 201 single photon emission computed tomography for coronary artery disease, the flow velocity in the distal left anterior descending coronary artery was obtained with transthoracic Doppler echocardiography. The mean and peak DSVR values were calculated using mean and peak coronary flow velocity. DSVR was successfully measured for 82 patients (86.3%), including 33 patients with reversible perfusion defects in the left anterior descending coronary artery territories. For predicting reversible perfusion defects in thallium 201 single photon emission computed tomography, the best cut-off points were 1.5 for mean DSVR (sensitivity 81.8%, specificity 85.7%) and 1.6 for peak DSVR (sensitivity 75.7%, specificity 83.6%). Noninvasive measurement of DSVR with transthoracic Doppler echocardiography provides physiologic estimation of the left anterior descending coronary artery stenosis severity at high success rate, without stress tests.

Intraoperative assessment of coronary grafts by novel digital epivascular imaging

OBJECTIVE

We sought to validate and evaluate 2 novel intraoperative ultrasound probes for epicoronary and epiaortic imaging.

BACKGROUND

The noninvasive intraoperative assessment of successful coronary artery bypass grafting remains a challenge.

METHODS

A total of 19 consecutive patients (4 female, 15 male; mean age 60.5 +/- 13.8 years SD, range 34-84) underwent coronary artery bypass grafting. The epivascular probes (GE Ultrasound) were validated in vitro and intraoperatively. Coronary arteries, grafts, and ascending aorta were imaged and quantified.

RESULTS

Mean adjusted flow measured by flowmeter was 3.25 L, SE 0.47 (range: 1-5.5 L) and was 3.15 L, SE 0.46 (range: 1-5.0 L) by ultrasound, with r = 0.97, P <.0001. Intraoperatively, 56 native coronary vessels were bypassed using 15 left internal mammary artery grafts, 25 vein grafts, and 16 venous jump grafts. A total of 15 left internal mammary artery grafts (100%), 12 left internal mammary artery anastomoses (80%), 20 vein grafts (15 left anterior descending coronary arteries, left circumflex artery grafts, 5 right coronary artery grafts) (80%), 4 jump grafts (25%), and 15 ascending aortas (78%) were successfully imaged by inexperienced surgeons. Doppler flow measurements were possible in 50 vessels (89%). Mean lumen diameter for graft arteries (veins) was 2 mm (2.87 mm), maximal velocity was 72 cm/s (46 cm/s), and mean velocity was 29 cm/s (21 cm/s) with a mean flow rate of 70 mL/m (55 mL/m).

CONCLUSIONS

We conclude that: (1) the novel intraoperative probes measure validated flow; (2) intraoperative hemodynamic assessment of graft patency is feasible without a learning curve; and (3) these findings should encourage the routine use of these intraoperative epivascular digital ultrasound probes.

Epicardial colour-Doppler scanning of coronary artery stenoses and graft anastomoses

OBJECTIVE

Epicardial ultrasound scanning was applied during coronary surgery to assess coronary artery stenoses and quality of distal graft anastomoses, with special emphasis to the left anterior descending artery (LAD).

DESIGN

Twenty-three patients with coronary artery disease (M:F 19:4, mean age 65.0 +/- 9.5 years) had coronary artery bypass grafting (CABG) on cardiopulmonary bypass. Intraoperative scanning of coronary artery stenoses and graft anastomoses was performed with a new 10 MHz linear array Vingmed transducer connected to a GE Vingmed System FiVe echocardiography unit. Coronary stenoses detected by ultrasound were compared with preoperative angiograms. Intraoperatively, coronary graft flow was assessed with a Medi-Stim transit-time flowmeter.

