The phantom of "myocardial sinusoids": a historical reappraisal

A Coronary Artery-left Ventricular Fistula through the Sinusoid

A 78-year-old woman was referred to our hospital because of repetitive suppurative arthritis at the artificial left knee joint. Her plasma brain natriuretic peptide level was 122 pg/mL. A 12-lead electrocardiogram showed a QS pattern in the inferior leads. A two-dimensional echocardiogram revealed hypokinesis at the inferior wall and hypertrophy at the apical lateral wall. Color flow imaging revealed this hypertrophic region to be a myocardial sinusoid, demonstrating diastolic coronary to left ventricular flow and early systolic flow vice versa. This was a very rare case of coronary to left ventricular fistula through a sinusoid without cyanotic congenital heart disease or severe coronary artery disease.

An under-recognized phenomenon: Myocardial volume change during the cardiac cycle

BACKGROUND

Myocardial volume is assumed to be constant over the cardiac cycle in the echocardiographic models used by professional guidelines, despite evidence that suggests otherwise. The aim of this paper is to use literature-derived myocardial strain values from healthy patients to determine if myocardial volume changes during the cardiac cycle.

METHODS

A systematic review for studies with longitudinal, radial, and circumferential strain from echocardiography in healthy volunteers ultimately yielded 16 studies, corresponding to 2917 patients. Myocardial volume in systole (MVs) and diastole (MVd) was used to calculate MVs/MVd for each study by applying this published strain data to three models: the standard ellipsoid geometric model, a thin-apex geometric model, and a strain-volume ratio.

RESULTS

MVs/MVd<1 in 14 of the 16 studies, when computed using these three models. A sensitivity analysis of the two geometric models was performed by varying the dimensions of the ellipsoid and calculating MVs/MVd. This demonstrated little variability in MVs/MVd, suggesting that strain values were the primary determinant of MVs/MVd rather than the geometric model used. Another sensitivity analysis using the 97.5th percentile of each orthogonal strain demonstrated that even with extreme values, in the largest two studies of healthy populations, the calculated MVs/MVd was <1.

CONCLUSIONS

Healthy human myocardium appears to decrease in volume during systole. This is seen in MRI studies and is clinically relevant, but this study demonstrates that this characteristic was also present but unrecognized in the existing echocardiography literature.

Cardiac MRI demonstrates compressibility in healthy myocardium but not in myocardium with reduced ejection fraction

BACKGROUND

The professional guidelines assume that the myocardial volume in systole (MVs) is equal to that in diastole (MVd), despite some limited evidence that points to the contrary. The aim of this manuscript is to determine whether this is true in healthy myocardium using gold standard cardiac MRI, as well as transthoracic echocardiography (TTE). The secondary aim is to determine whether there are similar MV changes in patients with heart failure with reduced ejection fraction (HFrEF).

METHOD

A prospectively derived cohort at Mayo Clinic of 115 adult subjects (mean age 42.8 years, 58% female) with no cardiac risk factors was identified. Cardiac MRI was obtained on all 115 patients, 51 of whom also consented to a TTE. MRI from a retrospectively derived cohort of 50 HFrEF patients was also collected. MVs and MVd was calculated using standard approaches with inclusion of the papillary muscles.

RESULTS

In the healthy population, MRI demonstrated MVs/MVd = 0.87 (SD 0.04) and TTE demonstrated MVs/MVd = 0.79 (SD 0.07), suggesting compressibility (p < 0.0001). In the 51 healthy patients who received both imaging modalities, MVs/MVd was 8.0% higher in MRI than TTE (p < 0.0001), but both modalities had MVs/MVd < 1 (p < 0.0001). A Bland-Altman plot demonstrated that as the mean MVs/MVd increases, the difference in MVs/MVd MRI-TTE declines (r = -0.53, p < 0.0001). However, in HFrEF populations, MVs/MVd = 1.01 (0.03), suggesting myocardial incompressibility.

CONCLUSION

Contrary to currently accepted standards, healthy myocardium is compressible but HFrEF myocardium is incompressible. The ratio MVs/MVd merits further study in an expanded normal cohort and in disease states.