RESULTS

Twenty LADs were investigated. In 17 LADs (85%) stenoses were clearly identified. In three LADs (15%) stenoses were not identified because LADs were deeply intramyocardial or the stenosis was very proximal. There was a significant correlation between LAD stenoses detected by ultrasound and angiogram (R = 0.7; p < 0.01). Mean number of grafts was 3.8 +/- 0.9. Of 26 LAD anastomoses assessed, good images were obtained in 22 cases (84.4%); the mean LAD diameter measured 1 cm below the anastomosis was 1.6 +/- 0.2 mm. In two LADs images were rated fair and in two LADs images were poor because of intramyocardial LAD. No technical error of the anastomoses was detected. All grafts had good flows as ascertained by flow measurements.

CONCLUSION

Epicardial ultrasound scanning with the new 10 MHz transducer allowed satisfactory imaging of coronary stenoses and graft anastomoses. Factors limiting the quality of imaging are proximal lesions, intramyocardial vessel, vessel tortuosity, and extensive calcifications. Epicardial ultrasound scanning with updated technology should become a further advancement to graft assessment during off-pump coronary surgery.

Value of acceleration flow and the prestenotic to stenotic coronary flow velocity ratio by transthoracic color Doppler echocardiography in noninvasive diagnosis of restenosis after percutaneous transluminal coronary angioplasty

OBJECTIVES

The study evaluated the value of coronary flow velocity measurement by transthoracic color Doppler echocardiography (TTCDE) for the noninvasive diagnosis of restenosis after percutaneous transluminal coronary angioplasty (PTCA) for left anterior descending coronary artery (LAD) lesions.

BACKGROUND

Recent advances in TTCDE provide coronary flow velocity measurements in the LAD under the guidance of color flow mapping.

METHODS

We studied 53 patients who underwent successful PTCA for LAD lesions and follow-up coronary angiography (18 patients with restenosis [Group-R], 35 patients without restenosis [Group-N]). We searched localized color aliasing corresponding to local flow acceleration to obtain coronary flow velocity at PTCA sites in the LAD. When localized aliasing was detected, we measured coronary flow velocity at the aliasing (stenotic site) and the prestenotic site.

RESULTS

Using TTCDE, it was possible to measure mean diastolic velocity (MDV) in the LAD in 41 (77%) of 53 patients (14 of 18 patients in Group-R; 27 of 35 patients in Group-N). Localized aliasing was displayed by color flow mapping in 14 (100%) of 14 patients in Group-R, and 15 (56%) of 27 patients in Group-N. Stenotic MDV in Group-R was significantly higher than that in Group-N (60.3 +/- 21.1 vs. 35.1 +/- 7.6 cm/s, p < 0.01), although prestenotic MDV did not differ between Group-R and Group-N (20.2 +/- 3.0 vs. 19.6 +/- 2.3 cm/s). There were significant differences in the prestenotic to stenotic MDV ratio between Group-R and Group-N (0.36 +/- 0.10 vs. 0.57 +/- 0.09, p < 0.001). Localized aliasing with the prestenotic to stenotic MDV ratio <0.45 as the optimal cutoff value had a sensitivity of 86% and a specificity of 93% for the presence of restenosis in LAD lesions.

CONCLUSIONS

Detection of localized color aliasing and measurement of the prestenotic to stenotic MDV ratio in the LAD by TTCDE are useful in the noninvasive diagnosis of restenosis after PTCA for LAD lesions.

Evolution of changes in the ventricular rhythm during paroxysmal atrial fibrillation

Changes in the RR interval within episodes of paroxysmal atrial fibrillation (PAF) have not been fully characterized. A database of 177 24-hour Holter recordings were created from patients with PAF in the CRAFT studies. PAF episodes of > or = 1 minute duration containing < or = 20% noise and preceded by > or = 1 minute of sinus rhythm with < or = 20% noise were selected. Sections of each AF episode containing 10 and 25 RR intervals were identified at the onset, middle, and termination of each episode. Descriptive characteristics (mean, SD, and RMSSD of RR intervals) were calculated within each section, and compared using a nonparametric, paired Wilcoxon test. In 25 patients (17 men, 60.6 +/- 12.2 years old), 231 episodes from 44 recordings met the selection criteria. The mean RR interval increased slightly between the onset and mid-portion of AF episodes (565.9 +/- 128.3 vs 580.3 +/- 144.7 ms, P < 0.001). The RR interval at the termination of AF was significantly greater than that at the start (627.1 +/- 156.1 vs 565.9 ms, P < 10-11) or mid-portion (627.1 +/- 156.1 vs 580.3 +/- 144.7 ms, P < 10-13). SD of the RR interval increased significantly between onset and mid-portion (111.1 +/- 60.2 vs 118.2 +/- 66.7 ms, P < 0.001) and more substantially between mid-portion and termination (118.2 +/- 66.7 vs 201.8 +/- 93.7 ms, P < 10-21). During paroxysms of AF, the mean RR interval and the variability of RR intervals increases. Termination of a paroxysm is preceded by a marked increase in RR interval variability.

Noninvasive assessment of coronary flow velocity and coronary flow velocity reserve in the left anterior descending coronary artery by Doppler echocardiography: comparison with invasive technique

OBJECTIVES

The purpose of this study was to evaluate whether transthoracic Doppler echocardiography (TTDE) can reliably measure coronary flow velocity (CFV) and coronary flow velocity reserve (CFVR) in the left anterior descending coronary artery (LAD) in the clinical setting.

BACKGROUND

Coronary flow velocity measurement has provided useful clinical and physiologic information. Advancement in TTDE provides noninvasive measurement of CFV and CFVR in the distal LAD.

METHODS

In 23 patients, CFV in the distal LAD was measured by TTDE (5 or 3.5 MHz) under the guidance of color Doppler flow mapping at the time of Doppler guide wire (DGW) examination. Coronary flow velocity in the distal LAD were measured at baseline and hyperemic conditions (intravenous administration of adenosine 0.14 mg/kg/min) by both TTDE and DGW techniques. Coronary flow velocity reserve was defined as the ratio of peak hyperemic to basal averaged peak velocity in the distal LAD.

RESULTS

Clear envelopes of basal and hyperemic CFV in the distal LAD were obtained in 18 (78%) of 23 study patients by TTDE. There were excellent correlations between TTDE and DGW methods for the measurements of CFV (averaged peak velocity: r=0.97, y=0.94x + 0.40; averaged diastolic peak velocity: r=0.97, y=0.94x + 0.69; systolic peak velocities: r=0.97, y=0.91x + 0.87; diastolic peak velocity: r=0.98, y=0.95x + 1.10). Coronary flow velocity reserve from TTDE correlated highly with those from DGW examinations (r=0.94, y=0.95x + 0.21).

CONCLUSIONS

Noninvasive measurement of CFV and CFVR in the distal LAD using TTDE accurately reflects invasive measurement of CFV and CFVR by DGW method.

Circadian variation in atrial fibrillation in patients with frequent paroxysms

Determinants of the duration of episodes of atrial fibrillation (AF) in patients with paroxysmal atrial fibrillation (PAF) are poorly understood. However, autonomic tone shows circadian variation and is known to affect atrial electrophysiology. We therefore compared the duration of episodes of AF with an onset during the day (08:00-22:00) to those with an onset during the night in a database of 24-hour ECG recordings in patients with frequent symptomatic PAF. The heart rate in the 30 seconds prior to AF onset was also compared. From 42 recordings, 296 episodes of AF > 30 seconds duration and preceded by > 60 seconds sinus rhythm were identified. The 165 nocturnal episodes tended to be shorter (median = 1.15 min) than the 131 diurnal episodes (median = 1.5 min) and the distribution of nocturnal and diurnal durations was significantly different (P = 0.007; Kolgomorov-Smirnov test). This was also true in recordings containing at least 1 diurnal and at least 1 nocturnal episode. The mean heart rate prior to AF onset was lower at night (62.2 +/- 11.8 vs 75.6 +/- 16.4 beats/min; P < 0.0001 Wilcoxon test). These findings suggest that in patients with frequent symptomatic PAF, autonomic influences affect the duration of episodes of AF and has pathphysiological and therapeutic implications.