Thickness and Ratio of Noncompacted and Compacted Layers of the Left Ventricular Myocardium Evaluated in 56 Normal Fetuses by Two-Dimensional Echocardiography

The thickness and ratio of noncompacted and compacted layers of the left ventricular (LV) myocardium in the normal fetus were investigated by fetal echocardiography. We aimed to investigate the compaction process of the LV myocardium during the normal gestation period and provide reference for echocardiographic diagnosis of a fetus with ventricular myocardium noncompaction. A total of 56 pregnant women in the gestational period of 23–30 weeks were included. Complete fetal echocardiography was performed with system ultrasonographic examination to exclude congenital heart malformation or extracardiac malformation. All 56 fetuses showed normal development. In the short-axis view of the fetal heart, the LV wall was divided into an upper and lower section at the level of the papillary muscle. Each section was then further divided into four segments, namely, anterior, posterior, lateral, and inferior wall. Thus, the LV wall was divided into eight segments. The thickness of the ventricular noncompacted and compacted layers and the ratio of the ventricular noncompacted to compacted layers of these segments at end-systole were measured and calculated. In echocardiography, the fetal LV myocardium is a two-layered structure: the endocardial noncompact myocardium (NC) with higher echo and the epicardium compact myocardium (C) with lower echo. The noncompacted layer is thinner than the compacted layer in the anterior wall, but thicker than the compacted layers in the posterior, lateral, and inferior wall. With respect to the upper and lower sections of the LV myocardium, the noncompacted layer in each segment of the upper section is thinner than that in each segment of the lower section, whereas the compacted layer of the upper section is thicker than that of the lower section. This study suggests that the densification of the fetal LV myocardium occurs gradually from base to apex and from the anterior to lateral, posterior, and inferior walls. This finding aids in further understanding the process of myocardial densification and provides a diagnostic reference for noncompaction of noncompaction cardiomyopathy (NCCM).

Preservation of Functional Microvascular Bed Is Vital for Long-Term Survival of Cardiac Myocytes Within Large Transmural Post-Myocardial Infarction Scar

This study was aimed to understand the mechanism of persistent cardiac myocyte (CM) survival in myocardial infarction (MI) scars. A transmural MI was induced in 12-month-old Sprague-Dawley rats by permanent coronary artery ligation. The hearts were collected 3 days, 1, 2, 4, 8, and 12 weeks after MI and evaluated with histology, immunohistochemistry, and quantitative morphometry. Vasculature patency was assessed in 4-, 8-, and 12-week-old scars by infusion of 15-micron microspheres into the left ventricle before euthanasia. The infarcted/scarred area has a small continually retained population of surviving CMs in subendocardial and subepicardial regions. Surprisingly, whereas the transverse area of subepicardial CMs remained relatively preserved or even enlarged over 12 post-MI weeks, subendocardial CMs underwent progressive atrophy. Nevertheless, the fractional volume of viable CMs remained comparable in mature scars 4, 8, and 12 weeks after MI (3.6 ± 0.4%, 3.4 ± 0.5%, and 2.5 ± 0.3%, respectively). Despite the opposite dynamics of changes in size, CMs of both regions displayed sarcomeres and gap junctions. Most importantly, surviving CMs were always accompanied by patent microvessels linked to a venous network composed of Thebesian veins, intramural sinusoids, and subepicardial veins. Our findings reveal that long-term survival of CMs in transmural post-MI scars is sustained by a local microcirculatory bed.

Effect of experimental coronary sinus ligation on myocardial structure and function in the presence or absence of structural heart disease: an insight for the interventional electrophysiologist

AIMS

To study the effect of coronary sinus (CS) occlusion on normal hearts and hearts with structural disease.

METHODS AND RESULTS

We included 32 dogs, divided into 4 groups: (1) CS ligation (CSL): subjected to CSL; (2) control group: no intervention; (3) MI-CSL group: subjected to myocardial infarction (MI) induction followed by CSL after 1 week; and (4) MI-control group: subjected to MI induction, then open thoracotomy after 1 week without CSL. Electrocardiography, echocardiography, histopathology, and immunohistochemistry were done before and after CSL. In CSL group, there were no significant electrocardiographic or echocardiographic changes after CSL, although there was interstitial oedema that decreased after 1 week with the appearance of Thebesian vessels and positive staining for vascular endothelial growth factor. In MI-CSL group, there was significant increase in left ventricular (LV) end-systolic diameter (P = 02), decrease in LV fractional shortening (P = 0.0001), and LV ejection fraction (P = 0.002) in comparison with MI-control group, associated with severe myocardial degeneration.