Age and gender influences on rate and duration of paroxysmal atrial fibrillation

The influence of age and gender on the character of paroxysmal atrial fibrillation (PAD) has not been described.

METHODS

The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing < or = 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test).

RESULTS

236 episodes from 55 recordings in 32 patients (all patients: 61.4 +/- 12.8 years; men (19): 58.5 +/- 12.6 years; women (13) 65.5 +/- 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 +/- 35 beats/min vs 115 +/- 20 beats/min, P = 0.02) and during the remainder of the episode (120 +/- 25 beats/min vs 112 +/- 22 beats/min at the start, P = 0.01, and 116 +/- 26 beats/min vs 108 +/- 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS).

CONCLUSION

PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.

Mid- and long-term similarity of ventricular response to paroxysmal atrial fibrillation: digoxin versus placebo

The effects of digoxin on ventricular response during atrial fibrillation (AF) and consequent effects on arrhythmic symptoms have still not been fully explained. This study investigated whether the treatment by digoxin contributes to mid- and long-term stabilization of ventricular cycles in patients with paroxysmal AF. A population of 45 patients with paroxysmal AF underwent 24-hour ECG recordings during each arm of a randomized crossover trial comparing digoxin and placebo. This yielded 30 Holter recordings from 22 patients that contained AF episodes lasting in excess of 2 minutes and with acceptably low Holter noise. Each AF episode was divided into nonoverlapping segments of 30 seconds and the distribution of RR intervals in each segment was compared with the distribution of all other AF segments in the same recording using the Kolmogorov-Smirnov test. The percentage of tests that revealed significant differences at levels of P < or = 0.01, and P < or = 0.001 were sorted according to the time between the segments compared. The comparisons of these results were performed between: (a) all recordings on placebo (n = 16) and all recordings on digoxin (n = 14), and (b) between recordings on placebo and on digoxin in 8 patients in whom paired analysis was possible. Adjacent AF segments (distance 0) differed significantly only in < 30% of both recordings on placebo and on digoxin. However, with increasing the distance between segments, the proportion of the significant differences between RR interval distributions increased more with placebo than with digoxin (P < 10(-300), Chi-square test). Paired data revealed larger differences between placebo and digoxin with increasing distance between segments. Thus in patients with paroxysmal AF, digoxin leads to more reproducible patterns of ventricular cycles that may be better tolerated clinically.

Distribution of fast heart rate episodes during paroxysmal atrial fibrillation

OBJECTIVE

To investigate the defibrillator waiting time (time between the recognition of atrial fibrillation and the actual shock) by studying paroxysmal atrial fibrillation episodes with RR intervals shorter than a certain limit (that is, episodes during which defibrillation should not be attempted).

METHODS

Long term 24 hour Holter recordings from a digoxin v placebo crossover study in patients with paroxysmal atrial fibrillation were analysed. In all, 23 recordings with atrial fibrillation episodes of at least 1000 ventricular cycles and with < 20% Holter artefacts or noise were used (11 recorded on placebo and 12 on digoxin). For each recording, the mean ("mean waiting time") and maximum ("maximum waiting time") duration of continuous sections of atrial fibrillation episodes with all RR intervals shorter than a certain threshold were evaluated, ranging the threshold from 400 to 1000 ms in 10 ms steps. For each threshold, the mean and maximum waiting times were compared between recordings on placebo and on digoxin.

RESULTS

Both the mean and maximum waiting times increased exponentially with increasing threshold. Practically acceptable mean waiting times less than one minute were observed with thresholds below 600 ms. There were no significant differences in mean waiting times and maximum waiting times between recordings on placebo and digoxin, and only a trend towards shorter waiting times on digoxin.

CONCLUSIONS

Introduction of a minimum RR interval threshold required to deliver atrial defibrillation leads to practically acceptable delays between atrial fibrillation recognition and the actual shock. These delays are not prolonged by digoxin treatment.