CONCLUSION

Acute CS occlusion could be compensated in normal hearts, but may be detrimental in the presence of structural heart disease.

Abnormal coronary artery connection to the left ventricle in a patient with coronary artery disease

We report the case of a 53-year-old man who presented with typical angina and dyspnea on exertion. Besides coronary artery disease based on atherosclerosis, the patient demonstrated a rare coronary anomaly consisting of an atypical connection of the left coronary system with the left ventricle. Both pathologic conditions could be treated successfully by cardiac operations. Besides conventional coronary angiography examinations, cardiac computed tomography angiography (CCTA) studies help to demonstrate the complex anatomy in congenital coronary anomalies.

Pulmonary atresia with intact ventricular septum and right ventricular dependent coronary circulation through the "vessels of Wearn"

We present an autopsy case of a male baby born at 35 weeks of gestation with pulmonary atresia with intact ventricular septum (PAIVS), who had coronary blood flow that was dependent on outflow from the right ventricle through the vessels described by Wearn. At 7 weeks of age, he underwent single ventricle palliation consisting of ligation of a patent ductus arteriosus and placement of a modified Blalock-Taussig shunt. The patient experienced a perioperative myocardial infarction, requiring extracorporeal membrane oxygenation. Progressive hemodynamic decline resulted in death 8 days after surgery. Autopsy revealed acute and remote infarctions in both ventricles and fibromuscular dysplasia of the subepicardial and intramural coronary arteries. In 1926, Grant first reported the association between PAIVS and secondary dysplasia of the heart vasculature and hypothesized that the high pressure resulted in dilation of the myocardial sinusoids. Confusion secondary to the unmeritorious dismissal of the myocardial sinusoids has obscured the pathogenesis of PAIVS and led to several publications suggesting second heart field abnormalities as a disease model for PAIVS. We discuss the pathogenesis of PAIVS, the ventriculocoronary arterial connections and the sinusoidal relationship to the vessels described by Wearn, and we attempt to correct the solecism plaguing the nomenclature of myocardial vasculature.

Case report. Isolated left ventricular myocardium non-compaction: MR imaging findings from three cases

The purpose of this study is to report three cases of left ventricular myocardium non-compaction (LVNC), with emphasis on the MRI findings. From May 2006 to February 2007, three patients -- 2 females (6 years and 42 years of age) and 1 male (18 years of age) -- presented to our radiology department, two of them with fatigue, shortness of breath and episodes of syncope and arrhythmia, for further investigation by cardiac MRI because an apparent asymmetrical pattern of hypertrophy of the left ventricular myocardium was suspected by transthoracic echocardiography. The 18-year-old patient was only experiencing arrhythmia, and arrhythmogenic right ventricular dysplasia was suspected. The images (produced by a 1.5T MRI system) were interpreted by two experienced radiologists and post-processed with Argus software (Siemens, Germany) for ejection fraction calculation. In all three patients, MRI aided in the correct identification of prominent ventricular myocardial trabeculations and deep intertrabecular recesses communicating with the ventricular cavity, as well as areas of hypokinesia with depressed systolic function, and showed the absence of myocardial delayed enhancement and other structural heart defects. In conclusion, cardiac MRI was useful for correctly identifying this rare congenital heart disorder and appears to increase diagnostic accuracy. Although considered a rare anomaly, radiologists should be capable of recognizing LVNC, as current non-invasive imaging methods have increased the frequency of this diagnosis and timely detection is vital in considering early-stage transplantation.