A relationship between fluctuations in heart rate and the duration of subsequent episodes of atrial fibrillation

A relationship between autonomic tone and the onset of paroxysmal atrial fibrillation in some patients is recognised. Episodes of PAF may vary enormously in duration, however, from a few beats to many hours. Whether autonomic tone influences the duration of the episodes has been less well investigated. From a database of Holter recording taken from patients with symptomatic PAF, we identified all episodes of at least 30 seconds duration which were preceded by noise free sinus rhythm. This study examined the heart rate prior to AF onset, the change in heart rate over the final minute of sinus rhythm and the time of AF onset, and compared the data from those episodes of AF of more than 5 minutes duration to the shorter ones. Heart rate was slower before long episodes of AF, but this was found to predominantly represent data from separate recordings. A highly significant rise in heart rate was detected prior to long AF episodes compared to shorter ones. Daytime AF episodes were slightly longer than nocturnal ones. The most important finding was that longer AF episodes were typified by a heart rate acceleration. This suggests that, regardless of underlying aetiology, and increase in sympathetic tone may be important in the sustenance of episodes of PAF.

Performance of basic ventricular tachycardia detection algorithms in implantable cardioverter defibrillators: implications for device programming

Around 20% of patients with third generation implantable cardioverter defibrillators receive inappropriate therapy, usually triggered by atrial fibrillation. This is because the criteria used for ventricular tachycardia detection by current implantable cardioverter defibrillators are based on the analysis of a sequence of RR intervals and may be inappropriately satisfied by supraventricular tachyarrhythmias. Algorithms for ventricular tachycardia detection were challenged against the full RR interval sequences from 482 spontaneous episodes of atrial fibrillation and 260 spontaneous episodes of ventricular tachycardia to determine their ability to discriminate between the arrhythmias. The sensitivities and specificities of the algorithms were calculated over a wide range of programmable parameters. For a given window length and detection interval, the most stringent algorithms, that required all beats to be classified as "fast", were more specific than those allowing a proportion of "normal" intervals, even after adjustment for differing sensitivity. These differences were less marked for faster tachycardias. Specificity increased with the detection window length to a limit of approximately 18 beats. We conclude that ventricular tachycardia is detected with the highest specificity if all beats in an analyzed sequence are required to be "fast," even after lengthening of the tachycardia detection interval to maintain sensitivity. Further improvement in algorithm performance may require the incorporation of criteria such as tachycardia onset and stability.

Graphical representation of complex data--diurnal patterns of initiations of atrial fibrillation episodes

A construction of a purpose designed graphical display is demonstrated in a study investigating the circadian distribution of patterns of RR interval sequences preceding episodes of paroxysmal atrial fibrillation (PAF). Based on a comparison with a (80%, 120%) range around the median of preceding 10 RR intervals, each RR interval is classified as normal, short, or long. Classifications of RR intervals in n-tuplets (n = 1, ...,5) preceding PAF episodes are used to compute probabilities of individual types of sequences occurring within 4-hour periods of the day (between 1 am, 5 am, 9 am, 1 pm, 5 pm, and 9 pm). Graphical representation of the data is proposed using a hierarchy of bar graphs. The graphical system has been filled with data of 327 atrial fibrillation episodes recorded in 46 24-hour ECGs in PAF patients. The graphical analysis supports a link between PAF initiation and cardiac autonomic status.