The perspective of ventricular noncompaction as seen by a nonagenarian

The persistence of so-called spongy myocardium was first reported in humans in the 1960s. Subsequently, a few reports described the condition, utilizing inconsistent facts and terminology. In 1990 the first report appeared using the term "noncompaction", and detailed its clinical implications. Following this report, more descriptions of patients with noncompaction entered the literature. Prior to the availability of high resolution cross-sectional echocardiography, most cases of noncompacted myocardium escaped detection, as few patients underwent angiography. In this essay, I seek to adjudicate and clarify several confusions and controversies in the current literature including the acquired nature of hypertrabeculation, the fate of the so-called sinusoids, the relationship to coronary arteries, and noncompaction as another congenital malformation. The embryonic timing of cessation and reinitiation of compaction is conjectured as an explanation of the varied configurations of noncompaction as seen as a clinical entity. The clinical outcomes of decreased contractility, arrhythmia, and thromboembolism, have been stressed in the current literature, but more study is needed of the gray area between the normal variant and minimal noncompaction. A plea is made for the standardization of methods and terminology.

Guidelines for the Clinical Use of Transmyocardial Laser Revascularization

Patients with chronic, severe angina refractory to medical therapy who cannot be completely revascularized with either percutaneous catheter intervention or coronary artery bypass graft surgery (CABG) are clinically challenging. Transmyocardial laser revascularization (TMR), as sole therapy or as an adjunct to CABG, may be appropriate therapy for these patients. The recommendations are based on a review of the available evidence including expert consensus opinions. The author follows the format of the American Heart Association and the American College of Cardiology guidelines for diagnostic and therapeutic procedures. There are class I indications for sole therapy TMR and class IIA indications for TMR as an adjunct to CABG. TMR is indicated for selected patients: as sole therapy for a subset of patients with refractory angina. It also may be effective as an adjunct to CABG for a subset of patients with angina who cannot be completely revascularized surgically.

The Society of Thoracic Surgeons practice guideline series: transmyocardial laser revascularization

BACKGROUND

Patients with chronic severe angina refractory to medical therapy who cannot be completely revascularized with either percutaneous catheter intervention or coronary artery bypass graft surgery present clinical challenges. Transmyocardial laser revascularization, either as sole therapy or as an adjunct to coronary artery bypass graft surgery, may be appropriate for some of these patients. Although transmyocardial revascularization has consistently been demonstrated as an efficacious means of relieving angina, the mechanism of its effects are still debated, and criteria for the selection of patients for this novel therapy have not been adequately defined.

METHODS

We reviewed the available evidence to allow us to make recommendations for the appropriate therapeutic applications of transmyocardial revascularization following the format of the American Heart Association and the American College of Cardiology guidelines for diagnostic and therapeutic procedures. Our recommendations were classified as class I, IIA, IIB, or III. For each recommendation we defined the level of supporting evidence as A, B, or C.

RESULTS

We identified class I indications for transmyocardial revascularization as sole therapy and class IIA indications for transmyocardial revascularization as an adjunct to coronary artery bypass graft surgery with levels of evidence A and B, respectively.

CONCLUSIONS

Transmyocardial laser revascularization may be an acceptable form of therapy for selected patients: as sole therapy for a subset of patients with refractory angina and as an adjunct to coronary artery bypass graft surgery for a subset of patients with angina who cannot be completely revascularized surgically.

Echocardiographic and pathoanatomical characteristics of isolated left ventricular non-compaction: a step towards classification as a distinct cardiomyopathy

AIM

To determine clear cut echocardiographic criteria for isolated ventricular non-compaction (IVNC), a cardiomyopathy as yet "unclassified" by the World Health Organization. The disease is not widely known and its diagnosis mostly missed.

METHODS AND RESULTS

In seven out of a series of 34 patients with IVNC the in vivo echocardiographic characteristics were validated against the anatomical examination of the heart removed after death in four and due to heart transplantation in three patients. Four morphological criteria diagnostic for IVNC were found. (1) Coexisting cardiac abnormalities were absent (by definition). (2) A two layer structure was seen, with a compacted thin epicardial band and a much thicker non-compacted endocardial layer of trabecular meshwork with deep endomyocardial spaces. A maximal end systolic ratio of non-compacted to compacted layers of > 2 is diagnostic. (3) The predominant localisation of the pathology was to mid-lateral (seven of seven patients), apical (six), and mid-inferior (seven) areas. The pathological preparations confirmed the echocardiographic findings. Concomitant regional hypokinesia was not confined to the non-compacted segments. (4) There was colour Doppler evidence of deep perfused intertrabecular recesses.

CONCLUSIONS

Four clear cut echocardiographic diagnostic criteria were established. It is suggested that the WHO classification of cardiomyopathies be reconsidered to include IVNC as a distinct cardiomyopathy.

Transmyocardial laser revascularization

Low-powered lasers were first used in the early 1980s to produce transventricular channels as an adjunct to coronary artery bypass graft surgery (CABG). Early results were encouraging, but because of the combined procedure, could not be attributed directly to use of the laser [1]. High-powered lasers were introduced into clinical practice in 1990 [2]. These lasers are powerful enough to create a transmyocardial channel with minimal thermal damage to surrounding tissues [3]. Clinical studies, using transmyocardial laser revascularization (TMR) as the sole operative therapy for patients with severe and diffuse coronary artery disease (CAD) who have Class III or IV angina, and are on medical therapy, have been conducted since 1993. Based on the results of these studies, the FDA granted approval for the use of TMR as a sole therapy. Clinical studies are currently underway to assess the results of combined TMR and CABG [4]. Results of four controlled randomized studies have been published [5-8]. The data from two of these studies formed the basis for FDA approval of two different types of laser systems. The results of these studies have not provided any additional insights into the mechanism of action of TMR, which remains the Achilles' heel of this procedure. In this review, background information about the TMR procedure will be discussed along with an analysis of the recently published randomized studies.

Dissociation between improvement in angina pectoris and myocardial perfusion after transmyocardial revascularization with an excimer laser

Xenon chloride excimer laser transmyocardial revascularization significantly reduced angina in all patients and increased regional myocardial perfusion in most patients; however, there was no correlation between symptomatic improvement and flow improvement. Patients' symptomatic improvement preceded improved perfusion by several months.

Myocardial laser revascularization: the controversy and the data

The clinical and experimental data relevant to the theoretical mechanisms and clinical results of laser myocardial revascularization are reviewed. Both transmyocardial and percutaneous approaches are considered. Both types result in a reduction in anginal symptoms in patients refractory to conventional therapy and are likely to act through common pathways. The proximate mechanisms for the transmyocardial revascularization effect most likely relate to myocardial inflammation, secondary stimulation of growth factors, and denervation of the myocardium.

Transmyocardial laser revascularization: current status

Transmyocardial laser revascularization (TMLR) has been widely evaluated for treatment of the ischemic myocardium either in conjunction with coronary artery bypass grafting or as sole therapy. Clinically, it has shown significant improvement for angina symptoms, but the mechanism by which this modality works is unknown at this time. The original premise on which transmyocardial revascularization was established depended on its ability to essentially generate channels that would directly carry blood from the ventricle into the ischemic myocardium. This theory, however, has not been substantiated, so other mechanisms have been postulated. This article gives a historical perspective on the advent of transmyocardial revascularization and the many animal and human studies that have paved the way for its clinical use. Current controversies are examined, along with the new advances in laser technology and where the future of TMLR is headed.

Transmyocardial revascularization: the fate of myocardial channels

Attempted cardiac revascularization through laser-made channels has gained considerable recent notoriety. Although the treatment reduces angina, its ability to enhance perfusion is unclear, and the mechanism of action unknown. The fate of the channels appears an obvious place to look for insight. Therefore, this review focuses on temporal and spatial changes in channel morphology. An appreciation of the natural history of the channels not only has potential to elucidate mechanisms, but also to provide the basis for optimization of channel-making.

Are there vascular density gradients along myocardial laser channels?

BACKGROUND

Clinical studies suggest that transmyocardial laser revascularization may improve regional blood flow of the subendocardial layer. The vascular growth pattern of laser channels was analyzed.

METHODS

Twenty pigs were randomized to undergo ligation of left marginal arteries (n = 5), to undergo transmyocardial laser revascularization of the left lateral wall (n = 5), to undergo both procedures (n = 5) or to a control group (n = 5). All the animals were sacrificed after 1 month. Computed morphometric analysis of vascular density of the involved area was expressed as number of vascular structures per square millimeter (+/-1 standard deviation).