Effect of digoxin on the ventricular rate variability during paroxysmal atrial fibrillation

This study investigated whether the irregularity of ventricular cycle length during atrial fibrillation (AF) is affected by digoxin. Patients (n = 41) with paroxysmal AF enrolled in a randomized crossover comparison of digoxin and placebo underwent 24-hour ambulatory monitoring during each treatment. Tapes containing AF episodes lasting at least 2 minutes were selected (24 recordings on placebo and 17 on digoxin). The mean (mRR) and standard deviation (SDRR) of RR intervals was calculated for each 30-second segment of AF. The resulting SDRR values were clustered according to bins of mRR values ranging from 350-650 ms in 25-ms steps. In each bin, the SDRR values of all placebo and all digoxin recordings were statistically compared for the top 5, 10, and 15 percentiles of each bin which represented the extremes of ventricular cycle length irregularity during AF. There were no significant differences between the total data of SDRR values in individual bins of mRR. However, the top 5, 10, and 15 percentiles of SDRR values corresponding to mRR values from 350-550 ms were significantly reduced by digoxin (P < 0.0001). The study concludes that although digoxin does not influence the mean variability of RR cycles during AF paroxysms, it suppresses episodes in which a fast ventricular response is associated with extreme variability of RR periods.

Improved Doppler detection of proximal left anterior descending coronary artery stenosis after intravenous injection of a lung-crossing contrast agent: a transesophageal Doppler echocardiographic study

OBJECTIVE

This study was designed to verify the usefulness of transesophageal Doppler recording of blood flow velocity in the proximal left anterior descending coronary artery, after a peripheral injection of a lung-crossing contrast agent (SHU 508A), in detecting and locating a hemodynamically significant stenosis (vessel narrowing > or = 50%) affecting this portion of the vessel.

BACKGROUND

Transesophageal Doppler echocardiography has a limited diagnostic impact on the evaluation of proximal left anterior descending coronary artery stenoses. Peripheral injection of SHU 508A, a lung-crossing contrast agent enhancing Doppler signal to noise ratio in coronary arteries, may allow recording of localized disturbed blood flow velocity at the stenosis site even in the absence of a clear B-mode visualization of the vessel.

METHODS

Transesophageal Doppler echocardiography, before and after echo contrast injection, was performed in 31 patients who underwent coronary angiography. Using color Doppler as a guide, pulsed wave Doppler recording of blood flow velocity in the left anterior descending coronary artery was attempted to detect a localized increase in blood flow velocity. B-mode evaluation of the vessel was also performed.

RESULTS

Angiography showed a significant proximal left anterior descending coronary artery stenosis in 16 patients (group 1) and no stenosis in 15 patients (group 2). In 15 of 16 group 1 patients, Doppler after contrast injection revealed a localized velocity increase of at least 50% of the reference value; mean (+/-SD) percent increase in velocity was 150 +/- 89% (range 367% to 0%). In group 2 Doppler after contrast injection revealed a mild localized increase in velocity in four patients and no increase in velocity in the remaining 11 patients; mean (+/-SD) percent increase in velocity was 5 +/- 7% (range 21% to 0%, p < 0.001 vs. percent increase in group 1). When a percent velocity increase > or = 50% of the reference value was considered a positive criterion for detecting significant stenosis, the sensitivity and specificity were 92% and 100% respectively. The sensitivity of the evaluation before contrast injection or considering B-mode imaging alone was much lower (25% and 19%, respectively, p < 0.001 vs. evaluation after contrast injection). In addition, color Doppler after contrast injection correctly located the stenosis along the vessel, as compared with angiography.

CONCLUSIONS

Blood flow evaluation of the proximal left anterior descending coronary artery by transesophageal Doppler echocardiography after contrast injection is a feasible and reliable method for detecting and locating significant stenoses affecting this part of the vessel and is an improvement over the traditional ultrasound approach.