RESULTS

The vascular density of the scar tissue of the laser channel was significantly increased in comparison with myocardial infarction alone: 49.6+/-12.8/mm2 versus 25.5+/-8.6/mm2 (p < 0.0001). The vascular densities of subendocardial and subepicardial channel areas were similar: 52.9+/-16.8/mm2 versus 46.3+/-13.6/mm2 (p = 0.41). The area immediately adjacent to the channels showed a vascular density similar to that of normal tissue: 6.02+/-1.7/mm2 versus 5.2+/-1.9/mm2 (p = 0.08). In the infarction + transmyocardial laser revascularization group, the channels were indistinguishable from infarction scar.

CONCLUSIONS

Scars of transmyocardial laser revascularization channels exhibit an increased vascular density in comparison with scar tissue of myocardial infarction, which does not extend into their immediate vicinity. There was no vascular density gradient along the longitudinal axis of the channels.

Transmyocardial and percutaneous myocardial revascularization: current and future role in the treatment of coronary artery disease

Transmyocardial revascularization (TMR) is a new treatment modality under evaluation in patients with severely symptomatic, diffuse coronary artery disease, in whom the potential for medical or interventional management has been exhausted. Preliminary clinical trials show improved ischemic symptoms within the first 3 months in about 70% of TMR-treated patients. The original proposed mechanism of surgical or catheter-based TMR (percutaneous myocardial revascularization [PMR]) was that channels mediate direct blood flow between the left ventricular cavity and ischemic myocardium. However, several alternative explanations for the clinical success of TMR have recently been suggested, including improved perfusion by angiogenesis, an anesthetic effect by nerve destruction, and a potential placebo effect. This article reviews the clinical role of TMR/PMR, its possible pathophysiologic mechanisms, and its controversies. It provides an overview of the actual scientific and clinical status of TMR and details future directions.

An examination of potential mechanisms underlying transmyocardial laser revascularization induced increases in myocardial blood flow

Within the past few years, transmyocardial laser revascularization (TMR) has attracted the attention of cardiologists and cardiac surgeons as a therapy for patients suffering from otherwise treatable coronary artery disease. Clinical studies have consistently shown symptomatic improvement that lasts at least 1 year in a majority of patients. The original hypothesis that prompted development of the technique was that direct myocardial perfusion from the chamber could be achieved through chronically patent channels, as is the case in reptilian hearts. Results of our early studies failed to support this hypothesis and we turned to investigations aimed at testing other possible explanations. The experiments, which are reviewed in this article, showed that TMR enhances vascular growth in ischemic myocardium.

Neovascularization after transmyocardial laser revascularization in a model of chronic ischemia

BACKGROUND

The mechanism of clinical improvement after transmyocardial laser revascularization (TMR) is unknown. One hypothesis holds that TMR causes increased myocardial perfusion through neovascularization. This study sought to determine whether angiogenesis occurs after TMR in a porcine model of chronic myocardial ischemia.

METHODS

Six miniature pigs underwent subtotal left circumflex coronary artery occlusion to reduce resting blood flow to 10% of baseline. After 2 weeks in the low-flow state, dobutamine stress echocardiography and positron emission tomography were performed to document ischemic, viable myocardium. The animals then underwent TMR and were sacrificed 6 months later for histologic and immunohistochemical analysis.

RESULTS

Histologic analysis of the lased left circumflex region demonstrated many hypocellular areas filled with connective tissue representing remnant TMR channels. Histochemical staining demonstrated a highly disorganized pattern of neovascularization consistent with angiogenesis located predominantly at the periphery of the channels. Immunohistochemical analysis confirmed the presence of endothelial cells within neovessels. Vascular density analysis revealed a mean of 29.2+/-3.6 neovessels per high-power field in lased ischemic myocardium versus 4.0+/-0.3 (p<0.001) in nonlased ischemic myocardium.

CONCLUSIONS

This study provides evidence that neovascularization is present long term in regions of ischemic, viable myocardium after TMR. Angiogenesis may represent the mechanism of clinical improvement after TMR.