Stenosis enhances role of platelets in growth of regional thrombus and intimal wall thickening in rat carotid arteries

The authors present the results of a study in which stenosis was induced, resulting in either thrombus or intimal wall thickening, in rat carotid arteries. At > or = 75% stenosis in mildly denuded arteries, an acute and occlusive thrombus formation was induced, but the thrombus was significantly reduced in thrombocytopenia. Thrombus formation near the site of stenosis decreased with decreasing degree of stenosis, whereas the percent formation in the distal region (percent total thrombus) increased. Numerous mural platelet microthrombi were noted at the distal region of the stenosed arteries. After chronic 50% stenosis of the carotid artery for 2 weeks, significant intimal thickening was observed, without any occlusive thrombus formation. The combination with mild denudation was critical in eliciting the effect of stenosis. The magnitude of intimal growth in the stenosed artery was marked by day 6 and plateaued thereafter, whereas it was slight in nonstenosed arteries. The 5-bromodeoxyuridine index of the cells of the medial layer at day 3 was significantly increased by the stenosis, and the effect was reversed in thrombocytopenia. Complete reendothelialization of the intimal surface was observed by 7 to 10 days after surgery in the stenosed arteries. These findings suggest that the introduction of stenosis in these arteries enhances the interaction of platelets with the damaged arterial walls under abnormal fluid shear and that this enhancement leads to acute and occlusive thrombus formation associated with more marked stenosis as well as to sustained increase of intimal wall thickness in less marked stenosis.

Identification of atrial fibrillation episodes in ambulatory electrocardiographic recordings: validation of a method for obtaining labeled R-R interval files

Current systems for analyzing ambulatory electrocardiograms (ECGs) are unable to distinguish precisely between sinus rhythm and atrial fibrillation (AF) episodes, and are unable to produce RR interval listings that distinguish AF from sinus rhythm on a beat-to-beat basis. We describe a method for obtaining such a computerized listing ("Composite Rhythm" file) from ambulatory recordings containing episodes of AF. The file lists the rhythm of each beat, its real time, and the QRS complex morphology. A visual inspection is made of a full printout of the recording to identify the precise time of onset and termination of each episode of AF. These times are entered into a computer and identified with the corresponding beats on a conventional RR interval file generated by Holter analysis. The method was validated using 1-hour segments from 20 ambulatory ECGs containing 145 episodes of AF. These were visually identified by four independent observers with a mean sensitivity of 99.1%. The first beat of AF was identified concordantly in 96% of episodes, with a discrepancy of < or = 3 beats in the other episodes. The times of 200 selected QRS complexes were then entered into the computer by each observer; 91.1% of these complexes were identified exactly and 100% were identified to within one beat. The Composite Rhythm files have several potential applications for testing AF detection algorithms and studying the mode of onset of AF.

Thermal coronary angiography for intraoperative patency control of arterial and saphenous vein coronary artery bypass grafts: results in 370 patients

BACKGROUND AND AIM OF THE STUDY

Early graft failure is often associated with technical failures and is therefore potentially avoidable. We used thermal coronary angiography (TCA) for intraoperative graft patency control in 370 patients undergoing routine coronary artery bypass graft surgery to determine whether consequent intraoperative bypass graft control may result in improved patency rates.

METHODS

The temperature differences generated in between the myocardium and the grafts by injecting cold cardioplegic solution into the proximal end of a vein graft or by warmer blood running through an internal thoracic artery (ITA) graft were detected using three different infrared camera systems. The resulting "heat pictures" were evaluated for anastomotic patency and to outline graft anatomy.

RESULTS

A total of 693 vein grafts were visualized. In 9.4% TCA failed to produce usable images. In the remaining 628 grafts, TCA revealed intraoperative patency in 98.8%. Out of 370 ITA grafts, only 14 could not be sufficiently visualized by TCA. Nineteen ITA occlusions (5.3%) were found: 5 intimal flaps; 11 suture imposed strictures; and 3 proximal ITA occlusions. All occluded grafts were subsequently revised or replaced. All sequential ITA as well as 15 right ITA grafts proved to have patent anastomoses.

CONCLUSION

Using TCA an early graft dysfunction rate of 1% for vein grafts and 5.3% for ITA grafts could be demonstrated. Most occlusions were due to technical mistakes at the distal anastomosis. TCA outlines grafts and the attached coronaries by temperature differences without the need for a contrast agent. There is no interference with the surgical procedure. It is an ideal, noninvasive method to immediately document the success or failure of myocardial revascularization.