Angiogenesis: a possible mechanism underlying the clinical benefits of transmyocardial laser revascularization

While clinical reports indicate that significant relief of angina is achieved with transmyocardial laser revascularization (TMLR), the mechanisms of benefit are still a matter of considerable controversy. Studies in our laboratory, as well as in the laboratories of other investigators, have challenged the classic hypothesis that benefits are derived from blood flow through chronically patent channels. While several alternatives have been proposed, our work has focused on investigating the possibility that TMLR stimulates vascular growth in the region around the TMLR channels. We have performed studies looking at histologic markers of vascular growth (including vessel counting and cellular proliferation assays) in order to test this hypothesis, the results of which are reviewed. In brief, we find that TMLR markedly enhances myocardial vascular growth above what is seen normally in ischemic myocardium. We hypothesize that the underlying mechanism relates to liberation of growth factors by inflammatory cells, which are recruited in response to the laser induced myocardial injury. Clarification of whether this mechanism contributes to observed clinical benefits is of fundamental importance, since such understanding may suggest means of enhancing the process.

Percutaneous transmyocardial revascularization

Transmyocardial revascularization (TMR) is a potential therapy for patients with severe angina pectoris and coronary anatomy deemed unsuitable for traditional revascularization techniques. Investigations of TMR are reviewed with emphasis on studies relevant to the development of a percutaneous, catheter-based transmyocardial revascularization procedure (PMR). The results of the preliminary animal studies and description of the PMR procedure are discussed. The recently initiated human PMR protocol is summarized and possible future investigative directions are outlined.

Percutaneous method of laser transmyocardial revascularization

Laser transmyocardial revascularization (TMR) creates conduits from the left ventricular cavity into the myocardium and has been forwarded as a potential method of perfusing ischemic myocardium. The procedure typically employs a CO2 laser to produce transmyocardial channels from the epicardial to the endocardial surface via an open thoracotomy. Preliminary studies in animals and human subjects have yielded promising results, and clinical trials evaluating the long-term efficacy of the procedure are in progress. We now report the use of a percutaneous method of TMR using a laser delivered through a novel catheter system. To assess the feasibility of performing percutaneous TMR, studies were performed on 15 adult canine subjects utilizing a holmium:YAG laser. Via a femoral artery approach, novel laser catheters were introduced into the left ventricular cavity under fluoroscopic guidance. Biplane coronary angiography, ventriculography, and transesophageal echocardiography were employed to direct catheters to specific regions and assess the efficacy of creating transmyocardial channels. Multiple channels could be created in the anterior, lateral, inferoposterior, and septal regions as demonstrated by contrast ventriculography with confirmation by subsequent gross and histologic examination. The procedure was tolerated well without any ventricular dysfunction or sustained ventricular arrhythmias. We have demonstrated that laser transmyocardial revascularization via a percutaneous approach is feasible with creation of channels from the endocardial surface of the left ventricle into the myocardium. On gross and histological examination, these channels are similar in appearance to those created by the currently employed open chest, epicardial method of TMR.

Evidence of improved microvascular perfusion when using antegrade and retrograde cardioplegia

BACKGROUND

The maximum degree of microvascular distribution of cardioplegic solution is considered important to achieve optimum myocardial protection. This study attempts to demonstrate that the addition of retrograde cardioplegia to antegrade cardioplegia improves overall microvascular perfusion.

METHODS

Explanted human hearts (n = 6) were treated with cold cardioplegic arrest and bicaval cardiectomy. Blood cardioplegia (37 degrees C) containing colored microspheres (color A for antegrade, color B for retrograde) was simultaneously infused antegrade at a pressure of 80 mm Hg and retrograde at a pressure of 40 mm Hg for 2 minutes. The ventricular myocardium was then sampled at three sites to determine absolute and relative cardioplegic microvascular flow.

RESULTS

Of the total microvascular capillary flow, 27% to 32% was found to be the contribution of retrogradely delivered cardioplegia.

CONCLUSIONS

Despite being delivered simultaneously and at a lower pressure, retrograde cardioplegia contributed substantially to overall microvascular perfusion. This suggests that antegrade cardioplegia alone does not perfuse all available myocardial capillaries and that the addition of retrograde cardioplegia enhances overall microvascular distribution and perfusion.